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Anton Trzesniowski1

1 Institut für Forsttechnik, Universitat für Bodenkultur, Peter Jordan-Straße 70, A-1190 Wien, Austria.


In the introduction the possibilities of logging in skidder and cable terrain are presented. Different logging systems and methods like ground skidding (pulling and dragging), forwarding and cable yarding, are dealt with and the methods suitable for steep terrain are emphasized. A main part of the paper deals with various cable logging systems. The use of mobile cable cranes is described, as well as gravity and all-terrain methods. One, two, three and four-cable systems are outlined in sketches. Mobile cable cranes are divided into those without spar, those with spar and those with self-propelled carriages. Mention is made of cable-drives (winches, pulleys, capstans) with carriages, cables and fixing devices, supports and anchors, mounting equipment and telecommunication-devices. Planning and organization of work when operating cable cranes is very important and it is the deciding factor for the success of the work. The coordination of opening up patterns and the selection and definition of extraction methods are necessary preparatory activities for further planning of cableways. Distinct mounting rules are as important as a correct procedure in mounting and operating a cable crane. Questions of ergonomy and accident prevention, directional felling, marking of trees to be felled, job execution and control of work are important organizational activities. Laws, standards and rules for cable crane operation are mentioned briefly. Significant influences, performances and costs of cable logging are described in detail; and data on site and area, technical and performance determining parameters are presented. The Federal Austrian Forests have developed their own cable system for determining the performance of cable yarding in the "cut to length method", that now is in the testing stage. Finally, other methods of logging in steep terrain are described; the limits of human and animal working power are also given. The plastic chute "log-line" and logging methods using construction cranes and helicopters are also briefly mentioned.


Austria has 3.88 million ha of forests, which makes up 46.2 percent of its total land area. Approximately 75 percent of the forested area is on steep land with slopes greater than 40 percent. Due to this, harvesting in mountainous regions has always played a significant role. In the last 50 years Austria's forests has been provided with an almost complete road network. There are currently 97 000 km of forestry roads and a further 39 000 km of public roads which are predominantly in forested areas and provide essential routes for the road network.

Approximately 15 percent of the timber is currently harvested with mobile cable systems. The amount of timber harvested with cable logging systems has doubled over the last ten years. Mobile yarders in conjunction with the road network also belong to the future of the forest industry. On these grounds this paper focuses primarily on the opportunities for mobile yarders.

Out of ecological and economical reasons, people differentiate between skidder and cable logging terrain. In addition to the slope of the terrain, the ability to travel on the soil is a deciding factor. Further, other important factors are optimum reach of the various harvesting system possibilities, as well as consideration of the logging direction (uphill or downhill) and the total harvesting distance, are important factors.



Logging of timber

(Forest Report 1992 and 1995)

Type of logging

million m3 yield







Ground skidding


1 690



- 11.6





- 18.0





- 1.3

Cable crane




+ 2.4

Chutes, sledges














- 38.9





Ground skidding by hand (man and gravitation) is applied in small forest holdings for extraction of small amounts of timber over short distances.

Animal skidding, mainly by horses, is used for pre-skidding for distances between 30 m and 100 m.

Mechanical skidding is carried out by tractors of all types. There are 80.000 agricultural tractors with all-wheel drive and approximately 34 000 winches; some of them are also equipped with grapples. They are used in farm forests and sometimes also in big holdings by piece-rate workers and subcontractors. Approximately 300 specialized forestry skidders are used by the Federal Forest Estate, big private forest enterprises and harvest contractors.

Cable logging by hauler has increased 100 percent over the last ten years. Its share has grown to 33 percent in the Federal Forest Estate and up to 75 percent in private mountainous forests.

Chutes and sledges have lost their significance in mountainous terrain with the development of forest roads. Only pre-logging in thinnings is carried out by log lines.

Forwarders are employed increasingly and successfully because of their ecological advantages. Their share of logging work continues to grow.

Other types of logging include the use of autocrane in case of windfall areas, and helicopter extraction in special cases.

