Octabuoy SDM, a compact semi-submersible design for deepwater applications

A new floater concept based on proven technology but combining this technology in a novel way has been designed for Deepwater operation in the Gulf of Mexico and other deepwater locations. The Octabuoy SDM (Shallow Draught, Mooring assisted) is a semi-submersible with 6 design and a tuned mooring system that ensure improved motion characteristics compared to other semi-submersibles. This makes the floater very well suited for accommodating Steel Catenary Risers (SCRs) in the Gulf of Mexico and dry tree solutions for West Africa. Motion results calculated for a typical Gulf of Mexico wave environment, using a coupled time domain approach are confirmed by extensive model testing of the concept, which proves the ability of the proposed concept to accommodate SCRs specifically for the Gulf of Mexico. Because of its relative shallow draught (23m) the platform is less susceptible to vortex induced motions (VIM) in loop currents compared to SPAR and other deep draught floaters. Theoretical considerations and model tests have proved the favorable platform behavior with respect to VIM. The Octabuoy SDM has a favorable topside load-to-hull weight ratio, which makes it a highly competitive solution compared to other semi-submersibles. Another advantage is that the platform may be outfitted and commissioned quayside.