Graduate Thesis Or Dissertation
 

Prebunching with a low investment skyline yarder in thinnings

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2227ms79d

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  • This study compares the production rates and yarding costs of prebunching with a low investment skyline yarder and swinging with a larger skyline yarder to full-cycle thinning with the larger yarder The study analyzes two slackpulling techniques (manual and haulback assisted) and two carriages (a multi-span carriage and a clamping carriage) during the prebunching phase of the operation. The swing yarding employed a multi-span, clamping carriage requiring manual slackpulling. The full-cycle thinning employed a slackpulling carriage. All of the prebunch and swing units required multi-span skylines, while the full-cycle thinning units required single-span skylines. The study took place in a stand of young second-growth Douglas-fir and western hemlock with a mean volume of 6600 cubic feet per acre (30,300 board feet per acre). The mean log size was 12.3 cubic feet (55.4 board feet). Maximum skyline yarding distances ranged from about 500 feet to 1100 feet, with lateral yarding distances up to 140 feet perpendicular to the corridor. The analysis indicates that the full-cycle thinning was significantly less costly than prebunching and swinging techniques. No significant differences were detected between the slackpulling techniques or carriage types used for prebunching. The average cost of prebunching and swinging was $46.76 per cunit ($103.91 per MBF), while the average cost of full-cycle yarding was only $19.14 per cunit ($42.53 per MBF). The average yarding costs increased linearly at a rate of $1.70 per 100 feet of maximum yarding distance. Full-cycle thinning produced 3744 cubic feet per eight-hour day (16,850 board feet per day) or 304 logs per day. Swinging produced 4305 cubic feet per eight-hour day (19,370 board feet per day) or 350 logs per day, and prebunching produced 1882 cubic feet per eight-hour day (8470 board feet per day) or 153 logs per day. The combined production rate of prebunching and swinging was 1413 cubic feet per day (6360 board feet per day) or 115 logs per day. Prebunching production varied as a function of lateral distance and volume per acre removed in the thinning. Regression analysis was used to develop production equations which can be used to predict how each system would function over a similar range of conditions on other operations. The full-cycle thinning performed most consistently during the study. Both the prebunch and swing operations had a higher percentage of unexplained variation in the yarding cycles. The average delay-free yarding cycle for full-cycle thinning required 5.08 minutes, with an average turn volume of 47.4 cubic feet (213.3 board feet). The average delay-free yarding cycle for swing yarding required 5.01 minutes, with an average turn volume of 60.1 cubic feet (270.4 board feet). The average delay-free prebunching cycle was 2.45 minutes, with an average turn volume for prebunching of 19.1 cubic feet (86.0 board feet). The prebunching operation was affected most seriously by delays, with only about 52 percent of the total time spent in delay-free productive yarding. Both the swing operation and the full-cycle thinning operated at about 75 percent delay-free productive yarding time. A parcel model, developed to analyze prebunching production, shows promise as a tool for analyzing time study data.
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