Forest Service 

Predicting Bunching Costs for 

the Radio Horse 9 Winch 

Northeastern Forest 

Experiment Station Chris B. LeDoux 

NE-RP-595 Bruce W. Kling 

Patrice A. Harou 
Abstract 

Data from field studies and a prebunching cost simulator have been assembled 

and converted into a general equation that can be used to estimate the 

prebunching cost of the Radio Horse 9 winch. The methods can be used to 

estimate prebunching cost for bunching under the skyline corridor for swinging 

with cable systems, for bunching to skid trail edge to be picked up by a skidder 

or forwarder, or bunching to roadside for stand cleanings and firewood sales. 

~osts'can be determined easily with a hand calculator. The equation can also be 

incorporated into larger stump-to-mill desktop and mainframe computer 

programs. 

The Author 

CHRIS B. LEDOUX is Project Leader at Morgantown, West Virginia, with the 

Northeastern Forest Experiment Station. BRUCE W. KLING, MSlMBA was 

Research Assistant at the time of this research, and PATRICE A. HAROU, Associate Professor, both at the Department of Forestry and Wildlife Management, 

University of Massachusetts at Amherst. 

Manuscript received for publication 22 August 1986 

Northeastern Forest Experiment Station 

370 Reed Road, Broomall, Pa. 19008 

February 1987 
Introduction 

Because timber harvesting is shifting to young-growth 

stands, forest managers and loggers are faced with the 

challenge of matching logging equipment to stand conditions in order to maximize productivity and minimize costs. 

Harvests in young-stands entail moving large numbers of 

small logs; production rates are lower and logging costs 

higher. One method for increasing production is to 

prebunch logs (bunch prior to yarding, skidding, or fomarding) into decks with small relatively inexpensive winches 

thus allowing the more expensive swing, skidding, or forwarding machine to develop larger payloads. The expensive and time consuming task of prebunching logs is 

charged to the less expensive winch, whereas the high 

payload of the more expensive machine is efficiently used 

during swinging, skidding, or forwarding. Methods are 

presented for estimating the bunching costs of such a 

prebunching winch, the Radio Horse 9.' 

Background 

Prebunching has been applied widely to: helicopters 

(Dykstra and others 1978), cable systems (Kellogg 1976; 

Gonsior 1978, 1979; Mason 1979; Keller 1979; Zielinsky 

1980), the helistat (Gibson and others 1982); and groundbased systems (Harou and others2). A simulation model 

called THlN (LeDoux and Butler 1981) has been developed 

to simulate prebunching operations. Sensitivity analysis 

and equipment configuration evaluations have been conducted (LeDoux and Butler 1982). Prebunching cost estimating methods have been developed and implemented for 

west coast logging conditions (LeDoux and Starnes 1986). 

Recently, prebunching tests were conducted for the Radio 

Horse 9 winch on five southern New England sites (Harou 

and others 1985) (Table 1). The field studies quantified the 

variables that significantly affect the productivity and cost 

of the Radio Horse 9 winch. A general equation was developed for estimating the prebunching cost of the Radio 

Horse 9 winch using the data provided by Harou and others'; 1986 new equipment, labor, and fuel costs (Table 2); 

and the THlN (LeDoux and Butler 1981) prebunching simulation model. 

'The use of trade, firm, or corporation names in this 

paper is for the information and convenience of the reader. 

Such use does not constitute an official endorsement or 

approval by the U.S. Department of Agriculture or the 

Forest Service of any product or service to the exclusion of 

others that may be suitable. 

'Harou, P. A.; Kling, B. W.; MacConnel, W.; Thompson, 

C.; Morin, D.; Zheng, C. Financial feasibility of the Radio 

Horse 9 winch. Cooperative Agreement 23-792. Final 

Report. Broomall, PA: 1985. U.S. Department of Agricul- tural, Forest Service, Northeastern Forest Experiment Station; 107 p. 

Prebunching Cost Equation 

Simulated, delay-free data points for prebunching cost were 

developed for the Radio Horse 9 winch under a wide range 

of diameter breast height (DBH), volume cut per acre 

(VOAC), and average slope yarding distance (SYD). The 

model stand contained 1,400 A3 per acre. The stand was 

thinned, using an arithmetic mean diameter of cut 

treeslarithmetic mean diameter of stand ratio (d/D ratio) of 

1 .O to levels of 33 and 50 percent. The trees cut from each 

treatment were bucked into logs (LeDoux 1985) by d.b.h. 

and the pooled data points (Table 3) used to develop a 

general equation for prebunching cost by arithmetic mean 

DBH of cut trees, VOAC, and SYD: 

$/ft3 = - 0.1 2640 

+ 1.1965 (1 IDBH) 

+ 0.00023 (SYD) 

+ 235.30853 (1 /(VOAC DBH)) 

R2 = 0.867 

where: 

DBH = Arithmetic mean tree diameter at breast 

height, in inches; variable limits = 4 to 12. 

