Experiences From Handling Mooring Line Polyester Fibre Ropes During Installation and Retrieval

The use of fibre ropes made by synthetic fibres have been used more frequent as the offshore industry is moving towards larger water depths. An important aspect is the effect of handling on the large, but delicate, ropes during installation offshore using tools and equipment that easily can destroy the load bearing capacities of the ropes. In order to get hands on experience in the field large polyester ropes have been used as inserts in catenary mooring lines for Mobile Offshore Units (MODU) working on depths ranging from 80 to 350 meters. The ropes have been integrated in the catenary chain mooring lines both in the suspended part and in the bottom part of the mooring leg thus having been exposed to seafloor clay. Subsea buoy have been attached to the ropes using smaller size fibre ropes in order to lift the mooring lines from the seafloor. The paper will detail how the large fibre ropes have been mobilised and demobilised repeatedly from/to storage drums to/from the installation vessel winch drum. During installation and retrieval the fibre ropes have been installed from the vessels winch drum using regular anchor handling equipment and vessels. When the MODU has been moved between locations some ropes have been retrieved to the vessels winch drums while the others have been used to tow and to keep the units station. Samples of the used ropes are taken and is subjected to a test program in the laboratory in order to document the effect of extensive use and handling and exposure to seabed clay.