I - Short distance or minor transportation
II - Long-distance or major transportation
III - Transportation by water and air: loading timber
F. I. CERMAK AND A. H. LLOYD
F. I. CERMAK was formerly professor of Forestry Utilization at Bogor University, Indonesia.
A. H. Lloyd was, until his recent retirement, at the Imperial Forestry Institute, Oxford, England.
1. Manpower without equipment
2. Manpower with nonmechanical equipment
3. Minor transportation by animals
4. Mechanical traction
5. Self-propelled logging vehicles, crawler and wheeled tractors
6. High-lead yarding with portable spars
LOG ROLLING ON BARE GROUND OR ROLLWAYS
The oldest, simplest and cheapest form of log transportation is by rolling along the ground, if possible directly from the stump to the place of utilization or conversion, or to a water-landing, for rafting or shipping. As only a few wooden poles are needed, rolling is still widely used in many tropical countries for short distances, which are usually determined by local labor costs and by the sale price of the timber. Cylindrical logs can be rolled along the bare ground or over small poles laid along the ground to reduce rolling resistance (Figures 1a and 1b). It is hard and slow work, and the maximum rolling distances beyond which this method cannot be applied economically are quickly reached. Given favorable ground conditions, these distances may vary between 400 and 700 meters, reaching 1,000 meters or more in exceptional cases when timber sale prices still leave a profit and where other methods of transport are not available.
The rollway is laid down in as straight a line as possible, but experienced rolling crews prefer to go around the bigger trees and their big buttress roots, instead of felling them. The width of the rollways exceeds the log length by about a meter, the log length itself being determined by the volume or weight of the logs, keeping within the limits of easy manual handling. Experienced crews can roll and load logs of 6 tons or more, if necessary, but their greatest efficiency is obtained with logs of 2 to 3 tons, 4 to 6 meters long. These sizes are also suitable for hauling on hand-pushed narrow-gauge railroad cars. Millions of tons of logs have been rolled in this way in the past, and more millions will be extracted by the same method along river banks and lake shores before mechanized logging over short distances becomes cheaper.
Another log rolling method, used for large logs of irregular shape, consists of pushing the logs lengthwise over rollers, either laid across skids or flat on the ground. This method is common in the Amazon forests. Four to five rollers of convenient size are used, about 2 meters long and 15 to 20 centimeters in diameter. These rollers, when freed at the rear end as the log advances, are picked up and laid again in front of it. Log rolling on skids, or on the bare ground, is usually the most economical method where manual labor is available and cheap.
FIGURE 1a. - Rolling okoumé logs in Gabon. Photo, Cermak
FIGURE 2a. - A double rollway ii, use in Kalimantan, Borneo. Photo, Cermak
In some countries, the ground surface is so irregular that special double-decked rollways have to be made for log rolling (Figures 2a and 2b). In such conditions, big heavy logs are first laid across the ground, to support the runners which are raised in this way about 40 to 50 centimeters above ground, to avoid rocks, tree stumps or other obstacles. If the available timber sizes are too small to raise the runners sufficiently, a second similar rollway is built on top of the first one. This is a very costly method even where much of the construction timber used on the rollway can be salvaged and used again.
When considering these primitive log transportation methods by manpower, it must be emphasized that, in countries with insufficient labor, such log rolling may only be cheaper than mechanical methods on short distances of up to 100 meters. On the other hand, in countries with abundant labor, local social conditions may postpone the use of mechanical equipment.
SKIDDING LENGTHWISE
Pulling logs along the ground lengthwise is harder work and requires more labor than log rolling. A crew of eight to ten men can roll a round log of 2 to 3 tons on flat ground, but 20 to 30 men are needed to pull a squared log of the same weight on bare ground or on skids. The necessary equipment is very simple and consists only of a few wooden poles to guide the log and about 50 meters of lianes or ropes for pulling. A great advantage of skidding logs lengthwise, by man or by any other motive power, is the narrow track to be cleared in the forest and the consequent ability to select the most favorable ground conditions (Figure 3). With the introduction of the crawler tractor, log skidding by manpower has almost disappeared in tropical Africa but it is still being used in the Far East, especially in Indonesia, British Borneo and Sarawak where it is called kuda-kuda (Figure 4). Short wooden wedges, driven into the sides of the log, give the men a good hold to control and push the log lengthwise over wooden cross-skids on a narrow track. The log length is determined by its diameter and the available labor. Skidding distances may be over a mile where there are no alternative methods of extraction.
WOOD CARRYING
In forests where log-rolling or skidding is impossible for topographical reasons and where mechanized logging would not pay, timber extraction has to be effected by the carrying of wood by men, women or animals, and these loads are usually borne to the nearest road or water landing-place (Figure 5).
Valuable but heavy ebony "bolts," of 25 to 30 kilograms as single loads, and up to 50 kilograms for double loads, are carried for 40 to 50 kilometers to the nearest timber market. In the Far East, large hand-sawn squares and railway ties are carried long distances on the backs of men and women or with the help of yokes. Such transport is nearly always done for low wages which are willingly accepted, if the work is not hurried and if it can be done as a side-line at any time of the day or night. As it requires no road-building, it is not only the cheapest transport method but very often the only possible one where local labor is available.
FIGURE 4. - Log skidding lengthwise by hand (kuda-kuda). Photo, Cermak
Carrying small logs in wire slings, by crews of four to eight men, two per sling, is still common in the sawmills of the Far East both for handling in the log yard and for loading on railway cars, trucks and boats. It is evidently not a speedy or efficient method, but is suitable for the slower production organizations in hot climates.
All three methods of wood transport by manpower - by rolling, skidding or carrying, and without any mechanical equipment - represent a primitive way of hauling which may continue in places with excess manual labor, but which is superseded wherever sledges or wheeled vehicles can be used and prove to be more economic than manual work.
NARROW-GAUGE RAILWAYS
Logging by manpower ceases in any tropical country as soon as the distance for rolling or skidding of logs becomes too great, and when yarding costs become so high that they cannot be recuperated by the sale price of the timber. Depending on the various timber values of veneer logs, sawlogs or construction timber and on local wages, this distance may vary between 500 and 1,000 meters and any timber located beyond this limit remains unfelled until other log transport methods are available.
One of these methods is by the use of narrow-gauge railways. The cost of these includes the acquisition of rails, plates and bolts to connect them, and of spikes to nail them down on wooden sleepers. Additional requirements include about 12 wheeled axles for the construction of cars; and also bolts, screws, and working tools.
Purchase and construction costs of the track have to be considered with regard to the length of time a line is expected to be in operation and to the traffic volume it is hoped to carry. Rails of 7 kilograms with two crossties per meter are quite sufficient to support the passage of three-ton cars at slow speeds, but the best type of rail for secondary narrow-gauge railroads is the 9-kilogram rail which is also strong enough to be used for mechanical traction when it becomes necessary. Rails of 12 kilograms, or heavier types, are indicated for semipermanent or permanent forest railroads with mechanical traction. Track sections 60 to 90 centimeters wide are obtainable with the rails already fixed on round wooden sleepers, about 20 centimeters in diameter, and 1.20 to 1.50 meters long. The spacing of the sleepers depends on the traffic, 50 to 75 centimeters being sufficient for any kind of traction.
The track location should be planned if possible in such a way that no earth moving is necessary, that no trees of 30 centimeters or more in diameter need to be felled, and that all topographical obstacles, rivers, swamps and big rocks are avoided. Ground preparation for the tracks should be limited to the clearing of bush and big roots in order to lay the track sleepers on solid undisturbed ground, so that all the sleepers are supporting the rails evenly with their whole length, bigger sleepers being sunk into the ground. In soft, swampy places, the length and the number of sleepers are increased and laid on a base of timber 3 to 4 meters long (Figure 6). If the tracks sink after a certain time, a new layer of timber is put under the tracks to bring them up to the desired level.
If bridges cannot be avoided, their construction should be as simple and cheap as possible (Figure 7). Either two to three strong timber beams or stringers, cut in the neighborhood of the projected bridge, and placed on timber sills on each bank, can be used for the bridging of spans up to about 6 meters. If the available stringers are too short for long spans, a low cribwork pier of round timber built on a solid base can support them in slow currents or still water, but not on fast streams or where floods may occur. No decking is needed, but strong crossties are used at short intervals and are notched on the underside to sit tightly on the stringers and to prevent any shifting of the rails.
The track gradients should be as low as possible, not exceeding 6 percent, so that crews of six or seven men per log car can usually handle it alone or, when needed, with the help of another crew. Two crews should always work together, to lend a hand if a car gets off the tracks. Special curved track rails for bends are not necessary for light secondary lines. When laid on the ground the rails can be bent into curves with a special tool called a "jim-crow" and kept in the bent position with the help of heavy wooden pegs driven well into the ground. Bent track rails of good steel usually straighten out by themselves when they are dismantled and the pegs are released.
The construction of forest railroads is done with much care in those sections which are expected to serve for several years. Any spur lines, which change their position every one to two years, are built at the lowest possible cost. For the construction of the line, 10 to 15 track rails are loaded on a car, transported to the end of the line under construction and unloaded one by one, the car advancing as soon as the rail section has been placed into position. When dismantling the line, the track rails are disconnected and loaded on a car which recedes as the work progresses. The maintenance of railroad tracks in the forest should consist only of repairs of damage caused by heavy rains or by fallen trees and branches. The frames of the log cars are built with hewn or sawn lumber of medium weight. Two frames of 12 × 20 centimeters are connected by three crossties, and bolted together with wooden pegs. The axle bearings are made from tough hardwoods, and the wheel axles are fixed to the frame with strong iron bolts and screws. These, and the axles, are the only metallic parts used in log car construction. The total weight of the log car should not be more than 200 kilograms in order to avoid unnecessary deadweight. Logs up to 5 or 6 meters in length are easily transported by such cars if the loads are properly balanced. If derailed, the lever action of the overhanging logs often enables the car to be rapidly put back on the tracks. Heavy single logs are not attached to the car frame, but are held fast by wooden wedges, but two or more logs are bundled and attached to the car. Timber over 6 meters long is hauled on two log cars, fitted with low bunks.
Hauling is best done on a piece-work basis independent of the felling or the preparation of the logs for transport, the haulers being free to form the crews from members with whom they like to work.
Successful planning of narrow-gauge railroads is much less a question of forest engineering than of accurate cost calculations, with special regard to the existing topographical conditions, the timber value, and the efficiency of the available labor. Spur lines should always lead as near as possible to the main groups of trees to be cut, and log rolling by manpower should not exceed 100 to 200 meters on flat ground, resulting in logging strips of 200 to 400 meters in width. The ground configuration will determine whether parallel strips or fan-like tracks are best (see Figure 8). The calculation of the necessary railroad material and of its capacities is shown by the following example:
The map of the logging scheme in Figure 9 shows clearly which track sections will have to be built more strongly, for longer use and greater log volumes, expressed graphically by one to four lines, and how the cuttings may progress, fan-like, in 400-meters-wide strips (a), (b), (c), etc. When logging is finished in strip (a), the temporary spur line is dismantled and rebuilt in strip (b), and this is repeated until the whole area is logged.
For a forest area of 1,400 hectares, with an average log volume, per hectare, of 20 cubic meters, the total volume to be logged is about 28,000 cubic meters and only 4,000 meters of track would be needed. The total logging time is four years and projected yearly output, 7,000 cubic meters.
FIGURE 8. - Wooden frame cars for log transport narrow-gauge railway. (All measurements given are in centimeters.)
FIGURE 8. - Wooden frame cars for log transport narrow-gauge railway. (All measurements given are in centimeters.)
A. wooden pegs;
B. iron screws;
C. wooden bearings;
D. wooden frame
FIGURE: 9. - A logging scheme map, showing which tracks have to be well built for longer use (indicated by 4, 3 and 2 lines) and in which way the logging operations can progress by 200- to 400-meter wide felling strips (a-al, b-bl c-cl, drill). When logging is finished in a-al, the tracks are dismounted and a 'flying' line is built in b-bl, and so on until the whole area in covered. The 800-meter deep shore section has been logged by manpower: at this point yarding costs became too expensive and the back area is to be economically logged by means of portable railways, tracks and hand-pushed care.
FIGURE: 11b. - Diagram of platform f or log loading by manual labor for heights above 70 centimeters. The melt stand on the skids which support the logs and on small poles slipped between the skids. The platform width is 300 to 100 centimeters, a width which should permit the accumulation of sufficient logs to avoid operational delay when loading cars.
For the transportation of 50 cubic meters of logs per day, six log cars plus two reserve cars would be needed, each making three trips a day, loading and unloading included, at an average distance of 2.5 kilometers or 5 kilometers per round trip. Average load per log car: 3 cubic meters. Average load for six cars: 18 cubic meters. Three trips at 18 cubic meters equals 54 cubic meters, with a safety margin of 4 cubic meters per day. With six men to push one car, 36 men, working at a capacity rate of 1.4 cubic meters per man/day, are necessary for the hauling.
Log cars of the above construction have a rolling resistance of about 10 kilograms per ton, and loads of several tons can be pushed by men for any distance. The limit at which other traction power, animal or mechanical, becomes cheaper depends chiefly on the cost and efficiency of the available labor, and has to be computed for each case individually. Under normal working conditions in the tropics, limits for hand-pushed cars may vary between 3 and 5 kilometers but, under exceptional circumstances, for example where small loads have to be hauled before the power traction can be started, or after its removal to some other logging area, daily hauling distances by man-power can reach 15 to 20 kilometers, for a two-day round trip (Figure 10).
Log transport by hand-pushed cars on narrow-gauge railroads are giving satisfaction in many countries and in severe competition with road transport. For the crossing of soft ground and of bogs or swamps, which often occur in tropical coastal regions, the narrow-gauge railroad may be recommended as the best solution.
The loading of locally-made timber-frame log cars with big single logs can be carried out without any mechanical equipment by the use of loading decks, which avoid damage to the logs or to the cars. (For construction details, see Figures 11 a, 11 b, 12 and 13.)
The log-deck, built with selected round timber, is made just long enough to hold the amount needed for one transport group of four to six cars. Round timber is also used to build the incline leading from the ground to the log deck, at the level of the log cars, and as close to the tracks as possible. The car is placed opposite to the center of the log, so that overhanging ends may be of equal length, as far as possible. When rolled from the deck, the log is controlled by wedges placed on the crossties of the car. For extra safety, two or three strong wooden poles are pushed into the ground between the rail and the car frame, to avoid the log rolling over the far side and onto the ground. Fastening the logs on to the car with ropes or wire is not necessary; four to six wedges are sufficient for the usual slow travel speed of 3 to 4 kilometers an hour.
For the unloading, the wedges on the unloading side are knocked out from under the log, the log rolled down to the ground, and then down to the river or lake. When reloading, the logs are rolled from the cars on to another log deck prepared alongside the track. All the work when loading, unloading or hauling is done without any tools except for strong wooden poles about 2 meters in length.
A. Upper terminal and uppermost wood lauching point
B. Descending load of bolts
C. Small slitted hardwood block, serving as an expendable wood carrier
D. Descending load of loge (same load carriers as in B and C; cling wire loops bent double)
E. Load of bolts, uppermost of which serves as carrier. This bolt has a narrow 1.3-2.5-centimeter deep notch cut by saw or axe for riding upon the suspended wire.
For selective fellings of about 25 cubic meters per hectare which in many tropical forests is still the usual average density of merchantable timber species, this kind of log transportation by manual railway cars is the best for remote logging operations wherever sufficient labor is available. Depending on the log weight and condition of the track, seven to ten men are needed to push a log car, and after some experience it is not difficult to calculate how many crews can be formed from the available labor, and the number of men required for all the other logging work.
TRANSPORTATION BY GRAVITY
Gravity transport of timber by earthen or wooden chutes, or by portable corrugated-iron chutes, has not been widely used in tropical logging operations in the past, although it exists in forests where the conditions are especially favorable. Known by mountain loggers in northern forests for many years, this simple wood transportation method is generally unsuitable to the tropics because of the small timber volume available at one point, and is insufficient to justify the construction costs of chutes. In addition, the damage to the timber often makes it unprofitable for high priced heavy timber. It is, however, sometimes used on suitable sites for the transportation of low wood grades, especially pulp wood.
Chutes for pulpwood from tropical hardwoods have not been needed up to now, as pulpwood production in industrial quantities has been going on only for about ten years. One pilot plant has been operating in the tropics on the Ivory Coast, in more or less flat coastal forests. However, it should be emphasized that the trend of many tropical countries to become independent of costly paper imports by growing their own pulpwood, will soon call for the use of timber or metal chutes, wherever the terrain is steep and suitable. Their operation requires no specially trained labor, and their capacity can be adapted to any desired output. All work is usually done by directly hired labor: building the chute, timber cutting, yarding it to the intake, and finally the loading. On favorable sites, the yarding of pulpwood bolts or of whole trees to the chutes may be done by animal or mechanical traction.
Wooden chutes for big heavy timber, built with round logs, provide a permanent transportation system, but at present their utilization cannot be generally recommended for tropical logging conditions as their construction needs skilled and experienced labor. Their economic use may, however, be possible for future logging of pure stands of coniferous and hardwood timber, planted in tropical countries for local pulpwood supplies.
WIRE OR CABLE SKIDDING BY GRAVITY
This gravity method of transporting fuel, pulpwood or small logs down steep slopes on a suspended steel wire of about 5 millimeters in diameter, is a simple and cheap method which should not be confused with cable cranes or power-logging. It has been used for pulpwood skidding in the tropics, including Indonesia. Owing to its simplicity, wire skidding of logs down steep slopes has been known in the Alps and the Scandinavian mountains for over a century, and firewood, hay, milk and other farm products are also skidded down to the valleys. Pulpwood skidding, by steel cables down to the lakes and rivers, is also well known in Canada.1
1See KOROLEFF, A. and COLLIER, R. D. Wire skidding, wood transportation by gravity over suspended wire. Montreal, Canada, 1954.
Only the main wire or cable is usually purchased, as the other equipment can be made locally from materials available in the forest. The wire, made of high tensile strength steel, can support loads up to 200 kilograms. It is suspended over maximum spans of about 500 meters between a tree or tree stump on top of a mountain, and another at the bottom. The load of single logs or of wood bundles is carried along the wire by one or mole slings made of flexible wire which has been passed through a slotted hardwood block suspended on the wire. When launched the load slides at high speed down the wire to the terminal, where it is automatically released by the impact of the load against the tail tree. An old tire, hung over the suspended wire and guyed with a cable, can serve as an intercepter to discharge the load at the base or at any desired intermediate point (Figures 14 and 15).
FIGURE 15.- Wire skidding of wood down steep slopes.
A. Old tire (b) hung over suspended wire (a) and guyed (d) to a tree, intercept wood load to discharge if automatically directly into a stream (c)
B. Load of wood eliding down suspended wire (a) with uppermost notched (b) bolt (d) serving as load carrier: (c) are slings
C. Correct wire anchoring to tail tree - wire in wound around it five or six times, slightly upward, then its end is bent and spiked
D. Correct stretching (uncoiling) of wire - coil is revolved
E. Incorrect practice - the coil kept stationary makes the wire twist and likely to kink in its stretching and tensioning
F. Front view of crude wooden winch (capstan) for wire tensioning 1b, lever, inserted into drum's socket; c, wire)
G. Same as F. side view
H. Wood load, tied with a rope to wooden crotch, hooked upon suspended wire cable
With proper care and handling, a steel wire is very durable. The wear, due to the friction caused by carriers sliding over it with their loads, is so small that it may be almost disregarded. However, the wire should never be bent at a sharp angle and never kinked, as that would result in its breaking under tension.
When installing the wire it is easier to take the whole wire coil up to the top terminal, uncoil it downhill and anchor it to the tail tree. On short spans the wire may be tensioned by hand, on longer spans by a small hand-operated capstan or wooden winch. Two workers can install a skidding wire 500 meters long in a day; and about 28 cubic meters of wood have been transported daily in this way in the Canadian softwood forests. The simple wire-tightening device, shown in Figure 15 F. is a primitive horizontal capstan, supported by two trees or posts, and is rotated by means of sturdy levers inserted into its sockets.
The load carriers consist of 4- to 5- centimeter hardwood blocks which are 8 to 10 centimeters in length, made of tough durable wood and have a round hole 2 centimeters in diameter, with a slot opening to allow the main wire and the slings to be passed though. They can carry loads up to 150 or 200 kilograms and are used several times until they are finally broken by the shock of the impact at the lower landing.
The wire for the slings should be as cheap as possible though strong enough to support the loads safely while going down, and break through at the bottom impact. They are not used more than once.
Practicable slopes for gravity wires or cables should have a minimum gradient of 25 to 30 percent and not exceed 60 to 70 percent, to avoid speeds which are too high. Wood breakage by this wire transport system is usually very small and the cost of sling-wires and carriers almost negligible. In tropical countries, the wire for slings may be replaced by cane or other strong vegetable fibre of locally available raw materials. Naturally grown wood crotches are often used instead of the wooden block load carriers but may not always be available in sufficient quantity and strength, and their collection and preparation may take much time and cost more than the mechanically manufactured blocks. The attachments for crotches are also more complicated than the simple slots of the wooden block carriers.
Single bolts, attached to the load carrier, are lifted up to the main wire and then released. For loading small wood bundles convenient platforms may be prepared below the wire, from which the bundles can be easily launched.
Designed originally for the skidding of short bolts, this method has also been used for skidding logs 3 to meters in length, using correspondingly thicker wire and stronger load carriers. Limited trials made in Canada, with 3.5-meter logs of 35 centimeters in diameter, indicated that they can be wire skidded as efficiently as short bolts. Since the loads are raised clear of the ground, wire skidding meets the needs of topsoil conservation on steep slopes which are vulnerable to erosion.
Up to the present time, there has been very little need for wood transportation by gravity in the tropics, as pulpwood and fibreboard production is only beginning; but this situation is changing very rapidly, partly owing to the steadily increasing plantation areas of coniferous species for pulpwood supplies, and partly because of the increasing number of tropical hardwoods found suitable for mixing with softwood pulp. These plantations have been made in hilly and mountainous country, with slopes of suitable gradients for wire skidding and where it should be applied because of its simplicity and great economy.
Another gravity timber transport system which should be seriously considered for possible use in tropical mountains is the pendulum cableway for conveying big timber quantities from the top of a hill to its base near a river or road landing. The loaded carriage, with a capacity of about I cubic meter traveling downhill, draws an empty carriage up. Loading at the top and unloading at the base is done simultaneously as only two carriages can be operated. A cabledrum with strong brakes, necessary to control the speed of the descending carriage, is mounted on wooden or iron skids, and installed either at the top or at the bottom station. Up to 50 cubic meters of timber can be transported during a working day of eight or nine hours, in coniferous forests. The crew is usually four men: one brake-operator, two men for the loading and one for the unloading. This crew takes seven to ten working days for the installation of a pendulum cableway and about five days to dismantle it. Similar cableways, for shorter distances, have been used in the Austrian Alps and are still being operated successfully in Norway.
GROUND SKIDDING
Yarding with animal power is much rarer in the tropics than would be expected. Horses, donkeys, oxen and elephants are of great help for yarding and hauling, but they are not available everywhere in sufficient number or cannot always be used for various reasons. In some countries, they do not exist because of the lack of fodder, as in Kalimantan, Indonesian Borneo; or, owing to the sleeping sickness attacking men as well as animals, as in Gabon; some animals cannot be tamed, such as the wild elephants on the African west coast. Because of their small size, light weight and consequent small hauling capacity, horses are seldom employed in tropical forests.
Horses, donkeys, and mules
Big heavy horses, such as are bred in Europe or North America, are unknown in hot countries because they do not stand the heat, and lighter local horses are used only for riding or pulling a cab or light carts.
Donkeys are much tougher and more heat resisting than horses and are used as wood carriers and for pulling small one-axle carts. They are, in general, not strong enough for skidding, log-bunching or other forest work. Mules, though standing heat well, are used mainly in the subtropics of the Near East where they are often the only means of transport.
Oxen buffaloes, water buffaloes, and cattle
These animals are the most important representatives of this type of traction in the tropics, except equatorial Africa and Indonesia, where they cannot live. They possess, when in reasonable physical condition, a much greater pulling capacity and a much greater resistance than horses. Their large splayed feet enable them to pass over soft ground where horses and donkeys would sink, and their only disadvantage is their slow movement and their small individual output. They are not so intelligent as horses but, on the other hand, a team of six or eight horses can never equal the pulling effect of the same number of oxen.
The physical condition of the draft animals must be well considered in the tropics because of the great weight differences shown by the cattle during the dry and rainy seasons. In many tropical countries the cattle are not fed and have to find their own food. During long dry seasons there may often be very little to be found on the dried out grazing grounds. Hay feeding to bring the cattle through the yearly dry season is unknown in the tropics, and it is evident that very little work can be expected from half-starved animals.
On average, traction power is estimated at approximately 16 percent of an animal's weight. Thus a well-fed and well-harnessed ox weighing 500 kilograms can give a tractive effort of 70 to 80 kilograms, which may be doubled for short distances. The most advantageous method, however, is to work with ox teams in pairs having a steady traction power of about 140 kilograms, the power loss for teamwork being deducted.
