Abstract: A marine structure situated in a seabed having mooring means designed to provide resistance to the environmental forces acting on the structure. Weights are attached to the mooring means at a distance above the seabed so that the weights do not touch the seabed during normal operating conditions. When extreme environmental loads move the structure a certain distance leeward of its original locations, the weights on leeward mooring means contact the seabed, significantly and immediately increasing the restoring force provided by the mooring means.

Abstract: The semi-submersible platform comprises a submersible lower hull including a plurality of spaced-apart hull segments. A wave-transparent stabilizing superstructure extends from the lower hull. An upper hull is supported by the superstructure. A wellhead system is suspended from the platform. A catenary mooring system moors the platform to the seabed, and plurality of risers connect the individual wellheads on the platform to the wellbores in the seabed.

Abstract: The floating structure comprises one or more catenary mooring cables for anchoring the structure to the seabed. An extensible dynamic tensioner system is provided for maintaining a predetermined dynamic tension in each mooring cable, as the structure responds to cyclic wave forces, and for increasing the natural periods of oscillation of the pitch, roll, heave, surge, sway, and yaw motions of the moored floating structure by reducing the spring stiffness of the mooring system. A motion damping system is coupled between the dynamic tensioner system and the structure for damping the linear and angular displacements of the structure relative to the tensioned cables. The damping system selectively applies frictional forces against a movable member in the tensioner system. The movable member does not move relative to the cables.

Abstract: The floating structure has limited heave oscillations. A long member has a lower end coupled to the seabed. An extensible tensioner is coupled between a platform deck and the upper end of the long member. The tensioner suspends the upper end of said long member and applies a predetermined tension thereto. The tensioner includes anti-heave force-exerting means for exerting downward-acting forces on the floating structure.

Abstract: The floating structure has a structural frame and a long member which has a lower end anchored to the seabed. The structural frame has limited heave motion relative to the long member. An extensible tensioner is between the frame and the long member. Mechanical brakes apply braking forces against the long member only when the floating structure heaves up. The brakes are inactive when the floating structure heaves down.

Abstract: The semi-submersible, deep-drafted platform includes a fully submersible lower hull, and a plurality of stabilizing columns which extend from the lower hull to an upper hull. At least one column has means adapted to reduce the water plane area within a portion of the dynamic wave zone of the column and to increase the natural heave period of the platform.

Abstract: The mobile marine drilling structure is of the submersible type for operation in ice-covered waters. The structure comprises a base for placing the structure on the sea bed, a hull extends from the base, and a deck is supported by the hull. The deck is located above the water line for conducting drilling operations. The hull has an internal frame assembly including ballast tanks, and external wall sections at different inclinations to the horizontal to engage and break up the moving ice masses encroaching on the hull. These external wall sections include a plurality of matching polygonal, frusto-pyramidal, apex-up and apex-down walls extending above the base, and two transitional wall sections to provide two inflection points to the hull.

Abstract: The emergency well-control vessel is capable of being moved above an offshore live oil or gas well, over which all normal controls have been lost. The vessel carries special purpose equipments and specially trained personnel for the purpose of bringing the erupted well under control, thereby stopping the pollution of the water body with the ejected formation fluids which form a so-called "plume". Such equipment is adapted to allow the vessel to move over and continue to dispel the plume while simultaneously attempting to regain control of the well. In one aspect, control of the abandoned wellhead and blowout preventers is established with divers working from the vessel or from an auxiliary craft. After control of the blowout preventer stack is confirmed and the same is fully operational, a kill string is lowered through the open blowout preventer stack and as deep down into the well as necessary.

Abstract: The method involves erecting a very large-diameter column from a plurality of buoyant columnar members at a selected site in a body of sea water. Each columnar member is floated erect to the site. The first or lowermost columnar member is pulled down and fully submerged to a predetermined depth over the site. The second columnar member is then positioned directly over the lowermost member. The lowermost member is allowed to move up and lift the second member out of the water. The two columnar members are securely interconnected to each other in a watertight fashion. The partial column is then pulled down to a fully submerged condition and the third columnar member is positioned directly over the second member. The partial column is allowed to move up and lift the third member out of the water. A secure watertight connection is made between the third columnar member and the second columnar member.