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, offshore drilling and/or production platform is equipped with a rail-mounted transport system that can be positioned at a plurality of selected positions over the well bay of the vessel. The transport system can move a drilling riser with a drilling riser tensioner system and a blowout preventer from one drilling location to another without removing them from the well bay of the vessel. Using the transport system, the drilling riser is lifted just clear of a first well head and positioned over an adjacent, second well head using guidelines. The transport system may then move the upper end of the drilling riser (together with its attached tensioner and BOP) to a second drilling location. A dummy wellhead may be provided on the seafloor in order to secure the lower end of the drilling riser without removing it from the sea while production risers are being installed.

Abstract: A method and apparatus for replacing a tendon flex bearing on a tension leg platform includes installing a tendon tensioning tool on the Length Adjustment Joint (LAJ) of a tendon and providing a supplemental buoyancy module on the tendon. The tendon tensioning tool is used to disengage the slips from the top tendon connector. The buoyancy of the supplemental buoyancy module may then be adjusted to support the tendon whereupon the tendon tensioning tool may be disengaged permitting removal and replacement of the tendon flex bearing. Following installation of the new (or refurbished) flex bearing, the steps of the procedure may be reversed to return the tendon to its normal operating state. In certain embodiments, top clamp actuation means is provided in the tendon tensioning tool for removing slips from the top clamp.

Abstract: A top-tensioned riser system comprises a substantially vertical riser extending upward from the seafloor; a conductor surrounding an upper portion of the riser in spaced-apart relation; a coaxial keel guide surrounding a lower portion of the conductor; a tensioner attached to the conductor and the riser; a keel guide support structure attached to the keel guide and connected to the keel of a dry-tree, semi-submersible vessel; and, a keel joint centralizer attached to the riser proximate the keel guide and sized to prevent radial movement of the riser relative to the conductor. Side loads on the riser (such as those arising from displacement of the vessel from its nominal position or currents acting on the riser) are reacted from the riser to the conductor via the keel joint centralizer and then to the keel of the vessel via the keel guide.

Abstract: A floating, offshore drilling and/or production platform is equipped with a rail-mounted transport system that can be positioned at a plurality of selected positions over the well bay of the vessel. The transport system can move a drilling riser with a drilling riser tensioner system and a blowout preventer from one drilling location to another without removing them from the well bay of the vessel. Using the transport system, the drilling riser is lifted just clear of a first well head and positioned over an adjacent, second well head using guidelines. The transport system may then move the upper end of the drilling riser (together with its attached tensioner and BOP) to a second drilling location. A dummy wellhead may be provided on the seafloor in order to secure the lower end of the drilling riser without removing it from the sea while production risers are being installed.

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 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 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 disconnectable buoyant turret mooring system for an FPSO is vulnerable to damage from collisions between the buoy and the buoy turret cage during mating and de-mating operations. It is therefore desirable that the buoy separate quickly from the turret of the FPSO vessel during a disconnect operation. A buoy turret cage is provided with a certain degree of porosity that allows a flow of seawater from the outside of the receptor to the inner surface of the receptor. Introducing water in this way relieves the suction forces and allows for a quicker separation of the buoy from the turret of the FPSO vessel, minimizing the time during which an uncontrolled collision between the buoy and the FPSO vessel is most likely. Filling a portion of the turret above the mooring buoy with water prior to releasing the buoy also decreases the separation time.

Abstract: A top-tensioned riser (TTR) is supported by a tensioning system on the deck of a floating platform. The tension ring may include an elastomeric layer which permits small angular and lateral displacements of the tension joint. The tension joint comprises a tapered section to resist the bending moment and shear imposed by the vessel's motion. The riser tension joint may be supported laterally by rollers below the tension ring. The rollers react on the tapered section when the riser strokes up and down. The tapered section may be engineered to maximize the use of the tension joint, and to reduce bending moment and shear loads imposed on the tensioning system. In certain embodiments, there may be a small gap between the rollers and the tapered section. In certain other embodiments, the rollers may be spring-loaded to increase the stability of surface equipment on the upper terminus of the riser.

Abstract: A floating, offshore drilling and/or production platform is equipped with a rail-mounted transport system that can be positioned at a plurality of selected positions over the well bay of the vessel. The transport system can move a drilling riser with a drilling riser tensioner system and a blowout preventer from one drilling location to another without removing them from the well bay of the vessel. Using the transport system, the drilling riser is lifted just clear of a first well head and positioned over an adjacent, second well head using guidelines. The transport system may then move the upper end of the drilling riser (together with its attached tensioner and BOP) to a second drilling location. A dummy wellhead may be provided on the seafloor in order to secure the lower end of the drilling riser without removing it from the sea while production risers are being installed.

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: 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 disconnectable buoyant turret mooring system for an FPSO is vulnerable to damage from collisions between the buoy and the buoy turret cage during mating and de-mating operations. It is therefore desirable that the buoy separate quickly from the turret of the FPSO vessel during a disconnect operation. A buoy turret cage is provided with a certain degree of porosity that allows a flow of seawater from the outside of the receptor to the inner surface of the receptor. Introducing water in this way relieves the suction forces and allows for a quicker separation of the buoy from the turret of the FPSO vessel, minimizing the time during which an uncontrolled collision between the buoy and the FPSO vessel is most likely. Filling a portion of the turret above the mooring buoy with water prior to releasing the buoy also decreases the separation time.

Abstract: A flexible element in a basket-like structure supports a Steel Catenary Riser (SCR) on a subsurface buoy or “artificial seabed.” A riser collar transfers the tension load of riser to a compressive load on the radial bearing. Relative motion between the subsurface buoy and the riser is accommodated by the flexible element. A flexible jumper is connected to the riser for fluid transfer. Motions of the riser relative to the subsurface buoy are accommodated by the flexible jumper. In this way, a transition from an SCR to a flexible jumper may be accomplished without the need for either a stress-joint or a flex-joint.

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 top-tensioned riser system comprises a substantially vertical riser extending upward from the seafloor; a conductor surrounding an upper portion of the riser in spaced-apart relation; a coaxial keel guide surrounding a lower portion of the conductor; a tensioner attached to the conductor and the riser; a keel guide support structure attached to the keel guide and connected to the keel of a dry-tree, semi-submersible vessel; and, a keel joint centralizer attached to the riser proximate the keel guide and sized to prevent radial movement of the riser relative to the conductor. Side loads on the riser (such as those arising from displacement of the vessel from its nominal position or currents acting on the riser) are reacted from the riser to the conductor via the keel joint centralizer and thence to the keel of the vessel via the keel guide.

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.