Oxen cannot maintain this effort for long and have to stop every 50 to 100 meters to recover their strength. For this reason skidding distances with oxen or buffaloes should be kept short. No exact figures can be given, though the optimum average distance seems to be between 200 and 300 meters, giving the animals sufficient breathing time during the empty return trip. Longer distances exhaust the animals too much; they need more recuperation time and their daily output capacity drops below the level of short distance skidding.
The harness of draft animals has a great influence on their traction capacity, which is seriously reduced by the unbelievably poor harnessing methods in most tropical countries. A wooden yoke and a few pieces of rope or chains, casually adjusted, squeeze and wound the flanks of the animals, which cannot give their full traction effort under such conditions. More surprising still is the indifference of the teamsters, and even more so the lack of interest of team owners in increasing output by improved harness and by better working conditions.
Cattle, usually raised in the tropics for meat and not for milk production, are seldom used for skidding. They are generally much too light and their pulling power correspondingly small. They are nearly always with calf or feeding one, and are not fit for hard forest work, whatever the harness may be.
The research work started during the last few years in India by FAO made possible a great increase of the traction capacity by the use of well-adapted harness and was a great success. The former low traction power could easily be doubled by the use of the harness designed by a Swiss forestry expert, Dr. H. G. Winkelmann, and sent to India.
Yarding and hauling with oxen can be most successfully done in tropical and subtropical countries, like Argentina, Burma, Indonesia, Malaya, Paraguay and Thailand, where the farmers' teams are available during the "winter" months, or where the cattle are relatively cheap. To give Javanese farmers the possibility to earn some money with their idle ox teams during the seasonal gaps in the farmwork, the Government of Indonesia has proposed the employment of farmers and of their teams for local forestry work, and no mechanical logging equipment may be used as long as sufficient labor and draft animals are available. This regulation, quite correct from the social point of view had, and still has, two unfavorable consequences. First, it forced the Indonesian forest service to install in the pure teak forests (managed on a permanent yield basis) a dense net of forest railroads, reducing the yarding distances to a maximum of 200 to 300 meters, and, in order to adapt the loads to the skidding capacity of the ox teams, only short logs of large diameter can be yarded. This meant heavy financial loss, as foreign markets accept short logs only with considerable price reductions, while teak logs of the desired length and diameter are supplied by other Far East countries like Burma, Thailand, and Viet-Nam. The Government of Indonesia canceled the transport regulation some years ago.
(Through the introduction of crawler tractors, Indonesian teak logs of greater length and diameter are now offering increasingly serious competition in the world market. At the same time, on the home market prices can now be raised for wood of shorter dimensions because of reduced production.)
Yarding a one-ton log on wet ground, with a skidding resistance of 350 to 400 kilograms per ton, requires four oxen either working in tandem position or side by side. Working side by side is not possible without clearing a wide skidding path, but tandem pulling is less favorable for the total draft capacity of a team. The best work is done, however, by two oxen working side by side, with a loss of not more than 5 percent of individual traction power. When yarding with a team of four instead of two oxen, total pull is not doubled, being slightly more than 240 kilograms. The average pulling capacity of a team of six oxen is not very much greater than that of four oxen, that is, 320 kilograms instead of 460 kilograms.
Loss of power may be less than that indicated above on good solid roads where the draft animals can walk freely, but it can be much more than the given average on soft or rocky soil with an uncertain foothold for the animals. The slow work of ox teams is gradually reducing this kind of traction, though it may continue for many years in several countries of the Far East, especially in forests owned by collective owners, villages or tribes, and logged in a small way to meet local needs for construction timber and firewood.
SKIDDING WITH SLEDS
Experience in the tropics with sled skidding or with dragging on wooden drays over bare ground has not shown much success in the past. It is rather difficult to understand why this transportation method, needing less traction power than ordinary ground skidding, has not been used more widely. The front end of the logs being supported, skidding resistance is reduced by about 20 percent, and loading and fastening the timber on to the sled, though taking time, is of no difficulty. The timber can be collected right at the stump, and sleds of any size and loading capacity can be constructed to suit the available animal traction. For the anticipated future pulp and fibreboard production in short bolt lengths, transportation by sleds should be considered because of its low costs, where traction animals are available.
SKIDDING WITH PANS
Skidding pans have been and are still being used in several tropical countries with much success, although the increase in their use with both animal and mechanical traction is still very slow. The skidways, though relatively narrow, have to be well clear of all obstacles, roots, stumps or rocks, to avoid the pan getting damaged; and the track has to go around such obstacles, thus lengthening the skidding distances. If the skidway can also serve for the extraction of bundled logs, the costs of clearing will be more justified than for skidding a few single logs. When the front lift of the logs is too small and the logs still drag on the ground for one half or two thirds of their length, there is little reduction of the traction power needed compared with ordinary ground skidding. The front ends of the logs are of course protected from digging into the ground, but otherwise the logs are exposed to similar damage as by ground skidding.
The primitive type of pan was only a bent iron plate with a raised nose and a couple of chains or ropes attached to the traction hook. Later, the front lift of the logs was increased by the installation of a rotating bunk or fork and a steel tongue rigidly fixed in a long slot on the upper side of the pan to facilitate the loading and to give it much better direction control. Steel ribs, welded to the bottom, reduced the skidding resistance and gave it a better hold on the road. So far, however, these improvements have had no effect on increasing the use of skid pans in the tropics, in spite of the fact that the pan is now well designed for animal traction. This is probably because of the unsuitable timber sizes. Logs of such small dimensions that the teamster could load them on to the pan alone or with the help of a second man, have been rare in tropical forests for, up to the present time, the emphasis in logging has been on large-size peeler and saw logs. A great change may however be expected in the harvesting of timber crops of smaller dimensions from the growing pulpwood forests now being planted in many tropical countries.
SKIDDING WITH BUMMERS
The American bummer consists of a large high axle supported by two large wooden or iron wheels about 50 centimeters in diameter and, in the newer types with tired wheels, guided by a strong, forked "tongue" (Figure 16). These do not appear to have been successful in the tropics: in Africa, because of the lack of draft animals; in the Far East, due to lack of knowledge and experience; and in Latin America, owing to the long established custom of transporting logs in high-wheel carts. Except on soft or very rough ground, where a bummer cannot pass owing to its small wheels, it can be used everywhere on dry, solid ground, and its loading technique is easy to learn.
The bummer, which has a pair of strong tongs fixed to its bunk, is backed alongside the log at its front end. The tongs are then fastened to the log, the bummer's tongue being in an almost vertical position. By pulling the tongue down and the bummer forward, the log is lifted over the wheel on to the bunk, or bolster, by the leverage of the tongue. Where animal or mechanical traction is available, loading can also be done by pulling the logs crosswise over the wheel on to the bolster. For unloading, the tong key is removed, the tong arms are shaken loose from the log, and the log is rolled over the wheel to the ground.
The much lighter, rubber-tired bummer, with low pressure single or double wheels, can be used either on soft or rocky ground, and should be found useful in the tropics for the skidding of small and medium-sized timber. The half-rolling, half-skidding resistance of log transport with bummers is only about 50 percent of ground skidding, thus doubling the load capacity for a given tractive power. It is exclusively a single-log skidding system when self-loading, but it is adaptable to a wide range of timber sizes if crosswise loading can be arranged. This requires some additional traction power, but there is no reason why it could not be used in the tropics for smaller logging operations, where tractors are not available or where their use would be too expensive.
Great precaution should be taken when skidding with a bummer downhill on steep or wet slopes, where gravity could overcome the skidding resistance and the loads get out of control and injure the draft animals.
SKIDDING WITH HIGH-WHEEL CARTS
This transportation system continues on a large scale in the cattle-raising countries of Latin America. The reason is that within short distances no cheaper traction
power for timber skidding and hauling exists. Even for long distances, the oxcart is still in many regions the only vehicle capable of use on earth roads all the year round without any maintenance.
For yarding, a passage is cut in the forest wide enough to get a team of two or four oxen to the felled tree, where the logs are loaded under the axle of the high-wheel cart and its long tongue. If the team cannot get to the tree, the logs are rolled by hand, or ground-skidded with oxen, to a nearby road landing. The high-wheel cart is usually pulled by four oxen, of which two are needed to pull down the highly raised front end of the long tongue when loading. The log, lying on the ground between the two big wheels, is attached with chains to a high square bunk, fixed on the axle, and is lifted about 30 centimeters above the ground by the lever action of the tongue when pulled down to its horizontal position. The teamster and his helper attach the log to the bunk just behind its point of balance, so that its front end which is still on the ground can easily be lifted and tied to the tongue. The logs are transported in this suspended position and very big logs, or two heavy loads of bundled timber, are hauled with the rear end skidding along the ground. The high wheels have a diameter of 2 to 3.5 meters which permits the suspended transport of logs up to 1.20 meters in diameter. Maximum loads for high-wheel transport are about 1 ton, and the maximum yarding-hauling distances 8 to 10 kilometers. The draft animals, between three and nine years of age, selected from the great cattle herds, cost little and are kept in service for five to six years. After that, they are fattened up for slaughtering or for sale. They do not work every day and working hours are short, and for the rest of the time the animals are grazing. Unless injured by an accident, there is little loss of sale value at the age of ten years, and there are no maintenance costs.
The simple rigging, consisting of a wooden yoke for two oxen, and a few meters of leather straps or chains, is all home-made and not expensive. The yoke is fixed with straps to the tongue, forcing both animals to the same effort at the same moment. In case of a faster movement at one side of the tong, the yoke pushes back the animal on the other side, which then has to give a much greater effort to get abreast. In Paraguay, owing to the low labor wages, yarding and hauling by draft animals can be kept going in spite of the slowness of the work and its low efficiency.
FIGURE: 16. - Log loading with animal traction on bummer with short tong.
DRAGGING BY ELEPHANTS
One of the most interesting animals used for logging in the Far East is the elephant, though its load capacity is not impressive. Even with the best rigging and harness its skidding power is usually limited to one-ton logs. Yarding distances and working hours have to be short, and monthly and yearly recuperation periods long. Five to six working hours a day are usual, with many stops in between to attach and detach the timber. Five days a week, with long and frequent rest intervals, and only- six to eight months per year, give an average yearly working time of only about 350 hours. Output figures show great differences. When yarding 3 to 4 cubic meters of logs per day for a distance of 2 kilometers, the yearly output in Thailand is given as 200 to 300 cubic meters, while in India and Pakistan it may be only 150 cubic meters a year, although these reported figures may not be fully comparable. In his FAO report, "Mechanical logging and timber production in Ceylon" R. W. Burwell has estimated an elephant's daily output as about one cubic meter skidded for a distance of 1,600 meters, and an output of 4.5 cubic meters (160 cubic feet) per day, for a skidding distance of about of 410 meters. The best service age for elephants in Thailand is between 20 and 50 years. The training of elephants in Burma starts at the age of 6 years, full time work begins between 12 and 15 years and continues until the age of 45 to 50 years, and sometimes even 60 if the elephant is still in good condition. They are not fed except with salt and are allowed to graze during free hours and at night. Payments for regular veterinary inspections and for a few medicaments are the only maintenance costs. They are very intelligent animals and learn quickly what is wanted and, once they have understood, very little or no guidance is needed. They work usually alone, with one mahout each, or in teams of two or three at landing places, in sawmill log yards and in the forests. They do more and better work in the rainy season and they like to work under light rain. Their dragging capacity is relatively small considering their weight.
Well-organized logging enterprises with trained elephants use a well-fitted, two-sided harness attached to the elephant's breast, enabling it to develop its full traction capacity and to give a good outturn (Figure 17). As only low-paid elephant mahouts or drivers are required, operation costs for elephant yarding and hauling in these Asiatic countries are always lower than by mechanized logging. Elephants let free in the forest to find their own food, which may not be there in the necessary quantity and quality, cannot work to their full capacity and they are usually given food grazing grounds or additional food. The African elephant, contrary to the Indian species, is still considered to be untamable and, except for a few cases in the Congo area, has not been put to work in the African forests. Training attempts made in Katanga during the last thirty years, with the help of imported Indian elephants, were however finally successful, but have remained very limited in number.
Animal traction of any kind used for yarding heavy long timber must be slow and of small capacity but may continue for some years in those forests where the timber is insufficiently concentrated to justify the use of expensive mechanical equipment designed for a big outturn. Ground skidding by animal traction is disappearing slowly, even in those countries where abundant labor and draft animals are available.
In spite of this, propaganda and training should be organized in all tropical and subtropical countries with available draft animals, to develop the widest possible use of vehicles with tires and either one or two axles for small wood transport. Also for the transportation of light logs up to 4 meters in length, loaded by hand or with the help of a team, these vehicles permit bigger loads for the same traction power, greater transport speed and less strain on the animals. Old vulcanized car or truck tires are often quite useful for low travel speeds and they are becoming available in increasing numbers. They can be fitted without great difficulty or expense; on suitable vehicles up to 5 tons, providing handy and economic transport for short or long distances.
Of great importance for the future tropical logging of pulpwood of smaller dimensions is the urgently needed training of local men to learn the use and application of pulley blocks and cables, and the simple methods of cable-skidding with animal traction on slopes and over difficult terrain. This has already been started by the logging training center at Batote, India, organized by FAO.
GROUND SKIDDING
In the extensive forests in the west of the United States of America and Canada, and also in the Philippines, steam engines with cable winches mounted together on heavy sleds, were used for hauling logs from the felling sites out to a road or railway, but these have now been replaced by tractors. Ground skidding is, however, likely to be still used for many years for the yarding of smaller pulpwood trees in their full lengths, both in the existing and the future pulpwood forests now being planted in several tropical countries.
Skidding logs along the ground with an endless cable is a common method in northern Russia for coniferous forests and is somewhat similar to the American high lead method but, instead of the reciprocating movement to and fro of the American hauling-line, a one-way continuous circulating 25- to 30-millimeter cable is used, running at a slow speed of about 2 meters per minute. Its direction is reversed for the extraction of the timber along the formerly outgoing track of the cable. Grip locks, fitted at one end of each choker line, are used for attaching the logs to the moving cable. For sidelining up to 50 meters, long choker lines are used. Two compensators, one manual and the other automatic, provide a steady, uniform tension on the hauling cable, and special devices prevent the cable slipping off the sheaves at the return point in the forest. The skidded timber is detached at the landing, and the chokers with the grip-locks are returned to the forest by the outgoing cable. A gang of seven men (one skidder engineer, three choker-men, one man at the sheaves at the cable return, one signalman, and one man at the landing to detach the logs and return the grip-locks) can yard 90 cubic meters over a distance of 300 meters in one 8-hour shift. With a maximum reach of 1,000 meters of the hauling cable, one setting area covers 10 hectares; equal to an outturn of about 800 cubic meters with an estimated logging volume of 80 cubic meters per hectare.
This system is particularly suitable for timber extraction in the clear-cutting of smaller trees and in tidal or swamp forest, where the ground is too soft for road or railroad construction.
The diesel-driven yarders which operated some years ago in west African forests cannot now compete with tractor hauling, and, in many forests logging methods changed from log rolling by hand and hauling by narrow gauge railroads directly to tractor skidding and hauling by road. However, a few logging companies in tropical countries are still using diesel yarders with good results. As neither water nor firewood is needed, labor is saved and operation costs reduced.
Up to date, electric-driven logging machinery has not been widely used in tropical forests owing to the lack of local electric power, and there is little prospect for it in the future, owing to the widely scattered selective fellings. However, when clear fellings of large areas of forest for pulpwood begin in remote forests, portable power stations, producing electricity from wood-gas generators, may be useful in places where the cost of transport of gasoline fuel would he too high.
FIGURE 20. - A lasso cable motor winch.
FIGURE 20. - A lasso cable motor winch.
HAULING WITH CABLE CRANES
For many years cable cranes have been used for opencast mines and quarries for conveying coal, stone or other materials, usually horizontally, for considerable distances. There are now many different kinds of cranes used but they may be divided into three main systems. The monocable system depends on a single horizontal cable kept slowly rotating and on which the loads can be hung at any point as the cable passes by. They can also be off loaded, at any point required, without halting the steady movement. The second type of cable crane has one fixed main cable and also a moving smaller line which hauls the loads by gravity along the static main cable. A third type of crane, which is the most frequently used for timber extraction from mountainous forests, is also a tug-cable system hut depends on a static winch or skidder at the top terminus to haul the crane uphill and also to control the loaded crane on its descent down the cable to the base, as in the Wyssen skyline crane. The same skidder also hauls the logs from the forest up to the skyline, as will be described in detail later (Figure 18.)
Lasso cable
The lasso cable of Basel, Switzerland, is a monocable system and is used for extracting small logs from the forest and also for sugar canes or similar loads. It can be used on level country as well as on slopes which are not too steep. The system consists of a circulating cable enclosing the area to be logged, and is suspended at about 2 meters from the ground, and at intervals of 20 to 80 meters, on trees or other supports. Single logs or small bundles of wood (Figure 19) are attached to the moving cable at any point along the circuit by chains ending in special hooks, designed to pass over the cogged wheels. These wheel supports are held in a vertical position on steel tube brackets which are attached, to supporting trees. The 10- to 15-millimeter thick cable used both as a carrier and a traction cable is driven at a slow speed by a 10 to 12 hp diesel winch (Figure 20), mounted on small skids or on rubber tired wheels. This winch is installed at the end of the cable line and near a road or river landing. At the unloading station the bolts are unhooked by manpower, or sometimes automatically by an inclined platform where the bolts are disengaged from the cable by the shock of the impact. Hooks and attaching chains are collected and sent back in bundles by the cable to the woods. Maximum loads of about 80 kilograms can be carried at intervals of 15 to 20 meters, depending on the weight and length of span. The endless monocable of the latest lasso cable type has a total length of 4 kilometers, with an operation depth into the forest of about 2 kilometers. Its operating direction can be reversed to enable the loads always to be carried downhill. The hourly production capacity in European forests is given as 10 to 15 cubic meters of cordwood, depending on the skidding loads and distances.
FIGURE 21. - A Wyssen skyline vane in operation. A Wyssen skidder being operated by African foresters in Nyasaland. Below, logo being hauled up to the main cable A by the operating cable B and the Wyssen carriage at C; below logo on carriage traveling down the main cable which is supported by two trees strutted apart; below offloading logo from the Wyssen carriage on skyline, in Cyprus.
A great advantage of this cable system is that it can be used in otherwise inaccessible areas, such as swamps, steep slopes, or deep ravines. The width of the operation strips varies with the skidding facilities of the logs from the cutting sites to the cable. In areas with small quantities of wood the strips may be kept wider to avoid frequent moving and rigging costs, but in places with a greater density distances should be kept short and the strips narrow.
The high purchase costs of this equipment, with ball-bearing mounted spiked wheels and their special supports, are partly compensated by low erection and operation costs. For heavier loads, up to 300 kilograms, an improved lasso cable is now available, using the ordinary circulating wire for traction only, the heavy loads being carried by a second stronger cable, attached above the traction cable on the same trees. As it is then a two-cable system, the cost price is correspondingly higher.
Wyssen skyline crane
The Wyssen skyline crane, made in Reichenbach, Switzerland, is now used in many parts of the world for the extraction of logs from forests in mountainous or other difficult terrain. There are now five different models of Wyssen Crane yarders and the largest will take loads up to ten tons and cover distances up to one and a half miles, but yarders which take loads up to 3 tons and 5 tons are the most generally used and operate over distances of a mile or more if necessary.
The Wyssen main cable, along which the skyline crane or log carriage runs, is usually supported at about 6 to 8 meters above the ground from standing trees in the forest and on pole trestles, in open country. The log carriage is moved up and down the slope controlled by a lighter cable called the operating line. This line, which is controlled by the yarder or skidder drum, is passed through a pulley on the crane and then down to the ground, where a choker hook is attached to it. The choker hook and line are then pulled out by hand to the logs in the forest and two or more logs are attached to the choker hook ready for hauling in. At a given signal by telephone, the yarder, which is anchored near the upper terminus of the main cable, hauls in the logs still attached to the hook, and pulls them up to the log carriage on the main cable. As soon as it meets the crane, the hook is clamped automatically to the carriage, which is then released and moves slowly by gravity down the main-cable, carrying its load of logs to the base where they are unloaded (see Figures 21 a, b, c and d).
FIGURE 24. - The radio-controlled Sepson towing winch (above) is driven either by the power take-of, of the transport vehicle or by a small petrol engine if mounted on an individual frame. A magnetic plate-clutch operated by a receiving set with 60-centimeter antenna replaces the usual brake. The operator (below) carries a small transmitting set and battery with 500-meter range over his shoulder, and a box with two push-buttons attached to his belt. Once the load is attached, a push-button actuates the starting of the winch, winding the cable at a speed of 60 meters a minute. The operator accompanies the load to guide or to help it clear obstacles by stopping the pull if necessary.
When installing a skyline crane, the skidder first hauls itself up to the top station on a short haulage cable fastened to successive trees as it ascends the slope. The main cable and later also the main carriage are both pulled up by the winch. The 20- to 25-millimeter main cable is attached at both the top and bottom and to trees and then tensioned with a multipulley block. The 10-millimeter operating line has a breaking strength of 5,000 kilograms. The setting up of a straight haul line 1 kilometer in length takes about four days with four men. Logs can be skidded from a distance of about 100 meters from both sides of the main line, depending on the height of the main cable and the accessibility of the logs (Figure 22).
The operation crew is composed of the skidder-operator, two men loading in the forest, and one man at the base landing station to unhook the loads. All the crew are connected by field telephones.
Hinteregger crane
The long-distance Hinteregger skyline crane (Figure 23), built at Kaernten, Austria, transports logs not only in the vertical position, but also horizontally, thus permitting the construction and use of lower cable suspension. The power unit may be installed at the bottom or at any suitable site along the main cable as well as at the upper terminal and an endless operation cable enables transportation on level ground as well as on slopes. A 15 hp motor transmits its power by V-belts to a special small unit, which can be used for the driving of gravity cableways over short and long distances. The traction cable-drum has a capacity of 800 to 1,100 meters of a 10-millimeter cable, and a traction pull of 1,000 kilograms. Maximum individual loads up to 1,000 kilograms can be skidded up to about 100 meters from either side of the cable.
In Sweden, a radio-controlled cable winch, the Sepson (Figure 24), is used both for ground skidding and loading or for other operations. An illustration of this winch is shown on another page. Other winches for cable cranes are the smaller Krasser, of Austria, and many others manufactured in Austria, France, the Federal Republic of Germany, Norway and Switzerland.
Buko-Universal skyline crane
The Buko-Universal skyline crane is built at Berne, Switzerland, and works on a two-cable gravity system but without the Wyssen stop device. All operations including clamping the carriage at any point along the main cable, the lowering of the hook to the ground and ground skidding the logs up to the main line and then the hauling of them up or down hill, are controlled from the skidder. This skidder or operation cable-drum, placed at the top station, has a cable capacity of 2,000 meters and is driven by a 30 hp motor. The main cable which is attached to trees and used for hauling distances up to 2,000 meters has a 16 to 22 millimeter diameter.
The operations and capacities of other similar cable crane systems, based on the Wyssen gravity cable, have so far been limited to their local operations and have not yet been used in the tropics, and detailed information is not available.
Küpfer cable crane
The L. &; B. Küpfer is a two-cable crane, built at Steffisburg, Switzerland. All operations are controlled by the traction cable. The Küpfer carriage can lift and convey loads up to 2 tons.
FIGURE 25. - Monorail transporter.
MONORAIL YARDING
One of the most recent hauling methods is by monorail transportation (Figure 25). It consists of a self-driven wagon unit and trailer which travels unattended along a single line of rail and is automatically stopped by special stop-devices placed at any point along the track. The wagon and trailer can transport loads up to 1.5 tons. Rail sections of 3.6 meters in length are supported by low expanding supports to enable the vehicles to ride clear of the ground, and these telescopic adjustable supports permit, within certain limits, the easy crossing of rough and irregular ground surfaces. On a cleared ground strip only 1.5 meters in width, the portable rail sections 74 kilograms in weight can be easily laid and assembled by two men. On steeper slopes, the speed of the loads descending by gravity can be controlled by a power-winch, placed at the top end of the slope, which also hauls the empty trailers back. A safety stop is provided to prevent any runaway danger of the trailers in case of a cable breaking.
Owing to its small carrying capacity, the present models of this monorail can be used only for the transportation of the smaller timber sizes, and it is mentioned here as a possible method for future pulpwood logging in the tropics.
Crawlers or caterpillar tractors were first introduced to tropical forestry in about 193O, and were soon recognized to be the best hauling tractors available for extracting big logs from the selective fellings of large dimension tropical timber, which needed great hauling power and good mobility, which the former stationary yarders did not possess. Extensive tests with tractor logging were made in Gabon, at that time the greatest producer of okoumé peeler-logs (Aucumea kleineana), the total log production exceeded that of the whole African west coast and its actual exports are still higher than of any other tropical timber species. This logging experience in Gabon with tractor skidding became a guide and incentive for the use of crawler extraction for tropical logging in many other parts of the world.
