Abstract: An apparatus and method reducing the motions of a marine structure anchored in a body of water over a hydrocarbon drilling or production site using a spread type mooring system. The structure's motions are reduced by increasing the amplitude and altering the dynamic tension variation of the mooring system, without affecting the static response of the mooring system under static loads.

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 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 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.