Design of mooring system for a floating production storage and offloading (FPSO) terminal

The use of FPSO for deep sea exploration of hydrocarbon resources has been on trend. Thus, there is a need for ensuring safety with regards to station keeping. However, there are mainly two materials used for mooring line fabrication: Synthetic and Steel. Polyester rope is regarded as a good synthetic option for deep water mooring application. This is as a result of its durability in cyclic tensile fatigue loading. This work compares the end forces between the proposed polyester (with top and bottom chains) rope with that of steel-wire rope from existing systems. From the dynamic analysis of the mooring lines with joint criteria for extremes dominated sea states, the maximum value of the end tension for wire rope is 1668.5722 kN of S-1 (Starboard-1) and the total force is 1668.5799 kN.  Conversely for polyester rope, the maximum value of the end tension is 1130.0381 kN of S-1 and the total force is 1130.0511 kN. This result shows that the force and tension in polyester rope are lower than those of steel wire rope: indicating the effects of reduced vertical (gravity) forces of mooring rope on the FPSO with an associated improvement in horizontal restoring force. The substantial decrease in rope weight reduces the complexity of installation, and increases the vessel’s payload. The latter enhances its capaciousness for crude oil cargo which consequently boosts its economic viability. Also, the fatigue life of the polyester rope is more than that of steel rope because of its low frequency load.