Influence of Load Volume on Productivity of Skidding Euro-American Poplar Stems with Tractor Timberjack 240C in Lowland Forests

This paper presents the results of research of Timberjack 240C tractor equipped with double-drum winch Adler HY16 in tree-length skidding method. The research was conducted in Euro-American poplar clearcut using time and work study method.Timber processing was done by teamwork of two fellers, one tractor driver and one feller-crosscutter (Fig. 3, Fig. 4 and Fig. 5). The volume of 759.03 m3 was skidded in 88 cycles from an average skidding distance of 760 m. The average load volume was 8.63 m3, and it consisted of 5.2 pieces with an average volume of 1.66 m3.During the research the tractor accomplished 68.63% of total time as effective time with delay time of 31.37% (Fig. 6). Travel unloaded accounted for 14.39% of total time, travel loaded 23.91%, felling site work 14.33% and landing work 16.00%. Daily output of 63.25 m3/day was achieved with average total time consumption of 359.32 min/day. The said total time consumption accounts for 78.86% of the legal working time (480 min).Variable times (travel loaded and unloaded by skid trails and landing, line pulling and winching) were analyzed by mathematical and statistical methods (Fig. 7, Fig. 8, Fig. 9 and Fig. 10). All other effective times were regarded as fixed and calculated as averages of recorded time.In effective time per turn, for skidding distance of 600 m (skid trail) plus 150 m (landing), travel times account for 18.14 min and felling site and landing work times account for 15.91 min. The effective time per turn, for skidding distance of 600 m (+150 m), is 34.05 min. With determined allowance time factor of 1.30, total time is 44.36 min. The average travel speed on skid trails is 6.52 km/h for unloaded tractor and 3.87 km/h for loaded tractor. The average travel speed on landing is 5.61 km/h for unloaded tractor and 3.73 km/h for loaded tractor (Table 2). The average speed of line pulling for the left drum is 0.97 km/h and the average speed of winching is 1.02 km/h. And for the right drum, the average speed of line pulling is 0.94 km/h and the average speed of winching is 0.85 km/h. (Fig. 3) Standard time of skidding ranges from 3.71 min/m3 (100 m) to 6.29 min/m3 (1000 m).The daily output for the average load volume ranges between 129.52 m3/day for skidding distance of 100 m and 76.34 m3/day for skidding distance of 1000 m. For skidding distances from 100 m to 1000 m, the skidding cost ranges from 22.18 HRK/m3 to 37.63 HRK/m3. The impact of different average load volumes on daily output and skidding cost is shown in Table 5 and Fig. 11.The results of this research show that Timberjack 240C tractor belongs to a group of highly-efficient special forest timber skidding machines. The principle of load size effect, as one of the key factors of timber skidding, on skidding productivity in different skidding distances has been proven by this detailed research. Hence, by increasing the load volume and decreasing the average skidding distance, the productivity of this tractor is significantly increased, thus lowering the cost per unit