Analysis of Long Distance Cableway Systems

Jim Sherar
USDA Forest Service
Treetrans Systems

Description of System
The system is comprised of a single drum winch that can be equipped with up to 2200 m of 22mm cable. Various sizes of drumsets are available with different spooling capacities. In a typical set up, the winch is positioned at the top of the slope and logs are lowered to the bottom of the set. A skyline cable is fixed at both the top and the bottom of the slope. The winch is used to power the carriage uphill and the braking system on the winch is used to lower the fully suspended logs downhill to the log landing. A carriage with multispan capability, designed to pass over intermediate supports is used. A number of intermediate supports can be rigged as necessary to provide lift over the terrain. Typically, a crew of 5 can be used to operate the system; a yarder engineer, 2 choker setters, a timber faller, and a chaser.

Downhill Cable System

Single-drum Winch

Multispan Carriage and Log Landing

History of System use in the U.S.
The long distance cableway system has been used since the early 1970s in the Western U.S. on National Forest lands. Typical distances were up to 4000’ (1200m). Several companies make single-drum winches that are used in this type of downhill logging system. Gantner, Wyssen and Fuji all make different sizes of single drum winches. The systems found a niche in western WA on long continuous slopes with limited road systems. They were used to harvest both green sales (clear cuts and partial cuts) and fire salvage sales. The systems require more time to set up than many mobile systems, therefore, more volume per setup is required than for some other systems. The long slopes and the application of the same silvicultural treatments were suitable for system economics. Short slopes in combination with light cut volumes per acre are not suitable for this type of cable system.

Long Span Corridors

Single-drum Winch, western WA, 1970s

Typical Logging Plan for Downhill Long Span

Suitable Sites for long distance cableway systems
The terrain in the Eastern U.S. is generally not suitable to long distance, downhill logging systems. However, there are some unique slopes and ownerships where the system could be used more economically than other systems as a primary swing transport system for bunched logs. These tracts would consist of high ridges with no haul road access to the top of the ridge thus necessitating either long distance downhill cable systems or helicopter logging systems. Potential sites could be found in the Southern Appalachian Mountains to demonstrate the system. There is currently a high level of interest in helicopter logging in the eastern mountains and this type of cable system could present a favorable economic alternative in some limited cases. Many of the eastern slopes have truck road access to the top of the ridge and logging is conducted away from the narrow drainage bottoms. Many of the larger tracts in the east are also roaded.

Typical eastern Appalachian terrain

The terrain in the Western U.S. is probably the most suitable for this type of system. Long, constant slopes with high road costs and an objective to minimize new roads make this system a tempting alternative. There are several drumsets from the existing systems of the 70’s and 80’s on the west coast. They are not currently active.

Typical Long Slopes of western U.S.

Single-drum winch, western WA, 1970s

System Economics and Analysis
In discussions with Swiss forester, Kurt, the system requires approximately 1 cubic meter of timber for each meter of line length in order to be feasible. The lateral yarding distance from the corridor is typically about 40-60m. It requires 3-4 men approximately 1- _ days to set the system up for an 800 m length. Using these numbers:

Area accessed for 800m x 100m = 8 has or about 20 acres
1 m3 of wood = 35.3 cf = 200 bf
Volume required for 800 m of length = 200 bf/m or 160 mbf of timber
Volume per acre required for 800m of length = 160 mbf /20 acres = 8 mbf/acre

This volume per acre is high for most partial cut volumes in eastern hardwood stands. Many eastern hardwood stands do not have consistency in stand structure and merchantable volume over an 800 m slope. Typically, the stand type and structure changes from a ridge top ecosystem through at least one mid-slope ecosystem to a lower slope ecosystem. The silvicultural needs and the harvestable volume will be highly variable from the upper slopes to the lower slopes. A cable system of 300- 400m in length would be more applicable to eastern stand conditions and slopes

Typical eastern hardwood skyline shelter wood cut

System Requirements for Appalachian terrain
The system that could be integrated into eastern harvesting alternatives would have the following system capabilities:
400 m of 7/8” skyline
400 m of _” winch line
2 _ - 3 ton multispan carriage
Mounted on a mobile carrier
Quick set-up and take down
35-45’ tower

Mobile Excavator Conversion Yarder

Mobile TMY 45 Skyline Yarder

Training
There are currently limited skills in cable harvesting in the East, with more highly skilled loggers in the Western U.S. Most cable loggers in the east are familiar with 2 drum uphill gravity single span systems. Multispan logging is not prevalent, although there are several loggers with multispan carriages in the east. Rigging for multispan logging is more complex and is not a common skill in the east as it is in the west. An intensive training effort would be needed to successfully train loggers in the use of both uphill and downhill multispan systems.

Other Considerations:
Peculiar to the downhill long-span cable systems is the need to fully suspend logs during transport. This necessitates the skyline cable being rigged high enough off the terrain to allow logs to ride the skyline free of the ground. In partial cut systems, a corridor must be cleared to provide transport of the logs. Hardwood trees often over hang corridors which make additional felling necessary. Cable systems that only partially suspend logs during transport don’t require rigging to be as high as full suspension systems and allows the skyline to stay somewhat below the canopy.