Dyson Peter, BSc.

The forest industry around the world is facing common challenges in accessing wood fiber on
steep terrain. Fully mechanized harvesting systems based on specialized machines, such as
winch-assist forwarders, have been specifically developed for improving the harvesting performances
in steep grounds. While the mechanization process is recognized as a safety benefit,
the use of cables for supporting the machine traction needs a proper investigation. Only a few
studies have analyzed the cable tensile forces of winch-assist forwarders during real operations,
and none of them focused on large machines normally used in North America. Consequently,
a preliminary study focused on tensile force analysis of large winch-assist forwarders was
conducted in three sites in the interior of British Columbia during the fall of 2017.
The results report that in 86% of the cycles, the maximum working load of the cable was less
than one-third of the minimum breaking load. The tensile force analysis showed an expected
pattern of minimum tensile forces while the forwarders were traveling or unloading on the
road site and high tensile forces when operating on steep trails, loading or traveling. Further
analysis found that the maximum cycle tensile forces occurred most frequently when the
machines were moving uphill, independently of whether they were empty or loaded. While the
forwarders were operating on the trails, slope, travel direction, and distance of the machines
from the anchor resulted statistically significant and able to account for 49% of tensile force
variability. However, in the same conditions, the operator settings accounted for 77% of the
tensile force variability, suggesting the human factor as the main variable in cable tensile force
behavior during winch-assist operations.