Large Column-Supported Floating Platforms

Abstract

Deep draft spar buoys provide the maximum decoupling from surface waves of any floating structures. The research vessel FLIP, developed at the Scripps Institution of Oceanography (SIO), demonstrated how the problems of transporting these very long buoys could be solved by towing them in a horizontal attitude and then ballasting them to the vertical position at the operational site.

As slightly larger stable platforms were required, particularly for offshore petroleum exploration, the semi-submersible concept was developed. By placing the major axis of the flotation volume in the horizontal, rather than the vertical direction, the need for rotation was eliminated at the cost of greater response to waves and higher structural loads.

As the size of the floating platform and its anticipated time on station are increased, and the need for mobility decreased, cost and reliability considerations suggest that the vertical column supported floating platform may again become the design of choice. The elements of such a large structure are amenable to serial production using highly automated shipyard techniques. They are then towed, or alternately barge transported, to the construction site and erected. The remarkable stability of the column structures facilitates joining them at sea into very large structures.

The development of this concept over a twenty year period at SIO is described. Following the success of FLIP, a multiple column unit was designed. Numerical and wave tank modeling preceded a 10 m draft (1/8 scale) system test at sea in which multiple elements were transported and joined to form a stable platform. Various applications are envisioned including airfields or sites for at-sea processing of sea floor minerals.