A steel suction anchor, 36" OD x 33" ID is being deployed as part of a mooring spread for a floating production platform located in 825 ft of water. The top of the anchor consists of a 1.1/2" thick steel cap into which a flapper type valve is incorporated. The sea water density is 8.6 ppg. The anchor has been lowered to the seabed (the soils below which are essentially impermeable and homogeneous) and the initial penetration is 5 feet due to the suction anchor's own buoyed weight.

(a) After closing the flapper valve and connecting the ROV pump, how much water should be evacuated from the anchor to achieve one foot of penetration into the seabed?

(b) If all resistance to downward movement of the anchor can be equated to the frictional resistance between the anchor's cylindrical surfaces and the seabed stratum, and if this resistance averages 400 lb/ft2, what length of suction anchor will be required so that the top of the anchor is 3 ft above the seabed at the end of the operation?

Caisson Mooring Cable Padeye Applied Load Insertion under Insertion under Completed self weight suction pressure installation Fig. 1. Installation and loading of a suction caisson anchor.