In spite of the great weight of crawler tractors, the Caterpillar D 7 weighing 12 tons and the Allis Chalmers 200 over 20 tons, their ground pressure is far below that of draft animals, such as oxen with 1.4 kilograms per square centimeter. Starting at 0.3 kilogram per square centimeter for small tractor of 40 to 50 hp. it reaches 0.6 kilogram per square centimeter only for the heaviest types. On soft swampy ground with a support capacity of 0.20 kilogram per square centimeter or less, such tractors were found too heavy and, to bring the ground pressure down, the length and width of the tracks had to be increased. This led to the construction of special crawler-tractor types, like the Water Buffalo (Figure 26) built by Albion Motors Ltd. This 70 hp tractor, of 8 tons, has a ground pressure of only 0.16 kilogram per square centimeter, which is less than one half of the standard crawler-tractor types, permitting its use on very soft level ground. Another similar tractor, of the same ground pressure, is the Long County tractor built by Commercial Cars Ltd (Figure 27). Both tractors have to be considered as machines built especially for working on very soft ground or in swamps, and are not used for yarding on hard rocky soil, which would very rapidly wear them out.
The great advantage of the standard crawler-tractor types is their capacity to penetrate into the forest right up to the stump of the felled trees, with no or very little road construction work. There, they pick up the logs and yard them to a landing place for further transportation. If necessary, they also use them for loading. As in North American forests, logging methods in the tropics have thus been revolutionized by the introduction of the crawler tractor. New forest areas have become accessible and exploitable, and log production increased. This applies to African forests as well as to those in the Far East.
The additional equipment such as dozer-plates, rooters and rippers, and loading devices of several types, enable the tractors to be used for hauling of roadmaking machinery, and for all kinds of work such as ground skidding or dragging, skidding with pans and sleds or with sulkies and arches and also for timber loading, highlead yarding and forest clearing.
As regards skidding equipment used in the tropics, it has been stated that some of the most simple but efficient accessories which could have improved both the quantity and the quality of log production have been generally ignored or disregarded. Skidding pans and cones to protect the leading log-ends, and locally built sleds, have been used on the African west coast by only about one percent of all logging firms. The chief reason, the lack of adequate traction power, was eliminated by the introduction of the tractor, but even now skidding pans are very seldom used, despite a 30 percent saving of traction power and much less damage to the dragged logs compared with skidding on bare ground. Yarding with mechanically driven bummers is an almost unknown transportation system in the tropics, and the high-wheel carts, used mainly in Latin America, are not designed for motorized traction.
The versatility of crawler tractors and the present rapid improvements in wheeled tractors, which have made progress in the same way and as rapidly as trucks and trailers, have revolutionized logging methods all over the world, including the tropics. Ground skidding with crawler tractors developed directly into yarding with crawler-track arches, considered for many years to be the most suitable logging equipment for heavy timber, are being replaced in recent years by wheeled arches and sulkies.
One important restriction, however, has to be mentioned. Although log output can be increased by tractor yarding, their quality suffers. Log skidding along bare ground, either full length or with only their butt ends, is much more damaging to the logs as well as to the ground, than log rolling by hand, especially for peeler and veneer logs. Often the bark is torn off- on dry hard ground, and the bare wood, before it can be converted, has to be carefully cleared of an outside layer damaged by mud, sand and gravel, dulling or breaking the cutting edges of machine tools and wasting a part of the valuable round timber.
GROUND SKIDDING WITH TRACTORS
Log transportation by tractor, though needing much power and damaging the logs on hard rocky soil, is widely used in the tropics, while sulkies (a two-wheeled, one-axle vehicle) and Fairlead arches are becoming more widely used. The best skidding distances vary between 200 and 500 meters, though scattered logs may be yarded from 1,000 meters and more. The logs are not usually nosed or sniped at their front end and are attached with wire slings or chokers to the tractor's drawbar. Steel cones or hooks for the protection of the leading end are seldom used. When ground yarding with pans, the latter are fastened to the tractor with chains or steel wire, but best by the tongue of the pan. By pulling the logs over the pan for loading, the rigid tongue connection between the tractor and the pan greatly facilitates the loading.
Crawler tractors of up to 200 hp. and wheel tractors up to 320 hp are used, with a tendency to increase the heavier types as more suitable for the skidding of heavy timber in long lengths. In order to profit as much as possible from the tractor's pulling capacity, and to avoid the bunching of logs for this purpose, the log lengths have rapidly increased to full bole length, and, in some countries, to whole tree lengths. Skidding of whole trees cannot often be applied to hardwood timber with voluminous crowns except under special circumstances. It is done in the natural pure teak forests of Java, where the fellings take place two years after the girdling of the trees, and most of the great dry branches are broken off by the shock of the felling impact.
Nevertheless, despite these and other log loading measures described later, the full traction capacity of the big tractor types is seldom reached and their use is often uneconomic (Table 1).
In tropical forests, where selective fellings are proceeding with special attention to their conservation, log lengths are often limited to 12 or 15 meters, to avoid heavy yarding damage to the young seedlings of natural regeneration, as well as to the roots and stems of the remaining timber.
TABLE 1. - SUGGESTION FOR IL DAILY OPERATION SHEET FOR SKIDDING WITH TRACTORS.
B & C. Logging Co., Logging site X...........................Date .......................................
Tractor type and number:.................Type of arch:..................Type of sulky:..............
|
Check at garage before start |
Times of |
Distance, in km
|
Waiting time for load
|
Real skidding
|
Distance in meters
|
Load, in m3
|
Times of |
Real skidding time |
Distance in meters |
Load, in m3 |
Times of |
Distance in km |
Total of motor running time, in minis |
Total of real working time, in minus |
Time of maintenance |
||||||||||
|
of tractor |
of arch |
||||||||||||||||||||||||
|
Fuel in liters |
Oils in liters |
Start from garage |
Arriving at site |
Start from landing |
Arrival at site |
Waiting for load |
Start from landing |
Arrival at garage |
Washing and cleaning |
Oiling and greasing |
Refueling |
Minor repairs |
Washing and cleaning, oiling, greasing |
Minor repairs |
|||||||||||
Logging crawler tractors are at present generally equipped with at least one winch, attached to the rear of the tractor and accommodating up to 110 meters of 1.5- to 2-centimeter hauling cable, depending on its diameter and the tractor size. If the tractor cannot get directly up to the stumps to pick up the logs, the latter can be drawn to the tractor by the winch. The hauling cable is pulled out by manpower and, if it is too short to reach the logs, an extension cable can be used. A second winch, for the mechanical outhaul of the hauling cable, is normally not mounted on the tractors, because of its high cost, but can be added.
To improve versatility, efficiency and traction ground adherence, many of the heavier crawler tractor types are equipped with a dozer plate for road building, and sometimes with specially designed log loaders.
In the past, crawler and wheel tractors were built for genera.! use and then adapted and equipped with various accessories for forestry work, which led frequently to unsatisfactory tractor types. More detailed research by tractor manufacturers into the special equipment required for logging in both temperate zones and tropics has resulted in the construction of tractors especially designed for logging purposes and far better adapted for skidding and hauling.
Nevertheless the current American and European tractor types are often too highly perfected and too delicate for tropical working conditions. What the tropics need is a tractor with a powerful engine, well-protected underneath and also over the driver's cabin, easy to drive and resistant to the rough going on poor forestry roads, and also capable of withstanding the often heavy handling and driving to which it is subjected. The tractor should have no delicate construction parts, which wear out too rapidly or deteriorate by heat and humidity. Following better collaboration between tractor builders and loggers, these short comings are now being eliminated or largely improved, and after a given training period local drivers are acquiring the experience necessary for correct handling and maintenance of the most modern tractors.
The advantages of tractor logging cannot and do not yet show the same good results in tropical forests as in the temperate zones. The disadvantage of costly and relatively delicate machines is emphasized in industrially less developed countries where several factors are opposing their profitable use. These are: high depreciation rates and operation costs, volumes of timber which are too small and too scattered, longer skidding distances, expensive spare-part stocks, few service and repair stations, and a great lack of trained labor and experienced loggers.
For these reasons, crawler tractor logging does not always give the expected favorable financial results when used in the tropics. Wheeled tractors, which are less expensive and operate at lower cost, are at present competing very successfully and will gain further ground in the future.
Crawler versus wheeled tractor
The question of selecting a crawler or a wheeled tractor for tropical logging purposes did not exist until about 1945 as wheeled tractors did not then possess the traction power of crawler tractors. They were too light and their ground adherence too small, but these have been improved during the last few years to such a level that logging with heavy crawler tractors has considerably diminished in the tropics, and it is anticipated that the all-wheel drive tractor will progressively replace the crawler tractor. Lower capital investment, smaller operational and maintenance costs, and greater flexibility and speed which enable it to be used in the forest as well as on public roads, are great advantages with which the crawler tractor cannot compete. The crawler will be chiefly limited to heavy tasks and to very rough or slippery ground conditions where wheel tractors cannot operate.
The small ground contact area of wheel tires, resulting in reduced traction power, has been greatly improved by the manufacture of wide-based tires of greater diameter, up to 180 centimeters, which mold themselves around the obstacles, and increase the ground contact area by a low inflation pressure.
Another possible way of increasing the ground adherence is by the use of removable wheel girdles (Figure 28), antigliding chains, or of full, crawler-type track chains (Figure 29), fixed to the rear wheels like the halfbacks of English, Swiss and German construction. There are also light, simple tracks consisting of two rubber bands fitted over both the rear and the front wheels with metal clamps, such as the Bombardier tractor widely used on snow roads in Canada. To avoid a rear wheel spin a rear axle lock controlled by the driver was built in, forcing both wheels to operate together. Driving and steering with small front wheels mounted with narrow tires became too difficult for the heavier tractor
types and, to improve it, the front axle was fitted with the same size of tires as the rear axle, thus increasing the ground-holding capacity. The one-axle drive was replaced, for tractors above 25 ph. by a four-wheel drive, and the difficult two-wheel steering replaced by four-wheel steering. As big wheels require great driving power, both the weight and power were increased, even beyond the heaviest crawler tractor, as shown by the following comparison:
|
Crawler tractors |
Type |
Weight (tons) |
Hp |
|
Caterpillar |
D 8 |
18 |
190 |
|
Allis-Chalmers |
HP 21 |
20 |
204 |
|
Wheel tractors |
|
|
|
|
Caterpillar |
DW 20 |
12 |
225 |
|
Letourneau Tournahauler |
|
24 |
270 |
|
Wagner |
LG 320 |
23 |
320 |
The tractor weight was increased partly by the heavier engines, and by the accessories for road building and log loading; weight can be added by filling the wheels with water and by the swan-neck coupling of the trailer, supported by the rear wheels of the tractor.
Research work on tractor tires has succeeded not only in finding new synthetic raw materials of greater resistance and longer durability than rubber, but also in adapting the cross-section of the tires to an elliptical, flat form, such as Lypsoid tires, which give smoother riding on rough ground and better stability on curves.
Strong raised rubber ribs, gripping the ground very efficiently, increase the traction power of wheel tractors and, as far as the durability of some synthetic tires is concerned, recent improvements have reached such perfection that one set of tires may be sufficient for a tractor's service life.
When starting, the traction power of wheel tractors is, of course, smaller than that of a crawler tractor of the same weight, but this is largely compensated for by its greater travel speed and by its capacity to ride both in the forest and on the road, thus avoiding the reloading that is necessary with crawler tractor skidding. The greatest improvement in this capacity is represented by the Tournaskidder, built a few years ago by the Letourneau-Westinghouse Company; a four-wheel-drive tractor skidder, moving forward and backward at the same speed, with two-way controls, permitting the driver always to face forward, with an all-wheel steering control and mounted with an arch and a powerful winch. Designed for skidding tree-length pulpwood, which can be hauled directly from the forest to its final destination, production costs have been lowered by 25 to 30 percent compared with those of the crawler tractors, giving the wheel tractor a high priority over the crawler tractor. It should be mentioned as regards driving power that the trend to utilize the heaviest tractor types is seldom profitable. Heavy bulldozing work may require 100 hp and more, but such high-powered engines are not always necessary for logging.
FIGURE 30. - Consumption of fuel and oil according to engine and operating conditions.
SOURCE: Tractors for logging, FAO, Rome, 1956.
A. Maximum theoretical consumption.
B. Consumption under difficult working conditions.
C. Consumption under normal working conditions.
D. Consumption under easy working conditions.
Practical experience has shown that in many tropical forests the 80 to 100 hp type of engine is the most suitable. Its power is sufficient for lighter bulldozing and its direct drawbar pull permits the yarding of 8-ton logs. Single hardwood logs of 15 to 18 tons are an exception in tropical forests and, if their extraction in full length is necessary, the tractor winch can do it.
The small number of man hours worked per year in tropical forests being one of the main reasons for high depreciation rates, the low tractor efficiency in forestry work should also be mentioned as a great factor increasing production costs. Control figures established with wheel tractors in north German forests during a period of seven years showed a quite surprising low utilization ratio, the average working loads for 45 to 50 hp tractors having been only 10 percent, and for 25 to 30 hp tractor about 25 percent of the tractors' capacity. Only three tractors out of 22 showed an average working load of 40 percent, leading to the conclusion that the smaller the tractor, the better its utilization ratio and the lower the production costs.
A much wider use of small tractors of 20 to 30 hp should also be made in tropical forests. Very often a 100 hp tractor is doing small jobs which two or three men could do much cheaper. If there is only one big tractor available, bunching of 4 to 5-ton logs by this engine may be justified but, in a general way, smaller logs of 3 to 4 tons would be much cheaper if bunched with a 30 hp tractor, which can also do a number of small tasks such as the transport of supplies and labor, light road maintenance, plowing and tilling in the nurseries, etc., thus raising the utilization ratio and decreasing costs.
The fuel problem
The price of fuel has of course a great influence on production costs (Figure 30). Although the available fuel may not be the best and desired one, the cheapest fuel may not be available or the motors not adapted to use it.
Gasoline and diesel oil engines represent the great bulk of motor-driven logging machinery. In some countries which have their own fuel supply, the use of the gasoline motor may appear cheaper in operation than the diesel motor, but in a general way the advantages of the diesel motor are so great that only small tractors up to 10 or 15 hp are still built with gasoline-driven motors, while all heavier tractor types are equipped with diesel motors. The diesel engine is more expensive to purchase, but its fuel costs and consumption are much smaller, if the diesel oil is not taxed too heavily. The higher purchase price of the diesel type tractor has to be compensated for by a certain number of working hours, to be calculated for each type separately. The actual number of working hours at which it begins to be cheaper in operation than a tractor operated on gasoline will also depend upon the price difference between the two fuels.
With regard to fuel transport costs, it must be remembered that the gasoline engine requires up to twice as much fuel as the diesel motor. This means also doubled transport costs for the gasoline, increasing the production costs.
The latest invention in driving power for logging engines is diesel electric power, transmitted by individual motors to each of the four wheels, to the winches and to all accessories. The diesel-driven generator of the Letourneau-Westinghouse tractor, is placed, for equilibrium and construction reasons, in the front of the tractor, across the driving direction. The normal flow of electric energy to the motors is automatically channeled in such a way that the wheels which carry the bigger load also obtain the necessary greater power. The electric braking, retarding each wheel, gives the tractor exceptional safety in operation. The weight of the motors mounted in the wheels substantially increases the ground adherence and, with it, the traction capacity. For greater versatility, this tractor can be fitted with roadmaking and loading equipment.
Tractor winches
Tractors, whether tracklaying or wheeled, are now usually equipped with a rear winch or sometimes with two winches, increasing their traction capacity versatility. Intended originally to rescue the tractors by self-hauling out of bad road spots, the winches have been improved and adapted for logging purposes. At the beginning, only one winch was mounted at the rear of the tractors, for hauling in the logs by ground skidding either singly or in bundles.
Winches are not built by the tractor manufacturers but by other firms which specialize in the making of tractor equipment, such as Hyster, Carco (Figure 31), Isaacson, Oliver-Cletrac, etc. Winches are designed for better stability, particularly of light tractors, for under-wind with capacities ranging between 2,000 kilograms for bare drums at a line speed of 35 meters per minute, and 50,000 kg for bare drums at a speed of 15 meters per minute. At full drum, the same winches still have a pulling power of 20,000 kilograms at a cable speed of 30 meters per minute.
Working alone, without a heavy crawler arch, the tractor cannot withstand the traction effort of the winch, much bigger than its drawbar pull, and has therefore to be attached to a stump or a tree, or to an anchorage-spade to avoid it moving backward (Figure 32).
For ground skidding with Fairlead arches the logs are lifted up by the winch to the upper roller at the crown of the arch and kept up there, during the transport, by the winch brakes, now mostly automatic. Newer winch types are also fitted with an automatic overload protection making the clutch slip when its load capacity is exceeded. Releasing the winch brakes allows the logs to slide to the ground.
As the line outhaul from the tractor to the logs had to be done by manpower, a second winch was mounted for this purpose and the cable length for both the haul and haulback line was increased to several hundred yards, thus transforming the tractor into a mobile ground-skidding unit, later completed for high lead skidding by the addition of a portable spar tree, and by a third drum for loading {Figure 38).
Tractor winches are frequently used in the tropics for loading trucks, trailers and railroad cars. If only one tractor is available and the loading is done with the same winch that is used for yarding the loading is too slow both for the lifting and for the lowering of the loads. On the other hand, an additional winch is expensive and it is a question of cost whether it can be recommended for the slower, tropical working conditions. For ground skidding, and for logging with Fairlead arches, only one winch is necessary and, as these are the most widely used skidding methods, tractors in tropical forest are usually equipped with only one winch.
SKIDDING WITH ARCHES AND SULKIES
Arches, and to a much greater extent sulkies, have several great advantages compared with ground skidding. The logs are brought to the arch by the tractor winch, and their front ends are raised to the horizontal roller on the archtop. The high position of the Fairleadroller produces a small "high-lead" effect for winching tree-length logs out from the felling site, on distances up to 100 meters and more, and the wide base of the crawler tracks gives the arch a great stability against tipping during the approach of the logs, as well as during the hauling. Being hauled in a half suspended position, the sliding resistance of the logs is less than 50 percent of horizontal ground skidding, thus permitting double loads for the same traction power and, at the same time, a faster hauling speed. A substantial advantage, besides cleaner and less damaged logs after removal, is the simplicity and speed of the unloading. By releasing the brake of the winch, the logs drop down to the ground and the chokers are unhooked. For bucking at the landing place, each log can be dropped singly at the desired place.
The disadvantage of crawler-borne arches is their great weight and certain difficulties of maneuver when backing up.
American-built, crawler-borne Fairlead arches of the Hyster and Carco type, with a loading capacity up to 25 tons, were the first to be introduced to the tropics, before and after the second world war but, though well appreciated when introduced, experience over the years has not been in their favor. A crawler-borne arch is expensive, it is heavy and it absorbs a good deal of the tractor's pulling power, especially for uphill skidding; also, operation and maintenance costs are high. A change from this heavy machine to the lighter, smaller and more economic sulky on rubber wheels, supporting an arched or square-framed axle with the Fairlead, was only a question of time. In many countries, the former crawler support of the arches has been replaced by wheels. The saving of yarding costs, by changing over to wheeled arches and sulkies, was found to be such a strong incentive for the manufacturers of logging equipment that they are now mounting nearly all their arches on wheels (some of the heaviest types of tractors and arches excepted).
Crawler tractors and arches with narrow steel ridges on their shoes to increase their ground holding capacity are not admitted on public roads or on smooth-surfaced forest roads. No such restrictions exist for wheeled vehicles within the permitted weight and speed limits.
The working field of crawler tractors and crawler arches is thus limited to skidding timber from the forest to a convenient landing place for loading and hauling. This method is the most common one, whether the yarding is done with a crawler-borne or wheeled logging equipment, though it is evident that the ideal solution of the log transport problem would be loading the timber at the stump and hauling it directly to the mill or other destination.
Practical experience has shown that the big Fairlead crawler arches can rarely be loaded to full capacity with single logs even of full tree length and that, even with prebunched loads, the tractor's full capacity is seldom reached. Logging arches on low pressure wheels of many types, dimensions and loading capacities proved to possess a surprising resistance and durability. Rubber wheeled arches lasted two and three times longer than arches with crawlers. A Caterpillar D 7 crawler tractor is often more efficient when pulling a well-loaded crawler arch, because its traction power can then be used nearer to its full capacity than that of a D 8 model which cannot get its full load. Wheeled arches need less traction power than the crawler-borne ones, and smaller, cheaper crawler tractor types can be used with a lower fuel consumption (Figure 34).
The problem of avoiding the loss of traction power required for pulling the arches, which are 3 to 8 tons in weight, has been resolved by eliminating completely the arch carrier and by mounting the arch directly over the tractor itself. This was first done over the tracked types and then later over the wheel tractors. The logs were carried on the rear of the tractor, protected with a steel plate. One of the first American tractors of this type was the Tomcat logging tractor, built by the United States Forest Service at Portland, Oregon. In later types, the protective steel shield at the rear of the tractor was abandoned, and the arch transformed into a strong frame mounted over the tractor and supporting a projecting block which enabled the logs to be skidded with their leading end suspended. The same solution was adopted later for the wheeled tractor, and is today the most suitable logging equipment for ground skidding tropical timber of various sizes Figure 35).
In hilly country, the calculation of capacity loads for crawler or wheeled tractors working with or without arches or sulkies depends a great deal on the slopes to be negotiated, as the pulling capacity of a tractor decreases rapidly when going uphill. On level ground, loads heavier by 20 to 30 percent can be skidded with crawler or wheeled arches than by ground skidding. The traction power difference between ground skidding and skidding with arches is more than 30 percent, but a part of this difference is absorbed by the pull of the arch or sulky.
For uphill skidding this power difference narrows with the increasing slope. For example, on 10 percent grades the arch-skidded load is about the same as the ground-skidded full capacity load on level ground. For slopes over 10 percent the pulling of the arch or sulky absorbs more and more of the traction power and reduces the weight of the utility load. It is possible, by dropping the logs at the bottom of a steep grade and then pulling the arch to the top first, to ground-skid the logs uphill. This is sometimes done on short distances, but ground skidding uphill should be generally avoided even on soft and wet ground. The logs dig heavily into the ground and may need even more power than the traction power required for the pulling up of the loaded arch or the sulky.
For downhill skidding traction power is increased by the gravity effect of the weight of the tractor, plus the load and the arch. Depending on the slope, up to four times the ordinary load can be skidded than is possible on level ground.
FIGURE 36. - Model D Tournapull whell tractor equipped with bulldozer plate and arch.
FIGURE 37. - Unimog tractor for universal use.
It is, therefore, not easy to establish the optimum skidding load for a given tractor type if uphill skidding cannot be avoided by a better road location. Wet or dry ground, rocky or smooth road surface, and, particularly, the tractor driver's personal ability, have a great influence on possible maximum loads.
The wheeled tractor, with a self-carried Fairlead arch, has a much higher mobility than two separate skidding units because it has greater ground adherence because of its greater weight. The purchase price is lower than that of the crawler tractor and its maintenance costs smaller, as only one engine has to be taken care of instead of two. Besides the big American tractors of recent design, the Letourneau Tournaskidder; and Tournapull (Figure 38) the Timberland Timber-cruiser, the Wagner-built tractors, the French Agrip and the German Unimog are all good tractors, able to deal with most timber hauling requirements.
The French CR 8 Continental, built by Ets. Richard Frères, is a four-wheel-drive diesel tractor of 160 hp. with a special steering system blocking completely the inside wheel when turning empty on the spot (minimum turning radius, 4.3 meters) or increasing the speed of the outer wheels when traveling under load. The engine and equipment are the same as the CD 8 crawler tractor, including a bull- or angle-dozer blade in front and a winch and a drawbar at the rear. Being exclusively a traction engine, its drawbar pull is 8,400 kilograms at 2.4 kilometers per hour, against the CD 8 crawler tractor with 13,000 kilograms at a smaller speed of 1.5 kilometers per hour. Its small ground adherence and consequent smaller traction power limits its use to smaller road-working jobs, and skidding with or without arches. Arches do not improve the ground adherence of the tractor, and it is intended to design the next Continental tractor types with the logging-arch mounted on the tractor itself.
The German Unimog manufactured by Daimler-Benz, at Stuttgart-Gaggenau, is a truck and tractor of universal use. The first type, a four-cylinder diesel motor vehicle of 26 hp was found too weak for forestry work in the tropics, and recent models are being equipped with a 32 hp diesel. With its four-wheel drive it can negotiate slopes of 60 percent, and it can pull loads of 40 tons on level ground and 6 tons on a 25 percent slope. The differential gears of both axles can be blocked either both or singly. Its six forward speeds range between 3.5 and 50 kilometers per hour in first and sixth gear respectively, reverse speeds being between 2.5 and 4.5 kilometers per hour. The winch, with a drum space for 70 meters of an 11 millimeter cable, has a traction power of 3,500 kilograms at a speed of 0.6 meter per minute and can be mounted at the rear as well as in front of the vehicle.
