An investigation into the system production balance within three mechanised harvesting case studies.
Degree GrantorUniversity of Canterbury
Degree NameBachelor of Forestry Science
Safety issues and high costs of traditional harvesting methods have been driving mechanisation increases in New Zealand. However, productivity increases from mechanisation alters system productivity balance. This can result in underutilised machinery and cause an increase in harvesting costs in real terms.
A time study was carried out to understand the system productivity balance between felling, extraction and processing and the factors affecting system component productivity rates, for three case studies. The three case studies observed were (1) a semi-mechanised cable yarder extraction operation, (2) a fully-mechanised swing yarder operation and (3) a fully-mechanised ground based operation.
There were large production imbalances between felling, extraction and processing in all three case studies. Felling was the most productive system component, being 98%, 37% and 88% (case studies 1 to 3 respectively) more productive than the bottleneck. System bottleneck for case studies 1 and 3 was extraction, and processing for case study 2.
The number of stems bunched, number of stems shovelled, wind throw interference and machine position shift affected felling cycle time. For every stem bunched, average productivity decreased by 35% (24m³/PMH) and 21% (20.9m³/PMH) for case studies 2 and 3 respectively. Every additional stem shovelled reduced felling productivity by 7.4m³/PMH for case study 2. Haul distance, the number of stems extracted and site factor affected extraction productivity. Haul distance and the number of stems extracted had significant impact on hourly productivity for all case studies. Site factor affected hourly productivity by 6.9m³ and 56.7m³ for case studies 1 and 3 respectively, largely attributed to the cable system employed and ground conditions. Processing was affected by the number of logs cut per stem and if delimbing occurred. Delimbing and each additional log processed, decreased productivity by 16% and 14% respectively.
These three case studies showed that mechanised systems are often not well balanced and result in system components being underutilised. Companies can consider task strategies, or machine sharing between systems to minimise the effect on cost.