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An analysis of the slackpulling forces encountered in manual thinning carriages

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  • The popularity of gravity-return skyline logging sys­tems is now increasing in the Western United States. Simplicity seems to be the basis for their success. While two drum yarders are most commonly used, ·some systems, such as the Wyssen, use only a single drum for yarding. Carriages commonly used with these systems in partial cuts often depend on manpower to pull slack. The carriages either clamp to the skyline or latch to a stop on the sky­line. The Koller and Wyssen carriages are examples of the clamping type, while the Maki and Christy latch to a stop on the skyline. The feasibility of logging with these systems may de­pend on whether or not the crew is able to pull line to the side to reach the turn of logs. Another consideration for standing skylines, rigged above the reach of the rigging crew, is the amount of weight that must be attached to the hook for it to drop from the carriage. A quantification of the force required to pull the mainline through the carriage may be useful in the design of carriages that provide some auxilliary means of pulling slack.
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