Figure 1 .-Delay-free prebunching cost 

surface for the Radio Horse 9 winch, 

VOAC = 700 cubic feet. 
Table 1.-Conditions for five field tests of bunching 

- - 

Average Average Average Cost 

Test .and Average stems volume side per unit Stand 

stand type d.b.h. removed removed slope Productivity produced treatment 

Inches Corddacre Percent Cords/hr $/Cord 

Test 1, White 

pine'hardwood 9.5 132 11.2 0 1.9 12.17 

Test 2, Oak 

hardwood 7.5 176 11.0 47 1.9 12.78 

Test 3, Spruce 

pine 

plantation 7.8 162 

Test 4, Red 

maple swamp 8.1 247 

Test 5, Hemlock 

hardwood 8.0 1 35 

Release cut to partially 

remove the overstory to 

enhance the growth of 

regeneration. 

lmprovement cut bunched 

in a three-step process 

(included reyarding), 

downhill pull. 

Single tree selection 

thinning, brush made 

bunching across the hill 

difficult. 

Area wide thinning 

lmprovement cut to make 

large hemlocks visible. Logs 

rolled downhill while being 

bunched. 

Source: Harou, P. A.; Kling, B. W.; MacConnel, W.; Thompson, D.; Morin, D.; Zheng, C. Financial feasibility of the Radio 

Horse 9 winch. Cooperative Agreement 23-792. Final Report. Broomall, PA. US. Department of Agricultural, Forest 

Service, Northeastern Forest Experiment Station; 1985. 107 p. 

Table 2.-Hourly bunching costs for the Radio 

Horse 9 wincha 

Table 3.-Log size parameters by d.b.h. for model 

stand 

Component Cost 

Winch 

Chainsaw 

Labor 

Total 

alncludes all new equipment (1986 costs). 

blncludes depreciation, insurance, interest, operating costs 

(fuel, oil, lubricants, maintenance, repair, and taxes) and 

rigging. 

'One faller and a winch operator, rates obtained from cost 

guide for empirical appraisals, USDA Forest Service, 

Region 9, Amendment 112. 

Lon size 

Standard 

D.b.h. Mean Minimum Maximum deviation 
SYD = Average slope yarding distance, in feet; 

variable limits = 25 to 150. 

VOAC = Average volume removed per acre, ft3; 

variable limits = 462 to 700. 

The equation is machine specific and the variable limits 

should be observed carefully. Figure 1 shows the delay-free 

prebunching cost surface for a volume removal of 700 

cubic feet. 

Delay-free costs must be adjusted to allow for nonproductive time. Delay percentage is the proportion of nonproductive time expressed as a percentage of total time. One 

minus the proportion of nonproductive time is the proportion of productive time. For example, if the delay is 10 

percent, the proportion of nonproductive time is 0.1, and 

the proportion of productive time is 0.9. The delay-free cost 

is adjusted by dividing it by the proportion of productive 

time to get the cost with delay. 

Prebunching Delays 

Data for estimating delays are presented in Figures 2, 3, 

and 4. Generally, the Radio Horse 9 was productive (Fig. 

2). Equipment, personnel, and hangup delays accounted 

for the bulk of the delay time. Closer inspection of the 

hangup delays (Fig. 3) reveals that most of the hangups 

were due to trees. Rocks, stumps, brush, and other logs 

made up the bulk of the hangup delays. Although the 

average slope yarding distance for the pooled data (all five 

sites) was 120.65 feet, most hangups occurred at a slope 

yarding distance of 75 feet (Fig. 4). The data from Figures. 

2 and 3 can be used to adjust the delay-free cost estimates. For example, a logger is estimating prebunching 

cost for a hardwood stand with an average arithmetic tree 

PRODUCTIVE TIME 

HANGUP DELAYS PERSONNEL DELAYS 

6% 14% 

Figure 2.-Percentages of observed productive and delay time for the Radio Horse 

9 winch. 

