Patent ID: 7413384

Claim:
A deep draft semi submersible structure having a center of gravity below a center of buoyancy comprising: at least three vertically oriented buoyant columns having a top end and a bottom end to extend downwardly into water, each column having a shape selected from the group: square, cylindrical, rectangular, triangular, each having at least one ballasted compartment, wherein the vertically oriented columns are spaced apart a distance of at least 1.5 times a diameter of one column to reduce vortex induced vibration amplitude (VIV); at least two connecting structural sealed trusses for maintaining structural positioning of the columns, wherein the trusses are disposed below sea level and wherein the trusses are connected to the columns to minimize hydrodynamic wave action and the trusses are adapted to transfer shear loads between the vertically oriented buoyant columns while remaining transparent to wave and ocean current motion; at least one strake disposed around each column to further minimize vortex induced vibration amplitude, wherein the strake has a width substantially equal to 0.1 times the column diameter; a plurality of risers connections; a deck disposed on the columns forming a self righting, and self upending semi-submersible structure having a center of gravity below a center of buoyancy, floatable in a horizontal position when completely assembled, and having a draft between 300 and 550 feet; and at least one horizontal plate supported by a truss engaging the bottom ends of the columns for increasing mass and minimizing vertical motion of the structure.