Abstract: A tension leg platform consisting of a platform deck (3) supported by a buoyancy structure (1), a bottom anchoring structure (2) and tension elements (4) extending between the buoyancy structure (1) and the bottom anchoring structure (2). The buoyancy structure (1) comprises a hollow, annular, substantially cylindrical wall forming a can-shaped body having a vertical axis and being fully open at the upper and lower ends, the height as well as the diameter of said body being substantially larger than the thickness of the annular wall in plan view, said wall consisting of closely adjacent, closed, substantially cylindrical, upright concrete cells (5, 7), of which at most half are extended to the platform deck (3) to form supporting shafts (7') therefor.

Abstract: Pressurized liquid filled tubular tendons provide a means for detecting leaks therein. Filling the tendon with a liquid having a specific gravity less than that of sea water provides increased buoyancy and reduces the weight supported by the buoyant structure. The use of a corrosion inhibiting liquid reduces the corrosion of the interior tendon wall.

Abstract: In order to reduce the risk of an offshore vessel capsizing in the event of a collision resulting in damage to its columns, a strengthening member is arranged in front of at least one of the columns, between the work platform of the vessel and the supporting hull. The strengthening member comprises a watertight box structure rigidly connected to the platform, and a tubular, also displacing part, extending between the box structure and the hull. The box structure has considerable volume and is situated so high that it will not be damaged in the event of a collision.

Abstract: In an arrangement including remotely releasable couplings for riser conduits between the sea floor and a floating plant processing crude oil and/or gas, the couplings are located in at least one chamber below the water line of the plant. This chamber is closed towards the atmosphere and provided with at least one downwardly directed opening communicating with the surrounding water. Structure is provided for governing the air pressure in the chamber, which is accessible through an air lock.

Abstract: A long strut between a sea-platform and the ocean bed needs to have its weight supported. Otherwise, much of its strength is used merely in supporting itself. The strut disclosed is made in sections, joined typically by screw threads. The joints need to be inspected periodically. The hollow sections of the strut have their buoyancy disposed internally, yet with the joints exposed internally for inspection by a probe that passes down inside along the length of the strut. The vulnerable joint area is made accessible to the probe. When the joint area includes welds, they too are vulnerable and need to be inspected; the fact that the buoyancy forces also have to be fed into the strut at the joint areas makes for even greater difficulty in providing access for the probe to all the places that need to be inspected. This access is provided in the various manners as shown.

Abstract: An improved semi-submersible unit for use in offshore operations which has a significantly reduced susceptability to heave motions in wave periods which are most likely to be encountered during practical operation conditions. The unit consists of a lower hull or hulls supporting vertical buoyant caisson which also support an upper deck or platform which supports and is supported by a centrally disposed, large diameter buoyant caission which contributes a significant portion of the total water plane area of the vessel when it is submerged to its operational draft. The vessel may be configured for offshore drilling operations, diving support, and various other offshore support functions. When configured for the offshore drilling operation, the central column serves as buoyant chamber and as a primary storage chamber for tubular products which are associated with the drilling function.

Abstract: A buoyancy system for a tension leg platform tether 10 or other element extending a significant vertical distance through a body of water. A series of bulkheads 25 divide the interior of the tether 10 into individual buoyancy cells 31. A central access tube 32 extends along the central axis of the tether 10, passing through a sealed penetration in each bulkhead 25. A series of cascade conduits 42 are provided the lower portion of each buoyancy cell 31 in fluid communication with the buoyancy cell 31 immediately above. A tool 82 is provided for injecting air into a selected buoyancy cell 31. As air is injected, water exists through the central access tube 32 until the buoyancy cell 32 is emptied of water, at which point air passes through the cascade conduit 42 into the adjacent upper buoyancy cell. The tool 82 can also be used to selectively flood individual buoyancy cells 31.

