UBC Theses and Dissertations

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UBC Theses and Dissertations

Skyline thinning production study. Hemphill, Dallas Campbell


Thinning is rapidly gaining importance in the Pacific Northwest as old-growth timber reserves approach exhaustion. In the past, thinnings have been extracted by wheeled or tracked machines, but the need for reducing soil disturbance, while operating in any kind of terrain, has led to the development of a number of skyline systems. Two of these systems were studied, a Washington Model 98 Skylok yarder rigged with a running skyline, and a West Coast Tower using a standing skyline. Both systems are described in detail. A time study was done on seven skyline "roads" for the West Coast Tower, and on two "roads" for the Washington Model 98. The construction of a computer simulation model of the yarding process is described. The various elements of the logging process were modelled in several ways, and the thesis shows how the model could be used to make guidelines for planning logging layouts, for sensitivity analyses, for cost and time prediction, for methods improvement, to assist in equipment selection, to help allocate machines, and to show the applicability of skyline thinning to an area outside of the Pacific Northwest. External yarding distance, over a wide range, was found to be unimportant in determining yarding costs. Stocking was an important factor. It was shown that there was an optimum road width for a given length and shape of skyline "road". Potential savings were shown in loading and yarding procedures. The standing skyline was found to have no advantage in deflection, and it was more expensive to set up than the running skyline. Improvements in tree marking procedure are suggested. Loading was found to have considerable potential for cost reduction. Suggestions are made for future research, and the lack of some very basic knowledge is noted. There is abundant room for, and a great need of, an extension of this analysis.

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