Offshore drilling structure

An offshore drilling structure, comprising a hull adapted to float on the water surface, during transit, a working platform upon which drilling equipment may be supported, legs supporting the platform above the hull, said hull and legs having ballast compartments which permit the hull to be raised and lowered within the water, when at a drilling site, said platform and hull having openings therethrough to pass drilling equipment between the platform and the subsurface, the bottom of the hull having a recessed area about the opening in the hull, said hull having holes connecting said recessed area with its top, and a thruster mounted within each hole for reducing the pressure within the recessed area so that, when the hull is supported on the subsurface, soil from the subsurface may be drawn into the recessed area.

An offshore drilling structure, comprising a hull adapted to float on the water surface, during transit, a working platform upon which drilling equipment may be supported, legs supporting the hull above the hull, said hull and legs having ballast compartments which permit the hull to be raised and lowered within the water, when at a drilling site, said platform and hull having openings therethrough to pass drilling equipment between the hull and the subsurface, said hull having holes therein connecting the top and bottom therein and arranged substantially symmetrically about the opening in the hull, a thruster mounted with each hole with its axis of rotation arranged substantially coaxially thereof, and means for selectively reversing the axial direction in which thrust from each of the thrusters is effective.

An offshore drilling structure, comprising a hull adapted to float on the water surface, during transit, and having ballast compartments which permit it to be raised and lowered within the water, when at a drilling site, a working platform supported above the hull, said platform and hull having openings therethrough to pass drilling equipment between the platform and the subsurface, the bottom of the hull having a recessed area about the opening in the hull, said hull having first and second sets of holes connecting said recessed area with its top, a thruster mounted within each hole of the first set for reducing the pressure within the recessed area so that, when the hull is supported on the subsurface, soil from the subsurface may be drawn into the recessed area, and a variable orifice arranged in each hole of the second set so as to supply said thrusters with a continuing supply of water.