Abstract: A pressure balanced tether buoyancy system 12 useful for reducing the load imposed on a tension leg offshore platform 24 by the tethers 10 securing it to the ocean bottom. The tether 10 has tubular tether walls 11 defining a central cavity 15 isolated from the surrounding seawater. A series of bulkheads 25 extend laterally across the interior of the tether 10, dividing it into a series of individual buoyancy cells 31. Each bulkhead 25 is provided with a differential pressure valve 34 establishing selective fluid communication between the two buoyancy cells 31 separated by the bulkhead 25. Preferably, each differential pressure valve 34 is adapted to open in response to a differential pressure across the bulkhead 25 exceeding the differential hydrostatic existing across the vertical distance separating adjacent bulkheads 25. This permits a pressure gradient to be established interior to the tether 10 approximating that of the seawater in which the tether 10 is located.

Abstract: A method and apparatus is presented for anchoring a tension leg platform to the ocean floor using an anchor having an upper and lower assembly. The anchor's upper assembly is operatively connected to the lower ends of the tethers forming the tension legs of the tension leg platform, and acts to space and align each tether in a vertical manner when the anchor's upper assembly is connected to the anchor's lower assembly, which has previously been secured to the ocean floor by anchor piles.

Abstract: A stabilized spar buoy construction for deep sea operations including an elongated submerged hull having a selected volume and a selected water plane area, mooring lines connecting the bottom portions of the hull with the sea bottom, said hull having oil storage chambers and variable ballast chambers to establish and maintain a constant center of gravity of the spar buoy at a selected distance below the center of buoyancy of the spar buoy, a riser system extending through a through passage-way in the hull, a riser float chamber having pitch oscillations of the same amplitude as the hull and maintaining tension on the riser system and minimizing pitch motions therein, the bending stresses in the riser system between the sea floor and the riser float chamber being minimized by maintaining a selected constant distance between the center of gravity and the center of buoyancy under different load conditions of the spar buoy, said variable ballast chambers in the hull extending above the oil storage chambers.

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 floating semisubmersible off-shore drilling platform or the like comprises an upper working level portion and a lower pontoon portion. When the platform is transported from one place to another, it floats on the pontoon portion, but when it is working as a stationary unit in open water, it is submerged deeper, so that the pontoon portion is at a considerable distance below the water surface and the working level portion is at a considerable distance above the water surface. The platform is adapted to withstand ice pressure from ice occurring in the ambient water by giving the pontoon portion of the platform a form particularly advantageous in ice conditions. When ice occurs, the platform is lifted to such a position, that its pontoon portion comes to float at the water surface level.

Abstract: A tension leg platform is provided with exterior buoyant columns located outside the normal tension leg platform structure. The exterior columns decrease the pitch period of the tension leg platform away from the point of concentration of the largest wave spectrum energy encountered at a particular marine location. Modification of the pitch period of the tension leg platform in this manner reduces the cyclic fatigue stresses in the tension legs of the platform, and thereby increases the useful life of the platform structure.

Abstract: A vessel, for example a semi-submersible is provided with at least a chamber for stabilizing it against any or all of heave, roll and pitch. The chambers are mounted on or in the vessel and disposed to lie at least partly below the surface of the water. Valves are provided for controlling the buoyancy of the chambers. Each valve has a first position in which the respective chamber is connected to atmosphere to permit air to enter or leave the chamber, and a second position in which the chamber is not so connected.

Abstract: The location of azimuth thruster propellers at the parallel hulls of semisubmersible offshore vessels, is arranged so the water jet from a propeller at one hull, which is occasionally directed towards the adjacent hull will pass mainly below last-mentioned hull. When thruster propellers are arranged in pairs the bottoms of the hulls will preferably be inclined upwardly/outwardly within the portion around a thruster propeller located outside of a longitudinal middle plane through the hull. In order to facilitate the docking of the vessel, the bottom plating in the fore and aft bodies of the hulls, where the thruster propellers are mounted, should be raised sufficient to prevent the propellers projecting below the base lines of the hulls.

Abstract: The present invention generally relates to devices and methods used to suppress the motion of an offshore structure due to wind, wave, seismic, and current forces. More specifically, the invention suppresses structural excitation due to secondary wave forces.The apparatus comprises a mechanical energy absorbing means and a submerged mass. The mechanical energy absorbing means may be a combination of linear or non-linear springs and dampers and is attached to the structure so the vibrating motion may be transferred to the motion damper. The proper weight or size of the damper and mechanical energy absorbing means is determined by first measuring the natural frequency of the structure and the mass of the structure then using those numbers in an equation to calculate the mass and spring constant for the desired apparatus.

