The effect on tether tension when using trees to redirect live machine tethers during forest harvesting on steep slopes

Abstract

Ground based forest harvesting machines are being used on steeper slopes with the aid of tethers to help maintain traction and stability. It is common to position a base machine containing the tether winch above the forest harvesting machine. This configuration is termed a live tether. The live tethers may be run around rub trees to reduce the time required to reposition the tether. This study developed a new model that includes both friction and cutting forces to estimate cable tension on either side of the rub tree. A dataset collected in the field was used to estimate the parameters in the model. The model appears to be promising; however, further work is required on the interaction of the cable cutting surfaces and the surface toughness of the wood. In general, it was found that the difference in the tension on either side of the rub tree increased with increasing change in angle, that the cable on average cut 3 mm deeper with each 10 m of the cable travel, and that the difference in tension was not correlated with the depth cut into the wood. • This study develops a new model that includes friction and cutting forces to estimate cable tension around a rub tree. • Data was collected and used to estimate the friction coefficient and cutting deformation coefficient in the new model. • The change in tension is independent of the depth the cable cut into the tree. • Interaction between the surface toughness of the wood and the frictional surfaces of the cable requires further study.