Log load securement in forest operations is often performed by using load wrappers or tie-downs that are made from steel cables with sections of chain on one or both ends that secure the logs to the truck or trailer (for the purpose of this article, load wrappers and tie-downs will be referred to as wrappers). Log truck drivers are required to throw wrappers over the log load which can be a challenge for some drivers due to the heavy weight of the wrapper. Performing this task several times a day and for several years can result in shoulder injuries, and the inability to throw wrappers can force drivers to leave the industry. One possible solution to help with this problem is to reduce the weight of the wrappers by replacing the heavy steel cable section with synthetic rope made from ultra-high molecular weight polyethylene (UHMWPE). Synthetic rope is much lighter, weighing between 1/6 and 1/8 the weight of steel cable.
In the first study performed in 2006, FPInnovations raised concerns with regard to the strength of UHMWPE rope. The study found that the rope’s strength decreased with use. With new rope technologies and the benefit that these ropes can provide to the industry and drivers, FPInnovations’ Transportation group decided to initiate a new study in 2017. The focus of this study was to verify the findings from the previous study and to better understand why the loss in strength occurs. If loss of strength continued to be a problem, then FPInnovations would suggest options to mitigate these losses.
The results from this study showed that loss of strength continued to be a problem. Damage such as abrasion, knots, and broken strands significantly decreased the rope’s strength, to the point where it was unsuitable for use and had to be removed from service. The study also found that dirt and abrasion appear to be contributing factors to the loss of strength.
FPInnovations recently initiated Phase 2 of this project. This phase tried to deal with the loss-of-strength problem in two different ways:
- Increasing rope size from 3/8 to 1/2 inch diameter, which increases the safety factor from 5:1 to 8:1. The rope may still incur some loss of strength, but the larger rope may still retain enough strength to safely secure the log load.
- Trying a new type of rope consisting of a UHMWPE core with a polyester jacket. The core is slightly larger than those used in the 2017 study, and the addition of the outer jacket should protect the inner rope core from abrasion and dirt contamination.
Both of these wrapper types are currently being field tested by FPInnovations members. Final results will be published by the end of March 2019.
For more information, please consult the technical report entitled Evaluation of Synthetic Ropes for Log Load Securement. You can also contact Rob Jokai, Principal Technologist in FPInnovations’ Transportation group.