ROCKS 

6% 

STUMPS 

13% 

Figure 3.-Percentages of observed 

hangup delays for the Radio Horse 9 

winch. 

diameter at breast height of 8.0 inches, an average slope 

yarding distance of 100 feet, and an average volume 

removal of 700 ft3. Delay-free bunching cost is: 

Adjusting delay-free cost with an average delay percentage 

of 0.23 (Fig. 2) = Q.088/(1-0.23) = 0.08810.77 or $0.1141ft3. 

The delay percentages summarized in Figures 2, 3, and 4 

are not exclusive, so users may wish to substitute their own 

delay percentage based on experience or observation. 

Deck Spacing 

The distance between prebunched decks significantly 

affects prebunching cost and productivity (LeDoux and 

Butler 1982). The farther apart the decks are constructed, 

the lower the productivity and the higher the prebunching 

costs. Constructing decks too close to each other could 

result in small decks and a substantial amount of time for 

moving and setting up the winch. An optimal deck spacing 

exists for each combination of stand operhting conditions 

and winch configuration. 
ROCKS LOGS STUMPS BRUSH TREES 

25 75 125 175 225 

SKIDDING DISTANCE, Feet 

Figure 4.-Percentage of hangups by slope yarding distance for the Radio Horse 9 winch. 

Accordingly, using the previously cited field data, stand 

conditions, and the THIN (LeDoux and Butler 1981) simulation model, we developed an optimal deck spacing for the 

Radio Horse 9 winch (Fig. 5). Results from the simulations 

suggest that deck spacings betwen 30 to 70 feet will result 

in maximum productivity and the minimum prebunching 

costs. Although the production rates and costs simulated 

for the extreme deck spacings may be optimistic, one 

would not normally expect to operate at the extremes. 

Application of the Costing Methodology 

To use the cost equation, the estimator will need to know 

(1) the arithmetic mean d.b.h. to be harvested; (2) the 

average volume cut per acre, in cubic feet; and (3) the 

average slope yarding distance. These items can be 

obtained from inventory data and cruise data, and the 

logging plan for the tract. The prebunching cost for a 10- 

acre tract is: 

Delay- free Average Cost with 

cost delay delay 

(Dollars/fP) (Percent) (Dollars) 

0.161 15 1,134 

Cut trees are 6 inches d.b.h., the average volume cut per 

acre is 600 cubic feet, and the average slope distance is 

100 feet. 

Additional adjustmenls to these estimated costs may be -, 

necessary depending on'their intended application. The - . 

estimated costs do not include an allowance for profit and . risk, nor do they include recognition of the tax,savi!gs : 

resulting from accelerated depreciation. . . 

Consideration for Managers 

The methods presented here provide a re!atively complete 

packaging for'estimating the cost for the Radio Horse 9 

winch operating in most eastern hardwood stands. Estimates can be developed for prebunching under the skyline 

corridor for swinging with cable systems, for bunching to,, ,- 

skid trail edge to be picked up by a ~kidder or foharder, or 

bunching to roadside for stand cleanings and firewood 

sales. 
DISTANCE BETWEEN DECKS, Feet 

Figure 5.-Simulated total prebunching cost for various deck spacings for the Radio Horse 9 winch 

Production and related costs per unit produced will vary 

with stand and site conditions (Table 1). The methods 

presented here consider this variability in site and stand 

conditions. Although the methods likely will not produce 

bunching estimates that match actual outcomes exactly, 

reasonable estimates can be expected. 

Prebunching winches have several advantages in that: 

(1) they are relatively inexpensive and labor requirements 

are minimal; (2) larger more expensive equipment is used 

most efficiently to swing, skid, or forward bunched decks to 

landings developing full payloads; (3) residual stand damage is kept to a minimum since the winches generally do 

not develop enough horsepower to "tear" things up; (4) 

soil compaction and understory vegetation disturbance is 

kept to a minimum because there is no equipment moving 

within the stand; (5) the small winches can be used in 

environmentally and esthetically sensitive areas eliminating 

in part the need for large noisy equipment; and the greatest advantage is that (6) prebunching improves the efficiency of the more expensive yarding, skidding, and forwarding equipment. 

Prebunching should not be envisioned as the cure-all solution to harvesting in young stands. A considerable amount 

of planning and layout must be done to ensure an efficient 

prebunching operation. Deck locations must be identified 

and fallers instructed to gun trees toward the desired decking area to minimize hangups. Landing areas must be 

designed to handle the increased flow of logs during a 

swing, skidding, or forwarding operation. Hauling must be 

scheduled to avoid congested landings and to haul away 

the high volumes of prebunched logs arriving at the landing. Hooking and skidding crews must be instructed to load 

their respective systems close to capacity to ensure that 

any gains in prebunching are not offset by an improperly 

loaded system. Prebunching operations require as much 

planning as any other harvesting operation. 

