| Abstract |
- This paper describes the analysis of data from a three-year gross time study of skyline, balloon, and helicopter yarding systems operating in Western Oregon. Data collection activities were designed and supervised by the Pacific Northwest Forest and Range Experiment Station, U.S.D.A. Forest Service. The specific logging systems studied were running skyline, North Bend standing skyline, long-span standing skyline, balloon (inverted skyline, highlead, inverted skyline yo-yo, and highlead yo-yo), medium helicopter, and heavy helicopter. These systems were observed under a wide range of silvicultural and landscape design prescriptions, timber type, terrain, and weather conditions.
The objective of this study was to develop yarding production equations, to sumarize delays, road change times,and landing change times, and to compare yarding production estimates made from both gross and detailed time study data. This kind of information is useful for the comparison of alternative logging methods in environmentally sensitive, landscape-designed harvest units.
The data were segregated according to the individual logging systems and analyzed via multiple regression. Then individual system data were combined into the categories of short-span skyline, long-span skyline, balloon, and helicopter. These combined data were also analyzed via multiple regression. Chi-square tests were performed to determine whether the equations developed from the combined data were significantly different from the set of equations developed from the segregated data. The results of these tests support a conclusion, at the 95 percent level of fiducial probability, that the equations developed from the combined data are as adequate for predicting yarding production rates for these logging systems as the equations developed from the individual-system data.
The variables shown statistically to influence yarding production rates for all logging systems studied were yarding distance and number of logs per turn. In addition, helicopter yarding productivity was also found to be influenced by the type of cutting prescription, and short-span skyline yarding, by chordslope. A variable combining aspect and the season of work was found to be significant for both the running skyline and the heavy helicopter.
Yarding delays were found to be affected by yarder, landing size, season, and crews' experience. In order to compare similar systems' delays, it was found important to segregate out weather-related delays.
In a separate study, detailed time studies were made on four of the yarding systems analyzed in this paper. This allowed a comparison between the measurements of yarding production rates made during the detailed time study and those made during the gross time study. The gross time study rates were consistently lower than the detail time study rates. This suggests that the detailed method does not reflect the total downtime as accurately as the gross method. Thus the gross method appears better suited for developing information that is useful for appraisal purposes and the detailed method is better suited for evaluation of system efficiency.
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