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Cable tensile forces in winch-assist harvesting have been investigated in order to assess the safety concerns of the technology. However, the literature is lacking, particularly in regards to the impact of winch design. In this study, a Summit Winch Assist tethering a feller-director on ground slopes up to 77% was monitored for four days. The cable tensile forces were simultaneously recorded at the harvesting and anchor machine at a frequency of 100 Hz. Cameras and GNSS devices enabled a time study of the operations and the recording of machine positions. Winch functionality and design were disclosed by the manufacturer and used for the interpretation of the results. The cable tensile forces reached 296 kN at the harvesting machine and 260 kN at the anchor machine. The slow negotiation of obstacles while moving downhill recorded the highest peaks, mainly due to threshold settings of the winch in the brake system activation. Lower but significant peaks were also recorded during stationary work tasks. The peaks, however, were limited to a few events and never exceeded the endurance limit of the cable. Overall, the study confirmed recent findings in cable tensile force analysis of active winch-assist operations and provided evidence of the underlaying mechanisms that contribute to cable tensile forces.

The interest in active sustainable management of mountain forests is increasing around the world. Great effort, in particular, is focusing on the identification of efficient, safe, and sustainable steep slope harvesting solutions adapted to different environmental conditions. The main attention is moving toward winch-assist harvesting systems on trafficable terrain and European designed standing skyline mobile tower yarders on non-trafficable terrain. These cable-supported harvesting solutions have similar safety issues related to the use of tensioned wire ropes and the use of natural anchors. This research focused on the analysis of cable tensile force while operating with these harvesting solutions in ordinary harvesting sites and operational conditions. First, a state-of-the-art about the steep slope cable-supported harvesting solutions and their main safety issues was completed. A particular focus was dedicated to the significant works on cable tensile force monitoring. Following, field studies were successfully carried out to monitor the cable tensile forces on ordinary logging operations. The survey interested eleven mobile tower yarders, observed on twelve different cable lines in the Italian Alps, and three large integrated-winch forwarders, observed on eight trails in the interior of British Columbia (Canada). A similar approach, based on the integration of tensile force monitoring, video recording of the operations, ground profile analysis, and load measurement/estimation, was applied to both the cable-supported systems. The case studies, the methodological approach used for the data collection and analysis, and the results of the monitoring are presented and reported in detail.

The objective of this case study was to develop and test a specific survey protocol for monitoring tensile forces for winch-assisted harvesters and forwarders with a mounted or integrated constant-pull capstan winch technology. Based on the designed survey protocol, the interactions between work phases, machine inclination, and tensile forces in typical work conditions were analysed. The established workflow, including equipment and the developed analysis routines, worked appropriately and smoothly. The working load on the cable during the study did not exceed 50% of the maximum breaking strength. A maximum tensile force peak at 56 kN was observed during delays for the forwarder, and a peak of 75.5 kN was observed for the harvester, both of which are still within the safe working load when considering a safety factor of two.

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.