Special Feature: Winch-assist Harvesting
Maximising the benefits of mechanisation Story: John Lowe, Acting National Safety Director of the Forest Industry Safety Council (FISC) and Safetree.
T
HE NEW ZEALAND FORESTRY industry has seen a huge shift from manual to mechanised harvesting in the past few years, greatly reducing risks to manual fallers and breakers-out. However, mechanised harvesting creates its own critical risks, particularly if machines and the people who operate them are working on steep and more difficult terrain. With winch-assisted technology now widely used around New Zealand, the forestry industry identified the need for a NZ Winch-Assisted Harvesting Best Practice Guide. This guide, published in July 2022, sets a benchmark for winch-assisted harvesting on steep slopes. Winch-assist is a ground-based harvesting system that uses wire rope(s) attached to a machine to operate in a broader range of conditions, often on steeper slopes. It is often called cable-assist or tethered harvesting. Winch-assist is specifically designed to extend the operating range of machines on steep slopes. It allows harvesting
machinery to operate on steeper slopes where previously no machine could have worked. It can also be used to support cable logging operations through mechanised directional felling for extraction, bunching and shovelling. A common New Zealand use of winchassist is steep slope felling or shovelling with a tracked excavator. However, a range of other machines can be successfully winch-assisted including skidders and forwarders. A big driver for winch-assisted harvesting systems has been to improve felling safety. Machines protect workers from many of the risks associated with manual felling. WorkSafe’s position on new technology is that companies should adopt it when it better manages risk. The move to winchassist has been an important safety step to protect workers through new technology. Companies using winch-assisted harvesting also report that, with correct management, it can benefit productivity, the environment, operational flexibility, and forest owner returns.
However, like any technology it brings its own set of risks. An analysis of data from the Incident Reporting and Information System (IRIS) shows recent winch-assisted incidents are split between three key areas: • Anchor set-up and anchor components: This includes winch components, controllers and site factors, and anchor lead angle incidents. • Rigging-related incidents: This includes ropes, chains, connectors and unintentional factors like binding and redirects.
Winch-assist incidents
Anchor Rigging Assisted machine
Source: IRIS data
How steep is too steep? Many factors other than slope affect machine operations e.g. soil conditions, operator skills, the machine and roughness of the slope. Operators say productivity drops on slopes greater than 42 degrees.
Slope (degrees)
Slope (%)
Consideration
17°
30%
This is considered a limit for when a wheeled ground-based machine can start to slide under poor conditions.
22°
40%
This is considered a limit for a tracked ground-based machine. It can start to slide under poor conditions.
28°
50%
Most purpose-built forestry machines, with good operators in good conditions, can work up to this limit. Beyond this slope it is wise to consider using winch-assist.
35°
70%
This is considered the absolute upper limit for ground-based machines without winch-assist. Only under very favourable soil strength condition, with a purpose-built steep slope harvesting machine and a very experienced operator, and then only traversing directly up or down the slope.
42°
90%
A realistic upper limit for all winch-assist operations.
45°
100%
Considered the absolute upper limit for any winch-assist operation. If any part of the rigging fails, a machine roll-over would be dificult to avoid.
30 NZ LOGGER | September 2022