Wood transportation possibilities in general

In the alpine regions of central Europe timber was transported with the aid of gravity to the nearest river and from there to the storage or processing locations. Subsequently forest railways replaced the waterways and then the forestry road network outdated the railways. Skilfully made log lines made the transport of timber over several kilometres possible. Horses were also often used, particularly in winter. The mechanization of road construction and the development of specialized harvesting machinery changed the technology completely. Today people distinguish between pre-skidding and skidding, and particularly with pre-skidding people try to minimize damage to the stands and to the soil. The various possibilities of cable yarding often allow the damage to be kept to a minimum. However, emphasis must be placed on comprehensive and careful planning, good organization and skilled workers.

Cable Systems

Cable logging can be carried out using ground pulling, highlead systems or with skyline systems. Although in Austria a lot of timber is extracted using ground pulling, in this paper no further attention is paid to either ground pulling or high-lead, since these systems are relatively well known.

Skyline systems enable timber to be fully suspended during transport and are therefore particularly environmentally friendly. Skyline systems can be classified according to their different characteristics, as presented in the following overview.

Categorization of skyline systems (Trzesniowski 1996)



cable way

cable crane

mobile yarders






fixed driving force

conventional winches

tower yarders

multi-purpose machines

self-propelled carriages

of the skyline



lowering possible


tension tower

sledge winches

trailer, tractor, truck, processor

tension device


one, two, three-rope cable ways

two-rope-system skyline and main line

two, three, four-rope-systems
2 - skyline and main line
3 - skyline, main line, haulback line
4 - skyline, main line, haulbackline, straw line

one-rope system skyline (+ hoist line)


> 10 (12) km

short 300 (400) m middle 300 - 800 m long 800-1600 m

short > 300 (400) m
middle > 500 (600) m
tall > 800 m

> 250 m
> (400) m


all-terrain (gravitation)


gravitation u. all-terrain



¯ ­ ®

¯ ­

­ ¯ ®

¯ ®

Classification of skyline systems according to anchor type

* Live skyline (one side anchored)

The skyline tension can be altered during operations, and sudden lowering of the skyline is also possible. The skyline is only anchored on one side.

Two-rope system.

* Fixed (standing) skyline (both sides anchored)

The skyline tension remains constant. The skyline drum cannot be moved during operations.

Two-rope system.

* Running skyline (neither side fixed)

No end of the skyline is anchored. The haulback line also has the function of the skyline.

Two-rope system

System as defined by the number of ropes

* One-rope system

Practically only used with self-propelled carriages (i.e. Woodliner)

* Two-rope system (skyline and mainline)

Practically used as gravity aided uphill and downhill harvesting.

* Three-rope system (skyline, mainline and haulback-line)

Practically used for downhill or all-terrain logging. Slack-pulling is organized through a specialized carriage.

* Four-rope system (sky, main, haulback lines, and strawline)

Limited mainly to downhill or all-terrain logging. Slack-pulling from the carriage is through the use of the helpline.

Cable harvesting

* Gravity system

The cable winch has to be positioned on the highest point of the logging line. The skyline is pre-tensioned and a minimum skyline slope must be observed. Both uphill and downhill logging is possible.

+ Gravity system uphill


· Simplest harvesting system
· Remains on the road or just above the road
· Few and low intermediate supports
· Head-high transport of all timber lengths possible
· Simple construction and dismantling
· Viable with small timber quantities per set-up


· Minimum slope of the skyline approx. 22%
· Higher fuel use
· Slower carriage cycle time, but only up to 300 m
· Timber is extracted uphill, with a truck transported to the valley


+ Gravity system downhill

Using long or medium distance yarders


· Environmentally friendly, while little soil disturbance (i.e. in protection forest)
· Independent of weather conditions (except storm or thunder)
· Extracted timber remains clean
· Larger single loads possible
· Lower fuel use
· Minimum slope 15%
· Line lengths up to 1600 m (2000 m)


· The yarder must pull itself up with the mainline (or transported with helicopter)
· Timber has to be fully suspended while being transported downhill, therefore cut-to- length
· High and/or more intermediate supports
· Larger amount of timber per line is recommended (1 m3 per 1 m of line)
· Operator and the breaker-out must climb the hill daily
· High construction costs
· Exact planning and surveying required
· Safety requirements such as lightning strikes must be seriously considered


All-terrain harvesting

The cable winch can be placed at any position along the line, but typically remains on the road (downhill side). The all-terrain harvesting method is independent of slope, is however mainly used for uphill logging of all lengths of timber. Three of four rope systems are used. Special slack-pulling carriages are recommended.

