Polyester Mooring Rope: Length Determination and Static Modulus

Recent deepwater mooring projects using synthetic rope have identified two critical issues which are not adequately addressed in present industry design guidelines. The first issue is proper determination of rope length. A test procedure is presented to determine the relationship between manufactured length and installed length. The installation load history greatly influences the amount of permanent elongation during hook-up. Therefore, accurate length determination depends on testing which simulates the installation load levels experienced by the mooring line. The second issue relates to the static modulus used to predict the offset of a deep draft vessel in a loop current event. The present guidelines provide static modulus values biased by an initial loading to 55% MBL. Testing has shown that the static modulus is dependent upon the amount of permanent elongation during installation. Higher static modulus, resulting in lower vessel offset, can be achieved by permanently stretching the rope during installation