Abstract: In order to stay the columns in an offshore vessel of the type having two parallel pontoons and an operating platform carried thereby, also with respect to forces tending to displace the pontoons longitudinally in relation to each other, the columns located in the same transverse plane are interconnected by two transverse braces arranged in cruciform close to each other, but lacking direct connection.

Abstract: This invention concerns a semi-submersible marine platform comprising an above water deck, a support structure extending downwardly from the deck into the water and supporting the deck on pods providing buoyancy for the platform, and stabilizer legs spaced around the support structure and outrigged underwater thereby or therefrom, each stabilizer leg preferably being free to pivot under environmental forces about an underwater universal pivot and extending upwardly therefrom to project substantially above mean water level and provide a cut water plane area for imparting a righting moment against environmental forces acting on the platform.

Abstract: A tension leg means for a marine platform having a hawse pipe positionable over an anchor template guide frame means which includes one or more anchor pile members set in a seabed, each tension leg means comprising one or more tension pipe strings each including a plurality of pipe string members interconnected by couplings. A connector means secures each pipe string to an anchor pile member in a manner to lock the pipe string against relative rotation with respect to the anchor pile member. The pipe string extends into said hawse pipe and a quick latch connector means supported by the platform is arranged to quickly latchably connect the upper end of the tension pipe string to the latch connector means and platform while permitting adjustment of tension in the tension pipe string. Tension pipe strings are adjusted to substantially uniform tension by the latch connector means.

Abstract: Pressurized gas filled tubular tendons provide a means for detecting leaks therein. Filling the tendon with a gaseous fluid provides increased buoyancy and reduces the weight supported by the buoyant structure. The use of a corrosion inhibiting gaseous fluid reduces the corrosion of the interior tendon wall.

Abstract: A floating offshore structure which is moored at a fixed position on the sea by means of mooring hawsers and anchors connected to the ends thereof respectively for conducting a submarine excavating operation from a deck of the structure. The structure includes a moorage hull part provided with a vertical through-hole formed therein for receiving an excavating drill pipe and the mooring hawsers and a movable hull part connected to the moorage hull part so as to be rotatable within a horizontal plane. The movable hull part is constituted as a hull defining the outer wall of the floating offshore structure and connected with the moorage hull part by inserting it into a moorage hull part receiving hole formed at a position closer to the bow thereof.

Abstract: A method of conducting offshore well operations including exploration drilling and production from a single floatable platform which is converted from semisubmersible exploration mode to tension leg production mode at a well site.

Abstract: A semi-submersible offshore platform comprises an operating deck carried by four cylindrical columns supported by a pontoon structure comprising four-sided boxes formed into a square ring. Each pontoon box is subdivided into two compartments by a longitudinal centerline bulkhead, the compartments being further subdivided into tanks by transverse bulkheads. Tanks outside the centerline bulkheads are used for ballast water, and tanks inside the centerline bulkheads are used to store the oil produced.

Abstract: A floating platform used in exploiting subsea oil shoals and a method for installing the platform which comprises a platform structure and an array of vertical tubular anchoring lines connected to the uprights of the platform and to anchoring blocks lying on the sea bottom, the tube sections which form the anchoring lines being connected together in sequential order by welding to make up a solid entity.

Abstract: The invention relates to an elongated buoyant arm mounted below the water line of a drilling vessel. The arm is of variable buoyancy and is attached to a drilling riser extending between the drilling vessel and the sea bottom to maintain tension on the riser.

Abstract: An oil well rig having a flotatable hull and support legs which are lifted and supported by the floating hull for moving the oil well rig and moved down to engage the sea bottom and jack up or raise the hull above the water at an operating site for drilling or servicing a well or serving an offshore well platform. A water tower has pipes longitudinally mounted by brackets on each side on a beam and is mounted for vertical movement in a well in the hull. An elevator mechanism mounted in the hull is employed to raise and lower the water tower which has guide means fitting a guide portion of the well to provide guided vertical movement of the water tower. When the water tower is lowered, a pump at the bottom of the pipe pumps sea water through the pipe to machinery on the hull to meet the water requirements of the machinery.

