Abstract: Flexible hang-off arrangement is provided for a catenary riser suspended from an offshore or inshore platform, which includes floating or fixed platforms, vessels or/and buoys. The bending loads in the top segments of the said riser are reduced by incorporating a pivot at the riser hang-off. Pressure containing welded, bolted, rolled or swaged pipe spools transfer fluids, including hydrocarbons between the riser and the platform. Along significant spool lengths the tangents to the center lines of said spools are orthogonal to and offset from the tangent to the center line of the riser at the hang-off. The said pressure containing spools include arbitrary looped, spiral and helicoidal designs that are subject to torsion.

Abstract: A tendon is assembled in a horizontal orientation using connectors or by welding at a weld station on a barge or other vessel located at or near the installation site of a tension leg platform. During assembly, the tendon is pulled away from the assembly vessel and tensioned by a tug or offshore work vessel. When fully assembled, the tendon may be up-ended in a manner similar to a wet-towed tendon, and then either pre-installed using floats or passed over to a TLP which is on-site and ready to receive tendons.

Abstract: A gimbal that provides for passive vertical latching and unlatching of a Cold Water Pipe (CWP) in a floating vessel such as an Ocean Thermal Energy Conversion (OTEC) facility is sealingly connected to a cold water sump on the floating vessel. The CWP gimbal is capable of reacting all static and dynamic forces of the suspended CWP at angles on the order of +/?20 degrees while remaining sealed at high differential pressures.

Abstract: A tendon is assembled in a horizontal orientation using connectors or by welding at a weld station on a barge or other vessel located at or near the installation site of a tension leg platform. During assembly, the tendon is pulled away from the assembly vessel and tensioned by a tug or offshore work vessel. When fully assembled, the tendon may be up-ended in a manner similar to a wet-towed tendon, and then either pre-installed using floats or passed over to a TLP which is on-site and ready to receive tendons.

Abstract: A mooring system for offshore vessels uses a chain stopper within a preset mooring line. The chain stopper has means for attaching a removable hydraulic chain jack actuator which may be used to stroke the chain through the stopper assembly while both the stopper and the mooring line remain under load.

Abstract: A tendon is assembled in a horizontal orientation using connectors or by welding at a weld station on a barge or other vessel located at or near the installation site of a tension leg platform. During assembly, the tendon is pulled away from the assembly vessel and tensioned by a tug or offshore work vessel. When fully assembled, the tendon may be up-ended in a manner similar to a wet-towed tendon, and then either pre-installed using floats or passed over to a TLP which is on-site and ready to receive tendons.

Abstract: A floating, semi-submersible offshore drilling vessel has a blowout preventer located on the semi-submersible instead of on the seabed. The mud return housing is attached directly to the blowout preventer without the use of a slip joint. This configuration allows for a significantly reduced drill floor height and, consequently, a lower vertical center of gravity for the rig.

Abstract: A floating, offshore drilling and/or production platform such as a tension leg platform, semi-submersible, spar or the like is equipped with a ballast tank system that comprises the traditional tank and a shaft that runs typically vertically from top-of-hull level to the top of the tank. This shaft is large enough to allow the ballast pipe, sounding lines, instrumentation piping, etc. to be installed within it. In certain embodiments, the shaft itself functions as a vent line.

Abstract: Flexible hang-off arrangement is provided for a catenary riser suspended from an offshore or inshore platform, which includes floating or fixed platforms, vessels or/and buoys. The bending loads in the top segments of the said riser are reduced by incorporating a pivot at the riser hang-off. Pressure containing welded, bolted, rolled or swaged pipe spools transfer fluids, including hydrocarbons between the riser and the platform. Along significant spool lengths the tangents to the center lines of said spools are orthogonal to and offset from the tangent to the center line of the riser at the hang-off. The said pressure containing spools include arbitrary looped, spiral and helicoidal designs that are subject to torsion.

Abstract: A hawser system between a tension leg platform (TLP) and another vessel employs two lines, oriented in a V-shape, to restrict the vertical motion of a hawser near the bow of the other vessel which may be a semi-submersible tender assisted drilling vessel (TAD). Drilling operations may be performed from the TLP while the semi-submersible provides the supporting services for the drilling operation, e.g. drilling fluid and drill pipe storage. The restricted vertical motion of the hawsers significantly reduces the possibility of the hawsers contacting each other. A hawser system according to the invention couples the semi-submersible TAD vessel to the TLP and may be implemented without passing the hawsers through sheaves.

Abstract: A design and construction method reduces the amount of structural material (e.g., steel) required when applying the corrosion allowance to the design of floating offshore structures. The (hull) structural elements involved are typically flat or curved panels where at least one side is wet, e.g.; inside a ballast tank or exposed to seawater. The method minimizes the area to which the largest corrosion allowance is applied. One principle of this method is to have a maximum of one wet side for each hull watertight plating element. The stiffening of this hull structural element is applied to the dry side, i.e., the side that requires the lesser amount of corrosion allowance. Practice of the method typically results in a hull design wherein ballast tanks do not share a common structural element with either another ballast tank or the hull external shell.

Abstract: A floating, offshore drilling and/or production vessel has supports for steel catenary risers mounted on a riser keel guide. This allows the riser attachment points to be located closer to the vessel's center(s) of rotation of pitch, roll and yaw thereby decreasing roll-, pitch- and yaw-induced displacements of the risers.

