Benefits and Limitations of Winch-Assist Technology for Skidding Operations

Skidders are very cost-effective extraction machines, and winch-assist systems may extend their operating range to increasingly steep terrain. The use of winch-assist skidder systems is relatively new, and little information is available about their operational efficiency and potential soil impact. A productivity and soil disturbance study was carried out in Southland (New Zealand) to gauge the benefits of winch assistance by comparing the performance of the same two-axle skidder with and without winch assistance on increasingly steep trails (30 and 40% gradients). The delay-free productivity approached 100 m(3) solid volume over bark per productive machine hour (PMH) under the best conditions and declined with the extraction distance, reducing to approximately 40 m(3) PMH-1 at 300 m. On the 30% slope trail, winch assistance allowed an 8% productivity gain through a significant increase in the payload size. However, on the 40% slope trail, the increased payload size allowed by winch assistance was unable to offset the much lower empty speed and, therefore, the control treatment (no winch assistance) performed better. A preliminary soil disturbance assessment was carried out over the whole harvest site using a line transect method. The assessment was conducted at the end of the harvest and reflected the impact of all the operational activities, including mechanised felling and skid trail construction, not just skidding. Soil disturbance appeared to be low, as ruts deeper than 15 cm covered only 2% of the inspected surface.