Operational Analysis of Grapple Yarding in New Zealand: A Case Study of Three Mechanized Harvesting Operations

Abstract

The New Zealand forest industry has increased its use of swing yarders when harvesting on steep slopes. Swing yarders can more readily operate with grapple carriages, both mechanical and motorized, in comparison to tower yarders. Especially when coupled with mechanized felling, grapple yarding has led to improved productivity and safety. The effective use of grapple yarding is dependent on the level of knowledge of the working capability of the machines. This productivity study analyzed the operational capability of grapple yarding at three different harvest sites in North Island, New Zealand. The swing yarders were the T-Mar 650, T-Mar 550, and Madill 124 models. Parameters including average piece size, extraction distance, turn volume and the number of pieces were recorded for each cycle, as well as the level of bunching, with a minimum of 125 cycles, were measured at each site. The average delay-free cycle time for the three sites ranged between 2.8 and 3.7 min, which is very fast compared to yarder operations using chokers. Productivity ranged from 50 to 55 tons per productive machine hour. Extraction distance, piece size and stem presentations significantly influenced productivity. Stem presentation, especially bunching, across the cutover influenced the mean payload per yarding cycle resulting in higher productivity. In addition to providing productivity capability information at three case study sites, the analyses linked stand and terrain parameters such as tree size and extraction distance with production variability. Managing variability is critical to achieving consistently higher rates of production efficiency.