FESA Technical Notes 2002/01 FESA Technical Notes 2002/01 October 2002 October 2002

1. Introduction 1. Introduction The articulated wheeled skidder is an important component in the primary transport of timber In South Africa. Unlike agricultural tractors, wheeled skidders are specifically designed to winch and skid trees from the point of felling to a landing site. They are heavy, robust machines, with their centre of gravity positioned well forward. The power to weight ratio has been chosen for efficient performance when skidding trees.

Main factors influencing skidder productivity are: • Skidding distance • Bunch size (felling operation) • Terrain (travel speed) • Grapple and engine capacity • Operator decisions.

2. Types of skidders

Technical Note 1/5-2002 There are three skidder configurations, based on the attachments fitted to the machine: • Cable • Grapple • Clambunk Articulated Skidders Cable and grapple skidders suspend one end of a load behind the machine, while on the other hand; clambunk skidders support the load on a bunk on the rear chassis. All three configurations may be used to skid full trees or tree lengths. Compiled & produced by: Centre of Forest Operations Management (CoFOM) 2.1 Cable skidders Cable skidders are defined as four-wheel drive, rubber-tyred tractors with articulated steering that use a main winch cable and cable or chain chokers to assemble and hold a load (Stokes et al., 1989). Cable skidders are used mostly with large, motor-manual felled timber. Productivity is severely reduced in smaller timber, due to time losses associated with hooking or unhooking chokers, and the physical limitations to the number of chokers that can be handled or carried.

Contact Francois Oberholzer FESA Forest Engineering Southern Africa Institute for Commercial Forestry Research P O Box 100281 Scottsville, 3209 South Africa Tel +27 33 3862314 * Fax: +27 33 3868905 E-mail: [email protected]

Figure 1: A cable skidder

© FESA 2002 Page 2 © FESA 2002 Page 3 FESA Technical Notes 2002/01 FESA Technical Notes 2002/01 October 2002 October 2002 • More costly to maintain. Taglines can be used to increase a skidder's output by increasing the load size and reducing delay times. In small sized timber, taglines facilitate the accumulation of a There are two types of grapples available, namely sorting and bunching grapples. A greater number of stems. sorting grapple is used in large timber where a full load involves one or a few stems. On the other hand a bunching grapple is used for large loads of small stems. It is also Cable skidders offer the following advantages over grapple and clambunk skidders: preferred on rough ground for picking up uneven piles of scattered timber. It is • Greater flexibility due to their use over a wide variety of terrain conditions. important to match the grapple and the skidders kilowatt output, to timber piece size • They are relatively inexpensive, compared to grapple and clambunk skidders. and stem count. Grapple skidders are of the single and/or dual arch type, with the dual • Operator training is easier than for grapple and clambunk skidders. arch giving more flexibility, due to some degree of reach, in more difficult terrain • Improved stability on side slopes and rough terrain. conditions.

On the other hand, they may have the following disadvantages: 2.3 Clambunk skidders • The operator must dismount or have chokermen to choke or dechoke loads. A clambunk skidder is defined as an articulated rubber-tyred or tracked vehicle for • Choking and dechoking times are relatively long. transporting full trees by supporting the butt-end clear off the ground in a top opening • Loads are dragged on the ground, creating potential problems at the landing or log bunk or inverted grapple. Clambunk skidders are equipped with a grapple loader for sawmill as far as abrasive dirt accumulation on the stems or logs. self-loading (Kellogg et al., 1993).

2.2 Grapple skidders Like grapple skidders, this machine eliminates the role of chokermen and cable. For An articulated grapple skidder is defined as a four-wheel drive, rubber-tyred tractor with best results, trees should be neatly bunched and indexed at a low angle to the skidder articulated steering for transporting a load by lifting the log ends clear off the ground in transport direction and near skidding trails with the butt-ends forward. a grapple. (Kellogg, Bettinger & Studier , 1992). Grapple skidders therefore require no cables, chokers or chokermen.

Figure 2: A grapple skidder Figure 3: A clambunk skidder

Clambunk skidders are designed for high volume, long extraction distances, particularly Even though cable skidders could be used to sling pre-bunched timber, grapple when trees are large, terrain easy and the ground has suitable bearing capacity (Staaf skidders are better suited when working in combination with feller-bunchers. According & Wiksten, 1984.) The use of clambunk skidders has gained acceptance in certain to Gringras (1988) they offer the following advantages over cable skidders: parts of the world, as they have numerous advantages over the more conventional • The operator does not need to get on and off the machine to set chokers means of skidding. Some stated advantages include: chains or cables. • The ability to accumulate many pieces into an optimum payload. • Quick loading and unloading means shorter cycle times. • The capacity to carry loads of between 14 - 25m 3. • Night shifts are an option. • The capacity to skid large loads of small sized timber. The following are disadvantages: • High payloads allow economic long distance skidding. • More sensitive to terrain since the load cannot be released to negotiate • Less ground disturbance, because fewer trips are required to extract a obstacles. particular unit of area. • High purchase prices. • Reduced soil compaction because infield traffic is minimised.

