Cable Yarding. Cable yarding involves the use of steel cables, or wire ropes, to skid logs to a truck road or log landing using a yarder that is set up on the truck road or landing. A yarder has a number of powered drums filled with wire rope, and a vertical tower or leaning boom that is necessary to elevate or provide lift to the cables as they leave the machine. The tower ("pole") or boom that provides this lift is held in position by three to eight wire rope guylines that are also stored on powered drums on the machine. With rare exception, logs are yarded uphill with cable systems. Cable yarding is usually described as either "high lead" or "skyline", depending on how much lift is applied to logs as they are yarded. High lead logging essentially attaches logs directly to the end of the "mainline" that exits the top of the yarder tower. The only lift provided is that resulting from the difference in elevation between the location of the log and the top of the tower. This system is quick to set up and is effective over short distances (generally less than 500') where, depending on terrain and tower height, the resulting lift will be sufficient to prevent the logs from digging into the soil surface during yarding. Over longer reaches some form of skyline logging is preferred to provide lift sufficient to increase productivity (reduced drag over long distances significantly increases yarding speed) and minimize ground disturbance. Skyline logging involves use of a skyline cable that extends from the top of the tower to an anchor located at some elevated point beyond the edge of the logging area. This anchor is usually a xxxxx on an opposing hill slope, but can be a suitable tree at the perimeter of the logging unit that has been climbed and rigged to provide the necessary elevation for the skyline. Logs are attached to a carriage that rides on the skyline, and the carriage is pulled to the landing with the yarder's mainline (also referred to as the skidding line in this application). Depending on which variant of skyline logging is used, the skyline can be lowered to attach the logs and then raised to provide lift, or the carriage can spool out its own skidding line through one of various mechanisms and then lift the logs towards the skyline. Either way, enough lift is provided to suspend the uphill end of logs above the ground surface unless an unusually large log is encountered or the only available skyline anchor point cannot provide enough lift.
