Cable Yarding

    The basic design of a cable yarder is very simple really. just a set of winch drums with an engine hooked to them. Where the technology comes into effect is HOW the drums pull the line. There are too many factors involved for me to explain them all, but here are a few. You usually have 2 drums in a simple skyline configuration one pulls the skyline tight which runs from the machine to an anchor point, I.E. a stump or large tree. The SKYLINE drum usually has one job in this configuration, pull the line tight, set the parking brake, and that's it. Medium size yarders have a skyline drum pull somewhere in the range of 45,000 pounds. Next is the MAIN drum, which is what pulls the logs up the hill. The main line is hooked to a device called a carriage (I will explain carriages later) this drum is a little more complex. It has to be able to have a LOT of power at a slow speed to be able to pull the logs out of their beds where they can often be stuck or hung up. Then slowly and safely pull the logs to the carriage. After the logs have become airborne via the skyline suspension, the main drum is shifted into high gear where it pulls the logs up the hill as fast as possible. Where the distance's can reach up to 5,000 feet or more you want it to move as fast as possible. The newer machines have the available power to bring a 20,000 pound or more, turn of logs up at speeds over 50 miles per hour! The drum also has to have a braking system that is able to withstand much abuse. When the carriage returns down the hill, the operator puts the drum in free spool and lets it go down the skyline on gravity. Where it can reach speeds of 60 to 70 miles per hour then it has to be stopped when the rigging slinger signals the operator that the carriage is where he wants it. The main drum usually has a water-cooled band or disk brake with lots of surface area to dissipate heat in order to get long life out of the unit. As I mentioned above the drum is shifted into low or high gear to change speeds. Either a torque converter or hydrostatic transmission attains this. The most common is the torque, and it functions almost the same as the auto matic transmission in your family car. Actually some of the new mini yarders out today have car transmissions in them. Not sure how reliable those are though...hmmm....

     The next set of drums includes the HAUL BACK the HAYWIRE and the TAG LINE. The haul back is used where the ground is too flat or even up hill as though not to allow the carriage to return back to the logs. So a cable is laid out all the way to the end where the skyline hooks up. However it is positioned off to the side as not to interfere with the operation. Then it is doubled back through a pulley and hooked to the carriage where it is used to pull the carriage back to the logs. The haywire and tag lines are used for setting the whole thing up. They are very small cables light enough to be pulled out by hand to the tail holt(skyline stump or tree) then they pull the skyline out to be hooked up. A skyline is usually 1 inch in diameter and very heavy. A man could only pull out a 100 feet or so and then fall down with exhaustion. Let alone ever pull out 2000 feet!

     The next item is the carriage. That is where all the technology is placed. Over the years there have been many many different types of carriages. The most basic type I am familiar with is the christy carriage. It is simply a pulley that coasts down the skyline until it hits a stop. Then after locking on to the stop the choker setter pulls the line out to the logs by hand...only effective on steep ground and relatively short turns...750 feet or less. The next style, which is the focus of this writing, is the motorized slack puller. This particular unit is the most advanced as they get. It looks like a large box; inside of it sits a small diesel motor that runs a hydraulic system and a small drum. The hydraulic system is for the skyline clamp and the main line clamp. The skyline clamp holds the carriage in place as though when the main line is released the carriage does not take off. The main line clamp is for locking the main line to the carriage as though to pull the whole unit up the hill. The drum in it enables the option of feeding the main line out, rather than having to pull it by hand. Allowing the yarder to reach almost any distance needed to be the most effective. The whole carriage is radio control from starting it to shutting it off. A small unit how ever costs about $30,000.00 dollars and the large ones over $100,000.00 combine that with a yarder that cost around half a million dollars and you can see why not every one has one of these in their back yard.

The 6250 is $650,000.00 for bare machine.

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