Equipment Specs
(Redirected from Yarders)


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(Redirected from Yarders)
Forestry Equipment

A yarder is a piece of forestry equipment used in cable yarding to lift and pull logs by cable from the felling site to a landing area or to the side of the road.

In his book, Logging Practices, Steve Conway describes a yarder as a stationary machine that transfers power to the logs by means of one or more flexible steel cables called lines. The process of moving logs to the machine or landing while the machine remains in place is called yarding. The term applies to cable systems that are capable of vertically lifting logs.

Yarders come in various configurations but share one common feature: a cable, fastened to a drum on a winch, is used to pull a payload from one location to another. A yarder will therefore typically consist of a wire rope line or cables, rigging attachments, and blocks through which the lines are threaded for control of line direction and movement.

Yarders are typically built on a rectangular frame of welded I-beams and powered by a diesel engine bolted at the rear of the frame, through a transmission at the engine output shaft. The transmission is either a four-speed or a hydraulic torque converter with a two-speed gear. A roller chain connects the transmission with the rear drum shaft. On more modern yarders, a compressed air cyclinder and piston controlled through a hand operated air valve engages the drum. The yarder is typically power driven by a diesel engine ranging from 90 to 700 horsepower with the largest yarders being produced with twin diesel engines and having at least one drum and as many as up to four. These drums serve to store the lines and transfer power. It is typical for most modern yarders to have at least three drums.

The machines can also be mounted upon various platforms. In the past, a yarder was mounted on heavy sleds made out of timber. Though wood sleds are sometimes still used, yarder sleds today tend to be crafted from steel plates. The more recent trend is to mount yarders on wheels, primarily rubber-tired, for greater accessibility on roads though tracked undercarriages also exist. Currently three types of wheel mounts exist: truck tractors, motor trucks, and undercarriages powered by the yarder engine. There are also self-propelled crawler mounts of both a tractor type and military tank type.


[edit] History

[edit] Dolbeer's Developments

In 1881 John Dolbeer altered cable yarding in the Pacific Northwest with the invention of the first steam donkey. The steam donkey, the earliest recorded version of a type of yarder, was a machine with a vertical boiler, one cylinder, and a drum. This model consisted of a 150-foot (46-m), 4.5-inch (11-cm) manila rope wound several times around a horizontally mounted spool with the other end of the rope attached to the log.[1] The cable was then pulled directly out to the log by a line horse and the logs skidded along the ground to the landing site.

Up to this time, logging operations had been dependent on animal power to drag logs to level ground or water where the logs could be floated to mills. This was expensive and slow and had obvious restrictions since animals could not work on steep and hilly terrain.

In 1882 Dolbeer patented his steam donkey and the machine was eventually modified to include a haulback line through a pulley system attached to a stump, eventually putting a stop to the practice of using horses to haul logs. With time, donkeys mounted on barges pulled large rafts of logs and lowered logs into car trains down steep inclines. Steel and iron wire cables also replaced rope that had been originally used. In addition, internal combustion engines began to replace steam engines in the 1920s.

Similar pieces of machinery also began to appear bearing names such as Humboldt, Tacoma, Willamette, Seattle, Crackerjack, Duplex, and Halfbreed.[2]

Dolbeer’s brand of logging became known as ground lead.[3] This meant that the logs had to be pulled and guided around every stump that came across their path. This was a time consuming process and loggers began to cut stumps higher hanging a block on top of the stump. This provided a slight lift on the actual skidding line when dragging the log towards the landing site. As time passed, short stumps lead to higher stumps with blocks and this gave way to full trees with blocks and guylines being used. In about 1905, highlead cable yarding was developed on the West Coast regions of the U.S. and Canada.[4] Today it remains the predominant means of cable yarding in these areas.

[edit] The First Cable Yarding System

Dolbeer may have invented the steam donkey, but it was a man by the name of Horace Butters from Michigan who established the first cable yarding system in 1886 when he patented a skidding loading machine that consisted of two spar trees, a carriage, and a steam yarder. This invention enabled him to physically lift the logs out of the woods and transport them to awaiting railway cars.[5] This would become know as skyline cable yarding and was introduced to the West Coast in 1904.[6] Skyline cable yarding became increasingly popular and was practiced in conjunction with railroad logging.

When trucks began to replace railroads, the use of skyline cable yarding diminished. However, it made a comeback in 1949 when the first skyline crane was imported to North America from Switzerland. New developments in interlocking drum yarders for running skyline systems and of labor saving grapples to eliminate choker-setting all led to a resurgence in the practice of skyline cable yarding during the 1960s.[7]

[edit] Features/How it Works

Cable yarding basically refers to the movement of logs from stump to landing. Pulling in a cable rope mainline on a drum barrel yards the logs. A choker is looped around the log hooked to butt rigging attached to the end of the mainline. This butt rigging is dragged out to where the log is by another cable called the haulback or outhaul line. Blocks usually hung on stumps or adjacent trees control the lead, the direction of movement of these lines. Currently two systems of cable yarding are practiced in logging today—highlead and skyline.