The cable system can be sledge mounted, on wheels or tower yarders.

+ All-terrain harvesting with sledge mounted winches


· Cable machine remains on the street (or in the vicinity)
· Winches can be cheaply fitted with parabolic or friction disks
· Available winches can be utilized
· All log lengths can be extracted
· Slack-pulling (bridling) with the mainline is relatively lighter


· Additional tension tower recommended
· Higher construction costs
· Additional blocks are necessary
· A haulback corridor is required next to the skyline corridor
· Slack-pulling carriage is recommended


+ All terrain harvesting with tower yarders

Tower yarders (tipping or telescoping mast) have experienced rapid development in Austria in the last few years and now, and together with mobile cable yarding, systems are the latest technology. From a forest road logs can be extracted up or downhill and stored.


· Tower yarders are fully mobile and remain on the road
· Quick construction
· High productivity
· Few intermediate supports
· No head spar required
· Quick dropping of the skyline in case of danger
· Computerized carriage controls


· Mobile yarders can block the road
· Suitable tree anchors are required for the guy-lines
· Slack-pulling carriage is required for downhill logging
· Timber storage ability is limited, quick removal is recommended
· Synchronized mainline and haulback are required


Machine classification

According to technical specifications and the utilization possibilities, the following cable systems can be differentiated:

· Conventional cable systems (sledge mounted or wheeled winches)
· Tower yarder (with integrated tower)
· Combination machine (cable system with processor)
· Self-propelled carriage (built in motor)

Conventional cable systems

Typical is the winch system, usual built on a sledge, wheeled also possible but not common. The skyline comes from a storage drum and is tensioned between the hill and valley anchors. The required intermediate supports are constructed using available trees.

Sledge mounted winch with air break for uphill and downhill (Gantner), reach up to 2000 m.

Storage drum on one axle trailer with PTO connection

Winch location on sloped terrain with tree anchoring

Winch location on flat terrain with tree anchoring

Tower yarders

Tower yarders, sometimes with telescoping masts, are mobile machines, and consist of a carrying base with a collapsible tower as well as drums for all the required wire ropes. Depending on the base machine, the following categories can be established:

· tractor bound tower yarder
· tractor bound telescoping tower
· trailer mounted fixed or telescoping tower
· truck mounted fixed tower
· truck mounted telescoping tower with loader arm

Tractor mounted tower yarder

The tractor bound tower yarder is mounted on the three point hydraulic system or constructed on its own axes. It is powered by the PTO.

Trailer mounted tower yarder

Koller K 300. K 501, MM 2000, Wandefalke

Trailer mounted tower yarder is built on single or dual trailers. It is powered by an own motor.

Koller K 3 00-Interlock

Three drum machines for uphill and downhill logging as well as flat terrain, mounted on a single axle trailer. For thinning, pre-harvesting and final harvest in sorts.

Truck mounted tower yarder K301, URUS, Hydrofalke

Truck mounted tower yarders are constructed on truck with two or three axles. The power is obtained from the truck motor. The controls are housed in a separate cabin or on the deck of the truck.

Truck mounted tower yarder with loader arm

These truck mounted tower yarders utilise a hydraulic loader arm which can remove and stack the extracted timber. On some models the loader arm is attached to the control cabin and therefore rotatable, to allow easy visibility by sorting and storage work. With a platform mounted on the side of the truck, the operator can unhook the load without having to leave the truck.

Multi-purpose machines (yarder and processor)

On this machine the loader arm can be replaced with a processor head. Most common is the combination with the Steyr-KP 40 or the Konrad-Woody processors. Combination yarders are the most advanced technology for mountainous areas.


A carriage used in skyline logging is a wheeled device that rides back and forth on the skyline and from which logs are suspended.

