The Twisting Effect on the Polyester Ropes during the Deep-Water Mooring Installation

Abstract Whilst the polyester rope is considered to be a matured technology that has been used as a mooring line in the offshore stationkeeping for more than 25 years, nowadays questions regarding synthetic rope constructions and its behavior still arise. One of these queries is related to the possible twisting that can be induced on the rope during the steps of mooring line installations. Although the recommendation of allowable twist can vary between manufacturers, the need to undo the twist to achieve those permitted twist levels could be a significant challenge. So the need to explore the behavior of synthetic ropes under those circumstances to refine the decision-making process is perceived. Industry experience states that the induced twist may affect the synthetic mooring rope performance, i.e., in general the breaking strength and fatigue life can be reduced due to the influence of torsion in the rope construction. However, even after many years, there is no sufficient data that provides the short and long-term impact of twisting spread over the rope. Eventually the questions that should be answered are: what twist level could be permitted without performance loss? What could be the impact regarding the rope performance if the twisting exceeds the recommended by the rope manufacturer? Different rope constructions might affect the twisting loss performance? As manufacturers, it is incumbent upon us to address these questions; otherwise, we will lack test evidence to guide installers in the face of practical situations that demand more than empirical experience during offshore mooring rope installations.