5.1 Introduction
5.2 Felling and Bucking
5.3 Skidding
5.4 Loading
5.5 Truck Transport
5.6 Typical Stump to Mill Logging Systems
Logging unit costs are estimated by dividing machine rates by the production rates for the various logging activities. Logging components considered here are felling, bucking, skidding, loading, and transport.
The major variables in felling and bucking are the tree diameter and the number of bucking cuts after felling. An example of a formula for the time to fell and buck a tree is
T = a + b D2 + c B
where T is the time per tree in minutes, b is the minutes per unit diameter and the D is the diameter, c is the time per bucking cut and B is the number of bucking cuts. The coefficient a is the time per tree that is not related to diameter such as walking between trees or preparing to cut. Sometimes terrain and brush are taken into account by using equations of the form
T' = (1 + f) T
where f is an adjustment factor for terrain or brush. The production rate, P, in cubic meters per hour is
P = V/T
where V is the volume per tree, m3, and T is the time per tree, hr. The unit cost of felling is
UC = C/P
where C is the machine rate for felling and bucking and P is the production rate.
EXAMPLE:
A power saw and operator cost $5.00 per hour and the time to fall and buck a tree is
T = 4.0 + .005 D2 + 2.0 B
For a tree with volume 6 m3, dbh of 80 cm and 1 bucking cut
T = 4.0 + .005 (80)(80) + 2.0 (1) = 38.0 min = 0.63 hr
P = V/T = 6/0.63 = 9.5 m3 per hr
UC = 5/9.5 = $0.52 per m3
For a tree with volume 1.25 m3, dbh of 40 cm and 1 bucking cut
T = 4.0 + .005 (40) (40) + 2.0 (1) = 14.0 min = 0.23 hr
P = V/T = 1.25/.23 = 5.4 m3 per hr
UC = 5/5.4 = $0.93 per m3
Skidding production is estimated by dividing the volume per load by the time per round trip. The round trip time, T, is the sum of the times for travel unloaded, hooking, travel loaded, and unhooking.
T = a N + b1 x1 + b2 x2
where a is the combined time for hooking and unhooking per log, b1 is the minutes per meter for unloaded travel, b2 is the minutes per meter for loaded travel, x1 is the distance from the landing to load pickup point and x2 is the distance from the load pickup point to the landing. If the outhaul distance and inhaul distance are the same, the roundtrip time can be expressed as
T = a N + b x
where b is the minutes per roundtrip distance and x is the one-way distance. The coefficient b is calculated as
where v1 is the travel speed unloaded and v2 is the travel speed loaded.
EXAMPLE:
A skidder is bringing in 3 logs with a volume of 4 m3. The unloaded speed is 200 meters per minute and the loaded speed is 100 meters per minute. The hook time is 1.5 minutes per log and the unhook and decking time is 1.1 minutes per log. The skidding distance is 300 m. The machine rate for the skidder and crew is $40 per hour.
T = (2.6) (3) + 300/200 + 300/100 = 12.3 min = .21 hr
P = 4/.21 = 19.5 m3 per hour
UC = 40/19.5 = $2.05 per m3
alternatively,
b = (200 + 100)/[(200) (100)] = .015 min/m
T = (2.6) (3) + .015 (300) = 12.3 min
The cost of hooking, unhooking and decking is
UCF = (C/60) (aN)/V
UCF = (40/60) (2.6) (3)/4 = $1.30 per m3
The cost per cubic meter of wood per unit distance (measured one-way), UCV, is
UCV = (C/60) (b)/V
UCV = (40/60) (.015)/4 = $0.0025/m3-m
At a skidding distance of 300 meters
UC = UCF + UCV = 1.3 + (.0025) (300) = $2.05 per m3
The same method can be used to estimate the skidding costs with agricultural tractors and trailers, animals, or with cable systems.
EXAMPLE:
A team of oxen brings in one log with a volume of 0.8 m3. The unloaded speed is 30 meters per minute and the loaded speed is 30 meters per minute. The hook time is 2 minutes and the unhooking and watering time is 5 minutes. The skidding distance is 100 meters. The rate for the oxen and driver is $3.00 per hour.
T = (7) + 100/30 + 100/30 = 13.7 min = .23 hr
P = .8/.23 = 3.48 m3 per hour
UC =3/3.48 = $0.86 per m3
Loading production is estimated by dividing the volume per cycle by the minutes per cycle. The time per log for loading single logs is often as simple as
T = a
where a is the time per cycle.
EXAMPLE:
A truck is being loaded by hydraulic knuckleboom loader. It is loading 1.0 m3 logs individually at an average rate of 2 per minute. To prepare for loading trucks, however, the loader spends 30 minutes per hour sorting logs. What is the loading production rate and cost?