Abstract: A self-propelled semi-submersible column stabilized service vessel for tending offshore production and drilling operations is disclosed. The vessel includes a pair of submersible hulls haing ballast compartments for controlling the buoyancy of the hulls. A rectangular service platform which includes fire fighting equipment, rig inspection equipment, repair facilities, and load lifting equipment is supported by means of vertical stability columns which are compartmented and include ballast chambers for controlling the buoyancy of the columns. The fire fighting equipment includes an extendable fire boom for clearing debris and for positioning explosives on the deck of a burning production or drilling platform. An array of monitors is also provided for establishing a curtain of water for thermally shielding the service vessel and for extinguishing a fire on the platform.

Abstract: A tying arrangement is described for use with an offshore terminal wherein a transfer structure near the sea surface is anchored by a group of anchor lines extending at downward inclines to the sea floor. A bumper line extends between a pair of anchor lines, so a ship heading for the transfer structure first encounters a bumper line that gradually stops it. The bumper line also enables the coupling of anchor lines to transfer energy from one to the other, to increase the energy absorption capacity and stiffness of the system.

Abstract: A tension-leg offshore platform comprises a positively buoyant, floating upper unit in which an operations platform is supported above an ocean surface by a plurality of spaced vertical columns defining buoyancy chambers. The lower ends of the columns are connected to the ocean floor by a corresponding plurality of tension-leg assemblies. Each tension-leg assembly is comprised of a plurality of positively buoyant tubular members having their lower ends connected securely against upward movement to the ocean floor. The tubular members are of substantially equal length less than the pertinent water depth by an amount adequate to cause their upper ends to be located below the area of significant surface wave action yet substantially above the ocean floor. A separate flexible tension member for each tubular member connects the lower ends of the columns to the upper ends of the corresponding tubular members.

Abstract: A floating-type offshore structure, of which the main body comprises a lower hull and plurality of struts mounted on the struts and supporting a platform above the sea level and is moored through mooring wire ropes or chains at a predetermined offshore location, and which is adapted for use under both of an ice-covered and an iceless conditions of the sea by adjusting the amount of ballast water contained in a ballast tank or tanks formed in the lower hull and/or the struts and adapted for causing ice floes to undergo downward flexural failure on account of bending stresses when they move into the sea water along the ice contacting face of the strut which is inclined inwardly toward below.

Abstract: A heave resonant damper for semisubmersible platforms includes tanks and ducts constructed so that their resonant period approximately equals the resonant heave period of the platform, wherein the ducts have selectively varied cross-sectional area to optimize damping.

Abstract: In apparatus for connecting a tension member, such as an element of a leg of a tension leg platform, to an underwater anchoring base, actual connection to the anchoring base is accomplished by a connector which is joined to the tension element by a flex joint which is spaced above the connector but surrounded by a tubular element rigid with the anchoring base, the flex joint carrying an annular stop surface which is closely embraced by the tubular element. Lateral loads applied to the flex joint by the tension element are transferred directly to the tubular element and the anchoring base rather than to the connector.

Abstract: A tension connector, and offshore platform mooring system embodying the connector, characterized in that the connector can be made up remotely and released remotely. The connector comprises a male connector member, typically attached to a string of pipe which serves as a mooring element, and a female connector member, typically secured to an anchoring base at the bottom of a body of water. The connector is made up simply by inserting the male member downwardly into the female member by manipulating the pipe string. Advantageously, two remote release means are provided, one operating hydraulically, the other by manipulation of the pipe string.

Abstract: A mooring apparatus for a semi-submersible oil exploration and drilling rig includes eight drum anchor hoists and winches on which are carried eight wire rope mooring lines. Each of these lines extends up over one of eight head sheaves and vertically down the outside face of the oil rig through a fairleader rotatably mounted with respect to the rig at a bottom submerged portion thereof. A linear line pull machine is mounted to the rig in encompassing relation to each of the vertical runs of mooring line between the head sheave and the fairleader. These eight mooring line assemblies are distributed around the periphery of the rig. Two mooring lines extend at 90.degree. from each other at each corner of the rig.