© FESA 2002 Page 4 © FESA 2002 Page 5 FESA Technical Notes 2002/01 FESA Technical Notes 2002/01 October 2002 October 2002 • Low ground pressure (bogie combination and high flotation tyres) for mobility 4. Applications in soft ground. • Cleaner wood, two thirds of the load is lifted off the ground. According to the Guidelines for Forest Engineering Practices in South Africa (1999), the • Potential for shift work. application of ground-based extraction machines are limited to the following terrain conditions. • Mechanisation advantages such as reduced physical stress and reduced Wheeled skidders Clambunk accident risk. Criteria Normal tyres High flotation skidders

Slope (%): Up 0 - 10 0 – 20 0 – 25 On the other hand they may have the following disadvantages: Down 0 - 30 0 – 40 0 - 40 • Long loading times of between 5 and 15 minutes. Ground roughness 1 – 2 1 – 3 1 – 3 • Complex loader and loading operation means long training periods. Ground conditions 1 – 2 1 – 4 1 – 3 • The machine is expensive. Skidding distance 50 – 300m 50 – 500m 50 – 1000m • Large machine size limits their use to clearfelling. • Has no winch and, therefore, must approach to within loader reach of every 5. Contact details tree. It also has no ability to winch past wet and adverse patches. • Terrain is a limiting factor. For more information on skidders, contact the following people: • A clambunk skidder is not the "ultimate solution" machine and will not replace Pierre Ackerman Stellenbosch University 021-808 3300. Pieter de Wet PE Technikon (Saasveld) 044-801 5111. the cable skidder nor the cable yarder. Larry Alcock PE Technikon (Saasveld) 044-801 5111. • Clambunk skidding will become the dominant element in the system and a mechanical breakdown or scheduled maintenance could bring the entire 6. Reference list system to a standstill. • Mechanisation disadvantages: Advanced mechanisation may lead to lower job • Brink, M.P. & Shuttleworth, B. 2001. Best Operating Practices. [Online]. Available at: satisfaction resulting from increased mental strain, social isolation and shift http://www.forestrysolutions.net . [2002, May 23] work • Forest Engineering Southern Africa. 1999. Guidelines to Forest Engineering Practices in South Africa . Silverton, Pretoria. • Gingras, J.F. 1988. The feller-buncher/grapple skidder system. Optimising bunch size . 3. Production standards FERIC. Quebec. Canada. Depending on certain variables such as average tree volume, average lead distance, • Gleason, A.P. 1985. Clambunk skidders. Do they have a place in the New Zealand Logging Industry? Project report number 26. LIRA, New Zealand. slope condition, ground condition, ground roughness and distance of roadside skidding, • the production standards for the different machine sizes are given in the table below Kellogg, L.D, Bettinger, P. & Studier, D. 1993. Terminology of ground based mechanized logging in the Pacific Northwest . Forest Research Laboratory. Oregon State University. (Forestrysolutions, 2002): Oregon. • Staaf, K.A.G. & Wiksten, N.A. 1984. Tree harvesting techniques - Forestry sciences . Lower limit Upper limit Type of Machine size Martinus Nijhoff/Dr w. Junk Publishers. Boston. Type of skidder (m³/7 hr (m³/7 hr operation (kW) • Stokes, B.J.C., Ashmore, W., Rawlings, C.L. & Sirons, D.L. 1989. Glossary of terms used in shift) shift) timber harvesting and forest engineering . Louisiana general technical report. USDA Forest Cable skidder Pine extraction 90 84 231 Service. New Orleans. 112 100 277 • Taylor, R.W. 1979. Skidding coniferous clearfelling with wheeled skidders . CSIR. Pretoria, 130 126 347

Gum extraction 90 74 210 Editorial committee: 112 88 252 Pierre Ackerman Larry Alcock 130 103 294 Forest Engineering Pieter de Wet Grapple skidder Pine extraction 90 112 378 Department of Forest Science Department of Forestry 112 133 448 Faculty of Agricultural and Forestry Sciences George Campus 130 168 560 University of Stellenbosch Technikon Gum extraction 90 95 343 Private Bag X1 Private Bag X6531 112 112 406 Matieland, 7602 South Africa George, 6530 South Africa 130 123 441 Tel: +27 21 8083300 * Fax: +27 21 8083 603 Tel: +27 44 8015 021 * Fax: +27 44 801 5031 Clambunk Pine extraction 18 000kg 40 350 [email protected] [email protected] skidder [email protected] Gum extraction 18 000kg 40 325 www.sun.ac.za/forestry www.petech.ac.za

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