Productivity and utilisation of winch-assist harvesting systems : case studies in New Zealand and Canada.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Forestry Science
Winch-assist technology is now a well-established system to support forest harvesting on steep slopes. The winch-assist harvesting system is a combination of the winch-assist machine (WAM) at the top of the slope that allows steep slope machines (SSM) to manoeuvre down slopes. The SSM is attached to a winch rope from the WAM to carry out tasks such as mechanised felling. Winch- assist harvesting systems are expensive and little is known about their productivity and utilisation rates, or the factors that affect this. This research aimed to improve knowledge of winch-assist harvesting systems in terms of productivity and utilisation through six case studies in New Zealand and Canada.
Two to five days of continuous operational data were collected at each of the six case studies. Productivity of the winch-assist harvesting system was determined by measuring the volume harvested in the time that the SSM was carrying out its primary tasks of felling, bunching, moving between trees, and brushing. The Utilisation is then the ratio of the productive machine time (PMH) as a percentage of the total scheduled machine time (SMH). The difference between PMH and SMH will be the system working on tasks other that its primary tasks, or in delay. Delay time was further defined as operational, mechanical, or personal. Productivity per SMH is then the product of the m3/PMH and utilisation (%) and calculated using the product of the utilisation rate and the volume harvested per PMH.
The average productivity recorded through the six case studies was 61m3/PMH, ranging from 34m3/PMH to 102m3/PMH. The site with the lowest productivity was a result of small piece size and while the site with the largest productivity was a result of large piece size and long even slopes leading to less WAM relocations.
The average winch-assist harvesting system utilisation recorded in these six case studies was 52%, ranging from 25% to 63%. Delays and shovelling were common, accounting for 48% of the total recorded time (delay 37%, shovelling 11%). Operational delays summed 69% of total delay time; these delays included relocating the WAM, moving setting, setting up and planning, line handling, diesel activities, radio communication and assisting with other operations. Short corridor lengths meant increased WAM relocations and had the largest relation to operational delay. Mechanical delays, when the machine was not able to work due to repair or maintenance, accounted for 17% of total delays. Mechanical delays included greasing the machines, chain and bar issues and general maintenance. Thick undergrowth and small trees within the forest stand had a large impact on chain and bar issues. Personal delays involving the operator taking a break were 14% of total delays.
As a result, average productivity per SMH was 33m3/SMH, and ranged from 11m3/SMH to 58m3/SMH in the six case studies. This highlights the effect of low utilisation in that it almost halves the productivity potential, but it is important to understand the reasons for delays, many of which are unavoidable.
Winch-assist supported shovelling, while being considered an operational delay in this study because it limits the SSM in its felling task, was a common practice through the six case studies. Shovelling is in support of the extraction activity, for example moving stems to a visible location for cable extraction or to an area able to be accessed by ground based extraction machines. So while this effectively increases the felling cost, it increases the productivity of the next process in the harvesting system.