Patent ID: 6206614
Filing Date: 2001-03-27
Classification: B63B,E21B

Abstract:
A catenary moored spar-like floating offshore drilling/producing structure having its center of gravity below its center of buoyancy and its natural period longer than the peak wave energy period, comprising:a. a plurality of vertically oriented buoyant columns in closely spaced arrangement adjacent each other;b. drilling and production risers located within the interior portion of the multiple column assembly;c. a plurality of horizontal plates that extend to the perimeter of the column assembly and that connect the lower portion of the column assembly together and fix the lower portion of each column's horizontal position relative to each other and are sized to entrap a sufficient mass of water to increase the natural heave period of said structure such that it is longer than the peak energy wave period, said plates being spaced along the length of said column assembly and located below the water level at a distance below significant wave energy;d. a plurality of vertical plates connecting the upper portion of the column assembly together and fixing this portion of each column's vertical position relative to each other, said vertical plates being located in the wave zone and extending above and below the still water line so that the risers are protected from wave forces; ande. vertical plates connecting the lower portions of the columns together and fixing the vertical relationship of the columns relative in the horizontal to each other and providing additional mass to the structure in this region to reduce surge motion.