[edit] Highlead Cable Yarding

The highlead system is the most common and yet rudimentary form of cable yarding practiced. Associated widely with yarders and wooden spar trees or portable spar-yarder combinations, the highlead system is when the mainline lead block is hung high above the ground on a spar tree or steel tower and operates similar to a clothesline. The purpose of this kind of cable yarding is to exert enough force to be able to vertically lift the log over stumps, obstacles, and other debris. This process consists of using a yarder with a two-drum winch. One drum holds the heavier mainline cable and the other drum, the lighter haulback cable. The haulback line is fastened to the mainline at an axis point where chokers are attached with butt rigging. The haulback line is run through two sheaves from the butt rigging and secured at the backline cable and then back to the yarder. The butt rigging apparatus is raised by applying tension to one line while applying pressure to the other. This means that only one end of the log is usually lifted off the ground. In highlead yarding, the layout will therefore come to represent a triangular formation.

Highlead yarding is not a very sophisticated system. In fact, it has minimal equipment and low training requirements that translate into overall lower capital costs to set up and operate.

Two different types of equipment are commonly used in headline yarding but can also equally apply to skyline yarding too. A mobile yarder loader is a wheel mounted loading machine that has been adapted to handle yarding. The yarder loader usually has two drums, one to run the mainline as well as the loading line and another drum for the haulback line. In place of a spar a loading boom is used supported by two guylines to handle the stress of yarding logs. These machines are used primarily in the clear-cutting of smaller logs, for thinning operations or salvaging timber.[8]

Another machine is a yarding crane that performs only the function of yarding. The crane’s mast is longer then a yarder loader and uses two guylines positioned opposite the direction of the pull. Yarding cranes have the capacity to yard logs 700 to 800 feet (213 to 344 m).[9] They are also used in grapple yarding.

[edit] Skyline Cable Yarding

In skyline systems, logs are dragged or carried suspended from a carriage that rides on a cable stretched between the head spar at the landing and a tail spar at the back of the yarding road. There is a broad range of skyline systems that encompass simple conversions of highlead systems, to high mobile swing yarders, to large skyline towers. The commonality is that the cable is what provides the lift to a carriage by means other than simple braking pressure on the haulback cable line. It is important that the carriage be clear of the ground at all points along the skyline. In some circumstances the carriage can run on the haulback cable, otherwise called a running skyline. If the actual skyline can be raised or lowered during yarding, it is referred to as a live skyline or slackline and if the skyline operates in a fixed position it is called a standing skyline.

One of the advantages of skyline cable yarding is that logs are able to achieve a higher lift. This obviously assists in eliminating snagging on stumps and other debris along the ground and provides better clearance over sensitive terrain drastically reducing ground disturbance. In addition, the yarding distance can also be greatly extended.[10]

The cost of operating a skyline cable yarding operation is high. A very skilled crew is required, especially if back spars are used. This is because the cables on skyline systems can lift and carry higher payloads making them more dangerous to operate. Capital costs are also substantially greater due to the sophistication of machinery, labor, and training involved to set-up and run a skyline yarding system.

[edit] Types

[edit] Swing (Grapple) Yarder

Even though they are more or less designed to be stationary, yarders can be further subdivided in terms of mobility. For example, a common type of yarder is a swing yarder or grapple yarder. A swing yarder can be distinguished because it is mobile and has a rotating base, inclined booms and is built on track-mounted or rubber-tired carriers. In cable logging, swing yarders are used in roadside applications where a landing site is not necessary as the machine has the ability to swing and pile logs on either side. Due to its mobility, swing yarders are designed to move with relative ease between logging sites.

[edit] Tower Yarder

Another type of yarder is a tower. A tower yarder is used in one place for an extended period of time and anchored to fixed locations when operating. Without the ability to swing, towers drop the logs in a pile near the landing site. As a result, the landing often gets congested and an auxiliary piece of equipment is often needed to clear and move the logs away, either a loader or a skidder. One advantage of a tower is that it is taller than a swing yarder and has better deflection.

[edit] Common Manufacturers

[edit] References

  1. John Dolbeer invents the donkey engine and revolutionizes logging in August 1881. Historylink. 2008-09-28.
  2. John Dolbeer invents the donkey engine and revolutionizes logging in August 1881. Historylink. 2008-09-28.
  3. Stenzel, George and Walbridge, Thomas A. Jr. and Pearce, J. Kenneth. Logging and Pulpwood Production, 2nd Edition. Wiley-Interscience: 1985. 230
  4. Conway, Steve. Logging Practices: Principles of Timber Harvesting Systems. Backbeat Books: 1982. 198
  5. Conway, Steve. Logging Practices: Principles of Timber Harvesting Systems. Backbeat Books: 1982. 198
  6. Stenzel, George and Walbridge, Thomas A. Jr. and Pearce, J. Kenneth. Wiley-Interscience: 1985. 230
  7. Stenzel, George and Walbridge, Thomas A. Jr. and Pearce, J. Kenneth. Wiley-Interscience: 1985. 230
  8. Stenzel, George and Walbridge, Thomas A. Jr. and Pearce, J. Kenneth. Wiley-Interscience: 1985. 204
  9. Conway, Steve. Logging Practices: Principles of Timber Harvesting Systems. Backbeat Books: 1982. 204
  10. “Harvesting Systems and Equipment in British Columbia,” Forest Engineering Research Institute of Canada, pg. 76.