A normally un-manned semisubmersible has been developed, consisting of three columns spanning between a deck box structure and a very deep submerged pontoon. The platform, called the EDP (Extended Draft Platform) Buoy, can be used for various applications such supporting a low cost subsea development of a marginal field with controls and power and other surface processes, or serve as a science platform for gathering long term oceanographic, meteorological and geotechnical data. The EDP Buoy is designed to be towed to site in a stable collapsed configuration like a Jack-up MODU by offshore tug supply vessel and/or Anchor Handling vessel, and self-erect with minimal human intervention. The columns and pontoon of the EDP Buoy are raised for construction and installation. When lowered, the structure behaves like a very stable deep draft semisubmersible. It is suitable for very harsh, but ice free, environments and no water depth limit with use of synthetic mooring lines.
The deck box and the pontoon structures are Y-shaped. Within and atop the spacious EDP deck box there is sufficient area to locate processing, power, communications, instrumentation and material handling equipment, and provide sufficient bulk storage space for fuel and other fluids. Multiple risers and umbilicals can be accommodated on the platform. The facilities on the platform can be expanded in the future including adding more equipment, risers and umbilicals.
The configuration and size of the platform lends itself to simple low cost fabrication with rolled steel plate columns, and box girder deck and pontoon. The three leg design also makes for easy self erection. The paper describes the configuration, installation procedure and in-place performance of the EDP Buoy.