Abstract: A floating vessel is equipped with perforated plates which exhibit both an added-mass effect and a damping effect. The addition of porosity to an added mass plate phase-shifts the added mass force so that it becomes at least partially a damping force which does not depend on large velocities to develop a large damping force. Preferred porosity is in the range of about 5% to about 15% of total plate area. A semi-submersible vessel may have damper plates fitted between its surface-piercing columns, within a support grid in the area between the pontoons and/or extending from the sides of its pontoons. A truss spar offshore platform may have damper plates installed within its truss structure intermediate its hull and ballast tank. Drill ships and similar vessels may be equipped with damper plates extending from the sides of their hulls to reduce both heave and roll.

Abstract: A driven pile anchor suitable for securing a tendon of a tension leg platform to the seafloor is supplemented with added weight. A load frame is added to the individual pile to accommodate ballast weights. Pre-manufactured ballast weights are placed on the frame to increase the holding power of the pile anchor system. In a second embodiment, the pile is intentionally plugged and installed with the plug intact. Pre-manufactured ballast weights are then placed inside the pile and may be held in place by gravity. In a third embodiment, the pile is a conventional driven friction pile installed with an underwater pile hammer. The pile is initially open but subsequently evacuated and intentionally plugged near its pile tip. Pre-manufactured ballast weights are placed inside the pile to increase its holding capacity. The first embodiment may be retrofitted to existing, driven-pile anchor systems.

Abstract: A sleeve, suitable for temporary use on a tendon for a tension leg platform (TLP) equipped with a bottom tendon connector, covers selected portions of the tendon and bottom tendon connector so as to provide an outer surface having fewer and/or less pronounced discontinuities in the outer diameter of the assembly. This improves the handling characteristics of the assembly in pipe tensioning devices and the like. The sleeve may be in form of split halves which may be held together around the selected portion of the tendon by band straps. The sleeve may be removed subsea by cutting the band straps using an ROV. In certain embodiments, the sleeve comprises an open frame arrangement of contoured segments held in a spaced-apart configuration by bolt-together or hinged clamps. The sleeve may provide an annular space between the tendon and the sleeve which may be used to house a flotation device.

Abstract: An apparatus for installing means to supply cold water from depth to a floating vessel comprises a template having a plurality of receptacles for receiving a plurality of vertically-oriented Cold Water Pipes. A method for installing a plurality of Cold Water Pipes at a floating, offshore Ocean Thermal Energy Conversion facility comprises: lowering such a template to the seafloor; inserting vertically-oriented pipes into the receptacles on the template; providing sufficient buoyancy near the top of the pipe to maintain the pipe in a generally vertical state; positioning a floating vessel having receptacles configured to engage the upper ends of the pipes over the template; raising the template with the inserted pipes from the seafloor until the upper ends of the pipes engage the receptacles; and, locking the pipes in the receptacles such that the pipes are in fluid communication with a Cold Water Sump on the floating vessel.

Abstract: A hull, suitable for use as a tension leg platform (TLP) or as a semi-submersible vessel, comprises columns having a generally polygonal transverse cross section at least one axis of which is generally radially aligned with the central vertical axis of the hull. Buoyant, subsurface pontoons interconnect adjacent columns. The pontoons are generally rectangular in cross section and the outboard, generally vertical surface of each pontoon is connected to a side surface of an adjoining column at a location which is substantially inboard of the outermost face of the column. In certain embodiments of the invention, tendon porches (configured to receive the upper tendon connectors of a TLP) are mounted to the outboard surface of one or more pontoons.

Abstract: A hull, suitable for use as a tension leg platform (TLP) or as a semi-submersible vessel, comprises four columns arranged in a rectangular planform with each column having a generally polygonal transverse cross section at least one axis of which is generally disposed at a 45-degree angle to a line between the center points of adjacent columns. Buoyant, subsurface pontoons interconnect adjacent columns. The pontoons are generally rectangular in cross section and the outboard, generally vertical surface of each pontoon is connected to a side surface of an adjoining column at a location which is substantially inboard of the outermost face of the column. In certain embodiments of the invention, tendon porches (configured to receive the upper tendon connectors of a TLP) are mounted to the outboard surface of one or more pontoons.

Abstract: A semi-submersible vessel comprises pontoons having a generally five-sided transverse cross section. In the case of a 4-sided semi-submersible, the columns may be arranged in a generally rectangular form with a column at each corner of the rectangular form, each column having with four sides disposed at a right angle to at least one adjacent side and a fifth side on the exterior of the generally rectangular form disposed at 45 degrees to each adjacent side.

Abstract: A floating vessel is equipped with perforated plates which exhibit both an added-mass effect and a damping effect. The addition of porosity to an added mass plate phase-shifts the added mass force so that it becomes at least partially a damping force which does not depend on large velocities to develop a large damping force. Preferred porosity is in the range of about 5% to about 15% of total plate area. A semi-submersible drilling rig may have damper plates fitted between its surface-piercing columns and/or extending from the sides of its pontoons. A truss spar offshore platform may have damper plates installed within its truss structure intermediate its hull and ballast tank. Drill ships and similar vessels may be equipped with damper plates extending from the sides of their hulls to reduce both heave and roll. In certain embodiments, the damper plates are retractable so as not to interfere with docking and to reduce drag while the vessel is underway.