Performance Of Mooring System Tension Members

Abstract

The subject of mooring lines encompasses a broad spectrum of service requirements (water depths, sea states, tensile loadings, and useful service lives) and a wide variety of candidate mooring members (chain, wire rope, synthetic fiber rope, electromechanical cables, or combinations of these elements). For some systems, a suitable mooring line may have a breaking strength of only a few hundred pounds, a length of up to 20,000 feet, and an operational life measured in weeks. In other cases, a mooring line must have a breaking strength of several million pounds, a length of just a few thousand feet, and an operational life measured in decades. A highly elastic mooring line may be required where large amplitude system motions must be accommodated, while an inelastic mooring line may be needed if it is necessary to assure accurate system positioning. Some systems may require that the mooring line survive prolonged cyclic tensile loading, while other systems may be dependent upon the ability of the mooring line to survive repeated bending over sheaves or saddles. To meet these diverse operational requirements, system designers must choose from among a variety of mooring members, each of which has a unique combination of strength, size, weight, elasticity, corrosion resistance, abrasion resistance, and ability to withstand extensive cyclic tension loading or cyclic bending. In nearly all cases, some compromise is required because of conflicting system requirements. This paper discusses some of the important considerations in the selection of a suitable mooring line, reviews certain mooring line characteristics, and describes laboratory testing methods for assessing the suitability of candidate mooring members for specific applications.