The Unimog is a real multipurpose tractor for all kinds of work and transport, in agriculture, forestry or road building (Figure 37). Apart from the basic machine with its powerful winch for approaching and loading logs, the tractor can be equipped for logging with a log clamp and accessories for self-loading, and for wood transportation with or without sulkies, or with or two four-wheel trailers. Its versatility is greatly increased by adding implements needed in forest nurseries, for tilling, sowing, fertilizing, planting, hole digging; for spraying to control pests and diseases and for fire-fighting.
One of the latest models for heavy logging purposes has been equipped with a Kreiling skidding device, a two-drum winch, each drum having 3,000 kilogram traction power, and which can be operated independently or together with a 5,000-kilogram pull. Another model has a single-drum Pan winch of 3,000 to 5,000 kilogram traction power, which can be switched to 5,000 to 7,000 kilograms. To avoid their backing up while approaching the logs, the spades of both tractors can be elevated to the travel position and carry a horizontal roller over which passes the winch cable, thus holding the front end of the logs in a suspended position; this greatly assists ground skidding. For working conditions in European forests, the daily log outturn is given as 50 to 60 cubic meters for a maximum hauling distance of 800 meters.
Summing up, the following points may be borne in mind when tractors for logging are to be purchased:
(a) The great advantages of the improved wheel tractor make them well adapted for tropical logging. Their lower purchase price, repair and maintenance costs, and their versatility give them high priority over crawler tractors.(b) The use of crawler tractors remains justified for big jobs only, and for rough, soft or slippery ground, where the wheel tractor cannot operate.
(c) The most suitable tractor motor is the diesel. The saving of operation costs with diesel traction is so substantial that few possibilities remain open for the gasoline motor.
(d) Diesel electric-driven vehicles present a recent improvement in the power supply for wheel tractors. This equipment is relatively expensive and its use in tropical forests can be recommended at the present time only for big logging companies with a sufficient log output to keep depreciation rates and operation costs within limits which the sale prices can support.
(e) For the time being, and for most logging jobs in the tropics, the medium - heavy, all - wheel drive tractor of 60 to 100 hp. with interchangeable equipment for bulldozer or angledozer plates and with root rakes, road rippers and loaders, and which can be operated with logging arches and sulkies, will give much better financial results and higher efficiency rates than heavy tractor types. These latter are expensive in capital outlay and in operation costs if their great production capacity cannot be fully or very largely used; and this is seldom the case in tropical logging operations.
(f) The use of small wheeled tractors, supplementary to the medium and heavy wheeled ones, must be strongly recommended for bunching and loading, and for the many small transportation jobs frequently necessary in any logging operation.
SILVICULTURE ASPECTS OF TRACTOR LOGGING
The silviculturist has to view tropical logging operations from two standpoints: damage and destruction, and the conservation and regeneration of the forest.
Keeping in mind that tropical logging consists mainly of selective felling of single trees, growing alone or in small groups from which the tractors have to fetch them, the damage to small trees due to the yarding and hauling equipment is chiefly limited to the loading sites and also to friction at the lower part of the trees and roots by the skidding of long timber. The longer the logs, the greater the possibility of damage to the remaining stand. Tropical trees with heavy crowns are not easy to guide during felling into a favorable skidding position and sometimes part of the felling waste has to be bulldozed out of the way to clear the log for skidding. Frequently this is not possible without slight damage to the surrounding trees. Damage to such trees as may be merchantable species below the exploitable felling diameter may however, with care, be avoided. If they belong to unsalable timber species, occasional damage or complete destruction is of no importance.
In road construction only the area of the surfaced main roads should be considered as a total loss, reaching for dense road systems 0.25 to 0.5 percent of the total forest area. Nonmetalled main roads and feeder roads recover quickly as soon as the traffic has ceased, with a layer of vegetation soon protecting the seedlings of the future forest trees.
Regarding damage by tractor logging from the forest conservation and regeneration side, it is often observed that tractor yarding may have a favorable effect in selective fellings. The forest soil, overturned and plowed by the skidded logs, is often in a more fertile condition than the surrounding dark, high forests, with badly aired, acid soils. The tree canopy, keeping off the sun and the air, is broken up by selective or heavy fellings. The shifting cultivation of the natives in the tropics is based on the great ground fertility of cutover forest, though it is also improved by the ashes of the burned felling waste.
The question whether the natural tree regeneration of valuable timber species in tractor-logged areas and on feeder roads can be as rich as in the adjacent forest, can be answered in a very positive way, provided the necessary number of mother trees has been left at convenient distances to produce sufficient seedlings. Observations made of the lanes cleared alongside the roads for quicker drying of the surfaces, and also of abandoned feeder roads, usually show great promise not only for full regeneration of the destroyed or damaged forest, but also for an increased percentage of desired timber species in favorable ecological locations.
Forests in the low and impenetrable jungle are very different from evergreen high tropical forests, which contain many desirable merchantable woods. Stretches of earth roads, and their lanes in the jungle, require much greater maintenance work to keep them free from vegetation than in the high forests. The intensity and speed of their reoccupation by the jungle is so great that, a few weeks after the traffic has stopped, a new passage has to be freed by bush-knives or by bulldozers.
As high-lead skidding is not possible without a suitable tree or a spar for attacking the line blocks and guy lines and as such trees in the desired location are not always available, the tractor manufacturers have taken the last step in the evolution of mobile skidding units and have now made portable high-lead equipment with steel spars of 18 to 35 meters. The lower end of the spar is hinged to the Fairlead arch, and the upper end
is dropped during transport into a cradle at the front of the tractor. A Caterpillar D 8 engine also furnishes the power for three Hyster winches: two for the skidding operation and one for loading. The three drums on the D 8 tractor carry 400 meters of 28 - millimeter main line, and 1,050 meters of 15 - millimeter haulback line.
The Skokum-Madill mobile spar tree is built in lengths of 20, 27 and 33 meters, steadied in the vertical position by 6 guy - lines and can be erected in two hours. The Gearmatic spar, a tabular telescoping spar of 30 meters in length, has a bottom diameter of 75 centimeters and is powered by a 275 hp diesel tractor (Figure 38). The complete unit weighs 55 tons and the direct pull of the hauling line is 45,000 kilograms. Cables of 28 and 18 millimeters are used for the main and return lines. Two men only are necessary to operate the unit, the tractor driver doing the skidding and the loading, with one chokerman. A third man does the felling. An optional fourth man may increase efficiency by bunching logs out of reach of the high lead with another tractor, and by helping the chokerman. Such a four-man unit is credited with an output up to 45 cubic meters of logs a day in coniferous forests.
This recent development of high-lead yarding with mobile steel spars makes for a hitherto unknown mobility and rigging speed, and should not fail to conquer the tropics in the near future when more merchantable
timber species per hectare will increase the yarding volume to such a level that high-lead yarding, because of its great capacity, will become cheaper than tractor yarding. The high rigging costs of stationary high-lead spar trees prevented, up to now, the general use of high-lead logging methods in the tropics, because the small logging volume could not support the high production costs. With portable spar trees, rigged in two hours, the unfavorable economic aspect of the application of this equipment can change to a profitable one, especially in view of the expected increase of the logging volume per hectare by new merchantable timber species.
Logger's dream
A much cheaper self-propelled logging equipment is the "logger's dream," originally designed for loading timber, but now largely used for ground skidding on short distances. Its capacities are much smaller than those of the above described mobile spar tree units and the A-frame is only 10 meters high, but the comparatively low purchase price makes acquisition possible for many medium and small loggers, who cannot afford to buy the mobile spar tree units. The short A-frame cannot give much lift to the logs when skidded over distances up to 200 meters. The two cable drums, mounted with the A-frame on a truck, are powered by a V-8 Ford motor of 100 hp. The main cable has a pull of 10,000 kilograms, quite sufficient for any dimensions and weight of merchantable logs. The total weight of the logger's dream being about 5 tons, it does not possess a sufficient ground adherence to stand a strong hauling strain, and it has to be attached by a strong cable and guyed by two lines to steady it during the skidding and loading. Both the drums for the main and rehaul line are fitted with an automatic clutch, releasing the drum in case of excess strain. This foolproof device is of great value for the operation of delicate machinery by inexperienced crews, who need a long time to understand the capacity limits of the machines put into their hands. The crew is composed of four men: the driver for moving the truck and for skidding and loading; one or two choker-setters and one man to unhook the logs. If the timber to be skidded has to be hauled from the sides to the skidding line with the help of pulley blocks and extension lines, a fifth man should be employed to avoid loss of time.
The skidding capacity of the logger's dream depends on the log dimensions, the working site and the ability of the labor, and may average about three logs per hour of up to 10 cubic meters. It can get to any place in the forest where a safe passage can be prepared for it, and can be rigged in a few hours. Its best location is at a railroad or road junction, where the cold-decked logs can be loaded.
COMBINED YARDING AND HAULING
Yarding and hauling were in the past quite different and independent operations. The mechanical equipment was suitable for only one part of the work. It could not be adapted to deal with the collection of the logs at the stump and also transport them, without breaking the load, to the final destination. The great evolution of logging methods due to the introduction of crawler tractors was limited by the unfitness of the crawler tractor for road hauling purposes. On the other hand, the wheeled-tractors, which appeared in the tropics almost simultaneously with the crawler-borne tractors, were too light and did not have the necessary ground adherence or the needed traction pull for yarding heavy tropical timber. They had to be improved to give more power and also adapted for better ground gripping.
One of the best examples of these improvements and adaptations is the French Latil tractor (Figure 39). The original four-wheel-drive gasoline engine has been replaced on recent types by diesel power. About 70 of these were already in use in 1950 in Gabon and what was then French Congo. The front winch has been replaced by a much more powerful winch at the rear, combined with a fork later improved to a heavy spade, digging deeper into the ground, the greater the traction-strain. Its original power of 65 hp was raised to 120 hp on the latest models.
Crawler tractor manufacturers are now also making wheeled tractors, of which the heavier types, starting with about 40 ph. are suitable for forestry work. In order to profit from the increased speeds of wheeled tractors of up to 30 kilometers per hour, which is three or four times faster than that of the crawler types, their power had to be increased to 275 hp for the Letourneau, and up to 320 hp for the Wagner log-skidders, Both built in the United States, they now represent mechanical logging equipment for combined yarding and hauling.
Russian tractor manufacturers have improved on the design of combined logging equipment and have also mounted a circular felling saw on their crawler tractors. The yarding and short hauling is adapted to the particular logging conditions in flat coniferous forest with small timber dimensions. The circular saw, placed low in front of the tractor, and driven by motor, cuts the trees a few centimeters above the ground. A special grapple device pulls the trees down on to a crossbar, mounted above the driver's cabin. Depending on the timber size, several trees are felled, loaded and transported together in full length, the tree crowns skidding on the ground. Only two men are necessary to operate this felling, loading, yarding, and hauling engine.
Improvements have been pushed still further by the Bush Combine, and a prototype pulpwood harvester manufactured by the International Pulp and Paper Company, which is sometimes called the King Kong of the woods. By an hydraulically operated cutter, trees up to 45 centimeters in diameter are neatly sheared off at ground level, limbs up to 12 centimeters in diameter are stripped off by a flexible steel belt, and the trunk is bucked into pulpwood length by a second hydraulic cutter, resembling a giant scissor. The pulpwood sticks are stacked in bundles and attached to the rear of the combine. Each package, of about 3.7 cubic meters, weighs some 3,000 kilograms and is loaded by a Bush loader on specially designed trailer frames. It is stated that one operator and a helper can cut and stack about 60 cubic meters of pulpwood in an eight-hour working day.
7. Hauling by animal traction
8. Hauling by railroad
9. Hauling by truck, and by tractor with trailer
10. Timber transportation by water
MAJOR transportation has been defined as the hauling of timber for long distances from a collecting point to a final destination. In Part II of this paper is discussed timber transportation by animals and by mechanical means, by land and by water.
Depending on the traction power, six different methods are discussed - by animals; railways; trucks or tractors with trailers; cable-ways; water transport and, briefly, by air with helicopters. Some of these methods are steadily declining, especially animal hauling. Small logging railways still operate in tropical forests which are managed on a permanent yield basis, but are now in competition with road transport by trucks and trailers which are getting more and more efficient. In some countries transport of big timber over long distances by state railroads and by water still continues. The use of skyline cableways for timber extraction is steadily increasing in mountainous countries for distances up to 3 kilometers. In South America very valuable logs are now being transported by helicopters where no other means of transport is possible.
Wood transportation on long distances by animals continues in some tropical countries where cheap and abundant draft animals, particularly oxen, are available. Farmers are usually glad to earn extra wages with their teams during slack seasons on the farms. Many Indonesian towns are still supplied with firewood by the farmers of surrounding villages. This is cut to the desired length, split, and carted at a speed of 2 kilometers per hour by a pair of oxen for distances up to 30 or 40 kilometers. Many sawmills in South Viet-Nam, Thailand and Burma still receive their logs on ox-carts and it is possible to see ox-teams of up to 20 head hauling teak logs for a daily distance of about 10 kilometers. Elephants are also used to haul short trains of three or four trucks, loaded with timber, on narrow-gauge railroads. In Australia eucalyptus logs are still occasionally hauled with ox-teams of 10 or 12 animals. In Paraguay small mills located up to 10 kilometers from the exploitable forests, get their round timber by animal-drawn high-wheel carts. They also haul the converted lumber by ox-teams up to 40 or 50 kilometers, to a distant railroad or a river landing. Motor-driven vehicles are not used as, even in dry weather conditions, transportation costs would be too high.
NOTE: Part II of an article begun in Volume 16, Number 2 and to be concluded in Volume 16, Number 4.
Transport of firewood, round and squared logs or sleepers, by donkeys, mules and camels is common in the Near East where cheaper transportation is not available. Long-distance timber transport by animals, however, survives only in exceptionally favorable local conditions and is rarely used for large and heavy logs.
Up to the end of the second world war, in some tropical countries, narrow gauge railways were the only means of moving heavy timber from the forest to a river landing or to the sawmill. Discussions on the comparative advantages of haulage by road or by railroad started long before 1939 and still continue in some countries. On the west coast of Africa millions of tons of tropical hardwoods were hauled, between 1920 and 1940, by narrow-gauge railroads by means of manpower, steam or motor traction. This system may continue where well-planned and well-built railroads are already in existence in forests which have adequate timber reserves and are managed on a sustained yield basis. With purchase and construction costs written off long ago, transport costs can be kept so low that no other transportation system can compete.
One of the best logging railroads of this kind is probably the small-gauge extraction line in the teak forests of Java (Figure 40). This excellent and compact network reduces considerably the distance to be covered by skidding with ox-teams: the organization of the Java teak forests on a permanent yield basis is probably unique in the world.
In many desired tropical forests logging is by selective cutting of the timber species, and complete extraction within a few years. The spur lines, penetrating into the cutting areas, have to be moved frequently, but the main line may carry the traffic for the entire duration of the logging operation. Depending on the volume of the extractable timber species, on the size of the logging areas and on the extraction rate, these main lines may have to serve for 10, 15, or even 20 years. This may give sufficient time to grow another timber crop in those sections where the logging started. Tropical forestry regulations limit the cutting of merchantable timber to certain minimum diameters at breast height, and in 10 to 15 years many trees too small to be cut at the first fellings may have reached exploitable dimensions, and logging can be started again. The volume of the second harvest may also be increased by other timber species, formerly unwanted and not logged, but now accepted for new utilization purposes. Thus the original single extraction may develop into a permanent logging operation, the occasional crop into a sustained yield. In this case, of course, management practices must be altered to protect natural regeneration.
Facing the probable future evolution of timber harvesting in the tropics, the question of railroad versus road haulage may become more difficult to answer, not only from the standpoint of the volume of timber to be moved, but also with regard to other requirements, directly or indirectly connected with the forest management. From experience of the largest railroad haulage in the past on the west coast of Africa, it may be suggested that a logging outfit which has rails or portable tracks at its disposal should continue to use them for spur lines and, over swampy ground, for main lines.
With regard to new logging operations, it may be cheaper to cross a swamp with a railroad than to build a long road going around the swamp (Figure 41). In order to avoid the double transfer of the loads, it may even be more economical to construct a large railroad track for the transport of platforms, carrying the loaded trucks.
For all other logging conditions, log transportation by road should be planned, wherever possible, with the trucks picking up the loads right at the stump, in the forest.
Railroad hauling is still common in those tropical countries where forest railroads have been used in the past for the transportation of timber crops from forests with a permanent yield, and also where existing railroad and rolling stock has justified the construction of permanent railroad hauling lines. It also continues in swampy, soft ground where road construction would be more expensive than the railroad. But in countries such as those on the west coast of Africa, where labor is in short supply, narrow-gauge forest railroads are being broken up because of the larger number of men needed for the maintenance of the tracks. Modern efficient mechanical equipment for road construction and maintenance requires very few men.
Calculation of the point at which log transportation by railroad would become cheaper than by road, is at present only of theoretical value owing to the rapid changes in the various relevant factors. To be effective a planner now requires not only great practical logging experience in a given tropical country but also a correct appreciation of its future potentialities, and a good knowledge of the new transportation systems in highly developed countries.
The location of tropical forest railroads is a difficult engineering problem. A main line must first be selected which can carry the full traffic load during the whole duration of the logging operation and from this the necessary secondary or spur lines must be constructed in order to allow access to the largest possible reserves of merchantable timber. Owing to the small number of timber species to be logged and the fact that they are usually widely dispersed, the extractable log volume per track-kilometer is much smaller than in the forests of temperate climates. The location of a projected railroad network, therefore, requires a very careful survey of terrain configuration and of expected logging volume.
TRACK-SURVEY AND TIMBER CRUISING
Topographical surveys by aerial photography using black and white film and the selection of track lines with the help of survey maps are the same as in more developed countries.
If an aerial survey is not possible, a ground survey combined with timber cruising has to provide the indispensable information needed for the location of the railroad track, but it is slow and hard work. As a rule, several possible track locations should be surveyed and staked out on the ground in order to facilitate the final decision of the most favorable main line.
Spur lines require the same careful survey as main lines, as their location is of great importance for skidding distances and, consequently, of skidding costs. Although they are used for the removal of timber from a limited area only, they may nevertheless have to serve for one year or more before the tracks are dismantled and used for another spur. Spurlines need not be built with the same perfection as main lines, but, on the other hand, the safety and desired speed of log transport can only be assured by careful construction of both.
In forests with heavy undergrowth and in jungle areas, it will usually be necessary to work with a compass at the beginning of the survey and, when staking out the track-lines, to proceed by sound instead of by sight before cutting trial lines for the junction of two selected points. Contour maps of virgin tropical forest do not often exist and, in many cases, the first rough surveys have to rely on bearings by sound, forward and backward to each station, to get a reliable average bearing of the magnetic direction.
After it has been marked out on the ground, the projected main line is cleared of all undergrowth and small trees are pushed off the track. Larger trees with spreading buttress roots are bypassed by narrow-gauge spur lines and, as far as possible, even by main lines. The track clearing should be wide enough to permit the sun to dry out the ground, while all decaying trees or those with large overhanging branches should be avoided or felled. In this way the risk of damage to the track by storm-thrown timber can be reduced.
RAILROAD CONSTRUCTION
The construction of main and spur lines should follow the general instructions given in Part I of this paper. The heavier loads and greater travel speeds used for long-distance timber transportation, however, call for particular care and attention when these railroads are under construction. Grades of 3:100 for tracks with uphill loads can be safely negotiated in all weathers and on long distances, by steam or motor traction. Steeper slopes, up to 6: 100, should be avoided or kept so short that trains can pass along them without additional traction power. It is usually better to build somewhat longer but less steep tracks by following the contours, than shorter, straighter lines with an accentuated profile. Downhill grades of up to 5: 100 may be permissible if the tracks are well built and will absorb the braking strain.
Cuttings and embankments are acceptable on main lines where the costs can be recuperated by shorter distances and by higher speeds, but they are seldom justified on spur lines which should be built, as far as possible, without any earth excavation.
Ditches, to drain the water from the right of way are excavated only along main lines. Spur lines are ditched only exceptionally, to prevent frequent flooding and track erosion during the rainy seasons.
Construction details for bridges and for crossing swamps have also been given in Part I. Railroad crossings of swamps, which occur in the flat coastal regions of the tropics or in temporary inundated areas, are never built with the intention of being used during high water. The tracks remain submerged during the rainy season, and hauling is resumed only after the waters have receded. Where there is no alternative, such as timber extraction by floating, or by barges, the logs are "cold-decked" on the site ready for hauling by railroad as soon as the water level makes this possible.
RAILROAD MATERIALS
Rails
The most suitable rails for forest railroads with mechanical traction, in tropical logging conditions, are of the 12-kilogram type (Figure 42), although rails of 9 kilograms per meter may be sufficient to support 10- or 12-ton locomotives, traveling at slow speed if the tracks are supported by good ties spaced not more than 50 centimeters apart.
Round wooden sleepers may be cut from the adjacent forest. They are rarely flattened at the bottom, and seldom even on the upper side to receive the rails. For a 60-centimeter track on solid ground, they are cut in lengths of 120 to 150 centimeters; for soft, swampy-ground sections, in lengths of 2 to 4 meters. To make all the sleepers give equal support to the rails, the larger ones are dug into the ground where they settle down firmly after rain has moistened the soil around them. Their natural durability offers reasonable resistance to decay, but, depending on the intensity of the traffic, they may be worn out rapidly, especially on the curves, by the spikes which hold down the rails. As soon as the spikes become loose and fail to grip the rails, the sleepers have to be replaced or, if of a durable species, they are turned or shifted slightly to one side so that the spikes can get a fresh hold.
In order to avoid frequent replacement of worn-out wooden sleepers, steel ties for bolt rails may be used, particularly for spur lines. For the heavier traffic of the main lines, two steel ties and one wooden sleeper per linear meter, are necessary. Straight sections of spur lines may, however, be constructed with steel ties set about 1.20 meters apart, with no wooden sleepers between them, without impairing the safety of the slower traffic. For spur lines manpower traction, portable track sections of 5 to 10 meters can be laid with a still smaller number of steel ties. Spaced at 2 to 2.5 meters, they serve mainly to keep the rails at a correct gauge, thus facilitating greatly the spiking of the rails to the wooden sleepers slipped between them where needed. When breaking up the tracks, only the rails with the steel ties and the spikes are salvaged, the wooden sleepers usually being abandoned.
The experienced logger will always try to build his main line at least one rainy season ahead of a logging operation, to allow it to settle down and to see where and what size of ditches are needed. By this means it is possible to get it into the best possible condition for the start of the hauling season.
Rolling equipment
In the tropics, the most commonly used vehicles for log transport on 60-centimeter gauge railroads are double trucks and flat cars of various types, dimensions and construction. Low, flat car platforms, placed on two four-wheeled trucks which have a loading capacity of 6 to 10 tons, can be built large enough to hold two logs 50 to 60 centimeters in diameter at the bottom, and one log of about the same size on top of them. When larger pieces of timber are involved, logs are transported singly by double trucks of 3- to 5-ton capacity, spaced apart by wooden pole "reaches" to suit the usual log length. For heavy timber, and for trucks carrying 5 or 6 logs, these pole reaches connecting the trucks are not always necessary if the pivoting bunks of the trucks are fitted with iron or steel points or teeth, which bite into the loaded timber. The log weight then not only maintains the spacing between the trucks, but also resists the traction stresses of the whole train, if the heavier logs are loaded on the leading double-trucks. The truck frames, fixed to exterior bearings, have a total width of 90 to 100 centimeters, but this does not hinder the loading and transport of logs with diameters of up to 150 centimeters or even more.
The spring-controlled "draw and puffer" gears, which have link-and-pin or claw couplings on the more recent equipment, make the running much smoother, but are also more expensive. The older trucks have simple hooks or rings, fixed rigidly to the frame and linked together with chains. The wheel axles generally run in full bearings, but newer trucks are now fitted with roller bearings. These trucks are of a sturdy construction and withstand well any loading and rolling stresses. The casing of the axle-bearings, which are the most exposed and the least protected, are often damaged when a car derails. Depending on the transport speed, the logs are attached with wires or chains to the bunks. Single logs may be steadied on the bunk by wooden wedges, driven between the log and the bunk on both sides.
TRACTION ENGINES
Steam locomotives of the piston type were for many decades the only existing traction engines for timber hauling in the tropics and, owing to their sturdiness and the simplicity and facility of maintenance and repairs, they remained in use so long as they could do all the hauling and could be repaired without needing spare parts which are now no longer available. Their service weight varied from the lightest, French-built, twin-axle Decauville locomotive of 7 tons, rolling on 9- or 12-kilogram rails, up to a 3- or 4-axle engine of 22 tons, used on rails of 18 and 22 kilograms. Geared locomotives, built for the broad-gauge forest railroads of the United States, are much too powerful for tropical logging.
All locomotives were fitted with special, woodburning fireboxes and required up to 15 liters of water per horsepower per hour. The space available for water and firewood on narrow-gauge locomotives was often too small, and water and fuel stations had to be organized on longer journeys. The servicing was long and sometimes complicated if the water had to be cleaned and filtered or decalcified..
