Steel cables with sections of chain on each end are commonly used as wrappers or tie-downs to secure log loads. These load securement devices can be relatively heavy and make it difficult for some drivers to throw over a log load. Some drivers develop shoulder injuries from throwing wrappers, which, in some cases can be career ending. For others, the inability to throw these load securement devices over a load may act as a barrier to entering the industry.
There are a few options that eliminate the need for the driver to throw load wrappers or tie-downs, such as using the loader to drape them over the load. Another option that makes them easier to throw is to reduce their weight, by replacing the heavy steel cable with a light weight rope, such as those made from ultra-high molecular weight poly-ethylene (UHMWPE) fibre. For an equivalent strength rating, these ropes are between 1/6 and 1/8 the weight of steel cables.
FPInnovations (then the Forest Engineering Research Institute of Canada, or FERIC) had previously evaluated synthetic ropes (Michaelsen, Careau; 2006) and found that, after a few months of use their breaking strength dropped significantly. From the observations made during this study, the apparent causes for this degradation appeared to be from abrasion; both external (from the logs) and internal (from dirt intrusion amongst the fibres). The concerns raised from this research prevented FPInnovations from recommending their use to members. However, increased focus on driver safety and retention, coupled with their increased use in some areas, led FPInnovations in 2014 to undertake another project evaluating these ropes for load securement.
New tie-downs and load wrappers were put into service, and periodically removed for break testing to determine how their strength changed with use. Ropes from three different suppliers were used and were taken to Cortland Ltd. in Anacortes, Washington for destructive break testing.
The results from these break tests, as did the earlier FERIC study, showed that the strength of the UHMWPE ropes decreases fairly quickly with use. This is a significant finding that users of synthetic rope need to be aware of. Continuing to use wrappers or tiedowns made from synthetic rope without adequately accounting for their decrease in strength is not recommended.
Should users continue to use these ropes, following the manufacturers’ inspection guidelines will ensure that damaged or weakened ropes are removed from service. However, this alone will not ensure that the ropes retain adequate strength required to meet the requirements of the cargo securement standards. To help mitigate the loss in strength, it may be worth considering using a larger diameter rope, by up-sizing the rope by 1 to 2 sizes, as was suggested by the manufacturer upon seeing the results from this study. However, selection of the appropriate diameter rope for the load retention application requires careful consideration. Further work is required to determine how the strength of larger diameter rope used as log tie-downs or wrappers changes with use, and to determine if using larger diameter ropes is a viable option for log load securement. The manufacturer also suggested that minimizing dirt and sand contamination will slow the rate at which the rope loses its’ strength.
For more information on this study, please consult FPInnovations’ Technical Report “Evaluation of Synthetic Ropes for Log Load Securement” or contact Rob Jokai, Principal technologist of FPInnovations’ Transport and Energy group, at email@example.com or 604 222-5694.