Dyneema® has become the ‘Gold Standard’ for performance running rigging. However, with new grades of Dyneema® being introduced and different treatments available, the decision as to which core is best can often be confusing.
SK75 – for many years the strongest Dyneema® grade and the standard material that everybody understands. Thanks to new and improved grades, SK78, 90 and 99 things have gotten even better.
DM20 – has slightly lower tenacity than SK78, but has one major advantage in that it exhibits virtually zero creep. Used mainly for static load applications such as standing rigging.
Creep can often have a negative effect on a rope’s performance and strength, when ropes are subjected to high loads for extended periods. Here Marlow explains…
– Initial loading will result in elastic extension. This is immediate upon loading and is immediately recoverable upon release of the load (elastic contraction).
– After the elastic extension of the initial loading the rope will experience what is known as viscoelastic extension. This is further extension over time and is fairly limited. Unlike elastic stretch, viscoelastic stretch will only recover slowly over time once the load is released.
– Finally there is creep, which is permanent, non-recoverable and time dependent. Creep occurs at the yarn molecular level when the rope is under constant load.
– Once the load is released and elastic and viscoelastic extension recovered the rope will ultimately have experienced an element of permanent extension. This is a factor of both creep and ‘bedding in’, which is when individual fibre components in the rope and/or splice settle into their preferred position when under load.
Complete report in Seahorse magazine.
Sailing With Devious, 2014 