This fact eliminated the use of the steam engine as soon as the motor-driven loco-tractor became available. One-cylinder, heavy-oil tractors with gasoline-driven four-cylinder engines led rapidly to the now generally used diesel logo-tractor. The higher purchase price of the diesel loco-tractor is rapidly compensated for by low fuel consumption costs, and by its instantaneous starting capacity. Made for 60 to 90-centimeter narrow-gauge tracks, they are low and compact and, at the same service weight, they possess greater traction power than steam locomotives.
The braking control of the steam engine is usually mechanical, by means of a powerful screw-brake and by reversed steam. The standard braking equipment of loco-tractors is also mechanical, with large, steellined shoes, effective on all four wheels. Air brakes (Westinghouse) or vacuum brakes (Bendix) are now optional for most types. For standard loco-tractor types, four to five separate speeds in both directions are available and may vary between 3 kilometers an hour in first gear, and 16 kilometers per hour in fourth and fifth gear. This is sufficient for log hauling on narrow-gauge forest railroads. Traction power varies from 1,300 kilograms for a 6-ton loco-tractor, to 3,600 kilograms for 15-ton models.
It is evident that heavier and more powerful traction engines have to be used on broader or one-meter gauge tracks of 1,000 or 1,067 millimeters, but it should be remembered that such railroads are rather an exception for logging purposes in the tropics. The most suitable gauge is the 60-centimeter track, cheap to build and to operate, and easily adaptable to unexpected load increases.
Log hauling by wheeled vehicles on roads naturally needs quite different mechanical equipment from that used for skidding. However, the recent great improvements in tropical logging methods has now combined the skidding and hauling operations into one continuous and direct transportation of logs from the tree stump to the mill. This revolution in logging methods began by the introduction of crawler and wheeled tractors. So far, this new method has not made as much progress in the tropics as in North America and in Europe, but eventually it will be generally accepted and the planning and construction of new hauling roads will have to be adapted to the future needs of high speed transportation of very big loads (Figure 43).
The alignment and construction of tropical hauling roads for modern transport have to comply with two important factors which determine the relative construction costs: the small marketable timber density in many of the proposed areas, and the short duration of seasons favorable to hauling operations. Dependent upon the volume of traffic to be carried, there will be a great difference between the main and feeder roads, and their methods of construction. Traffic and maintenance costs on earth or "dirt" roads will also depend upon the type of soil and the climate.
The average density of merchantable timber species in tropical countries varies between the limits of the highest density of one tree of 5 or 6 tons per hectare, such as okoumé in Gabon, to the lowest-known density of one tree of 6 to 10 tons per 16 hectares, such as mahogany on the Ivory Coast. Fortunately, the average density does not imply an even dispersion rate over the whole forest area, and logging is usually facilitated by finding small groups of marketable trees in certain parts of the forests.
Such widely scattered and difficult logging conditions have recently been improved by the increasing number of merchantable species now exploited in most tropical forests. In relation to such a larger volume of timber extracted, the costs per transported log are obviously lower and make possible the construction of better and more roads.
The duration of seasons favorable to hauling operations is another decisive factor when forest roads are to be constructed in the tropics. Some countries have definite rainy and dry seasons but, in others, dry spells may be interrupted by shorter or longer rains, reducing the time favorable for hauling to a few weeks per year. For example, in 1954, in the mountainous parts of central Paraguay, only 15 days could be used for hauling during the whole year. With a small log output it may be possible, by careful planning, to concentrate all the timber transport during the dry season or the dry spells. Wide lanes on both Hides of the roads should be cleared of vegetation to permit quick drying out. Hard road surfaces permit heavier loads and a higher average speed, and also less wear of roads and vehicles. Driving is easier and general efficiency higher
If the dry season is not long enough for hauling the entire volume of timber estimated, the planner has to consider the construction of all-weather roads, well built with a hard surface and low grades. The present trend of traffic needs in most tropical countries indicates the early construction of highways and super high ways, admitting loads of 40 to 50 tons, traveling at a speed of 80 to 90 kilometers per hour. In some countries of west Africa such highways already exist, in others they are under construction.
A suitable tractor for picking up a load in the forest and carrying it directly to the sawmill is the self-propelled, self-loading Tournahauler built by the Letourneau-Westinghouse Company. The present model can transport only 20 tons at a maximum speed of 40 kilometers per hour, but other tractors and semitrailers which take loads of 30 tons are already operating in several tropical countries, with speeds limited only by local road conditions.
CONSTRUCTION OF MAIN HAULING ROADS
Tropical countries do not often have good public roads which can be used as main hauling roads in the forest areas, and the opening up of new logging operations is often limited or even prevented by the lack of suitable public highways. Local regulations for wet weather may stop all traffic as soon as the rain starts, and it may not be resumed until the road has dried out to a degree decided by the road authority. Where no logging transport is permitted on public roads, the only alternative is obviously to build a maim road for the whole length from the forest to the terminal station if the log volume and the log prices can support the construction costs, or to abandon the whole logging project. As only low-class roads are usual in the forests of underdeveloped countries, this often determines the size of the projected logging operation.
The choice of grades for main hauling roads depends on the danger of erosion by rainfall, on the loading capacity of the trucks and trailers in use, and to some extent on the desired transport speed.
A truck with a given traction power on level ground, at a given speed, will lose 25 percent of this power on a 10 percent slope, and 50 percent on a 20 percent grade.
If timber transportation in the tropics, traveling at 80 kilometers per hour and with maximum loads of 40 tons, is to depend upon public highways, it would be advisable to build special roads for haulage with the same gradients and capacity which would have a solid roadbed and a concrete or oil-bound hard and smooth surface. However, owing to high construction costs, concrete or macadam hauling-roads have, so far, been built for only a few important logging sites and, if the timber volume per hectare cannot be substantially increased, there is no justification for these roads. Even in tropical countries where fast public highways already exist, timber transport must continue to bring out small loads on minor roads, which will necessitate reloading at the junction with the public highway. Haulage roads will therefore continue to be designed for the lower limits of both loads and speeds, with adverse grades up to 8 or 10 percent. On such roads, apart from the softening and deterioration of the roadbed by raindrops from overhanging branches, erosion of the road surface by the flow of rainwater has to be controlled. The steeper the slope, the greater the danger by the slipping of vehicles on earth and gravel roads, and the higher the repair and maintenance costs. A short heavy downpour may do much more harm than continuous soft rain, and the frequency and violence of rainstorms determine the choice of slopes for hauling roads. Records of the maintenance and repair costs of local roads damaged by rain are useful guides.
Truck speeds on straight stretches of low-class public roads will seldom exceed 40 kilometers per hour, and only the main highways constructed in recent years on the west coast of Africa admit truck speeds up to 80 kilometers per hour. Such a speed is an important factor when planning new hauling roads, which may have to be adapted in the future to these high speed limits. The time factor is very important since the introduction of tractor or truck hauling, as transport times are closely checked and their possible reduction is of economic importance.
Sometimes smaller loads which can travel at higher speeds on longer distances are more economic but, on short slow roads haulage costs can be decreased by transporting heavier loads. In some countries the load limits of public roads, built for animal traction, have been increased during recent years by improvements to the road surfaces but the bridges have not been strengthened sufficiently for heavy trucks.
The first task in road improvement is the consolidation of the existing roads to support 5-ton vehicles, to reinforce softer road sections and to widen the curves. To ensure the circulation of 5-ton trucks at an average speed of about 25 kilometers per hour is a considerable achievement and may satisfy for some years the demand for better transportation facilities.
The next step is usually the reinforcement of the existing bridges. Short bridges for only 3-ton loads, built in many countries in the past, may have to be reinforced and widened for the passage of 5-ton trucks, or tractors with trailers. On bridges with very short spans, only half the total load on a long vehicle may actually be on the bridge at one time, especially if a trailer is used.
For wide rivers, the cheapest way of crossing is often by ferries, of adequate carrying capacity, which may be replaced by bridges as soon as the traffic intensity requires it.
Construction and maintenance costs of forest roads have to be kept as low as possible owing to the relatively small volume of timber to be transported, and concrete or macadam roads are usually too costly. Most logging roads consist only of the natural ground surface cleared of all vegetation and of the humus layer. Smaller trees are uprooted by hand, or by a bulldozer which also pushes the roots and other vegetation to the sides of the road. Larger trees, with large buttress roots, are avoided where possible during the alignment. If not, the roots are cut about 20 centimeters below the future road level to prevent damage to the dozer and grader plates, and to the tractor shoes and truck tires. Large tree roots are seldom extracted completely because of the difficult refilling work which has to be repeated several times before the ground finally settles into the hollows left by the roots.
Dry clay soil or wet sand can each give very good ground support, but dry sand or wet clay soil are almost impassable by wheeled transport. These extremes are seldom found in tropical forests: owing to the lack of sand and gravel or of clay soil, it is often difficult to get a good ground mixture to provide the desired support. The natural soil roadbed should be given one year, or at least one rainy and one dry season, for natural consolidation before any traffic is permitted. Unfortunately this advice is not always observed by small logging enterprises, and much damage is often done to the roads.
To avoid such a long waiting period for a roadbed to consolidate, compacting with rubber-tired rollers may be successful, provided that the moisture content of the ground is suitable for cementing the mineral parts of the soil. Rolling dry ground has very little effect.
A far better method to increase soil compaction is with the Hyster Grid Roller or Letourneau's earth-packing Sheepfoot Roller or Power Packer. These have big drums fitted with short Hat-headed replaceable steel pegs of 15 to 25 centimeters in cross-section for crushing and packing the ground with the weight of the water or with sand-filled rollers, of 15 to 40 tons, distributed by the "stamping feet" over very small ground surfaces. A few passages with the Sheepfoot Roller, working in units of two to four drums, either pulled by tractors or self-propelled, packs the soil ready for traffic after a few hours of drying out. Such mechanical equipment is costly, however, and is rarely used on forest roads, as soil compacting is usually done by the crawler-tractors during the clearing and grading of the roadbed, and by the general logging traffic.
Road surfacing hardens the road surface and increases its impermeability. It also provides a better run-off of the rainwater. As tropical logging operations cannot support the high cost of concrete or macadam roads, except in a few exceptional cases, the usual surfacing of forestry roads consists only of giving them a crowned cross-section to maintain them in good rolling condition, and to avoid holes through which the rain can penetrate into the roadbed and so weaken its resistance. In order to improve the resistance of the surface of dirt roads, in sections with an unfavorable mineral composition, suitable soil should be added during the grading to obtain a good binding of the sand and clay particles. Suitable gravel or stone deposits may be found locally for the consolidation of the roadbed in soft places and on slopes. Laterites are frequent in many tropical forests and, when hardened by exposure, provide one of the best binding materials for sandy soils
Heavy loads of 15 to 20 tons, even when hauled at low speeds of 10 to 20 kilometers per hour, require a much stronger and more expensive road construction, especially where bridges have to be built.
Ditches on both sides of the road in flat country should be at least one meter wide and 50 centimeters deep. Standing water in the ditches, caused by insufficient slope or by vegetable or mineral obstruction, should not be tolerated, as it may soften the roadbed by infiltration and delay drying out after rain. The slopes of the ditches will generally be the same as those of the road, but for grades of 5 percent or more, frequent inspection is needed to avoid erosion.
For the construction of large culverts, durable hardwoods should be used, as for logging roads it is not advisable to make them of concrete. It will often be found that the original number and size of the culverts is too small and supplementary culverts are often needed to avoid road inundations and flooding.
More important for the drying of the roadbed is the felling and clearing of all overhanging trees to permit the exposure of the road to the sun and to increase the circulation of the wind for carrying off the moisture. The width of the clearances should be adapted to the amount of rain and to the geographical position and direction of the roads. For a road running east to west at 8 degrees north, the southern roadside clearance should be much wider than for the northern one, to get the longest possible sun effect during the day. For roads running north to south the clearances on both sides may have the same width, up to 10 to 12 meters each, determined by the height of the adjacent forest and the prevailing wind velocity.
FEEDER ROADS
Owing to the limited volume of timber and the short period of exploitation, the planning of feeder roads rarely offers any difficulty, and their construction costs are reduced to a minimum. Along these temporary tracks, cleared through the forest quickly and easily by one or two passages of a crawler tractor, trucks are able to penetrate the forest nearer to the felled trees. The shoes of the tractor also destroy the sharp edges of tree stumps which could damage the tires. Gradients should be, as far as possible, those adopted for the main hauling road. However, for short distances only, the grades of feeder roads may be anything up to 15 percent for adverse slopes, and up to 20 percent downhill.
To drain off the rainwater from feeder roads, a slight crossfall of the road surface toward the valley is usually sufficient, without causing any special erosion damage. In flat country it may be advisable to raise the crowned road surface above the rain water level and, if necessary, to dig ditches along both sides of the road for quicker draining and drying. Soft spots should be filled with gravel or stone where available, or temporarily with brushwood. For heavier traffic, use poles or slab wood from sawmills, laid across the roadbed and kept down at both ends by longer and heavier timber. If the cross-poles are not properly pegged down at the roadside transportation can be very dangerous and speeds reduced.
The necessity of clearing lanes along both sides of feeder roads for quicker drying out is a matter to be decided locally. If the periods of dry weather are long enough for the hauling out of all timber cut, any side clearing would be a loss of time and money. However, large boughs overhanging these roads, as stated above for longer roads, should always be cut or the trees felled, to avoid deterioration of the road by rain dropping from the branches.
LOG TRANSPORT BY TRUCKS
Trucks with a capacity of 3 tons have been used by small logging firms in west Africa during the last few years for short hauling from forest to river or to railroad landings. In this capacity they have proved to be quite suitable and efficient for low-class roads and slow loading with only simple mechanical equipment. They are either two-axle or six-wheel trucks, usually without a four-wheel drive or even a winch to get them out of bad places. They have not been designed for timber hauling and the bodies and engines do not last more than three or four years owing to the heavy strain to which they are exposed.
Despite all the difficulties which have had to be overcome by this method of transportation, some important conclusions can be reached for future logging operations. Log transport by truck is much cheaper than by railway. The flexibility and adaptability of trucks open up access to forests which cannot be logged by railroads, and often represent the only available economic haulage system. New trucks of European or American manufacture are now available of various sizes and capacities. Some types have devices and equipment specially designed for timber transport. Many of the two- and three-axle trucks have only a rear-wheel drive, and not always a front winch for self-salvage on the road. Some types are fitted with two hand-operated winches for log loading, and some with motor-driven winches for self-loading. It is not possible to give details of the many truck, tractor and trailer types that are available.
On the other hand, there are some disadvantages with truck transport. The tires of double wheels on the rear axles may develop two faults. During their use on low-grade forest roads, the tires are exposed to severe damage by stones squeezed in between them; and when rolling on hard-crowned roads, the inner wheels wear out quicker than the outer ones, and have to be changed frequently to get the same service life of the tires. These inconveniences are the chief reason for the present manufacture of single, wide-based tires of greater diameter, with which most heavy duty trucks and tractors of recent construction are now being equipped. Rolling with slow speed on rough or soft ground, with an air pressure of only 0.8 kilogram per square centimeter, the wide nylon tires mold themselves around the obstacles without being damaged.
They increase the ground adherence and the traction capacity of the truck, and compact the roadbed. Inflation and deflation of the tires, formerly done by hand, is replaced by a mechanical system, operated by the driver without stopping the truck.
Other disadvantages of these trucks are, first, their short platforms, limited normally to 4 meters, and not permitting the transport of logs longer than 6 meters; and, secondly, when logs are to be transported on public roads, the low maximum weight per axle or per wheel. On first-class public highways, this is fixed at 8,000 kilograms for a four wheel rear-axle, or 2,000 kilograms per wheel; and 3,600 kilograms for the two-wheel steering axle. The total weight of a loaded truck is generally distributed so that only one third to one quarter of it is supported on the front axle, and two thirds to three-quarters on the rear axles. For a 12-ton truck, and a one- to two-thirds load distribution, this means 4 tons on the front axle or 2 tons per wheel, and 8 tons on the rear. In the first case of the truck of 12 tons cross weight, with two axles and six wheels, all the wheels carry an equal load of 2 tons. In the second case, 12 tons for three axles and 10 wheels, the front wheels each loaded with 2 tons, and the rear wheels with only 1 ton. The load distribution of one to two thirds of the 16 tons cross weight is not possible, as the front wheels would then have to carry 5.3 tons or 2.65 tons per wheel, an overload which is not permitted on public roads. For reasons of safety (see also Figure 44), the truck loads cannot be moved farther to the rear, nor increased in weight or length, and so another load distribution on a greater number of axles is necessary. This is made possible by the addition of a trailer. The platform of the truck, which had become useless, is replaced by a bunk, mounted over the center of the rear axle, or of the two tandem axles, thus transforming the truck into a tractor.
FIGURE 44. - Position of log hauling vehicles on a 4-meter bridge supporting 5 tong. Above, a 2-axle, 6-wheel tractor with a 1-axle, 4-wheel semitrailer with a total load of 13.5 torte and a payload of 7 tons - in three bridge positions Below, a 2-axle, 6-wheel truck with a 2-axle, &-wheel trailer, a total load of 19 tons and a maximum payload of 12 tone - in four bridge positions. Note that, with a d-meter wheel spacing, the d-meter bridge is never supporting more than a maximum axle load of 5 tons, thus permitting the passage of tractors with semitrailers of 13,5 tons and of trucks with trailers of 19 tons.
LOG TRANSPORT BY TRACTOR AND TRAILER
The timber load on a tractor-trailer unit is so distributed that the front wheels of the tractor have to support only the weight of the motor and of the driver's cabin. The total weight of the load is carried by the two rear axles of the tractor, and by one, two, or even three, tandem axles of the trailer, thus permitting loading of all axles to capacity, which is up to two tons per wheel.
Such heavy loads however are admitted only on first-class highways, for travel speeds of up to 80 kilometers per hour, and never on lower-class forest roads. The total cross weight of the heaviest tractor-trailer types used on the west coast of Africa does not exceed 30 tons, carrying a payload of about 22 tons, distributed in the way shown in Figure 45. The ground pressure of the front wheels is the same as for the example cited above for main highways, but the lower travel speeds on the better main roads make them supportable. The eight wheels of the tandem axles of the tractor with the trailer could, theoretically, also support two tons each, thus increasing the load capacity from 26 to 36 tons; or to 16 tons on two tandem axles, which the road can support only at a minimum spacing of the axles. The smaller the spacing between the tandem axles, the greater the stress on the road for a given load and speed.
In industrial countries, tractors and trailers are built today to any required size and loading capacity. They are adapted and equipped for long timber transport with fixed wooden "reaches," or with telescopic steel tube reaches. The giant Euclid (Figure 46) and Berliet tractor-trailers cannot be used at present in tropical forests as there are no hauling roads capable of supporting them; but no limits can be set to the rapid evolution of 30-ton timber loads, rolling already on main hauling-roads in west Africa. The driving power for tractors and for trucks is usually provided by diesel motors but older vehicles are still using petrol. The engine power is normally transmitted to the rear axles, but many tractors and trucks are fitted with a front-wheel drive. The latest improvement in the transmission of the driving power is the diesel-electric four-wheel independent electric drive of the Letourneau-Westinghouse Tournahauler (Figure 47) or Tournaskidder.
The length of service of tires show great differences, depending on the manufacturer and the location of the plant. Goodrich tires, produced in the United States, are better and more resistant than those made in Goodrich plants located in certain rubber-producing tropical countries. The service depends on the road-class and gradients, and on the loads they carry; also, to a great extent, on the driver's ability. For rough roads, with steep grades, which need heavy traction power to pull the loads uphill and even more power for the braking on the downhill run, the maximum safe mileage for front tires can be as low as 4,000 to 5,000 kilometers. On better roads and with better grade conditions the average length of service may reach 15,000 to 20,000 kilometers. On good hard roads tires of reliable manufacture, mounted first on the front wheels and, after a certain mileage, on the rear wheels, may last as long as 80,000 to 100,000 kilometers. It is a good policy to use for the front wheels tires in top condition, to replace them after 40 to 50 percent wear and then to put them on the rear wheels. Having reached their "safe mileage" life, tires from high-speed transport can still give many miles of service on slower hauling roads, where they are not exposed to the hard wear of brutal braking.
Overloading vehicles, frequently done to profit from additional payloads, greatly reduces the service life of tires. Overloaded tires become hot very quickly and the risk of blowout is much greater. Heavy impacts on bad roads, which do not allow for the complete absorption of the shock entailed, are the most frequent reasons for bad damage to tires and also to other constructional parts of a vehicle.
Tubeless tires are becoming more generally used in the tropics. They are lighter, they do not accumulate heat as rapidly as tires with tubes, and they have good protection against normal blowouts. Reliable information regarding their wear and service life in the tropics is not yet available.
Heavy vehicle Lypsoid tires with an elliptical cross-section, of 44 × 28 inches; or 112 × 71 centimeters and with a low inflation of only 0.7 kilogram per square centimeter are mounted on a vehicle manufactured by the Anglo-American Export Company. The ground contact area, being larger than that of standard tires, keeps the ground pressure down to 0.32 kilogram per square centimeter, which is lower than that of crawler tractors, thus permitting easy traverse over soft sand or deep, swampy ground. The vehicle is equipped with two gas or diesel motors, of 120 to 180 total horsepower, and either of them can be detached at will, by push-button coupling or uncoupling. They are placed transversely in front of the wheels. This cross-country vehicle has not yet been used in the tropics, but its constructional features may be interesting for tropical logging in mangrove and swamp forests.
Tire maintenance
Tractor and tire manufacturers publish rules on tire maintenance, the observance of which helps to increase the service life of tires for all kinds of trucks, tractors and trailers. Tires should be selected to suit specific loads and the working conditions. Tire manufacturers have designed tires to meet heavy working conditions, but it is not always possible to get the right tire for a given job, and a compromise is often unavoidable.
Tire pressure should be checked regularly. Under-inflation causes excessive flexing and increased tire deflection which, in turn, leads to heating and uneven tire wear. When tires are used at comparatively low speeds over soft ground conditions, it may be desirable to reduce tire pressure from that recommended for transport on hard or paved road surfaces. This will promote better traction and less rolling resistance and will reduce the risks of tire cutting by sharp impacts. Overloading and over-inflation above the manufacturers' indications should be avoided, for they may result in high cord stress, with possible blowouts from sudden jolting and also increase the danger of cuts by sharp stones or flints. Tire pressure should be checked when the tires are cool. If checked when warm or hot, allowance should be made for the pressure built up by the higher temperature.
The surface over which the vehicles operate is a very important factor for the service life of tires. Good haulage roads not only prolong the life of tires, but also permit higher haulage speeds. Careful selection and training of drivers is also necessary. Good drivers will avoid obstructions which may harm the tires, and they will also avoid the spinning of the drive wheels.
The condition of the tire treads should also be checked regularly, especially in wet tropical climates. All damaged tires should be marked and removed for repair as soon as possible. Cuts should be probed for stones, nails or other foreign material. The steel rims should be checked for damage, particularly along the flange, as this may cause cuts in the tire bed. Tires in storage will deteriorate from exposure to direct sunlight, moisture, grease or oil, and should be kept in a dark place which is cool and dry. Tires should not be stored near electric motors, which are a source of ozone, nor near petroleum products or fumes. If necessary, they can be stored outdoors but then they should be covered with waterproof material. It is essential that moisture be kept from the inside of the tires, and the best way to ensure this is to mount them on wheels and to inflate them to 50 percent of the operating pressure.
For tractor-trailer units of a total weight of 8 to 10 tons, the powerful brakes of the tractors alone may be sufficient for small gradients and for speeds up to 40 kilometers per hour. But it is to be remembered that brake-linings and tires can be damaged by the heat produced from sustained long braking. For bigger vehicles and higher speeds, the trailer should be fitted with the same braking system as the tractor, which is usually with vacuum or hydraulic brakes, controlled by the truck driver. On forest roads with steep grades it is advisable to use trailers with brakes to avoid wear and fatigue of the motor used for braking.
FIGURE 50. - A two-axle, eight-wheel M.A.N. Ackerdiesel tractor with trailer, hauling long timber.
Semitrailers
Logs of more than 20 feet in length usually have to be loaded on to semitrailers. The heavier butt ends are supported by the bunks of the tractor and the lighter ends by the trailer. Depending on their density and size, the weight of large single logs may reach 8 or even 10 tons, and tractors and trailers have to be adapted for the safe hauling of heavy loads up to 20 tons and 50 feet in length (Figure 48).
Many of the tractors formerly mounted on double wheels, have now been replaced by those with large single wheels. Carrying no load on the return trip to the forest, the trailer bumps along the road, wearing out tires and coupling gear. This is often avoided by loading the empty trailer which weighs about 1,500 or 2,500 kilograms onto the tractor, and carrying it on the return trip (Figure 49).
To facilitate the loading and unloading of the semitrailer, a simple scaffolding is rigged at the terminal station. Its construction by local untrained labor is simple, and suitable timber is usually available on the site. Any available mechanical winch can be used. The telescopic tongue of the trailer, adaptable to a wide range of log lengths, is attached to the protective steel frame of the driver's cabin. A cable sling, permanently attached to the center of the trailer, permits easy lifting and lowering. The frame behind the driver should be strongly built or reinforced to protect the cabin against any forward shifting of the load on downhill sections or on sudden braking.
