WEAR AND FATIGUE OF NYLON AND POLYESTER MOORING LINES

Wear and fatigue in synthetic fiber lines depend on a multitude of mec hanisms, including cumulative creep to rupture, hysteretic heating due to cyclic loading of filaments or to relative displacement of structu ral rope elements, internal wear caused by relative movement between y arns or st:rands, and external abrasion against deck hardware or rough surfaces. Studies undertaken to evaluate fiber, yarn, and rope respon ses to each of these mechanisms, singly or in combination, vary signif icantly with the test conditions including cyclic load level (both axi al and transverse), cyclic strain level, and ambient conditions, i.e., temperature and moisture content (whether dry or wet in fresh water o r salt). Cyclic load limits depend on wave height, wind velocity, and mooring line dimensions and properties. The relative durability of nyl on versus polyester lines is considered as the lines are subjected to tensile cycling under storm conditions. While tensile fatigue as a cre ep phenomenon is operative over the free length of the mooring line, t he more critical location of rope deterioration is at its interactive contact with deck hardware. An ideal mooring system is composed of two segments. The one between the elements of deck hardware (cleats and c hocks) should possess maximum abrasion resistance and high tensile sti ffness. The other segment should possess high tensile compliance so as to minimize cyclic load. levels induced by waves and wind. A review o f yarn/yarn wear tests and rope abrasion tests is provided to form the foundation for recommendations.