Skyline tension and dynamic loading for cable yarding comparing conventional single-hitch versus horizontal double-hitch suspension carriages

Wire rope used in cable logging, where a series of cables facilitate the extraction of timber on steepterrain, experiences high tensions that must be managed to ensure safety. Innovations change practicesover time and double-hitch carriages, which allow trees to be extracted horizontally, are a recent example.This makes it feasible to harvest across terrain with limited deflection, increases the recovery of biomass,and potentially reduces high-dynamic load events associated with ground contact. In this study, astandard single-hitch carriage was compared against a new double-hitch carriage under controlledconditions. Tension was measured continuously and specific elements, such as tension when the carriagewas at midspan, maximum tension at breakout and inhaul, and magnitude of cyclic tension during inhaulwere identified, measured and compared against payload. While payload was similar in the treatments,the additional weight of the double-hitch carriage resulted in higher skyline tensions. In both treatments,payload and skyline tension when the carriage was at midspan were strongly correlated. Cyclic tensionwas reduced by the double-hitch carriage system. While a number of unique high-dynamic loads wereidentified that were not part of the normal extraction, they represented only 6% of the cycles and themaximum tension was similar to that experienced during break-out and inhaul. This study increased theunderstanding of skyline tension during logging operations and the effect of carriage type. It showed that,though tension often exceeds the safe working load of the cable, it does not exceed the endurance limitfor a well-designed and operated system.