Simulation of gum naval stores production systems

Abstract

A discrete event simulation model was developed to represent major aspects of gum naval stores production operations, including bark chipping, oleoresin harvesting, transport of work crews and products, equipment breakdowns and weather delays. Simulation models were executed for 61 different conditions involving two alternative labor management systems and 15 model parameters. Important findings indicated that present systems had a low degree of labor utilization, and a high level of yield losses (16 to 18%). Harvest efficiency averaged 43·4 kg per man-hour for all workers and 106·5 kg per man-hour harvesting. Daily productivity averaged 3069 trees chipped-treated, and 2·4 metric tonnes of oleoresin harvested. In comparisons between labor management systems, ‘flexible’ systems had a 23% higher harvest efficiency than ‘fixed’ systems because of the ability to meet temporary peak workloads. Delays caused by harvest workers waiting for the tractor-wagon represented a bottleneck in harvest activities. Adding a ‘backup’ tractor-wagon unit reduced harvest delays 39-fold. Operating parameters exerting strong effects on harvest efficiency were stand density, cup size, tree diameter, cup fullness threshold, and harvest inspection interval. Yields per man-hour varied by a factor of two between best and worst conditions. Under the base conditions simulated, the number of laborers could be reduced by 40% without sacrificing harvest yields.