When the loader is actually loading logs, the production rate is
P = (1.0)/.5 = 2.0 m3/min = 120 m3/hr
but the loading production per machine hour is 60 m3/hr.
The cost of log sorting can either be shown as a reduced effective rate of log loading or as a separate subunit cost of the total logging unit cost. If the sorting cost is included in the loading cost, the unit cost of loading is then
UC = 40/60 = $0.67 per m3
The method of estimating truck production depends upon the purpose of the analysis. If truck production is being calculated for the purpose of determining the number of trucks needed for truck haul, then the average truck load is divided by the total roundtrip time including unloaded travel time, loading time, loaded travel time, and unloading time. The calculation is similar to that for skidding with the roundtrip travel time, T expressed as
T = a + b1 x1 + b2 x2
where a is the combined time for loading and unloading, b1 is the hours per km for unloaded travel, b2 is the hours per km for loaded travel, x1 is the distance from the landing to load pickup point and x2 is the distance from the load pickup point to the landing. If the outhaul distance and inhaul distance are the same, the roundtrip time can be expressed as
T = a + b x
where b is the hours per roundtrip km and x is the one-way distance. The coefficient b is calculated as
where v1 is the travel speed unloaded and v2 is the travel speed loaded.
EXAMPLE:
A 22-ton truck carries an average of 30 m3 per trip. The haul route is 35 km. The unloaded truck travels 40 km per hour and the loaded truck travels 25 km per hour. The combined waiting and loading time is 30 min per load and the combined waiting and unloading time is 20 min per load. The cost per truck standing hour is $20 and the cost per truck running hour is $30. What is the production per hour?
T = (30 + 20)/60 + 35/40 + 35/25 = 3.11 hrs
P = 30/3.1 = 9.65 m3/hr
The "fixed" unit cost of truck standby for loading and unloading is:
UFC = ($20/hr) (30 + 20 min)/60 min/hr/30 m3 = $0.56 per m3
The "variable" unit cost of truck travel is:
UVC = ($30/hr) (35/40 hr + 35/25 hr)/30 m3 = $2.28 per m3
or expressed on a ton-km basis:
UVC = ($30/hr) (35/40 hr + 35/25 hr)/22 t/35 km = $.089 t-km
The total unit cost of truck haul is:
UC = UFC + UVC = 0.56 + 2.28 = 2.84 per m3
To illustrate the use of machine rates (Section 3) and the production relationships discussed in this section, stump to mill logging costs for three typical logging systems are shown. In each of these examples, the stump to mill or water harvesting activities are listed along with assumed machine rates and production data. The production data are then converted into production per hour with the conversion method depending on the form of the data. Unit costs for each activity and a stump to mill or water cost is calculated.
5.6.1 Plantation Large Wood
Assume clear felling of a pine plantation is being planned. An estimate is being made of the stump-to-mill harvesting costs for one possible alternative for the operation. The roads are already in place. The activities are:
1. Fell, delimb, and cross cut with power saw.2. Skid to roadside using a rubber-tired skidder.
3. Load truck trailer using a self-loading truck.
4. Transport by truck to the mill.
Machine rates (col 2) and production data (col 7) for this example are shown in Table 5.1. The machine rates for the various labor-equipment combinations of cutter with power saw, rubber-tired skidder with operator and helper, and truck driver with self-loading truck are developed using the techniques from Chapter 3. Production estimates are made from experience, available formulas or tables, or short time studies (Appendix B). A good source of felling, skidding and loading production for large plantation wood can be found in Planning Roads and Harvesting Systems by FAO, 1977.
The formula used for the hourly production calculation (Table 5.2, col 8) depends upon the information available. On the following pages production calculations are shown for various harvesting activities. For the felling, delimbing and cross cutting:
P = 4 trees/hr × 1.1 m3 per tree = 4.4 m3 per hour.
For skidding the logs to the landing by rubber tired skidder:
T = 5 + 200 m/(60 m/min) + 200 m/(100 m/min) = 10.33 min
Assume we have observed about 10 min per hour are involved in unplanned delays so we can either increase the average time per trip to
T = 10.33 min × (60/50) = 12.4 min per trip including delays
or we can reduce the effective hour from 60 minutes per hour to 50 minutes per hour:
P = 2.2 m3/load × 50 min/10.33 min per trip = 10.6 m3/hr
For loading the truck trailers a short time study indicates the time per log is 30 sec with an average log size of 0.55 m3. The loader only spends about 30 minutes per hour loading trucks and the remainder of the time decking and sorting logs. We have two choices here. We could reduce the loading rate to create a "sorting and loading production" rate or we could keep the two production rates separate. A combined sorting and loading rate is used in Table 5.1.