The movement of the carriage is through the mainline, the haulback line or an internal motor. Carriages can be classified by their ability or inability to slack-pull. Non-slack pulling carriages are either simple blocks or grapple carriages. In the slack-pulling carriages there is a differences between those that are pulled out by hand and those that are mechanically fed out. Those pulled out by hand are used in gravity systems, where the carriage is held in place using either the mainline, the haulback line, a skyline clamp or a skyline mounted block. The carriage integrated clamp can be activated either through a change in direction, through a timing mechanism or by radio control. The mechanical slack-pulling can be driven by an internal power source or driven by the other ropes. These types of carriages are predominantly used in all-terrain harvesting systems.

Classification of skyline carriages

Self-propelled carriage (built-in motor)

A diesel motor is mounted inside the carriage which propels it along the skyline as well as powering the drop-line.

carriage with chokers

grapple carriage

carriage with skyline mounted block

carriage with clamping device for gravity transport (Koller SKA1, self-clamping)

Carriage with mainline and haulback line, integrated skyline and mainline clamp, radio-controlled for downhill and uphill transport (Sherpa-Mayr-Melnhof -Universal for gravity and all-terrain system On 2, 3 and 4 rope systems)

Construction of cable systems

In conventional cable systems, a sledge-mounted winch is fitted with at least a mainline for the gravity system and an additional haulback line for all-terrain harvesting. The skyline is transported on a storage drum and pre-tensioned using a block and tackle with a clamp. In mobile cable systems additional cable drums (skyline, mainline, haulback line, strawline, dropline and guylines) are accumulated into a cable machine and mounted on a mobile base.

Power source by cable winches

Cable winches can be powered mechanically, hydraulically or with a hydrostatic clutch. The power is transferred using belts, v-belts, planet gears, toothed gears, chains or a combination of these. For consistent breaking an oil motor or an air break can be used.

The correct winding of the mainline onto the drum can only take place if a block at least 20 times the radius of the drum away is attached, which also allows the rope to approach the drum at a right angle.

Mobile winches usually have three or more rope drums (sky, main, haulback, help and strawline). The system is usually powered by the motor of the carrying base (e.g. tractor). These winch systems have been replaced by the modern cable yarders.

In all-terrain harvesting, the problem exists of having both the mainline and the haulback line operating at the same speed. To date this problem has been overcome using a capstan. A new and very simple solution is to use a synchronized driving force. Two extra large drums with a central diameter of at least 1 m are mounted on an axle. They are powered by a hydraulic motor. Turning these drums allows more than 3 m to be fed out or wound on in a single rotation. While the drums turn in the same direction, one rope is wound on while the other is wound out. With a simple driving force, the ropes reach a velocity of 8 m/s. While the diameter of the ropes on the drum remain relatively the same, similar rope velocities are reached.

Synchronized driving force

This system has been incorporated in the Synchrofalken yarder built by Mayr-Melnhof. The power is transferred through a hydrostatic clutch from which a maximum power of 2.5 t can be achieved. The tower is 10 m high, is lifted hydraulically and can be turned 120° either left or right. The controls of the machine are through simple hydraulic levers or by cable, controlled electronically at a distance. Cable control allows the carriage to be returned automatically to the last point of the yarding corridor. In addition, radio control of the skyline or mainline clamps in the carriage is possible. Also possible is automatic speed reduction of the carriage as it travels over intermediate supports. For emergencies, sudden lowering of the skyline is possible. On the cabin display board both the distance of the carriage from the tower and the carriage velocity can be viewed. With this automation, the operator has enough time to sort the timber with the hydraulic arm, or utilize the processor.

Supports and head spar

General support construction

Good survey notes and a material list that indicates the appropriate material for each support are important. In steep terrain the carrying of construction material is very strenuous and, therefore, special attention should be given to the weight of the material. The selection of appropriate material for the supports saves money. Supports are built stepwise down the slope to make the carrying of construction material easier. Lower supports up to 6 m are technically simpler than fewer higher supports.

