- United States

#-$ Department of

$$&!5 Argriculture

@‘E$ Forest Service

ulJ&

a. Southern Forest

Experiment Station

IResearch Note

so-290

April, 1993

Mor-Bell Logger: Skidding Case Study

Bryce J. Stokes, Jerry L. Koger, and Frank J. Pickle

SUMMARY

A production equation was developed for the

Mor-Bell logger for skidding while thinning a ,loblolly pine plantation. Production and costs for skidding and iron gate delimbing were determined for a

range of operating conditions.

Additional keywords: Plantation, thinning, production rates, costs.

INTRODUCTION

The Mor-Bell logger’ is a recently introduced machine with a trianglar (3 wheel) configuration. It has

several possible applications in timber harvesting.

Although originally designed for loading sugarcane

in South Africa, the converted machine can be used

in forestry operations to skid, load, unload, prebunch, or feed a chipper. The ,logger is being

marketed to interface with existing harvesting

equipment such as between a feller buncher and

skidder or skidder and processor.

Taylor (1978) evaluated the logger as a pulpwood

forwarder in coniferous thinning systems in South

Africa. He found that overall simplicity, ‘low operating costs, maneuverability, and high production

capacity for its size made it a very useful machine.

The objective of this study was to determine the

skidding production rates for the Mor-Bell logger

during a thinning application. Although the logger

is not designed specifically for skidding, it is impor-

‘The use or mention of trade or corporate names is for reader

convenience and is not necessarily an endorsement by the

U.S. Forest Service.

tant to-determine its skidding production and costs

since it does have potential to perform this function.

The logger does not have a steering wheel, clutch,

or brakes; instead there are two ,large independent

hydrostatically powered and controlled drive wheels

in front and one small castor wheel in the rear. The

direction and speed of the drive wheels are controlled through bidirectional foot controls. The machine has excellent maneuverability since it is possible to have one drive wheel rotating forward while

the other is in reverse.

A boom and grapple assembly is hinged above

the cab on a cross member. When traveling forward

the operator has excellent visibility. However, when

traveling backward as in skidding, the operator visibility is reduced due to the location of the fuel tank

Figure i.-Mar-Bell Logger.

Southern Forest Experiment Station/l-102lO U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Sewing Alabama, Arkansas, Louisiana, Mississippi, E. Oklahoma, Tennessee, E. Texas, Puerto Rico, U.S. Virgin Islands

1
and supporting framework. Selected equipment

specifications are given in table 1 and the logger is

shown in figure 1.

SYSTEM DISCUSSION

Other equipment in the operation consisted of

one skid-steer feller buncher and a knuckleboom

loader. The system was operating in a loblolly pine

(Pinus taeda) plantation on the southern coastal

plain of South Carolina. The method of harvesting

included clearcutting access corridors at 100 ft

intervals and selectively thinning within the strips.

Felled trees were placed in bundles containing from

one to four stems with the tree butts generally oriented toward the landing or nearest access corridor.

The logger consolidated the bundles in the stand

when necessary and then skidded by way of the corridors. Skidding proceeded from the landing toward

the opposite side of the plantation. A delimbing iron

gate was used near the landing to remove limbs. At

the landing, final delimbing and topping were completed with a chainsaw. The trees were loaded with

a knuckleboom loader onto trailers.

DATA COLLECTION

Sample plots were used to determine the stand

density before and after thinning. The stand contained 464 trees per acre before harvesting and 391

trees per acres after harvesting. Stand characteristics are. shown in table 2 and tree characteristics

are shown in table 3.

Skidding data were collected for two days. Skidding distance, number of stems, bundles per

cycle, and volume were measured on 26 cycle observations. Elemental times were recorded for consolidating bundles, travel loaded, travel empty, gate

delimbing, and decking. A skidding cycle included

all these elements except that in some cases bundles

were not consolidated and only a single bundle was

skidded. The time study data were summarized in

table 4.