Abstract: Tethered or bottom-ballasted offshore platforms preferably have a pyramidal configuration. Struts connect the apexes of a polyhedron configuration to form a triangle defining each face. The pyramidal configuration can be ballasted to the bottom in relatively shallow water. A hexadron configuration can be tethered in deep water with tension members and flotation members.

Abstract: In order to simplify the construction and to reduce the resistance to flow, and to provide a high amount of inertia in relation to all essential axes, an offshore vessel comprises two parallel under-water bodies, four columns mounted symmetrically thereupon, and a multi-deck box-like structure interconnecting the upper ends of the columns. This structure will increase the strength of the vessel so only one horizontal, transverse stay is required between each pair of columns. Below each column there is a 360.degree.-turnable shrouded propeller, which together can hold the vessel stationary, with a vertical line of symmetry in a desired position, for instance above a borehole. The box structure is outwardly completely closed at the bottom and sideplating, and will, in case of need, retain the vessel floating.

Abstract: A tension leg drilling platform of the type having a floating buoyant structure anchored to the sea floor by a plurality of vertical tendons is improved by the addition of flexbile extendable lines between the platform buoyant structure and the tendons to permit movement in the horizontal plane.

Abstract: A tether assembly (2) for a tethered buoyant platform for installation in a shaft (8) of a leg (10) of the tethered buoyant platform comproses a cable tether (4) having a terminal at one end for connecting to an anchor post (12) on the sea bed and having a bearing (16) which is a sliding fit in the shaft (8) of the leg (10) to transmit lateral forces from the tether to the shaft (8) of the platform. The assembly (2) further includes upper and lower bending guides (18 and 20) each providing a curved surface to control the bending radius of the tether (4) and a tether length adjuster (30) comprising a plurality of axially spaced apart members capable of engaging corresponding members associated with a releasable clamp (6).

Abstract: A stable offshore platform for surface or undersea work is provided by connecting a semi-submersible trailer unit with a workboat. Preferably, two columns of the trailer are joined by a beam member or truss, and this assembly is linked to the workboat via a truss-like trailer tongue with a ball swivel joint. When in transit, the semi-submersible unit is deballasted to a shallow draft condition and towed by the workboat.

Abstract: Improvements in an offshore platform and submarine storage facility for highly chilled liquified gas, such as liquified natural gas, are disclosed. The improved facility includes an elongated, vertically oriented submerged anchoring frame to which one or more insulated storage tanks are moveably mounted so they can be positioned at a selected depth in the water. The double piston tank is constructed with improved seals to transfer ambient water pressure of the selected depth to the cryogenic liquified gas without intermixture. This transferred pressure at the depth selected aids in maintaining the liquified state of the stored liquified gas. Structural improvements to the tank facilitating ballasting, locking the double piston cylinders together and further facilitating surface access to the tank for inspection, repairs and removal, and structural improvements to the platform are disclosed.

Abstract: A floating platform intended to be anchored to the sea bed incorporates a substantially vertical tether. The tether is fitted with a gas-operated tension spring device capable of generating an elastic tensile force in the tether. Means is provided for varying the nominal tensile force which the spring device is capable of exerting. The tether may include an adjustor nut movable along a screw-threaded portion of the tether so as to be engageable with an adjustor nut adaptor supported by the platform.

Abstract: The invention relates to a platform (1) having a platform (1) and at least three legs (2) movable in vertical direction with respect to the platform (1), the legs (2) being connected to the platform (1) by a lifting and locking mechanism (8,9,17,18,14) having locking bars (8,9) for holding the platform (1) with respect to the legs (2) and lifting jacks (17,18,14) for moving the legs (2) with respect to the platform (1) both locking bars and lifting jacks having elements (8,9,17,18) which can move in and out of engagement with the legs with clearance in vertical direction in recesses (11), safety structure being provided to check the completion of the movements of the elements, the safety structure having a time relay (t.sub.1,t.sub.2) in the control circuit of the jack system which relay (t.sub.1,t.sub.