The blending of field test data, simulation methods, and 

nonlinear regression methods, such as those summarized 

here, will not provide all the answers a manager or logger 

needs on prebunching. Such methods, however, provide 

tools for estimating prebunching costs for managing younggrowth hardwood stands. 
Literature Cited 

Dykstra, D. P.; Aulerich, E.D.; Henshaw, J. R. Prebunching to reduce helicopter logging costs. Journal of 

Forestry. 76:362-378; 1978. 

Gibson, D. F.; Taylor, W. R.; Gonsior, M. J. Prebunching 

small timber in steep terrain. ASAE Pap. 82-1581. 

Chicago, IL: American Society of Agricultural Engineers; 

1982. 20 p. 

Gonsior, M. J. New ideas for cable logging. Log. Hdbk. 

38:ll-14, 68-70; 1978. 

Gonsior, M. J. Potential benefits of prebunching for 

cable yarding systems. ASAE Pap. 79-401. Chicago, 

IL: American Society of Agricultural Engineers; 1979. 7 p. 

Keller, R. R. Prebunching with a low-investment skyline 

yarder in thinnings. MS. thesis, Corvallis, OR: Oregon 

State University; 1979. 138 p. 

Kellogg, L. D. A case study of prebunching and swinging. A thinning system for young forests. Corvallis, 

OR: Oregon State University; 1976. 88 p. M.F. Paper. 

LeDoux, C. B.; Butler, D. A. Simulating cable thinning in 

young-growth stands. Forest Science. 17:745-757; 

1981. 

LeDoux, C. B.; Butler, D. A. Prebunching? Results from 

simulation. Journal of Forestry. 80(2):79-82; 1982. 

LeDoux, C. B. Log bucking methodology. Southern Journal of Applied Forestry. 9(2):67; 1985. 

LeDoux, C. B.; Starnes, L. W. Cable-logging production 

rate equations for thinning young-growth Douglas-fir. 

Forest Products Journal. 36(5):21-24; 1986. 

Mason, D. Prebunching-making a profit in the corridor. 

Logging Management. 1979 December:36-37. 

Zielinsky, C. R. Operational prebunching: A logger's 

application to reduce thinning costs. Corvallis, OR: 

Oregon State University; 1980. 96 p. M.F. Paper. 
LeDoux, Chris B.; Kling, Bruce W.; Harou, Patrice A. 1987. Predicting 

bunching costs for the Radio Horse 9 winch. NE-RP-595. Broomall, 

PA: US. Department of Agriculture, Forest Service, Northeastern Forest 

Experiment Station. 7 p. 

Data from field studies and a prebunching cost simulator have been 

assembled and converted into a general equation that can be used to 

estimate the prebunching cost of the Radio Horse 9 winch. The methods 

can be used to estimate prebunching cost for bunching under the skyline 

corridor for swinging with cable systems, for bunching to skid trail edge to 

be picked up by a skidder or forwarder, or bunching to roadside for stand 

cleanings and firewood sales. Costs can be determined easily with a hand 

calculator. The equation can also be incorporated into larger stump-to-mill 

desktop and mainframe computer programs. 

Keywords: Prebunching; deck spacing. 
Headquarters of the Northeastern Forest Experiment Station are in Broomall, Pa. 

Field laboratories are maintained at: 

8 Amherst, Massachusetts, in cooperation with the University of Massachusetts. 

8 Berea, Kentucky, in cooperation with Berea College. 

8 Burlington, Vemt, in cooperation with the University of Vermont. 

8 Delaware, Ohio. 

8 Durham, New Hampshire, in cooperation with the University of New Hampshire. 

8 Hamden, Connecticut, in cooperation with Yale University. 

8 Morgantown, West Virginia, in cooperation with West Virginia University, 

-own. 

8 Orono, Maine, in cooperation with the University of Maine, Orono. 

8 Parsons, West Virginia. 

* Princeton, West Virginia. 

* Syracuse, New York, in cooperation with the State University of New York 

College of Environmental Sdiences and Forestry at Syracuse University, 

Syracuse. 

8 University Park, hnsylvania, in cooperation with the Pennsylvania State 

tJniversity. 

8 Wanen, Pennsylvania. 

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