Abstract: A jackdown tension leg platform is set forth which may be used for processing a commodity liberated from the ocean floor by one or more wells. The platform includes a closed buoyant hull which houses production equipment and at least one connector disposed on the hull for vertical relative movement. The connector has one end secured to the ocean floor and is moved upwardly relative to the hull to submerge the hull to a depth below the majority of the ocean's hydrostatic forces and, at the same time, tension the connector to hold and stabilize the hull over the wells. Conduits are connected between the wells and the submerged hull and between the hull and the surface. A crew module may be provided above the surface atop the connector with a trunk disposed between the module and submerged hull to provide access therebetween.

Abstract: A gravity-type offshore structure, useful as an offshore drilling platform, e.g., is provided for use in ice-covered waters such as offshore of the Alaskan and Canadian North Slope. The structure is composed of a plurality of floatable and controllably ballastable modules, each of which can be fully submerged. The modules are stackable by selective ballasting and deballasting operations in a suitable sequence to define a mobile offshore structure. The structure is assemblable adjacent a site of use and is floatable after assembly to, from and between successive sites of use. At each site of use the assembled structure is ballasted by sea water to be supported by the sea floor and to have sufficient deadweight, in combination with its support by the sea floor, to stand against ice loads urging the structure laterally of the site. Major ones of the modules preferably are constructed of reinforced concrete arranged within the modules in a honeycomb cellular fashion.

Abstract: A mobile offshore platform has a buoyant and ballastable mat base of substantial horizontal extent. A cylindrical pylon is fixed to and extends upwardly from the center of the base. The pylon has a height greater than the maximum operating water depth of the platform. A positively buoyant deck unit has a central opening through it within which the pylon cooperates. The deck unit is movable vertically along the pylon in response to the operation of jacking mechanisms and cooperating jacking legs located adjacent the corners of the deck unit. The jacking legs are engageable at their lower ends with the base whereby operation of the jacking mechanism causes the deck unit to be moved vertically along the pylon relative to the base. In use, the deck unit is elevated to the top of the pylon after the base is submerged into contact with a sea floor and the jacking legs are thereafter disposed in a retracted position with their lower ends adjacent the deck unit.

Abstract: An air cushion vehicle has a plenum structure surrounding the vehicle body and a plurality of skirt segments. Each segment is attached to its own rigid frame which supports a flexible membrane. The frame outer end pivots from the plenum structure, while the frame inner end can move upwardly relative to the vehicle body from an inclined deployed position to a horizontal retracted position. The skirt membrane is extended from the frame during hovering and can be furled to its frame for replacement. The skirt segments are replaceable from inside the vehicle's air plenum.

Abstract: A concrete offshore structure located in a body of water of selected depth and extending from a bed defining the bottom of the water body to above the water surface comprises at least two similar prefabricated concrete modular subassemblies interconnected in a vertical arrangement in such manner to define a horizontal interface between each such pair of subassemblies. vertically disposed shear resistant pin means between the subassemblies and cement at the interface secure them together.A method for deploying such a structure includes towing the subassemblies offshore, mating them, and towing the assembled structure to the selected offshore installation site.

Abstract: An ocean thermal energy conversion facility includes a long pipe assembly which is supported at its upper end by the hull of the floating facility. Cold water flows to the facility from deep in the ocean. The pipe assembly comprises an elongate pipe construction and a weight connected to the lower end of the construction by a line of selected length. A floatation collar is connected to the construction at its upper end to cause the construction to have positive buoyancy and a center of buoyancy closer to the upper end of the construction than its center of mass. The weight renders the entire pipe assembly negatively buoyant. In the event that support of the pipe assembly should be lost, as by release of the assembly from the facility hull in an emergency, the assembly sinks to the ocean floor where it is moored by the weight. The pipe construction floats submerged above the ocean floor in a substantially vertical attitude which facilitates recovery of the assembly.

Abstract: An ocean thermal energy conversion facility includes a long pipe assembly which is supported at its upper end by the hull of the floating facility. Cold water flows to the facility from deep in the ocean. The pipe assembly comprises an elongate pipe construction and a weight connected to the lower end of the construction by a line of selected length. A floatation collar is connected to the construction at its upper end to cause the construction to have positive buoyancy and a center of buoyancy closer to the upper end of the construction than its center of mass. The weight renders the entire pipe assembly negatively buoyant. In the event that support of the pipe assembly should be lost, as by release of the assembly from the facility hull in an emergency, the assembly sinks to the ocean floor where it is moored by the weight. The pipe construction floats submerged above the ocean floor in a substantially vertical attitude which facilitates recovery of the assembly.

Abstract: Apparatus for position stabilizing the lower end of an elongate duct, which is vertically disposable in an ocean and which is supported at its upper end, is described. The apparatus includes an elongate flexible tensile member which is disposable along the interior of the duct. The tensile member is adapted to be connected at one end thereof to a duct support structure and to extend through the duct. A weight of selected mass and size is connectible to the other end of the tensile member below the lower end of the duct. Means are connectible between the tensile member and the duct, at least adjacent the lower end of the duct, for establishing and maintaining a selected position of the tensile member relative to the duct.

Abstract: A long, vertically disposed ocean water upwelling pipe, such as a cold water riser in an ocean thermal energy conversion facility, is fitted at its lower inlet end with a self-cleaning inlet screen. The screen includes a right conical frustum of loose metal netting connected at its larger upper end to the lower end of the pipe. A heavy, negatively buoyant closure is connected across the lower end of the frustum. A weight is suspended below the closure on a line which passes loosely through the closure into the interior of the screen. The line tends to stay stationary as the lower end of the pipe moves, as in response to ocean current vortex shedding and other causes, thus causing the closure to rattle on the line and to shake the netting. The included half-angle of the frustum is about 20.degree. so that, on shaking of the netting, marine life accumulated on the netting becomes loose and falls free of the netting.

Abstract: A large diameter duct structure is adapted for vertical disposition in an ocean. An elongate tensile core assembly is adapted to be supported at one end, as from a floating platform, and to extend downwardly a desired distance. A plurality of duct wall sections, each of selected length, are alignable in serial order to define a tubular assembly having a diameter substantially greater than that of the core. Support means are engageable with the core at selected locations along the core and with the wall sections. The support means support the wall section substantially concentrically about the core and secure the wall sections from movement relatively along the core. Seals are engageable between the ends of adjacent wall sections disposed about and along the core, and define substantially liquid-tight connections between the wall sections.

Abstract: Apparatus for drilling a well at a location submerged below a body of water includes a buoyant foundation structure. The foundation structure is floatable on the surface of the body of water and is subject to vertical motion in response to waves and the like. A riser handling and tensioning mechanism is mounted to the foundation structure and is operable for moving a riser pipe along a substantially vertical line from and to the foundation into and out of connection with the submerged location. The riser handling and tensioning mechanism is also operable for applying tension to a riser pipe connected to the submerged location. The handling and tensioning mechanism includes vertically disposed hydraulic rams mounted to the foundation structure. Holding means are releasably engageable with a riser pipe adjacent its upper end and are connected to the rams for movement along the riser line by the rams.