The minimum hauling distance at which carrying a semitrailer on the return trip begins to be profitable, is about 30 kilometers on west African roads. The time taken in loading and unloading the trailer is of secondary importance, compared with the danger that the empty semitrailer can be badly damaged, even on short runs; and a higher travel speed is of course permitted with the carried trailer.
Tropical timber is usually produced in long lengths (Figure 50), and is often hauled by tractors with semitrailers. Another great advantage of the trailer is that it can be loaded without the tractor. But trailers are not permitted on public roads in several tropical countries, and they will probably not be used until the tropical forests are eventually logged for pulp wood.
CALCULATION OF TRACTOR OPERATION COSTS
When and where a tractor can profitably be used for logging purposes in the tropics, and when it should be replaced, can only be decided by a careful cost calculation based on meticulous records kept over a long period. Operation costs of any logging vehicles include four main items: fixed investment: estimated depreciation and repairs; fuel and maintenance; and, finally, wages, including welfare costs and unemployment compensation.
TABLE 2. - PROPOSED CHECK SHEET FOR THE TRANSPORTATION OF TIMBER WITH TRUCKS, TRACTORS AND TRAILERS
Logging company .............Timber yard .........yard .............Date..................
Truck or tractor and trailer: type and number: Driver ...............Assistant .............
|
Number of trips |
Outgoing journey |
Return journey |
Weight of load, in tons |
Dead weight |
Destination |
Distance, in kilometers |
State of road; wet or dry |
Weather; dry or rainy |
Hours or length of time spent |
Entry to be made daily or at end of each trip |
|||||||||||||
|
Consumption of |
Time spent |
||||||||||||||||||||||
|
Departure from garage or depot |
Arrival at timber yard B |
Loading |
Departure from timber yard A |
Arrival at timber yard B |
Unloading |
Stops en route |
Reasons for stopping |
Fuel - liters |
Oil - liters |
Grease - kilograms |
Washing and cleaning |
Oil change and greasing |
Fuel change |
Small repairs |
|||||||||
When calculating investment costs, it must be recognized that transport and delivery costs, import duties and taxes may reach over 100 percent of the original purchase price. Also that the tractor delivered to the tropical logging site may cost twice or three times as much as at the factory. Depreciation and repair costs require many years of recording and comparison before a proper estimate can be made.
Depreciation
In temperate zones, tractor manufacturers assume an average tractor life of 10,000 working hours or a service life of five years, based upon 2,000 working hours per year. If a logging tractor operating in tropical forests, with rainy seasons of four to six months, can average 180 to 200 working days of five to six hours per year, totaling 1,000 to 1,200 working hours, this is a good average achievement. The normal depreciation period in most tropical countries being estimated at five years means that a tractor may be written off after about 5,000 working hours.
Both the above figures - the five years' depreciation limit and the 5,000 working hours - are basic figures for cost calculation, but the real service life cannot be actually established until the tractor is finally scrapped, and this may vary very widely. Unpublished operation costs, obtained with crawler-tractor yarding on the west coast of Africa, give evidence of more than 9,000 working hours over a period of nearly eight years. Such good results are profitable for the tractor owner, but cannot be regarded as applicable to all conditions. With growing experience in the tropics, the average real service life of tractors has substantially increased above the original depreciation period, thanks to more careful driving and better maintenance. But, although tractors now have a longer life, the great increase in their cost price has prevented any reduction in actual logging costs.
As the number of working hours varies greatly, annual depreciation rates must be based on the actual working hour costs in the different years. The resale value of a tractor at any given time, or of separate parts such as the engine or usable spare parts at the end of its service life, will obviously be applicable only in those countries where a fair demand exists for secondhand tractors. A formula for depreciation, worked out for taxation purposes by the French Government with the intention of stimulating capital investment, may be of interest for tropical logging operations. As depreciation is heaviest during the first year, the following diminishing rates were established (Table 3).
TABLE 3. - DELIVERY VALUE OF TRACTOR, OR ANY SIMILAR MECHANICAL EQUIPMENT, VALUED AT $ 20,000 AND A DEPRECIATION PERIOD OF FIVE YEARS;
|
Year
|
Method of calculation
|
Depreciation balance |
|
|
U.S. dollars |
|||
|
1st |
40 percent of $ 20,000 |
8,000 |
12,000 |
|
2nd |
($ 20,000-8,000) less 40 percent |
4,800 |
7,200 |
|
3rd |
($ 20,000-8,000-4,800) less 40 percent |
2,88 |
4,320 |
|
4th |
($ 20,000-8,000-4,800-2,880) less 40 percent |
1,72 |
2,592 |
|
6th |
Estimated only |
2,692 |
2,160 |
|
|
TOTAL |
20,000 |
|
Repair costs
Repair costs are always very heavy in the tropics, not only because of the expensive spare parts, but also because of the lack of skilled mechanics and workshops within reach of forest operations. Repair costs and the much greater wear of all mechanical equipment in tropical countries has to be foreseen. Electrical equipment, for instance, suffers from moisture and from rough roads; sandy soils wear out the crawler tracks after 2,000 to 2,500 working hours (two or three sets are often used during the tractors' service life and one pair of crawler-tracks costs about one third of the tractor's purchase price). For wheeled tractors, the Forestry Equipment note No. C.14.56, of the Food and Agriculture Organization, assumes an average tire-life of 5,000 hours; i.e., 5,500 hours for tractors of 40 to 50 horsepower; and 4,500 hours for those of 25 to 30 horsepower. Time alone, however, without taking the mileage and road conditions into account, does not give a correct estimate of tire depreciation or of its service life. At an average speed of 8 kilometers per hour a tractor would travel 40,000 kilometers in 5,000 hours, or only 20,000 kilometers at half the speed. If the service life of a tire were to be reckoned in terms of time alone, which is, of course, not the case, its life per kilometer would be doubled when traveling at half speed.
Fuel and lubrication oils usually have to be imported, and their cost delivered to the logging sites is much higher than in industrial countries. The higher consumption rate for both fuel and lubrication in tropical countries is partly due to evaporation, and partly owing to the higher working temperature of the tractor engines.
Maintenance costs include cleaning, refueling, oiling, greasing and small repairs made by the driver. They are best dealt with as part of the wages of the driver and his helper, for the time employed. Under tropical working conditions, a rate of 20 to 25 percent should be assumed.
Wages and associated expenditure
Wages for the driver, and his assistant choker man, are generally lower than in industrial countries. Costs have to include all expenses for medical treatment, sick pay, health insurance, pensions, paid holidays, welfare collections, etc. Transportation costs to and from the logging area have to be added to the wage costs as well as part of the salary of the supervisor.
Overheads
To get a true picture of tractor operation costs, overhead expenses should only be charged against them in proportion to the total timber harvesting costs; including survey and cruising costs, camp construction and maintenance, felling, bucking, bunching, skidding, loading and transport. In small logging operations it is usually of little value to keep separate costs for bunching, skidding, loading and transport, and it is sufficient for all cost calculations to have a reliable total figure for all four items. Bigger enterprises, operating with two or more tractors, need separate daily working records for each operation.
Examination of operation costs incurred in tractor logging on the west coast of Africa, and their comparison with those of Kalimantan and Sarawak, confirm that the increasing experience of the Africans with crawler-tractor logging is gradually reducing costs. When tractor yarding started on the west coast of Africa some 30 years ago, it was only profitable to log timber species of high merchantable value, such as mahogany or okoumé, the sales prices of which could support the high logging costs. Other timber species, of smaller value, could not then be logged profitably with tractors. Tractor efficiency has now been greatly improved by roadmaking, better loading and forest clearing, and both managers and labor have had time to get familiar with mechanized logging. The resulting reduction of operating costs is now permitting the economic extraction of new timber species of lower merchantable value.
For the calculation of operation costs of the additional equipment used with tractors, such as skidding pans, sleds, bummers, sulkies and arches, winches and winch cables; they should be considered as forming a single production unit, to which all the above cost factors can be applied.
Observations and checking of the transport costs of about 1,600 logs on the Ivory Coast, made a few years ago, yield some interesting conclusions. Records have been made of vehicles with loading capacities of 8 to 26 tons, over transport distances from 20 to 260 kilometers, with truck and tractor-trailers, gasoline or diesel driven, also with loads carried by trucks only, or by tractors with semitrailers. Observations of hauling periods extending beyond the dry favorable season into the bad road conditions of the rainy season, demonstrate the necessity of reducing both the speed and the loads by 20 to 25 percent during the wet periods, thus producing a corresponding increase in fuel consumption per volume of timber. In other African equatorial regions, cost savings of up to 50 percent were claimed for diesel-driven vehicles.
The influence of better road conditions on transport coats are summarized below:
1. Increased hauling loads. High class roads permit heavier loads at normal speeds and this obviously reduces transport costs. If the wages of the driver of a 20-ton tractor with semitrailer are the same as for a 10-ton unit, the wage costs per ton are obviously 50 percent lower in the first case. High-class roads are normally built with easy slopes, permitting bigger loads to be transported without slowing down. A 100 horsepower tractor, with semitrailer, will pull a 10-ton load without difficulty uphill on a good road with an 8 percent slope. If a road cannot be improved, or if a steep slope cannot be avoided, loads may have to be reduced by 20 to 25 percent, representing a corresponding increase in costs. A transport manager will always try to keep transport costs down by well-calculated maximum loads for each type of vehicle and for the existing road conditions. During both dry and wet seasons, he will try to keep the loads for each trip as close as possible to the established maximum. From past experience he may let the morning transport start with smaller loads and increase them during the day if the roads are drying out.A useful cost-saving measure consists in stopping log-hauling on low-class earth roads as soon as it starts to rain, and to resume it after the roads have sufficiently dried out. In addition to the necessity to carry smaller loads with the same vehicles on soft, muddy wet roads, heavy expenses may have to be faced for the repairs to the roads damaged by the traffic. Experienced loggers in the tropics know that it is much more economical to concentrate or limit all timber hauling to dry weather periods.
2. Higher travel speed and shorter times. Transport speed has a similar influence on transport costs as the volume or weight of the loads, and shows the same trend. The faster a heavy load can be delivered, the smaller are the costs. It makes a great difference in cost if a bad road causes a tractor with a semitrailer to make four hauls a day only, instead of five at the same wages and almost the same fuel consumption.
3. Smaller repair and, maintenance costs. Drivers, interested on a bonus basis in the volume of timber to be transported, will try to get the best profit from a given hauling job, and tend to drive the engines they do not own themselves at the highest possible speed, without regard to road conditions or to the capacity of their vehicle. It must also be remembered that the daily cleaning and maintenance work is longer and costs more for vehicles on wet, dirty roads.
4. Smaller depreciation costs. A vehicle used on bad, rough roads is worn out faster than on good, smooth roads and, if it is written off in three or four years instead of five, depreciation rates will be 40 or 20 percent higher. Considering the delivery costs of a tractor-trailer unit to the tropics, costs which may be three to four times the purchase price at the factory, as already shown in the section on tractor costs, the actual depreciation costs per ton/kilometer kilometer will obviously be greater.
Relation between loads and hauling costs
The load weight on a vehicle is not the only factor influencing transportation costs, as the volume of the timber may be of equal importance particularly for bulky loads. A tractor with a semitrailer and with a loading capacity of 10 tons should be able to carry, theoretically, 10 cubic meters of logs with a wood density of 1,000 kilograms per cubic meter or 20 cubic meters of logs of 500 kilograms per cubic meter; but the actual loads also depend on the volume of each individual log and its weight, which must be kept within the capacity of the available loading equipment. Traffic regulations generally limit the loading-width of tractors and trailers to 2.40 meters, and sometimes to only 2.25 meters. Fortunately the limited width can be compensated by the load lengths, which are fixed generously at 12 or 15 meters, and often permit log loading up to the vehicles carrying capacity. However, the overhang of logs, loaded on trucks alone, should not exceed 50 percent of the length of the platform, or of the spacing between the bunks of the tractor and the trailer. For tractor-trailer hauling, the weight of the log overhang is generally balanced by the weight of the heavier leading butt ends of the logs. It is not difficult to compose loads of 12 to 15 tons with log lengths of 5 to 6 meters and with a density of 800 kilograms per cubic meter; but vehicles with a loading capacity of 18 to 20 tons or above require a minimum log length of 7 meters. Long logs should always be placed on the bottom layer and shorter logs on top of them to keep the main weight of the load between the bunks. The height of log loads is limited to the free passage height of overhead crossings, in most countries at 3 meters. For reasons of stability and safety log loads are very seldom loaded to such a height in the tropics.
One important factor which determines the composition of loads is the capacity of the available loading equipment. A loading crane capable of lifting 7 tons for a distance of 5 meters is an expensive machine, which is justified only for the handling of large volumes of timber. The lifting capacity reduces the loading length of a 120-centimeter log, of 600 kilograms per cubic meter density, to 10 meters, and to 6.3 meters for a 1,000 kilograms per cubic meter density. When in a green condition, many tropical timber species approach the 1,000 kilograms per cubic meter density, but rarely a diameter of 120 centimeters. If the mechanical loading equipment is not capable of lifting such heavy logs, they are loaded from a platform by cross-haul.
When loading a tractor-trailer unit of 10 tons capacity with a 7-ton log, this being the heaviest the mechanical loader can handle, the load has to be completed by adding a log of about 3 tons, to make up the full carrying capacity. A suitable log has to be picked out from the log pile, and this needs a correct log talley list. The total hauling volume needed for at least one day should always be stored ready at the landing place. It might be considered possible to make up the remaining 3 tons with another log 120 centimeters in diameter but, at the same density of 600 kilograms per cubic meter, this log would be only 4.3 meters long, which would be too short for the spacing of the bunks. A longer log should therefore be found with a smaller diameter; and a log 80 centimeters in diameter and 7.5 meters in length would give exactly the needed weight. However, such well-fitting logs are seldom available, and even with the best hauling organization, vehicles are rarely loaded to full capacity, thus increasing the actual hauling costs.
FIGURE 51 - A logging site on the Amazon river, Brazil, after inundation.
In the tropics transportation of round timber by water has always been important. Without the great facilities for floating and rafting offered by the numerous waterways in these regions, wood exports from the tropics could not have reached the present yearly volume of about 2 million cubic meters, with a grand total of about 15 million cubic meters for the period 1920 to 1940. In Latin America, the Amazon, Paraguay and Paraná rivers with their tributaries, are the most important (Figure 51). On the west coast of Africa, from the Ivory Coast to the Congo, there are many exploitable streams and lakes; and in the Far East, from East Pakistan to Indonesia and Viet-Nam, all timber-producing tropical countries profit from cheap water transport by driving, rafting, or on barges and ships; and, in one case, by seagoing rafts.
The different methods of transportation by water include extraction from mangrove and tidal forests, from swamps, and from seasonally inundated forests.
FROM MANGROVE AND TIDAL, FORESTS
Estimates of the total area of mangrove and tidal forests on the west coast of south America, and of west Africa and the numerous mainland and island coasts of the Far East are 10 to 12 million hectares, and these are now subject to an increasing, industrial utilization. Their exploitation includes the extraction of tannin-bark poles, firewood and charcoal; and of Nipa palms (Nipa fructicans) for house building and roofing materials (Figure 52). It also includes the logging of highly durable, shipworm-proof timber such as the Sonneratia and Excoercaria species, and, in the Ganges-Brahmaputra delta, the large-scale logging of Excoecaria agallocha for pulping.
When located in tidal areas, the tree roots emerge more or less completely at low tide, and access roads have to be opened up by axe and bushknife, owing to the numerous stilt roots, sometimes 1 or 2 meters in height, which cover the ground and leave no passage between the trees. There are also densely-growing air roots, called pneumatophores, just high enough to emerge with their round tops out of the usual high water level, but not strong enough to support man or animal (Figure 53).
All work has to be adapted to these special conditions and, in general, most of the wood and wood products extraction is still done mainly by hand labor, with the use of small paddle boats for transportation. Mechanization of transport by water and by land depends on the type of the existing waterways, whether of shallow or deep water, whether wide or narrow, the tidal variations of the water level, and the speed of the incoming or outgoing tides. These determine the size and draft of the boats and barges, and also the mechanical equipment they can carry. Such equipment can be mounted permanently on decked barges or scows, and progressively shifted to new logging sites; or it can be rigged up on the shore, on platforms supported by log mats above the high water level.
The mechanical equipment necessary for short hauling on land of nonfloating wood depends on the ground support capacity. If the ground can support tractors, transportation can be organized in the same way as in ordinary forests, with the precaution that all equipment must be parked above high water level. However, in most cases the wood is not transported to the mainland but to the deep water. When soft, swampy ground prevails, a narrow-gauge railroad and handpushed cars, operated only at low tide, will be the most suitable mechanical equipment for small timber. In mangrove and tidal forests where floating timber is quite simple, the trees are cut at low tide, and the timber is pushed along with poles at high tide to deeper water, to be then bound into rafts. As timber species do not float when in green condition, it is often possible to obtain temporary floatability by girdling the trees a few weeks, or a few months, before felling. If labor is scarce, the only way to speed up the yarding is by the use of small motorboats with flat bottoms, for pushing or pulling the logs.
For greater outturn of nonfloating timber, a motor-driven yarder, mounted on a scow or on a decked barge, is generally used for yarding and loading. The sheave-blocks for the main and out-haul cables are fixed to a strong tree near the scow, well anchored to hold its position during both the rise and fall of the tide. The sheave-block, to return the cable, is fastened to a tall tree in the forest about 250-300 meters distant. Depending on the yarder capacity and on the timber sizes, logs or whole trees are skidded to the barges and loaded. Sidelining of logs to the main line is rarely possible on distances of more than 50 meters and the half-circle area thus covered by a setting is about 12 hectares. Where the trees on the shore are not large or strong enough to support high-lead rigging, Logger's Dream yarders and loaders with a portable "A"-frame and a three-drum tractor for skidding and loading of big timber can be mounted on the scow.
A similar method, called the slack-rope system, was used for cypress logging in former days in the southern states of the United States of America. It was operated on distances of 1,000 to 1,200 meters and three or four logs were attached in tandem position, one behind the other, to the hauling cable, and dragged out at one haul to the skidder, to be bound into rafts or loaded on barges.
For ground skidding smaller, limbed timber in full-tree lengths, the reciprocating movements of the hauling line are replaced by the more efficient, one-way, circulating endless cable used for pulpwood yarding in the U.S.S.R.: this method could also be applied to the extraction of floating timber in mangrove swamps, by using lighter mainlines and grip locks, and thinner chokers. The traction power of the skidder could then be reduced and the problem solved of floating timber by hand labor to scows.
Apart from the extraction of bolt-wood and the collection of bark, which on a small production level is still done better and more cheaply by direct labor, capital investment, for establishing a small-size logging operation in mangrove forests, may be considered an economic proposition. This could be limited to a barge, large and solid enough to carry a two-winch, motor-driven yarder, such as a Skagit yarder-loader; or an old two-winch crawler-tractor with a double-speed drum for the mainline and a one-speed drum for the outhaul line. A workshop for repairs and maintenance, a stock room for spare parts, fuel and greasing materials, and housing and cooking facilities for the crew should also be located on the barge.
If loading skidded timber cannot be organized in this way, the logs could be rolled by hand from a prepared loading-platform into the barges and a third, independent, light loader would be needed. In addition, a 300 meter long, 25-millimeter gauge main-line, and about 400 meters of a 15-millimeter gauge return line with a certain number of sheave-blocks and grip-locks would be required, to complete the yarding equipment. In order to avoid too heavy a capital outlay at the start of operations, hauling could be arranged on a contract basis. A crew of ten: one foreman, one bookkeeper, one skidder engineer, two survey men to lay out the skid trails, three chokermen, one "whistle-punk" and one handy man should be able to yard an average of 800 to 1,200 cubic meters of logs per year, depending on the working conditions on the site.
YARDING IN SWAMPS
The planning of the yarding in swamps is far easier than in mangrove and tidal forests, as the small fluctuation in water-level simplifies the choice of working methods and of the required mechanical equipment. Such swamps are generally the undrainable low parts of seasonally inundated areas. These do not contain the same wood species as the mangrove forests, but mostly slow-growing durable, heavier hardwoods, often possessing physical or chemical qualities highly appreciated by the leather industry and for medical purposes.
When extracting by floating, two or more logs are usually tied together and, where possible, whole trees are topped and limbed, and then floated by manpower to a storage and rafting center. The mechanical traction may be a motorboat, dragging a line of logs attached end to end by chains, or by short cables. Several swamp species do not float until they are seasoned, and in very shallow water the yarding has to be done by high-lead cables or, if the ground can support them, by crawler tractors, skidding the timber through the water and mud.
FROM SEASONALLY-INUNDATED FORESTS
Most logging companies in the tropics have at times to operate in seasonably-inundated forests. Working methods and mechanical equipment depend first on whether the logged timber is a floating species or not, and secondly on the total volume of the planned output. Floating timbers cut with advantage during the dry season, are hauled out to deep water sometimes either by animal or manpower or, where the conditions are suitable, by mechanical transportation. On the river bank or by lake shores, the timber is made up into rafts and floated downstream to a shipping port or to a sawmill. In small creeks and rivers the high floodwater may last for only a very short period and, if all timber cannot be put into the water during this time, it has usually to wait on the shore for a whole year for the next flood. In order to reduce the yarding distance, small logging outfits sometimes take the risk of using landing places which high waters may reach only at very long periods of years and expose themselves to heavy depreciation losses of the yarded timber.
Larger companies cannot take such risks and have to yard and haul their logs to landings usable during the whole rainy season, or even the whole year.
Nonfloating timber has to be hauled over land to shipping ports, and on the usual low-quality hauling roads this is best carried out during the dry season unless forest railroads are available. Only the larger logging companies can afford the construction of all-weather, metaled roads for the transportation of their larger timber.
LOG DRIVING IN CREEKS AND RIVERS
This system is used for the descent of logs in creeks and rivers which are too narrow, too fast or otherwise unfit for the passage of rafts. The logs are floated down by the stream to larger rivers or lakes where rafts can be built for further transportation.
Driving tropical timber of big dimensions in creeks where the water level may rise or fall at the speed of one meter per hour requires good organization in order to profit from the short duration of suitable water levels. The system only works well if the necessary crews are available in time to roll the logs into the water, and if the high water lasts long enough to get all the timber away. Depending on the frequency and the intensity of the rains, and on the speed the water is running, it often happens that all logs cannot be floated in time or that they have been grounded during the drive and have to wait six or eight months for the next rainy season before there is another chance for driving. The logs, though more or less wormholed near the surface, may not lose much of their quality during the first season, and some durable timber species may not suffer at all, if not exposed too long to the sun. But, if the timber cannot be floated during the second rainy season and has to wait a whole year more, it can become a complete loss. Under such circumstances, logging becomes a highly speculative operation but it is still going on in forests where no other means of transportation exist.
To avoid jams, the logs are often guided by men with long poles and, once the timber arrives at the big river or the lake shore, it is made into rafts, which vary greatly in their construction.
RAFTING TIMBER IN RIVERS AND TAKES
Rafts can be bound with vegetable fibre, such as lianes and rattan, or with cable or chains. Rafting long logs in booms, as is done with softwood logs in Canada, is unsuitable for tropical timbers. Short logs of 4 to 6 meters, as they are usually cut, need no booms to keep them together in the mainly quiet water, nor individual attachment to cross ties. A wire, pulled through the rings of spikes which have been driven into the end of each log, is sufficient to hold the logs together and at the same time gives the necessary flexibility for going around river bends. Longer logs, rafted parallel to the stream direction, are attached to pole cross-ties, having the same length as the width of the raft. If sections of the same log length are formed, several sections are often tied together to form a long raft. Logs of different length on the other hand, are attached to the necessary number of riders, and are usually bound into a single long solid raft, with only one layer of logs. If the buoyancy of the floating timber permits it, sawn timber can be transported as a top load. Nonfloatable timber can also form top loads or be bound between floaters. In the Far East, the logs are attached to each other by thin strips of rattan, slipped through holes 10 centimeters in diameter which are cut out with narrow-edged axes, at about 12 to 15 centimeters from each end, in the side of the logs (Figure 54). As these holes are seldom cut on the same sawing line, this means waste during the conversion, and for the logger a loss of about 50 centimeters of the log length. Triangular V-shaped rafts are a peculiarity of the Amazon river. Two long logs, attached at the front ends, serve as an open boom, into which other single logs are wedged and tied to smaller cross logs riding on them.
The peoples of the Amazon river, who have no wire or ringed spikes, attach the short logs with vines, creepers, lianes, or any other solid vegetable binding material, to riders laid across at both ends of the logs, thus constructing a nearly rigid rectangular raft, steered at both ends with long wooden rudders.
