Spar Mooring
Taut Mooring
The mooring system for the spars built till date consists of a chain-wire-chain taut catenary system. A "taut" mooring is defined as one in which the anchor loads have an uplift component for all load condition, i.e. the anchor chain or wire never lies on the seabed.
The spar motions are small enough, even in the 100-year hurricane, that the taut system can be used without synthetic mooring lines. The taut system saves a considerable length of wire and chain needed for a conventional catenary mooring.
Mooring Lines
The platform chain is tensioned using chain jacks or windlasses, which are installed on the periphery of the upper deck of the hull. The chain runs from the chain jack to a fairlead, which is located from up to 350 ft below the mean waterline. The length of platform chain is determined by the amount chain, which needs to be pulled in or paid out to maneuver the spar.
The midsection of the mooring system consists of a spiral strand wire rope or polyester line. For long life the steel strand is typically sheathed with a urethane coating. the lower end is attached to a length of anchor chain. The length of chain and the mooring tension is selected so that the wire will not make contact with the sea bottom except under the most extreme condition.
Anchoring
The anchor chain is connected to a piled or suction anchor which can sustain uplift and lateral loads. The pile padeye is usually about 50 ft. below the mudline, so that the bending moment from the mooring forces is minimized.