P (loading only) = .55 m3/log × 2 log/min × 60 min/hr = 66 m3/hrP (sorting and loading) = 66 m3/hr/2 = 33 m3 per hr
For truck transport to the mill yard:
T (standing) = 45 min per trip = .75 hrP (standing) = 20 m3/load/.75 hr = 26.7 m3/hr
T (traveling) = 25 km/20 km/hr + 25 km/25 km/hr = 2.25 hr
P (traveling) = 20 m3/load/2.25 hr = 8.9 m3/hr
After the machine rates and production rates have been derived, the individual unit costs can be calculated (Table 5.1, col 9). The stump-to-mill cost for this harvesting alternative is $9.58 per m3. Road reconstruction or road maintenance costs should be added, if appropriate, using the techniques from Chapter 4.
Table 5.1 Large Wood Plantation Harvesting Example
|
(1) |
(2) Cost |
(3) |
(4) |
(5) |
(6) |
(7) |
(8) |
(9) |
|
Fell and cross cut |
4.20 |
- |
- |
- |
- |
4 trees/hr |
4.4 |
0.95 |
|
Skid |
35.00 |
60 |
100 |
5 |
10 |
200 m skid |
10.6 |
3.29 |
|
Load |
40.00 |
- |
- |
- |
30 |
2 logs/min |
33.0 |
1.21 |
|
Truck standing |
20.00 |
- |
- |
45 |
- |
20 m3/load |
26.7 |
0.75 |
|
Truck traveling |
30.00 |
20 km/h |
25 km/h |
- |
- |
20 m3/load |
8.9 |
3.38 |
|
Total |
|
|
|
|
|
|
|
9.58 |
5.6.2 Plantation Small Wood
Assume thinning of a young pine plantation is being planned. An estimate is being made of the stump-to-mill harvesting costs for one possible alternative for the operation. The roads are already in place. The activities are:
1. Fell and cross cut with bowsaw.2. Delimb with axe.
3. Skid to roadside using a hand-guided sulky.
4. Manually load agricultural trailers.
5. Forward by tractor to a transfer yard and unload using tilt-bed trailers.
6. Load truck trailer using small hydraulic grapple.
7. Transport by truck to the mill.
Machine rates (col 2) and production data (col. 7) for this example are shown in Table 5.2. The machine rates for the various labor-equipment' combinations of cutter, worker with sulky, loader, tractor operator with tractor and trailer, operator with hydraulic loader, and driver with truck and trailer are developed using the techniques from Chapter 3. Production estimates are made from experience, available formulas or tables, or short time studies (Appendix B). A good source of felling, skidding and loading production rates for small plantation wood can be found in Harvesting Man-Made Forests in Developing Countries by FAO, 1976.
The formula used for the hourly production calculation (Table 5.2, col. 8) depends upon the information available. The analyst must be flexible in the approach to converting the production data to production units per hour. Two of the production calculations are shown below.
For the felling, delimbing and cross cutting:
P = 5 trees × .1 m3 per tree = 0.5 m3 per hour.
For the manual forwarding operation using the hand-guided sulky:
T = 1 + 50 m/(10 m/min) + 50 m/(10 m/min) = 11.0 min/trip
P = (45 min/hr)/(11 min/trip) × .1 m3/trip = 0.41 m3/hr
Table 5.2 Small Wood Plantation Harvesting Example
|
(1) |
(2) |
(3) |
(4) |
(5) |
(6) |
(7) |
(8) |
(9) |
|
Bowsaw fell axe delimb |
1.00 |
- |
- |
- |
- |
5 trees/hr |
0.5 |
2.00 |
|
Manual sulky forward |
1.10 |
10 |
10 |
1 |
15 |
.1 m3/load |
0.4 |
2.68 |
|
Manual load |
1.00 |
- |
- |
- |
- |
30 logs/hr |
1.0 |
1.00 |
|
Tractor standing |
9.00 |
- |
- |
45 |
- |
3 m3/load |
4.0 |
2.25 |
|
Tractor traveling |
15.00 |
50 |
60 |
- |
- |
3 m3/load |
4.9 |
3.05 |
|
Load truck |
20.00 |
- |
- |
- |
- |
8 load/hr |
24.0 |
0.83 |
|
Truck standing |
20.00 |
- |
- |
45 |
- |
15 m3/load |
20.0 |
1.00 |
|
Truck traveling |
30.00 |
20 km/h |
25 km/h |
- |
- |
15 m3/load |
6.7 |
4.50 |
|
Total |
|
|
|
|
|
|
|
17.31 |
5.6.3 Tropical High Forest
Assume that selective harvest of tropical high forest is being planned. An estimate is being made of the stump-to-raft harvesting costs for one possible alternative for the operation. Costs for roads and unloading dock are not included. The activities are:
1. Fell, delimb, and, cross-cut with power saw.2. Skid along low standard skid trails to the high standard skid trail using a crawler tractor and deck logs for later swinging by rubber-tired skidder to road side.