RESULTS

The data were analyzed using a computerized

statistical package (SAS 1979). Linear regression

analysis was used to develop equations to predict

time for traveling empty to the bundles, consolidating and grappling bundles for skidding, and traveling to the delimbing gate. The following prediction

equation was developed by combining the prediction equations with mean times for the other elements of the total cycle.

Minutes per cycle=0.12+0.56 X bundles per cycle

+0.27X no. stems per cycle

+0.20Xskid volume (ft3)

+O.O04Xone-way skid distance (ft).

Equation R2=0.54

The constant, 0.12, was obtained by consolidating

the regression intercept and the means for other

cycle activities as explained:

Table 1 .-Mor-Bell logger specifications

Item description Specification

Engine Deutz 3-cylinder diesel (42 hp)

Dimensions

width 105 in

wheelbase 106 in

ground clearance 16 in

Boom lift capacities

full extension 1,500 Ibs

half extension 2,000 Ibs

full retraction 2,500 Ibs

Grapple

maximum opening 60 in

minimum opening 4 in

Machine weight 6,000 Ibs

Ground pressure 10 psi (unloaded)

Note: Specifications are based on manufacturer’s literature.

Table P.-Stand summary

Species

Pine

Hardwood

Total

Initial

276

166

464

Trees per acre

Removed

7 3

. . . .

7 3

Residual

205

166

391

Table 3.-Harvested tree characteristics

Variable

Mean

Dbh (in) 5.6

Total height (ft) 45.3

Volume per tree’ (fP) 5.4

‘Volume to 3-in top (i.b.).

Statistics

Standard deviation Range

1.6 2.0-10.9

10.0 26.0-65.0

4.2 0.21-21.6

Bryce J. Stokes and Jerry L. Koger are research engineers, Southern Forest Experiment Station, Forest Service-USDA at Forestry

Sciences Laboratory, Auburn, Alabama. Frank J. Pickle is a staff assistant, harvesting, with Union Camp Corporation, Savannah,

Georgia.

2
0.12=-1.31 (regression intercept for bunching)

+0.34 (gate delimbing mean)

t-O.70 (mean travel time from gate to deck,

round trip distance was 350 ft)

+0.393 (deck time mean)

Only with the larger skid loads over approximately 40 ft3 did the logger have any problems with gate

delimbing. Travel time to the deck from the gate was

dependent on the same fixed distance during the

study. Adjustments to the total cycle time should be

made for different distances between gate and deck.

Deck time included dropping the load and turning

around.

An equipment cost analysis using the standard

method of computing straight line depreciation and

average annual investment (Miyata 1981) is given

in table 5. The cost per machine hour (pmh) is estimated to be $23.15 which includes fixed, operating,

and labor costs.

SUMMARY AND CONCLUSION

Production rates and costs were determined for

a Mor-Bell logger operating in a commercial thinning of a loblolly pine stand. For an average skidding distance of 600 ft, the hourly production was

Table 4.-Observed skidding cycle time summary

Element description

Mean

Statistics

Standard deviation Range

Bunching time (min)

(consolidating bunches)

Travel loaded

travel distance (ft)

travel time (min)

volume per cycle (ft”)

number of stems

Travel empty

travel distance (ft)

travel time (min)

Gate delimbing time (min)

Decking time (min)

1.11

797 329 329-l 345

1.94 1.04 0.70-5.34

27.89 11.65 13.42-57.20

5.9 2.2 3-10

849 327 353-l 345

1.77 0.71 0.67-2.79

0.39 0.08 0.20-0.50

0.34 0.32 0.10-0.85

1.15 0.17-4.58

Table 5.-Cost analysis for the Mor-Bell logger

Item description

, Cost3

per year per pmh

Fixed Cost:

Depreciation ($35,500-$3,550)/4

Taxes, interest 8. ins. (20% x $23518.75’)

$ 7,987.50

4,703.75

Operating Cost:

Maintenance & repair (60% x $7,987.502) $ 4,792.50

Fuel ($1.25/gal x l.lgal/hr) x (1,500 hrs) 2,062.50

Oil & lube (33% x $2,062.50) 680.62

Tire replacement ($1475O/year) 147.50

Tire repair (15% x $147.50) 22.13

Labor Costs:

Wages ($5.5O/hr x 2080 hrs/year)

Fringes (25% X $11,440)

Total Costs:

$12,691.25

$ 7,705.25

$11,440.00

2,860.OO

$14,300.00

$34,696.50

$ 5.32

3.14

$ 8.46

$ 3.20

1.38

0.45

0.10

0.02

$ 5.15

$ 7.63

1.91

$ 9.54

$23.15

‘Average annual investment.

?Annual depreciation.

3Assumptions: Life = 4 years; Salvage value = 10 percent. Machine hours per year = 1500.

Labor hours per year = 2080.

3
estimated to be 378 ft3. Assuming a machine cost

of $23.15 per productive hour, the skidding cost

would be $6.12 per 100 ft3 of wood (table 6).

On level terrain, a volume of approximately 40 ft3

caused the lifting of the rear castor wheel and an

increase in cycle time. The tricycle configuration

and independent hydrostatic drive of the large

wheels gave the machine excellent maneuverability

within the stand. Bundles were easily consolidated

with little observed residual stand damage. The ability of the logger in forming large bundles from small

feller buncher bundles gave much flexibility to the

feller buncher operation.

Miyata, Edwin S. Determining fixed and operating

costs of logging equipment. Gen. Tech. Rep. NC55. Houghton, Ml: U.S. Dept. of Agric., Forest Service, North Central For. Exp. Station; 1981. 16 p.

SAS Institute, Inc., User’s Guide: Statistical Analysis

System (SAS). P.O. Box 8000, Carey, NC; 1979.

494 p.

Taylor, R. W. Forwarding pulpwood in coniferous

thinnings-a hydrostatic grapple-loader. Prestonia, South Africa: National Timber Research

Institute, CISR: H-2-78; 1978.4 p.

Table B.-Estimated production and cost rates-skidding and gate delimbing

Skidding

distance

Stems Bundles Volume Total time Volume Cost per

per cycle per cycle per cycle per cycle per pmh 100 ftJ

ft -----------no.-----------

200 4

200 4

200 4

200 4

200 6

200 6

200 6

200 6

400 4

400 4

400 4

400 4

400 6

400 6

400 6

400 6

600 4

600 4

600 4

600 4

600 6

600 6

600 6

600 6

600 4

800 4

800 4

800 4

600 6

800 6

600 6

800 6

1000 4

1000 4

1000 4

1000 4

1000 6

1000 6

loo0 6

1000 6

1

1

2

2

1

1

2

2

1

1

2

2

1

1

2

2

1

1

2

2

1

1

2

2

1

1

2

2

1

1

2

2

1

1

2

2

1

1

2

2

fP

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

3 0

4 0

min fP dollars

3.16 570 4.07

3.36 714 3.24

3.72 484 4.79

3.92 612 3.76

3.70 486 4.76

3.90 615 3.76

4.26 422 5.46

4.48 538 4.30

3.96 454 5.10

4.18 577 4.01

4.52 398 5.62

4.72 508 4.55

4.50 400 5.79

4.70 511 4.54

5.06 356 8.51

5.26 458 5.08

4.76 378 6.12

4.96 464 4.79

5.32 338 6.85

5.52 435 5.33

5.30 340 8.82

5.50 436 5.31

5.66 307 7.54

6.06 396 5.85

5.56 324 7.15

5.76 417 5.56

6.12 294 7.87

6.32 380 6.10

6.10 295 7.65

6.30 381 6.08

6.66 270 6.57

6.66 350 6.62

6.36 283 8.18

6.56 366 6.33

6.92 260 8.90

7.12 337 8.87

6.90 261 8.66

7.10 338 6.65

7.46 241 9.60

7.66 313 7.39