The logs, cut and rolled by hand to the shore, are not long in relation to their large diameter, and rafts with the log lengths parallel to the stream could not be formed with the short timber. The logs are laid across the stream direction and this position has now also been adopted for large towed rafts formed with ringed spikes and wire, as being the most practical and economical. Going down the stream at a speed of 1 or 2 kilometers per hour, held up twice a day by the incoming tide, and not traveling at night, such mengruded rafts take a long time to arrive at their destination. The raft sizes vary within wide limits, from two to three logs of 4 to 5 cubic meters guided by one man in swift water, to 80 or 100 logs of about 300 cubic meters.
Manually controlled rafts descending with the stream are much too slow to be an economic success and continue only where tug boats cannot pass, mostly because of the shallow water which may be deep enough to keep the timber floating but not deep enough for the tow boats which are not specially designed for the tropics and have a much greater draft than the timber. For safe and regular rafting of large volumes of timber it is indispensable to use two boats, now practically all diesel-driven and of suitable power. Traveling day and night, with rafts size up to 2,500 cubic meters, and stopping only at the coast at the time of adverse tide-water, these boats can double or treble the speed of manually controlled rafts, and can be guided safely round river bends and between sandbars.
The buoyancy of floating timber depends upon moisture content (with most species having a density of more than 600 kilograms per cubic meter at l 5 percent moisture content). This indicates that timber should not be rafted for long distances, in its green condition without floaters (Figures 55 and 56).
All timber to be rafted, floating or not, should be given time to season in order to increase buoyancy and, therefore, the duration of floating. The height above water of the emerging part of the log diameter is only an indication of the wood buoyancy at a given moment, and does not indicate the rate at which the water is being absorbed and how long its floatability will last when immersed. Some tropical woods pick up the water faster than others, whatever their moisture content at the moment of their immersion may be; some keep their floatability for years and others lose it after a few weeks or months.
Rafts of light timber, riding high on the water, need a smaller towing-power and travel faster than those of heavy floating timber or mixed rafts of floaters and sinkers which lie low in the water. Nonfloating timber, called sinkers, can be kept up in a raft by the buoyancy of some lighter wood species, by bamboo bundles, (Figure 57), by various palm species or, even by empty gasoline and oil drums; or, finally, by suspension from outriggers, supported by boats or barges (Figures 58 and 59).
When logging several timber species in a tropical forest with nonfloatable timber prevailing, the available light woods to serve as floaters may not be sufficient to carry all the sinkers. Where the logging site is located within the range of reverse-tide waters, the floaters can be towed up river and serve several times, if dried between the raftings.
Where bamboo is available, 100 to 200 poles of log length are bundled and attached to cross-ties, the bamboo bundles alternating with the sinkers. Sections of log length, with 5 or 6 logs between 6 or 7 bamboo bundles, are bound to big rafts, of 6,000 to 8,000 cubic meters and descend the Mekong river in Laos. Arriving at the destination or the sawmill, the mixed rafts are beached on the shore as high up as possible, in several progressive steps, to recover first the nonfloating timber and then the bamboo, which is a highly appreciated as construction material for houses and furniture.
If the timber has to be rafted from locations beyond the reach of the tidal water, to which the floaters cannot be towed back, the latter can be replaced by empty, sealed gasoline or oil drums brought in shiploads, as is done on the Paraguay river. The drums are placed end to end, in one or two rows, alongside the log and on both sides, and fastened to it with wire. Six to ten logs are bound together to make up the permitted width of the raft.
Similar developments are to be expected in the near future for the rafting of heavy timber in other tropical countries, in particular in the Far East, because of the lack of light timber and of bamboo floaters, and of the necessary binding materials. It takes much time and labor to fetch these materials from the forest and the construction of the rafts also requires thousands of working hours. Rafting may become so expensive, if not completely uneconomic, that the raft construction system will have to be replaced by using the more economic spiked-rings and wire (Figure 60) and attaching the timber to metallic floaters, or even by switching over from rafting to timber transportation by barges. In India, lack of floaters and of binding materials has already led to the projected use of special steel pipes, 12 meters long and 2 meters in diameter, for rafting nonfloatable timber (Figure 61).
Another system of rafting nonfloatable timber is by the suspension of the logs from outriggers laid across low barges, as is done in some rivers in Australia where four or six red gum logs (Eucalyptus camaldulensis) are suspended from two to four strong bamboo poles on both sides of the barges and towed down the river. In Paraguay, which has no bamboo, logs 4 to 6 meters long are attached to poles laid across rowing boats with two or three logs at each side, and so brought down stream.
In forest regions with an excess of floating timber and few sinkers to be transported, the assembling and binding of mixed rafts can be avoided by rolling a convenient number of sinkers from the shore on to the rafts across the floaters, wiring them tightly together so they will not shift.
Length of single tube: 12 meters
Diameter of tubes: 2 meters
Weight of single tube, weight of cables or chains included; 6 tons
Total volume of single tube: 33.5 cubic meters
Supporting capacity of a unit of two tubes, at 75 percent immersion: 41 tons
There are usually regulations for river traffic of this kind which state the maximum length and width of single or compound rafts, the colors and position of the lights on the tow boats and on the rafts, the minimum distances permissible between rafts, and the priorities of passage in narrower river sections. This is to avoid complications with the regular boat and ship traffic. Traffic regulations in rivers with public water transportation generally do not interfere with rafting during the favorable towing periods, which are determined by the rains. It is left entirely to the towing enterprises how long they estimate to be able to carry on with the towing at the end of the rainy season. A raft stranded on an unknown sandbank, which may have moved during the high waters, may remain there for five or six months until the floods of the next rainy season. The timber may be salvaged, log by log, at high cost, if the lower part of the river can be safely negotiated. Local rains, which have no perceptible effect on the water level in adjacent rivers and lakes, may have ceased and rafting can still be carried on safely, as the river level is kept high by the floods from the rains fallen several hundred kilometers away, and arriving three or four weeks later in the coastal regions. On the other hand, it may take three or four weeks after the beginning of the rains before the water level has risen enough so that rafting can be resumed. Grounding risks at the start of the rainy season are of small importance for, with rising water, the stranded tow boats and rafts may be afloat again within a few hours or days.
It is evident that rafting requires a very good knowledge of the rivers and of their water levels. Smaller logging firms, floating only one raft or so every month, prefer to call upon the services of established towing enterprises. Towing costs are paid per ton per kilometer, the distances being actual or costed by regions, and it is a question of calculation whether a hired towboat and crew would be cheaper, especially when all logging supplies have to be brought up by ship.
FIGURE 62. - Bamboo rafts the Boliche river on their way to Guayaquil, Ecuador.
(Photo, S. von der Recke)
Pushed rafts
Some years ago some logging companies in equatorial Africa started to push rafts down the rivers instead of towing them. Logs fastened solidly into rigid rafts of floating timber, or of combined floaters and sinkers, are much easier to guide and to control by pushing than by towing, provided the length and width of the rafts are properly adapted to the worst river bends and bottle-neck passages. By mounting a pushing blade onto the bow, a tugboat can be used independently for both towing or pushing rafts. The pilot has the raft right under his eyes and all boat maneuvers can be more easily controlled than with towed rafts which swing freely at the end of a 50-meter towline behind the pilot boat.
Along large slow rivers, the necessity for building more rigid rafts for pushing, which would increase transportation costs, has prevented a general change from the towing system.
Losses by floating are difficult to evaluate, as they may show big differences from one country to another and from one year to the next, and also depend upon the salvage possibilities of the sunken timber. Timber losses may vary between 0 percent in rivers with a well-organized rafting and towing service, and 10 percent or more when logs are floated by men with insufficient rafting experience, particularly when mixed rafts are badly assembled and broken up by stranding on sandbars or other nonvisible obstacles in the water. Sunken logs do not suffer much loss if they have been totally immersed without interruption, unless attacked by shipworm. If of high enough value, they can be refloated; if not, they may be abandoned.
Rafting bamboo
Many forests in the Far East from India to Indonesia include big pure bamboo reserves, which are harvested every three to eight years, depending on the species and on the accessibility. They play a very important role as substitutes for expensive wood for house building and furniture. They also possess excellent pulping qualities, which are now being called upon for papermaking.
Small rafts of bamboo are made up of 50 poles, 8 to 10 meters in length, attached together in three layers at the thicker leading end and spreading out fanwise at the rear end. Several such units may be assembled together, laid one on top of the other, without any binding. The rafts are floated down the river with the current, guided and pushed by a few men equipped with long poles (Figure 62). They advance only a few kilometers per day and sometimes get stranded at low water. They arrive at the mills at irregular intervals and the mills are forced to keep big stocks on shore to ensure continuous production.
Bamboo keeps its floatability as long as its cellular structure is not destroyed, and losses during the rafting are limited to bamboo sticks smashed or broken in collisions. Stranded rafts are disengaged from the rest of the floating ones and left to wait for high water. (To be concluded)
10. Timber transportation by water (concluded)
11. Timber transportation by helicopter
12. Loading timber by manpower or simple equipment
13. Loading by means of mechanical power
14. The future of tropical logging
BY BARGES
Log transportation by open wooden or steel barges is restricted in the tropics to those countries where light timber species, suitable for floaters, are not produced at all or in quantities too small to carry all the sinkers, such as in the Guianas, Surinam, Paraguay, and VietNam. Loading long timber, and its unloading from open barges, is long and difficult manual work; and mechanical loaders are available only where they can work all day and for the whole week, such as in paper mills, shipping ports, sawmills, etc., and it is mainly for these reasons that the total wood volume carried by barges is insignificant compared with rafting.
Selfpropelled landing barges, built for the transport of troops and material, have been tried for timber transport on the west coast of Africa. Their use has been discontinued, however, because of loading difficulties with long timber, the long delays and the necessity for relatively deep water inshore in order to get the barges near enough to the landing places. In addition, too much time was lost in loading and unloading, and transport costs were too high.
Scows, which are flat-decked barges used in quiet water in harbors and bays for the transfer of goods to and from cargoes or for pulpwood transport, are usually too heavy to be towed to the logging sites, up-river against the current. However, wooden scows, which can be built locally, should be considered for timber transport from forests located in coastal regions within reach of tidal waters.
BY CARGO BOATS
In some tropical countries such as northern Brazil, Paraguay and Indonesia, cargo boats can collect their timber loads from hundreds of kilometers inside the country, but usually they have to anchor at some distance from the shore opposite the forests, and the logs transported across the surf by some locally-developed means. The timber may also be loaded in a harbor, when the cargo boat is lying at anchor at a pier or wharf.
Freight rates for round timber are always high, for two reasons: first, because of the bulky shape of round timber which wastes about 30 percent of the loading space in the hold, secondly because of the lack of freight on the outgoing trip. Since the production of tropical timber became too heavy for tramp shipping, cargoes have had to be specially chartered by the logging companies, and regular cargo services organized by the shipping lines. Having little freight on the outgoing run, these ships had to travel under water-ballast, and all costs had to be carried by the timber freight on the return trip. This situation has improved since the end of the second world war owing to the shipment of great quantities of construction materials of all kinds to the tropics, but the regular cargo services still do not always find sufficient outgoing freight.
In the past, boats were used for log transportation which had been designed for the transportation of general freight, and usually could not take logs more than 5 or 6 meters in length into the holds, and their tackles could not handle loads above 5 tons. Longer logs had to be carried on deck and an overcharge paid of 15 percent. Logs over 5 tons could be shipped only by a few large ships specially equipped. These limitations kept the length and weight of individual logs down to the loadable limits. More recently, many boats increased the length of their holds to 8 meters, and the lifting capacities of their shiptackle to 8 tons, to meet the requirements of tropical timber transport.
For the loading of ships lying alongside a pier or wharf, the logs are hauled directly to the ship by railroads or roads. In harbors or bays with quiet water, rafts or barges are towed alongside the ship on both sides, and the logs are loaded one by one, or in smaller sizes, two at a time. Each log is attached to the hook of the winch-cable, lifted up and then lowered into the hold. In this way, when loading four holds at the same time, 500 to 600 cubic meters of logs can be loaded daily in double shifts of eight hours. In places where the logs have to be taken across the surf, they are lowered from a wharf on to surf boats and towed to the ship. Where no wharf exists, single floating logs or small rafts may cross surf by means of a towline.
FIGURE 63. - The Sikorsky crane helicopter S-60 lowering 7 a 2-ton utility pole into a predug hole.
BY OCEAN-GOING RAFTS
The possibilities of using ocean-going rafts were tried a few years ago by the Indonesian Forest Service, intending to supply the great lumber demand of Java with nonteak hardwoods from Kalimantan, by crossing the Java sea with round-timber rafts. At the present time some experimental work is in progress, and no information is available about smaller sea-going rafts which have attempted the crossing.
Ocean-going rafts have never been tried on the west coast of Africa, either for the coastal service or for exports to Europe, although some research work has been carried out in the past.
Compared with round timber, shipments of sawnwood, sleepers, plywood and veneers are ranging at present between 15 percent (west Africa) and 25 percent (Far East). However, a few luxury woods and timber for special uses excepted, it will not be possible in the future to continue to pay half of the freight, or more, for the transportation of conversion waste and of moisture. More conversion of the roundwood will have to take place in the tropics within the next 10 or 20 years and the volume relation of exported wood products to round timber may be reversed.
Tests with an air-borne hauling system by helicopter have been going on since 1945 and the results obtained, depending on the lifting and carrying capacity of the helicopter, are so encouraging that its practical application has already been tried particularly in mountainous countries, including the steep slopes of the Caucasus in the U.S.S.R. It has also been tried for the extraction of valuable timber from deep, steep-sided valleys in Colombia, Canada. Being a very expensive transportation method, it is not applicable to ordinary tropical logging operations but its potentialities are mentioned here because of possible favorable developments in the future.
The S-60 Flying Crane, as the Sikorsky Aircraft Corporation of Connecticut calls its helicopter, is especially adapted for timber hauling purposes (Figure 63). It is designed to carry a payload of 6 metric tons at an altitude of 2,000 meters, or of 5 tons only at 3,700 meters, over maximum distances of 100 kilometers. The total weight of the Flying Crane varies with the type of the driving motors, and is about 18 tons. The former piston engines have been replaced by a twin turbine of 5,000 horsepower: this also drives the winch for raising the load to a convenient aerial transport position, which for logs is vertical. The Flying Crane is sited in the air above the prepared logs and lowers the hoisting cable, with the cargo-hook, to the ground. The log is attached and raised by the winch to the base of the helicopter and flown to a landing site. As a forest clearing large enough to ground a helicopter near to the logpile for loading would be too costly, the hoisting cable has to be long enough to permit it to stay in the air during the loading. The winch, with a hoisting power of 5,500 kilograms is carried inside the helicopter, and is operated from the pilot's cabin, where the flight controls can be operated from a rotating seat to permit wider vision.
The oscillation of the vertically suspended log is difficult to control. Tests are being made to find the best method for conveying single and bundled logs, and for pulpwood.
The efficiency of timber transport depends largely on the loading and travel time, and on road conditions. Loading vehicles to their full carrying capacity with logs depends not only on the weight but also the volume of the timber. A sufficient number of logs of different dimensions and weights together form the most advantageous load. Stock lists indicating the dimensions and the weight of each log are indispensable for the efficient selection of the logs for each individual load, sod for the rapid compilation of the loading lists. For a given load and distance, improvements can only be expected by the reduction of the waiting time for loading and unloading. Time-saving methods and machinery have been developed for the handling of all kinds of goods, and some of them are suitable for the loading of tropical timber. Three main loading systems can be distinguished: sideways, by rolling or crosshauling the load; vertically, by lifting the load and lowering it on to the loading platform; endloading, by raising the logs up to the rear of the truck platform and pushing them on to it.
Whichever way it is done, manual loading is always slow and is therefore expensive. The cost of suitable, efficient mechanical equipment required for the loading of heavy timber is high, and loading costs can only be kept within reasonable limits by the handling of large volumes of timber.
Tractor winches are used for loading, but they are normally not designed for log loading, and the winch speeds are too slow for rapid moving of the logs. To decide which loading system to select for a given job depends on the value and size of the timber, on the cost of the loading equipment and on the estimated total volume of timber to be loaded. Prospective loggers can obtain valuable information for the solution of transportation problems by studying the working methods of other logging firms, and by checking the results with their own equipment. New forest operations, in countries where no logging has yet been carried out, should not be started without some all-round logging experience and even then on a small scale only, in order to gather experience of working methods and of the necessary mechanical equipment, without making the inevitable mistakes committed through ignorance.
BY MANPOWER ONLY
Though rarely efficient, manual loading is still the most economical system in many underdeveloped and underequipped countries which have cheap labor. If the market accepts timber of dimensions which can be handled by manpower, logs can be loaded by carrying them for short distances, as is done in the teak sawmills of Indonesia, Siam and Burma. Six to eight men carry logs 3 meters in length and 60 centimeters in diameter which have been placed in cable-slings attached to yokes from the log dump to the railroad cars, where they are rolled by hand, on two strong poles, up to the platform. For upper layers, the cars are moved along to a higher loading platform, from which shoulder-borne logs can be rolled on to the cars. The loading is slow, but may be economical where mechanical loaders would not be practicable, or if they could not be used to full capacity. A lift truck would do the work much more quickly, but probably at much higher cost, owing to depreciation rates and operation costs,
By rolling the logs onto narrow-gauge railroad cars
Until about 1940 this system was much used on the west coast of Africa for loading logs on narrow-gauge railroad cars. The platform method of loading was used for loading onto double-trucks which had to be large enough to hold all the timber for one train load. Instead of rolling the logs from the loading platform on to the trucks, they were rolled on two cross-ties, supported at both sides of the trucks, and from there lowered slowly to the trucks. Two or three men lift the log at one end with wooden poles (Figure 64). The supporting cross-tie is pulled out from beneath, and the log lowered and centered on the truck's bunk. The other log end is then lowered in the same way onto the second truck and placed in the correct position. The correct spacing between the two trucks is maintained by the log itself, and for smaller trains of 5 to 8 logs (or 15 to 20 tons), no reaches are needed, provided that the heavy logs are loaded on the leading end of the train. For smaller log dimensions, fixed spacing-poles are rigged between the trucks. Wooden wedges, suitable for the log diameter, steady it on the bunk, and no fastening by chains or wire is necessary for hand-pushed trucks traveling at slow speed averaging about three or four kilometers per hour. Nine men push the double-trucks and also do the loading, and at least two crews always travel together, to help each other on steep slopes. A similar crew of eight to ten men remain at the landing to prepare the load for the next train. For mechanical traction, the logs are fastened to the bunks by chains, in order to avoid accidents should the logs roll off the wagon. Steel trucks usually have a carrying capacity of 3 to 5 tons each, but are too narrow to load more than one big log. Their carrying capacity is thus reduced to 20 to 30 percent, as bigger logs cannot be manually loaded without great loss of time. To reduce waiting time for the trains, speedy mechanical loaders most be used instead of manual loading.
Manual loading of trucks, tractors and trailers
Trucks can be loaded by manpower by rolling the logs up skids and over the sides. It is not advisable to use the trucks' stanchions as skids by turning them on their hinges down to the ground, as they are always too short for such work, and rolling-up logs is partly a lifting process and requires more power. The log may also roll or slip back, especially during wet weather, and endanger the loading crew. For loading with a winch (Figure 65) the stanchions are unsuitable owing to the great strain on the truck and on the winch. Loading-skids should have a slope of 1: 2 as a minimum, for manual and for mechanical loading. When loading heavy timber, the platform of the truck should be supported on the loading side by short wood blocks to avoid damage to its suspension springs. This should also be done in order to prevent loading skids slipping off the platform. The loading skids should also be dug well into the ground. To speed up timber loading, it is advisable to build a simple wooden platform with strong poles, as high as the bunks of the vehicles, and large enough to hold a complete truck load. Or a deep loading ditch may be dug where the trucks can slide in, with the bunks at ground level. Loading a second log layer by hand from a platform is dangerous with larger logs and, for reasons of safety, should be done from a second platform of the necessary height. Loading in ditches may be delayed by rain or other water infiltration. Such ground may dry out very slowly, and the trucks may get stuck and have to be pulled out by another vehicle.
BY MANPOWER, WITH SIMPLE MECHANICAL ASSISTANCE
A cross-haul loading system, which is frequently used in the tropics, consists of rolling the logs along the ground to the vehicle and then pulling them up on skids to the truck platform by cables by means of one or two manpowered winches. The winches are mounted at the side of the vehicle opposite to the loading side. The end of a 5- to 8-millimeter cable, passed over a pulley, is hauled out by hand, slung around the log to be loaded, and then attached to the bunk at the bottom. The even raising of the logs up the skids is controlled by the two independently hand-operated winches. When loaded, the cable is pulled out from below the logs resting on the bunks, and the same operation is repeated. When loading logs of small dimensions, two or even three logs may be loaded at one time.
Any typo of truck, with adequately reinforced stakes, can be equipped with manpowered winches and become self-loading, but these slow manual winches are being replaced by mechanical ones, driven by the truck's motor. The winch installation and the loading system are the same and only two men are needed, the mechanical winches being operated by the truck driver.
Another log-loading system by manpower, which is now slowly disappearing, consists of lifting single or bundled logs with the help of a pulley, attached to a gin pole or to an "A" frame (Figure 66), built with strong poles on the side of a road or railroad. The individual logs, or log bundles, are lifted to the necessary height so that the vehicle can slip under the load, which is then lowered on to it. This loading system is still continued in many places, but manpower is replaced by mechanical power wherever possible.
Gin poles, "A" frames and tripods (Figure 67), though portable, can be used in a stationary position only, and have to be moved when the loading at a given landing is exhausted. The logs have to be skidded right under the hook of the lifting cable, and loading heights may have to be limited for trucks with high platforms, as the gin poles and "A" frames can rarely be longer than about 10 meters. Loading by tripods is very slow, as the logs to be loaded cannot be stacked ready under the pulley as is done with gin-poles or "A" frames. Loading by manpower alone is very slow and only suitable for small timber. Even with cheap and abundant labor it is generally more profitable to use some simple mechanical loading device.
In small-scale logging outfits, with only one tractor for skidding and no other loading equipment, trucks can be loaded by using the tractor's bulldozer-plate (Figure 68). The logs are rolled along the ground and then pushed up the loading-skids onto the platform.
The tractor advances slowly between the skids, lifting at the same time the pushing bulldozer-plate, which rolls the log onto the bunks.
Pushing logs onto the platform of a truck lowered into a ditch presents no difficulty. The truck platform being at ground level, the first layer of logs is rolled and pushed straight onto it and the succeeding layers of logs are pushed up on skids. Loading by this system has the disadvantage that, owing to the space needed for the tractor, only two logs can be pushed up at the same time. All other logs have to be stocked clear of the vehicle.
In logging enterprises where several tractors are available, the oldest one can do the loading as the required effort is very small for a D-6 or even a D-4 Caterpillar type crawler-tractor. Loading work thus increases the average service life of a tractor.
CROSSHAULING
Loading from the side, by crosshauling the logs with mechanical power, is more frequent in the tropics than loading by pushing up the logs. It does not need great motive power, and any portable or self-propelled winch or vehicle may be used and its capacity can be adapted to the size of the logs.
SELF LOADING TRUCKS
Any type of truck with adequately reinforced sides can be equipped with two motorpowered winches and transformed into a self-loader, independent and mobile, picking up its load wherever it can penetrate, and transporting it at high speed. These advantages of self-loading trucks for the loading and transportation of small, single loads, could not however be adapted for regular hauling in a logging operation. The reduction in loading time, realized with motor-driven truck winches, is not satisfactory owing to the limited size of the cable-drums, which cannot carrytthe required cable-length nor deliver the desired power and speed to the loading cable. These defects were the reason for abandoning the self-loading installation on the trucks, and replacing it by more powerful winches, carrying longer and thicker cables, and capable of higher hauling speed. The combination of a mechanically-powered winch, a cable and a pulley block, led to the construction of numerous types of loading systems and equipment.
One method is the sideway loading of trucks, tractors and semi-tractors, with one cable slung around the center of the log. One end of the cable is fixed to the bunk of the truck, or to any other fixed point at the opposite side to the loading, and the other end is pulled by a stationary winch or by a vehicle. Theoretically, the one-cable loading system should be satisfactory but, in practice, it raises so many difficulties that it is usually given up after a few attempts because of its inherent dangers. Owing to the irregularities of shape and surface, the logs do not move straight when being pulled up the skids and the winding cable does not stay at the balance center of the log, which slips on the skids, endangering both the men and the vehicle.
A better solution is by the traction of one cable with two free ends, slung crotch-wise round the ends of a log and attached to the bunks of the vehicle. Safer than the previous system, log loading with two free-cable ends is still exposed to frequent accidents owing to the difference between the sizes of the two ends of the logs, causing an uneven rise onto the loading skids. This cannot be corrected by the winch driver who controls both cable-ends with only one pulling cable. In the case of a vehicle pulling the loading cable by its own movement, the cable should be passed over a pulley suspended from a tree or a branch a few meters above ground near the vehicle to be loaded. The traction-hooks of trucks or tractors are generally attached too low at the rear of the vehicles for pulling a loading cable but, by lifting it with the help of a pulley, the small high-lead effect facilitates the loading and reduces the strain on the cable and on the vehicle. One driver and two men are necessary, the truck-driver also operating the independent pulling vehicle.
