Patent ID: 8251003

Claim:
A buoyant structure ( 10 ) for petroleum drilling, production, storage and offloading, comprising: a hull ( 12 ) defining a vertical axis ( 100 ) whereby said hull ( 12 ) is characterized by circular horizontal cross-sections at all elevations, said hull characterized by an upper cylindrical portion ( 12 b ), an upper frustoconical portion ( 12 c ) directly connected to the bottom of said upper cylindrical portion ( 12 b ) so as to have inward-sloping walls at a first angle (α) with respect to said vertical axis ( 100 ) between 10 and 15 degrees, a lower frustoconical portion ( 12 d ) disposed below said upper frustoconical portion ( 12 c ) and having outward-sloping walls at a second angle (γ) with respect to said vertical axis ( 100 ) between 55 and 65 degrees, a lower cylindrical portion ( 12 e ) directly connected to the bottom of said lower frustoconical portion ( 12 d ); a planar horizontal keel ( 12 f ) defining a lower hull diameter D 1 , and a generally horizontal main deck ( 12 a ); wherein said upper vertical wall section ( 12 b ) defines an upper hull diameter (D 2 ), said upper tapered wall section ( 12 c ) abuts said lower tapered wall section ( 12 d ) at a hull neck diameter (D 3 ), the height (h) of said hull ( 12 ), defined from said keel ( 12 f ) to said main deck ( 12 a ), is less than said hull neck diameter (D 3 ), said lower hull diameter (D 1 ) is the largest diameter of said hull, said hull neck diameter (D 3 ) is the smallest diameter (D 3 ) of said hull, said hull neck diameter (D 3 ) is between 75 and 90 percent of said upper hull diameter (D 2 ), and said lower hull diameter (D 1 ) is between 115 and 130 percent of said upper hull diameter (D 2 ); and wherein said structure ( 10 ) defines a center of gravity and a center of buoyancy, said center of gravity located below said center of buoyancy.