For evaluating the efficiency of wheeled skidder Timberjack 450C in ground skidding system, a forest in Caspian region was selected. In the research area, trees were logged downhill to the depot by a wheeled skidder Timberjack 450C. The work elements of a skidding cycle from stump area to roadside depots were travel empty, establishment time, release the cable winch, hooking, winching, travel loaded, unhook and piling the logs. 50 skidding cycles were evaluated in this study. Thus, some factors including skidding distance, volume per cycle, slope, the number of logs per cycle and winching distance as well as time of each element in one skidding cycle were measured. After data analysis, the skidding predicting equation was applied. This time model was mainly affected by skidding distance and interaction between skidding distance and slope. The gross and net production rate in the 980 m skidding distance was 20.199 and 16.58 m3, respectively. The unit cost considering the gross and net production rate was 4.7 and 5.7 Euro m-3, respectively. Delays in times of travel empty and travel loaded were the most frequent. The time of establishment and movements of skidder for winching was the third important part of skidding cycle.
Key words: Wheeled skidder, mathematical model, skidding, time study.
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