Since first installed at a water depth of 4,660 feet in 1997, polyester mooring systems have now been used on floating platforms in the Gulf of Mexico (GOM), Brazil and other regions. The Mad Dog Spar was the first floating production system (FPS) with permanent deepwater polyester moorings in the GOM. After the Mad Dog Spar, the deepest water depth is 7,800 feet in which a polyester mooring system was installed on the Perdido Spar. The polyester mooring systems have performed favorably, e.g., in the GOM, experiencing hurricanes without incident. The polyester rope in general is more advantageous than steel wire in deeper water due to reduced weight (and tension), high strength, durability (better fatigue and no corrosion), and improved floater global performances (less offset, etc.). Moreover, while a floating production platform is designed to support riser systems, fatigue damage of risers due to Vortex Induced Motions (VIM) of the platform are important design drivers particularly in the GOM. The polyester mooring system has a higher restoring force in horizontal (thus a higher lateral stiffness) in currents resulting in a significantly better fatigue performance (less current bins with VIM lock-in) than the steel mooring system does.
The paper herein presents a comparative study with two kinds of mooring systems (polyester ropes and steel wires) for the same platform. Differences between the polyester and steel mooring systems are evaluated for various aspects, such as the mooring system configuration and performance, installation risks, operations, and impact on hull and riser system design and performance. The results also indicate cost savings for the polyester mooring equipment and the overall production system.