Nylon three-strand dock lines, anchor rodes, and mooring pendants are the sailor’s safety net, so to speak, and have been for nearly a century. But as often happens with gear that has stood the test of time, the reliability of this cordage has to some degree given way to a false sense of security. Sun, sea, and salt rob rope of its tenacity, but just how much has never been accurately quantified.
Being skeptics at heart, Practical Sailor testers suspected our old nylon lines were a lot weaker than we thought, and decided to see just how much original oomph an old set of dock lines actually retained over time. In order to take a closer look at this issue of line longevity, we rounded up a set of in-service dock lines with a known history, and enlisted the patient help of Steve Parola and his quality-control team in the lab at New England Ropes.
Our approach was to take the weathered 10- to 12-year-old nylon three-strand line, cordage that for half of its life had been used as part- time dock line, and for the other half, enlisted as full-time (24/7) dock line, tethering a 41-foot sloop to a fixed pier in a very protected cove on the Chesapeake Bay. The nylon had weathered significantly, and chafed noticeably where the lines exited chocks and made contact with cleats. Our plan was to put these lines under increasing tension in laboratory conditions and test them to destruction.
During each test, it was interesting to note that as the nylon’s elastic deformation range was exceeded, filaments began to permanently stretch and the line would not return to its starting length when the load was removed. This is a classic example of what happens when a material exceeds its limit of elastic deformation and moves into the tenuous realm of plastic deformation. As the load was reinstated and continued to increase, there were crackling sounds of intra-strand fila- ment failure, and in several cases, the throw, or length, of the dual ram’s extension was not long enough to break the line in one run. In such situations, the ram was retracted and the permanently stretched line pulled shorter prior to the final test to destruction. The amount of elongation in the tested ropes prior to destruction was impressive, but it was still shorter than the up-to-25-percent elongation that new nylon cordage will exhibit prior to failure.
To read more about our findings, purchase Anchor Chain/Rode from Practical Sailor.