Support types

L-supports with tensioned cable

Approximately 2 m above the designed skyline height, a small block is attached to the tree. A cable and the guyline are attached to the hanger (jack); the cable is then tensioned until the hanger is 2 m below the block. With the guyline the jack is pulled the required distance from the tree. By using an artificial rope or cover, the block can be attached to the tree with minimum damage. The supporting tree is tied down with one or two guylines for safety.

L-supports with tensioned cable

M- supports

It is recommended to use two supporting trees that are almost of the same diameter and approximately at the same distance from the skyline corridor. Weaker trees must be supported using two guylines.


Galgen supports

Particularly suited to cross-sloped corridors and low supports, especially when appropriate supporting trees are available. This support can be constructed very quickly. With the help of a supporting tree of suitable height, a block can be attached and used to lift the beam. The thin end of the tree-beam is tied at the base of a suitable tree. Should a suitable tree not be available, then the whole crown should be left on the tree as a counter weight.


Finger supports

Trees that stand next to the corridor can be utilized as natural finger supports. Should they not exist, then artificial supports must be considered. The support tree is delimbed, fitted with climbing aides and in certain cases also topped. After attaching the block to the tree with a wire rope or an artificial rope, and attaching four guylines, a scarf is cut and removed on the skyline side, the back- cut made and the tree can be leaned across to a maximum of 30 cm per metre of tree. The block has to be attached at least 2 m higher than the final skyline height. For the calculation of the required diameter at breast height (dbh) of the support tree, a factor of 1.25 should be used. A factor of 1.35 is recommended for support trees over 15 m high. Finger supports are erected relatively quickly and are, therefore, used more frequently.


Head spar

Both standing or felled trees can be used, and therefore a higher support pressure must be calculated for the intermediate supports. The guylines should be in all four direction, or at least two if the pressure is relatively small.

Head spar

Calculations are made in the same way as for the intermediate supports. A head spar block or "saddle", mounted with an artificial rope, carries the skyline.

Calculations of the supports

Calculations for the supports depend on the change of angle in the skyline, or on the bending of the cross-beam. In practice, the tables provided by Pestal (1961) are used.

Skyline anchors

Mostly trees are used, sometimes also dead-man anchors. Dimensioning is more than dbh 2/3, for temporary trees dbh 2/2.

Planning and organization of cable systems

Timber extraction requires careful organization; planning is expected to take 40 percent of the time, organization 40 percent, and execution of the work 25 percent. There always remains a risk even with good work, and so 10 percent of the time should be used for work safety and productivity.






Cable corridors

Methodical work

Harvest planning

Anchors, supports



Felling plan

Work safety

System selection

Work progress

Work stress



Work rules








Cable harvesting is a relatively expensive harvesting method and it is, therefore, well worth paying careful attention to the successive planning steps. Very good knowledge is particularly important with regard to the correct choice of yarding corridors, which can go directly down the slope or also across slope. Across slope yarding corridors can be longer and more timber can be reached per metre of skyline. Also safety concerns regarding rolling stones can be minimized.

Cross-slope harvesting

Emphasis must also be placed on the felling sequence. With increased slack-pulling, the corresponding production rate decreases drastically. If a lateral pull of 10 m has a production rate of 100 percent, then for a lateral pull of 30 m the production rate drops to 65 percent. With greater lateral pulling, the damage to the soil and stands also increases.

Trzesniowski, 1995

To maintain work safety, a new set of organization rules should be written for each operational location. These rules should regulate all questions regarding the construction and running of operations, cover important safety measures and clarify the division of responsibilities. They need to be signed by the workers to indicate that the instructions are really understood.

Productivity and costs of cable yarding

To present a usable calculation, it is necessary to obtain data on harvest area, stands, as well as technical and production data. Data on harvest area and stands includes final timber destination, type of harvesting to be carried out (log sorts, stem or whole tree), work method (open or broken work chain), harvesting direction, predominant slope, length and width of work area, age of the stands, trees to be harvested, and allowable damage to the stands and the regenerating trees.

Technical data includes: the type of cable machine and carriage, recommended additional equipment such as loader or processor, forest road width in the working area, angle of the corridor, average corridor distance, skyline length, maximum and minimum skyline height, types of anchors, intermediate supports, head spar as well as other important survey points.

