Wear and Fatigue of Nylon and Polyester Mooring Lines1

Wear and fatigue in synthetic fiber lines depend on a multitude of mechanisms, including cumulative creep to rupture, hysteretic heating due to cyclic loading of filaments or to relative displacement of structural rope elements, internal wear caused by relative movement between yarns or strands, and external abrasion against deck hardware or rough surfaces. Studies undertaken to evaluate fiber, yarn, and rope responses to each of these mechanisms, singly or in combination, vary significantly with the test conditions including cyclic load level (both axial and transverse), cyclic strain level, and ambient conditions, i.e., temperature and moisture content (whether dry or wet in fresh water or salt). Cyclic load limits depend on wave height, wind velocity, and mooring line dimensions and properties. The relative durability of nylon versus polyester lines is considered as the lines are subjected to tensile cycling under storm conditions. While tensile fatigue as a creep phenomenon is operative over the free ...