3. Swing by rubber-tired skidder to road side and deck.
4. Load by front-end loader on to truck-trailers.
5. Transport by truck to water. Logs are unloaded by releasing the trailer stakes.
Machine rates (col. 2) and production data (col. 7) for this example are shown in Table 5.3. The machine rates for the various labor-equipment combinations of cutter and helper with power saw, crawler tractor with operator and helper, rubber-tired skidder with operator and helper, front-end loader with helper, and truck driver with self-loading truck are developed using the techniques from Chapter 3. Production estimates are made from experience, available formulas or tables, or short time studies (Appendix B). A good source of felling, skidding, loading, and transport rates for tropical high forest can be found in Logging and Log Transport in Tropical High Forest by FAO, 1974.
Assuming the various production data in Table 5.3 the details of converting data to hourly production rates are shown below.
For the felling, delimbing and cross cutting we might use a formula adapted from production studies such as:
P = 6 + .1 [DBH - 40 ] - N m3 per hr.
where DBH = the diameter at breast height (cm)
N = number of cross cuts made
If the average tree is 90 cm, has 8 m3 of usable wood and requires 2 bucking cuts, the production per 60 min hour would be:
P = 6 + .1 [90 - 40] - 2 = 9 m3 per hour
Adjusting for a 45 min effective hour we would have
P = 9 × 45/60 = 6.75 m3 per hour
For breaking the logs out of their beds and skidding by crawler tractor to the main skid trail, the time is estimated as:
T = 10 + 50 m/(40 m/min) + 50 m/(60 m/min) = 12.1 min
Assume we have observed about 15 min per hour are involved in unplanned delays so we can either increase the average time per trip to
T = 12.1 min × (60/45) = 16.1 min/trip
including delays or we can reduce the effective from 60 minutes per hour to 45 minutes per hour:
P = 4 m3/load × 45 min/(12.1 min/trip) = 14.9 m3/hr
For hooking the logs and swinging by rubber-tired skidder, the time is estimated as:
T = 3 + 500 m/(80 m/min) + 500 m/(100 m/min) = 14.25 min
Assume we have observed about 10 min per hour are involved in unplanned delays, so we increase the average time per trip to
T = 14.25 min × (60/50) =17.1 min per trip including delays.
or we can reduce the effective from 60 minutes per hour to 50 minutes per hour:
P = 4 m3/load × 50 min/14.25 min per trip = 14.0 m3/hr
For loading the truck-trailers a short time study indicates the time per log is 2 minutes with an average log size of 4 m3 and an estimated delay of 10 minutes per hour.
P (loading) = 4 m3/log × 1 log/2 min × 50 min/hr = 100 m3/hr
For transport by truck to the log dump we divide the trip into traveling time and standing time:
T (standing) = 45 min per trip = .75 hrP (standing) = 30 m3/load/.75 hr = 40.0 m3/hr
T (traveling) = 25 km/20 km/hr + 25 km/25 km/hr = 2.25 hr
P (traveling) = 30 m3/load/2.25 hr = 13.3 m3/hr
After the machine rates and production rates have been derived, the individual unit costs can be calculated (Table 5.3, col 9). The stump-to-water cost for this harvesting alternative is $12.17 per m3. Skid trail, road, landing, log dump construction and road maintenance costs should be added, if appropriate, using the techniques from Chapter 4.
Table 5.3 Tropical High Forest Harvesting Example
|
(1) |
(2) |
(3) |
(4) |
(5) |
(6) |
(7) |
(8) |
(9) |
|
Fell and crosscut |
5.30 |
- |
- |
- |
15 |
90 cm dbh |
6.75 |
0.79 |
|
Crawler tractor |
60.00 |
40 |
60 |
10 |
15 |
4 m3/load |
14.9 |
4.03 |
|
Rubber-tired skidder |
45.00 |
80 |
100 |
3 |
10 |
4 m3/load |
14.0 |
3.21 |
|
Front-end loader |
50.00 |
- |
- |
- |
10 |
2 min/log |
100.0 |
0.50 |
|
Truck standing |
25.00 |
- |
- |
45 |
- |
30 m3/load |
40.0 |
0.63 |
|
Truck traveling |
40.00 |
20 km/h |
25 km/h |
- |
- |
30 m3/load |
13.3 |
3.01 |
|
Total |
|
|
|
|
|
|
|
12.17 |