Abstract: An offshore installation, such as a producing platform, includes one or more supporting legs which extend from a working deck downward into the water. Process fluid utilized on the platform is cooled by heat exchange with the surrounding water through indirect contact, or through use of an intermediary fluid which is passed through a cooling circuit made up at least in part by segments of the various water contacting support structures of the platform.

Abstract: The invention relates to a method and apparatus for tension mooring an offshore platform having a deck and a plurality of buoyancy columns. An anchor system is initially installed upon the bed of a body of water. Permanent mooring lines are then connected to the anchor system and extend upwardly for support by a buoyancy system located below a lowest portion of the offshore platform and a zone of high oxygen content water adjacent the surface of the body of water. Sacrificial mooring lines are connected to an upper portion of the buoyancy system and extend upwardly through internal conduits with the plurality of bouyancy columns of the floating platform. In the event one of the sacrificial mooring lines becomes damaged the line may be selectively released from the buoyancy system, drawn up through a corresponding interior column and replaced from the deck of the platform.

Abstract: A connector apparatus for connecting a tension leg platform mooring tether to a subsea foundation, the apparatus comprising: a plug positioned on the lower end of the mooring tether for mating union with a receptacle positioned in the foundation so that the plug is readily positioned in the receptacle to maintain the mooring tether in connection with the foundation with the plug being readily removable from the receptacle when desired.

Abstract: A tension leg structure for use with a tension leg platform or the like to interconnect an anchor on the sea floor and platform in which the tension leg structure comprises interconnected buoyant pipe members for transmitting tension forces and for withstanding hydrostatic pressure. Each member has internal watertight bulkheads defining a buoyancy chamber. Tremie pipe extends through the bulkheads of each member and has ends terminating in a slipover coupling provided within a joint interconnecting adjacent tension buoyant members.

Abstract: A semi-rigid floating marina adapted for use in both ocean and inland waterways including a submerged structural frame interconnected to a floating surface structure by a plurality of rigid and flexible members. The marina is readily portable in nature to accommodate the changing water level and varying boundaries of inland waterways. A variable buoyancy anchor and an in-situ method of forming the same is provided which allows the anchor to be selectively submerged or buoyed from the bottom of the waterway.

Abstract: A tension leg cable is connected between a floating structure and a seafloor anchor means. The cable is a multi-strand cable having voids between adjacent strands. A fluid tight vulcanized rubber sheath is provided covering an outer surface of the cable. A fluid tight corrosion resistant tubular member surrounds said sheath so as to define an annular space between the tubular member and the sheath. Means is provided for supplying an inert gas under pressure to said voids and said annular space. Means is provided for monitoring the pressure of said inert gas in said voids and said annular space to detect changes in said pressure so as to indicate a leak in either said sheath or said tubular member. Methods of construction of said tension leg cable are also disclosed.

Abstract: A tension mooring system for a floating structure such as a drilling or production platform having a plurality of permanent mooring lines extending upwardly from a plurality of bottom anchors and terminating below the water level and having buoys connected to the upper ends thereof with sufficient buoyancy to maintain the upper end of the mooring lines in a generally vertical posture, replaceable mooring lines connecting from the buoys to the floating structure, the upper position of the permanent mooring lines being preselected to be below a highly corrosive area of the air-sea interface, and a pulling mechanism on the replaceable mooring lines to impart a preselected tension to the mooring lines, the bottom anchors being pre-positioned by drilling and cementing or driving piling through templates.

Abstract: A self-propelled semi-submersible column stabilized service vessel for tending offshore production and drilling operations is disclosed. The vessel includes a pair of submersible hulls having ballast compartments for controlling the buoyancy of the hulls. A rectangular service deck or platform which includes fire fighting equipment, rig inspection equipment, repair facilities, and load lifting equipment is supported by means of vertical stability columns which are compartmented and include ballast chambers for controlling the buoyancy of the columns. The fire fighting equipment includes an extendable fire boom for clearing debris and for positioning explosives on the deck of a burning production or drilling platform. An array of monitors is also provided for establishing a curtain of water for thermally shielding the service vessel and for extinguishing a fire on the platform.