A third, rarely seen, solution of loading with one tractor cable is to pull up the log in two separate operations, first at one end and then at the other. Such loadings are possible only on tractors with trailers, and can be done with one winch only. Because of the danger of accidents to which men and equipment are exposed, this loading system should be avoided wherever possible.
At the present time loading with two cables, pulled by two independent winches or vehicles presents the most favorable cross-haul loading system (Figure 69). As the speed of each loading cable is individually controlled, the logs can be evenly raised on the skids. As only two winches or vehicles are required, it is an inexpensive system where tractors are not available. It has already been stated that log-hauling on earth roads in the tropics should be carried out as far as possible in dry weather and that all efforts should then be concentrated on it. This includes the use of skidding tractors for loading, and has to be foreseen in the planning of a readily adaptable working program.
FIGURE 70. - Loading timber by means of lift tongs and an Allis Chalmers Hd-15G crawler tractor.
LOADING BY LIFTING
Log loading by lifting is a most efficient method, and owing to the high purchase costs of modern power-loaders is very often also the most expensive one! In principle, the logs are picked up by the hook or tongs of the loading cable, lifted, swung over the vehicle to be loaded and lowered down into it. The machinery used for this work is of many kinds, including fixed, portable or self-propelled cranes, but all work in a stationary position; mobile selfloaders may also be used for loading and carrying logs, such as the yarders, lift-trucks, lift-forks, self-loading trucks and tractors. At present, these are practically all Diesel-driven, mounted on wheels, or for heavy duty, on crawler tracks, and capable of operating over any kind of forest ground, excepting swamps. They have a lifting capacity of 10 to 12 tons, a reach of up to 7 to 10 meters, and can load up to 400 tons of logs per day (Figures 70 and 71).
Fixed cranes and derricks which are used frequently for log loading in railroad stations, transferring logs in sawmills, loading and unloading barges and ships, are included here with reference to timber handling. For light work they may be built with two strong timber poles, and equipped with a manual or motor winch. For the handling of bigger timber, steel-constructed derricks with rapid power-drive are used in sawmills and log depots, and for many years were the best available timber handling equipment; but today they are being replaced by better methods. Portable cranes, for operating in a stationary position, include gin poles, A-frame loaders, and tripod or square-frame loading installations.
Self-propelled loaders, also working in a fixed position but not self-loading, include all types of lifting equipment mounted on tractors or trucks. Fairlead arches, adapted for loading, and portable high-lead cranes have been described in Part I of this paper. Self-propelled and self-loading engines are also used for carrying the load and include self-loading tractors and trucks, lift trucks and lift forks, yardsters and the Tournahauler.
Crane loaders, mounted over crawler tracks or on wheels, are the most frequently used loading machines in tropical forests. Built for other industrial work, they can be used for log loading without any transformation or adaptation. They are often available as secondhand machinery in good condition, and need not therefore be expensive. For the loading of tropical timber of average size, crane loaders mounted on wheels have been proved to be successful, and manufacturers are now making similar crawler-borne cranes for work with larger sizes of timber. For the same lifting capacities, loaders on wheels are cheaper than crawler cranes; they have a much greater mobility and can get rapidly to any loading place, while the crawler-borne crane can move itself over short distances only and has to be conveyed to distant working areas. The comments and suggestions previously made on the operation and maintenance costs of wheeled tractors apply equally to mobile loading equipment.
Log loading with cranes, though quicker than loading by crosshaul, is still not very satisfactory. One reason for this is the relatively slow loading of single logs with chokers. The cable has to be slung around the log as near as possible to its weight center, to keep it in a horizontal position; and, when swung over the vehicle, the log has to be guided by hand or by ropes to the desired position or site. This takes time, and the logs also have to be taken to the loader by another winch or tractor, an inconvenience which cannot be avoided, except when loading with the Logger's Dream or with the Hystaway crane (see Part I) which are both capable of hauling logs from a distance of 150 to 200 meters. Crotch-lines with end tongs or, for heavy timber with double tongs and with slings attached to a horizontal boom, lift the logs in a horizontal position. Once they are swung over the vehicle, however, they must be guided by ropes from the ground, or by hand, to the desired loading place, and the disengaging of two tongs or two slings takes more time.
Methods of attaching the logs to the crane cable have been speeded up by the use of tongs; and a quick swing into position over the truck is obtainable with heel-boom cranes, swinging in a complete circle. Held fast by the tongs or by the loading grapples at about two fifths of its length, the shorter end is lifted to the heel boom and held against it by the overhanging end, thus avoiding any side swinging, and permitting it to be held exactly above the loading space. Loading with crotch-lines or double slings requires four men: one crane operator, two hook men, and one man for unhooking the logs. The heel-boom loaders need only three men: one crane operator, one for setting and one for shaking loose the tongs. With quick release tackles controlled by the crane operator, only two men are necessary. Heel-boom cranes represent the fastest type of loaders and are now built in a wide range of lifting and loading capacities, up to 50 tons and 900 cubic meters per day.
In order to eliminate the holes made by loading with mechanical or pneumatic tongs which penetrate 10 centimeters or more into the log sides, the use of grapples is strongly recommended. Otherwise, holed strips in sliced or rotary veneers must be cut out, or thick slabbings sawn off the outside of damaged valuable logs: these are unnecessary losses.
Previous observations regarding the use of efficient but costly mechanical equipment for yarding are also valid for log loaders. Their high depreciation rates require the handling of large volumes of timber in order l to justify their high costs, and only the bigger logging, companies can afford them.
Fairlead arches are also now used for log loading. These are of normal construction, but improved by increasing the lifting height by means of wooden or steel booms fixed above the fairlead to attach the pulley for the loading cable. The great advantage of these arches is their ability to collect the logs from any part of the landing and to carry them to the vehicle to be loaded. With a second log layer there are loading difficulties owing to the low suspension of the cable pulley, and the necessity of first backing up the arch to the log to be picked up, and then to the truck or tractor for loading. Approaching the logs with the loading cable from the side is not possible, as the arch may capsize. Operated by a skidding tractor, loading is slow because use of the bad maneuverability of the arch when backing up.
In order to increase the lifting height, the cable pulley can be attached to a 5- to 8-meter long steel spar, mounted at the rear of a crawler tractor such as the Hystaway Shovel tractor built by Caterpillar-Hyster, which is capable of taking loads up to 3 meters in height. Using tongs, slings or endhooks, it can load tree-length logs, as well as pulpwood bundles. Its log loading capacity reaches 500 tons per day, or 900 steres per day of bundled pulpwood. Equipped with bulldozer plate, the versatility of the Hystaway is improved and, by removing the spar, the Caterpillar D8 or D7 on which it is mounted can be used for road-building; and when converted, as a shovel, dragline, or excavator. Very efficient, it has the common disadvantage of modern equipment, its high purchase price and high operation costs, which are economic only if very large volumes of timber have to be loaded.
Tractor manufacturers are also constructing many types of self-propelled self-loading and load-carrying vehicles, called lift trucks, lift forks, carry lifts, log stackers, etc., of different sizes and loading capacities. They are mounted on wheels with solid or pneumatic tires, or on crawler tractors, and are capable of lifting loads up to 10 or 12 tons. For reasons of stability and owing to their small wheels, these engines cannot operate on ordinary soft forest ground. Their best performances, based on impressive travel and operation speeds, are obtained on concrete or on solid, even soil, as in sawmill logyards, railroad stations and harbors, where they are highly appreciated owing to their great maneuverability and the speed of the hydraulic raising or lowering of loads. For loading in the forest itself, lift trucks, lift forks and carry lifts have to be crawlerborne for better stability. Lift forks hold the logs fast, so they cannot slip during loading but, to avoid capsizing, the load must be well balanced. Being mounted in the front of the tractor, the forks can be replaced by a bucket or bulldozer plate. In this way, the same engine can be used for road building and maintenance, for earth-moving jobs, and, of course, for skidding with or without a winch attached to the rear. The crawler-mounted lift fork, also built by the Hyster Company and called the Traxcavator: and the wheelborne carry-lift, constructed by the Pettibone Mulliken Corporation, can never be used to capacity in tropical forests, and cannot be recommended for the actual logging volumes available.
The last, and possibly most useful, of this group of loaders is the Letourneau Tournahauler, a self-loading, 175 or 200 horsepower diesel-electric tractor, with a semitrailer arch, or a semitrailer platform on wheels, carrying up to 20-ton loads at a speed of up to 50 kilometers per hour. Logs 10 meters long can be loaded on the platform. The electric power, produced by a diesel-driven generator, is distributed independently and automatically in the quantity required, to four driving-wheels and to the loading winch. The upper structure for the loading monorail, fixed over the tractor, is not satisfactory for loading long timber, and is being replaced by a less bulky crosshaul equipment. Over a distance of 3 kilometers, the Tournahauler, with a semitrailer platform, can haul 100 to 120 tons a day, five or six trips; with an arch and, over a distance of 14 kilometers, it can haul about 50 tons a day, in four or five trips. The low pressure tires for the front wheels have two or three times the length of service life given by crawler tracks but it has been observed that there is heavier wear on the rear wheels. The substantially increased ground contact area of the large low pressure wheels permits a greater traction effort, and the four-wheel-drive and steering gives it a high mobility.
A combined felling and self-loading machine, with a special crawler-tractor is used in northern Russia for small pulpwood. A circular saw, mounted in front of the tractor, is driven right up to the trees, which are 20 to 30 centimeters in diameter, and fells them at about 5 to 10 centimeters above the ground. The felled trees are grabbed and loaded by pulling them down over the driver's cabin, and skidded in a semi-suspended position, the butt ends of the full trees resting on a steel bar above the driver's cabin and the tops skidding along the ground. Two men only are necessary to operate the tractor; and, depending on their size, 6 to 10 trees are skidded at one time. Being a new machine, it has not yet been tried out in the tropics, but there are possibilities for it in the fast-growing coniferous and softwood forests planted for the supply of pulp wood.
LOADING' FROM THE REAR END OF A VEHICLE
This loading system consists of pulling up the logs end-ways to the rear end of the truck platform, with two pulleys fixed on rectangular or arched frames, one at the rear and one at the front end of the platform; or by one pulley only, traveling on a monorail and mounted over the platform. The traction power is delivered by a winch which is driven by the truck motor.
Loading with two pulleys, using tongs to attach the logs, is done in two parts. First, the tongs are set near the front end of the log, which is pulled up against the rear end of the platform; the cable passes over the rear pulley, by hand or automatically, and the log is pulled onto the bunks of the truck and to the front end of the platform. The rear pulley can be moved sideways and clamped to the supporting frame, to guide the logs to the desired loading site. Log dimensions are determined by the admissible maximum width of the platform, usually 2.4 meters, and by its length. Logs longer than 6 meters should not be loaded onto platforms of 4 meters except as the bottom layer, and then should be well weighted down by short loge for the second layer. Such equipment permits the loading of only two layers, with maximum loads of four to five logs, up to 70 centimeters in diameter. Two men are needed: one truck-driver operating the winch and one tongs-setter. Logs can be picked up at any place in the forest where a truck can go alongside the roads, or even in such conditions where only loading from the rear is possible. A truck with a strong platform and fitted with a winch, requires only two strong frames and two pulleys for its conversion into a rear loader.
The second method of log loading from the rear end of a vehicle is by the monorail loader. This improves on the loading with two pulleys described above, by replacing one of them by a monorail, built over the platform. The second pulley is suspended loosely on the monorail and is pushed, with the cable, to the rear end; and the log is then attached. Winch action pulls the log up, and the pulley advances slowly toward the front end of the platform. This system proved less satisfactory than loading with two pulleys; as the pulley on the monorail could not be shifted sideways on the rear supporting frame to pull up the logs directly in front of the selected loading space on the platform.
Loading from the rear is even slower than by the cross-haul. Both systems have therefore been abandoned when there is a large volume of timber to be transported. Capital investment for both equipment and maintenance costs is small, but once rigged with it, the trucks cannot be loaded by any other means, neither by croashaul nor by lifting the logs. To avoid this immobilization of the trucks, the loading rigging has to be dismantled completely for the monorail system, and the rear frame only for two-pulley loading.
Both these rear loaders, often with locally built rigging, are typical of the numerous loading machines, invented and used chiefly by the smaller logging enterprises, in order to get longer service out of their wornout skidding and hauling equipment. All these ingenious systems have one common characteristic: their low capacity. They should not be considered as the chief means of loading timber but only as auxiliary. Loading is one of the most important parts of logging and can become the source of heavy production [oases if the loading equipment is not properly adapted.
UNLOADING TIMBER
Log unloading can be done in three different ways, adapted to the various logging operations: by hand, by gravity, and with mechanical equipment. Different methods are used for highly valuable peeler or veneer logs than for saw or construction timber of lesser value.
When unloaded by direct labor, peeler and veneer logs should be handled with great care. They should not hit the ground from a great height and never bump other logs or obstacles. The bark cannot completely protect the wood beneath it, and crushed fibres by impact can penetrate several centimeters deep into the wood, producing discolored, irregular spots on the peeler sheets or veneers, which have to be cut out and the holes repaired at great cost.
At landings or sites for rafting, heaps of soft earth should be prepared at the unloading places for railroad cars and trucks, so that the logs rolling off the vehicle fall down only a short distance and can be rolled smoothly to the river or seashore. Experienced buyers of rotary-veneer logs in the tropics see any damage by rough handling on the bark or on the wood and, depending on the market situation, may either refuse to accept such logs or pay a lower price. Careless handling of highly valuable logs during loading, transport, or unloading is not an economic policy, as the income from the increased output by speedier, rough handling will seldom compensate for the loss suffered from the sale of low quality timber. It should also be remembered that debarked logs show much more of any handling damage when they are not covered with a protective, insect-repelling coating. Unloading by gravity is not suitable for veneer loge because of the heavy damage which may occur, especially when the logs are dumped on top of each other. This is not permitted on well-organized logging sites, nor is the rolling of veneer logs downhill on long slopes.
Saw logs do not require special attention during unloading by hand, but it is not difficult to construct with one long log and two or three poles, a simple unloading platform, somewhat lower than the bunks of the vehicle. On flat ground, the first log dumped from the truck should immediately be removed, so that it will not, be hit by the following one and its bark torn off thus offering a favorable opening for attacks by insects and fungi. Heavy shocks during unloading are often the cause of splits on the crosscut faces of timber species with small shock resistance. If not checked rapidly with S or C irons, the splits may progress deeply into the log, and it will become unfit for sawmilling. Rough unloading by gravity is faster, and it must be decided where, when, and up to what limit it can be applied to a given species of timber. It must also be determined what damages are acceptable and what monetary losses will be caused by the degraded timber quality.
For mechanical unloading, the same equipment can be used as for mechanical loading, with the distinction that unloading sites have a more stable character.
They are seldom moved, and therefore fixed cranes, derricks, or mobile cranes on rails, have been frequently used in the past. At the present time, they are outdated as inefficient and too slow and are being replaced by lift trucks or mobile cable cranes equipped with tackle for quick release of the load, and mounted on wheels or crawler-tracks.
Lift trucks, lift forks and carry lifts are at present the fastest unloading equipment. If the lift forks can get under the bunks of a vehicle, they can unload it in one or two movements and carry the load to any desired storage place or transport point. In places where lift trucks cannot operate, particularly when barges or cargoboats are to be unloaded, the safest and best work is done with mobile cable cranes which lift the logs out of the horde and lower them to the ground. For short logs, crotch lines with end hooks are best, but for long timber chokers or slings should be used. The deep holes in the wood which tongs produce should not be permitted for unloading veneer logs, and grapple loaders should be used instead.
Forest utilization in the tropics has a double aspect: an individual one concerning the production side, and a general one in its direct connection with the local timber trade, and also overseas outlets for particular timber species.
Owing to the high cost of heavy mechanical equipment for logging and transportation, it seems that the small independent enterprise will exist in the future on a subcontract basis and then only for special or limited operations. One can give as an example, felling and bucking, or skidding and bunching with animal traction or even with tractors having mobile high-lead equipment. Longer hauling will be by truck, by tractor and trailer, by rafting and towing, or by air-lift. Felling and bucking, log-rolling or hauling by narrow-gauge forest railroads may still be economic by manpower but the cost of the necessary equipment for modem mechanization methods now becoming more generally available may soon reach the limit of capital available to the individual contractor. In the tropics, profits are often soon reduced owing to the high depreciation rate of the mechanical equipment which a contractor can very seldom use to full capacity. Overinvestment in logging equipment is a world-wide evil, but the consequences are comparatively smaller and are more easily absorbed by large production enterprises. Only companies with a sound financial backing can undertake the creation of integrated forest industries, and keep overinvestment within reasonable limits.
With regard to practical advantages and operation benefits, a logging company producing about 12,000 cubic meters of logs per year is the most economic working unit, under the operating conditions obtaining on the west coast of Africa. Assuming normal selective-cutting operations, a logging company would need capital of about U. S. $150,000 before felling the first tree, and about U.S. $200,000 before the first timber sales. The capital outlay necessary may be illustrated as follows:
The Caterpillar crawler-tractor, model D 7, the most used tractor on the west coast of Africa, delivered with bulldozer-plate, rear-winch and wheeled-arch, costs approximately U.S. $30,000. On distances between 200 and 500 meters it has an average daily yarding output of about 60 cubic meters during the dry season, and 40 to 45 cubic meters during the rainy season; or about 50 cubic meters a day for the whole year of 250 working days. This makes a grand output total of 12,000 cubic meters per year. A second tractor of the same capacity is indispensable for road-making, for accelerated yarding during favorable weather periods, possibly for loading, and also as a replacement for the first engine when it is under repair. The necessary felling and bucking tools, both manual and mechanical, may be costed at U.S. $5,000.
The transportation of 50 cubic meters of logs per day for a distance of 20 kilometers can be completed by a self-loading, 20-ton Letourneau-Tournahauler, in three trips carrying 15 to 20 cubic meters each; this will cost about U.S. $30,000. Alternatively, two self-loading Mercedes-Benz tractors with semitrailers can be used, making three daily trips and loading 8 to 10 cubic meters. At present costs, these two complete sets of equipment would cost about U.S. $20,000. Add to this expenses for forest survey and inventory, for the construction of an access-and-hauling road; for offices and housing; for installation and equipment of an adequate repair-shop, with spare parts stock, and for transport facilities for passengers and goods by road or by water; and a total of U.S. $150,000 would be a minimum. Salaries for one general manager, one logging superintendent, one surveyor, two mechanics and two accountants, and wages for a crew of about 80 men, will absorb, during the first three months of operation, (together with the cost of fuel, grease, and oil) U.S. $15,000 to 20,000 a month. This brings the initial outlay to U.S. $200,000.
The outlook for the future depends on the growing potentialities of local timber consumption and on the demands from oversee markets.
Two thousand million hectares, or nearly one half of the world's forests, are located in tropical and subtropical countries. It is difficult to understand why their potentialities as producers of one of the most important raw materials, wood, are not yet being fully appreciated, neither by the wood conversion and consumption industries, nor by the manufacturers of mechanical logging equipment or wood-working machinery. Wood has come into its own in rapid strides during the past 20 years so far as the utilization of the coniferous forests of the temperate and cold zones are concerned, but it has not yet come to the tropics, encouraging the stepping up of the use of tropical forests to a level corresponding to their productivity.
The comparatively small amount of wood removed from the tropics, which is far below what it could be when the increment volumes of tropical forests are considered, and the sharp disproportion of industrial wood against fuelwood removed at the present time, are the two outstanding characteristics of the present logging situation in the tropics. It should be noted that the firewood extracted from the tropics is actually much greater than the recorded figures.
Three reasons may be offered for the small output from tropical forests. First, the meager populations of the small agricultural settlements which shift across the forests have an insignificant wood consumption, limited chiefly to fuelwood and to a few branches for building huts. Wages, and income from the sale of agricultural or forestry products, are usually too low to permit savings for investment in house-building or furniture. Capital investment from outside is still small owing to lack of knowledge of the potentialities of tropical forests, and, in some cases, to political unrest. Secondly, mechanical conversion methods of tropical hardwoods by sawmilling and peeling has been almost the only outlet for the timber up to the present time, and it has been generally considered that tropical timber is unsuitable for pulping or for fibreboard production. Thirdly, the lack of local cheap transportation has kept the prices of construction wood too high for the small income of the local inhabitants, and high sea-freight rates have chiefly restricted wood exports to small quantities of timber of rare species and of great merchantable value.
Far-reaching changes however are now taking place in the tropical regions of the world. Population growth, based on sufficient food and improved hygienic living conditions, combined with economic and industrial evolution in many of the less developed tropical countries, is already requiring a steadily increasing volume of construction timber. The mechanization of the logging equipment and of local wood-conversion industries is already beginning to meet the increasing demand for housing and furniture, for newsprint, and for writing and packing paper.
The unsuitability of many tropical hardwoods for pulping is no longer an obstacle, as a great number of timber species can now be used. New chemical and semichemical pulping methods, which are both cheaper and more efficient, have already begun to increase the range of tropical hardwoods for pulping.! Many tropical countries with suitable wood reserves are now keenly interested in building their own paper mills as soon as possible in order to free themselves from the expensive paper imports. Together with the rapidly increasing paper requirements of many developing countries, there will be a continuing greater demand for writing paper for educational purposes, especially for the 30 to 40 million children born each year in the tropics; and with rising standards of living, for newspapers, books, and packing paper.
The actual number of tropical timber species now in use will be increased by the inclusion of many other woods, formerly disregarded but now marketable thanks to new methods of preservation, and accepted at the present time by local as well as by foreign markets. Some tropical countries, encouraged by the good results obtained by planting species of timber which are in demand, have already started to clear-cut forest areas stocked with unwanted and unsaleable species, and to replant them with better fast-growing species, such as conifers and eucalyptus, capable of increasing by eight to ten times the former yield.
The third problem, transportation facilities, is the most important, as the improvement of roads is essential for any future economic or social development, and especially for the home consumption of locally-grown timbers and of their export. Although of small value at the stump, the price of timber for either home or oversee markets is increased by 80 and 90 percent by transport roads. Apart from felling and bucking, all other log production work depends on transportation, adding nothing to the final timber value but raising its local costs by each handling, and by expensive transportation conditions. Construction costs for secondary, and often even primary, logging roads to connect the forests with the public highways, are always very high, and represent unproductive investment which the logging companies can amortize only by greater volume of timber to be transported, and by charging reasonable transport fees to their timber production costs.
More complicated, however, are the difficulties encountered in exporting timber: shipping space and freight rates. Even during normal quiet times, cargo space is not always available in the desired volume, or at favorable shipping periods, and both shipping space and freight rates are subject to serious interference owing to political disturbance. It is mainly for these reasons that the export of round timber has to be reduced to a minimum, and replaced by the shipping of timber products, for which local industries have to be created in the form of integrated forest utilization.
Such local industries cannot be established unless the forests are managed on a permanent use basis. This means that in the tropics it may not be possible to continue the present selective cuttings of single trees, and that the present primitive harvesting methods will have to be changed to scientific management if full utilization is to be made of the existing forests and if new forests of the desired species are then to be created. A well-planned system of permanent access roads is a first essential as is the application of the most economic logging and transportation methods.
The manager of a tropical forest must co-operate in the future with the logger, so that the least possible damage is caused to the remaining stands and damage to regrowth avoided by the skilful use of improved mechanical logging equipment. Wheeled tractors, replacing crawler tractors except for the heaviest loads, are already being equipped for skidding, loading, and road building. Lighter trucks, built with new alloys to reduce their deadweight, will carry bigger loads at greater speed on better roads, and the application of radio transmission to tractors and trucks in the field, and electronic control of cable-logging in mountains, will become normal equipment. The technical feasibility of air-lifts of timber and of forest products has been successfully proved in the Caucasus, and it is only a question of time before atom-driven helicopters needing no roads, will be used in the tropics for otherwise inaccessible forest hillsides.
These visions of future logging developments in the tropics cannot, of course, be made with the same validity for all kinds of forests in any tropical country. But the first steps in the right direction have already been taken in the most advanced areas of logging operations m equatorial Africa and in the Far East. Integrated forest utilization is one of the main factors in reducing transportation costs, and should make rapid headway.
Before reaching its zenith, integrated forest utilization may remain for some time at a different level in each tropical country, one determined by the available timber species and their respective conversion possibilities and also by local industrial and economic development. Full forest utilization, however, is not possible without full integration, and this in turn is not possible without adequate capital investment for the creation of local wood industries.
(Concluded)
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AIR SURVEYS FOR AID PROGRAMS The potentialities for using aerial survey techniques to speed up aid programs in the developing countries will probably form the theme of the next world congress of the International Society of Photogrammetry in 1984. This was recommended at a symposium on photointerpretation, organized by the Society at the Netherlands International Training Center for Aerial Survey in August 1962, at which D.A. Francis of the FAO staff presented a paper. All papers read at the Symposium will be printed in full, together with a summary of the discussions, in Transactions of the symposium on photo interpretation, available in English, French or German, price U.S. $16.00. Payment to the account of Uitgeverij Waltman, with Messrs. R. Mees and Zoonen, Bankers, Delft, Netherlands. |