Data on productivity is as follows: timber volume per set-up and per metre of the skyline, average dbh and average size of each piece of timber, weight of the loads, number of pieces per load, skid trails, bridling and angle of the lateral pull to the skyline, height of the skyline at the work places, slope and weather conditions.

Features of conventional and mobile cable cranes

Range, output/working-hour, charge/year of different types of cable cranes (according to Trzesniowski 1982, FPP 1986, Heinimann 1986, Fernsebner 1996)






range (skyline-length in m)


< 1600

< 350

< 500

< 800


< 1 000 (2 000)

< 300

< 500

< 800


< 2.300

< 400

< 600

< 800

output/h (m3/h)


5 (3 - 8)

4 (3 - 8)

8 (4 - 15)

12 (8 - 25)


3 - 7

1.5 - 6

6 - 11

8 - 20


4.9 (2 - 9)

SV: 4 (2 - 9)
BV: 2 (1.4 - 2.4)

7.1 (3 - 12)

11.2 (6 - 20)

output/year (m3/a)



3 000 - 6 000

5000 - 10000

8000 - 15000


2 400 - 7 700

1 050 - 7 800

4800 - 15400

6400 - 28000


3 300 - 3 900

4 800 - 5 600

6 500 - 7 700






SV: cut to length method
BV: tree method
FPP: Cooperation agreement between forestry, fibreboard and paper industry in Austria

With the help of the data collected and comprehensive time studies, the Austrian Federal Forestry Department has developed a table to determine the productivity and therefore also the costs of cable operations. The table is put together for cut-to-length extraction and gives points for various variables. In the pre-calculations the productivity of the breaker-outs, the complete extraction and the costs of the cable machinery are determined according to the tariffs. In this method, the weakest point in the work chain can be identified and subsequently an optimum work group created. Some variables, such as average dhb, are known accurately after the work has been finished and a post-work calculation must be carried out with the actual, instead of the estimated values. The tables have proved to be accurate for the many years they have been in use and are now being widely employed. The scope of this paper does not allow to cover the specifics of the table.

Guidelines for minimum economic volumes

according to Holzwieser adjusted in 1989 and 1996








K 300, URUS I, K 301


20 to 40 m3/corridor
100 to 200 m3/site

from 18 to 25 mean diameter up to 17 m lateral haulage possible


URUS II, K 400

­ ¯ ®

200 m3/site
300 m3/site

as from 25 mean diameter up to 17 m lateral haulage economical



­ ¯ ®

1 daily output
70 to 100 m3

consecutive operation nearby, total of 300 m3 required


KM 16, K 600, K 500

­ ¯ ®

150 m3 (100)

up to 20 m lateral haulage



­ ¯ ®

0,5 m3/m
1 m3/m

usually 500 to 1000 m length of corridor in Austria up to 500 m required, up to 1600 m technically possible

TRACTOR (agriculture)

­ ¯ ®

1 daily output 20 m3

for consecutive operation nearby, total of 200 m3 required




­ ¯ ®

50 m3
15 (40) m3/corridor
200 m3 total

for consecutive operation total of 200 m3 required lateral haulage of up to 17 m economica


TRACTOR (agriculture)

­ ¯ ®

1 daily output

for consecutive operation nearby, total of 300 m3 required



­ ¯ ®

12 m3/corridor
300 m3 total

lateral haulage up to 8 m possible

Other harvesting possibilities in steep areas

The harvester/forwarder technology is currently not suitable for use in steep areas and, because of rising personnel costs, there is no serious competition at the moment in mountainous areas. People are continually thinking of alternatives and sensible additions to mountainous systems. In isolated incidents, such as catastrophe harvesting (windblow, snow damage), civil construction cranes can be considered. These can extract whole trees or stems up to a 100 m distance from the road, and place them with great accuracy. Walking machines are currently in the developing phase. The use of helicopters is quite advanced in central Europe, particularly Switzerland. When the road network is inadequate, the helicopter can be a viable alternative. Intensive research and cost calculations are recommended for successful helicopter use. By evaluating the current state of the industry, as well as looking back, cable harvesting can and must be further developed to remain competitive in mountainous areas.

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