Field of the Invention

The present invention relates in general to modular framed structures, and in particular to floating, semisubmerged structures particularly useful for supporting offshore drilling and hydrocarbon production platforms and oil storage facilities and in combination with a frame structure for building a modular offshore base capable of landing aircraft, both utilizing a plurality of Y-shaped joints interconnecting leg or beam members of the structure. Background

The costs associated with providing suitable engineered structures for various applications, such as floating structures, including storage tanks, and roof structures for buildings of many types, continue to be a vexatious problem in the structural engineering arts These problems and the problems of modular structures in general are also discussed in my prior applications Serial No 08/644,570 filed May 10, 1996 on which priority has been claimed; Serial No 07/997,339, filed December 28, 1992, now patent 5,546,722 granted August 20, 1996; Serial No 08/418,545, filed April 7, 1995, now patent 5,525,011 granted June 11, 1996; and in my prior U S Patents 4,288,947 granted September 15, 1981, 4,583,330 granted April 22, 1986; 4,813,191 granted March 21, 1989 and 4,903,452 granted February 27, 1990, all incorporated by reference herein.

However, further improvements are needed in the provision of certain structures which may require modularization in order to build structures of the appropriate size and support capabilities There is a need to manufacture as much of such structures before being towed to the desired location at sea or on a relatively large body of water where a customized structure can be easily, economically assembled

One example of a complex and expensive structure which can benefit from the improvements of the present invention are certain types of floating, generally stationary structures used in the hydrocarbon development industry for drilling wells under large bodies of water, including the open oceans. Various types of floating drilling, production and service platforms have been constructed including, jack-up rigs, barges, submersible structures, semi-submersible tension leg structures, spars and free standing or the more conventional guyed towers See for example the Petty et al patent 4,983,073 granted January 8, 1991 to Odeco, Inc , incorporated herein by reference However, these structures could benefit from simplification and modularity and by the replication of the component parts

The problems associated with properly engineered and cost effective structures, such as pontoon structures, continue to daunt the structural engineering arts in that such structures, for

example, should be simple, include a minimum number of structural members but be adequately configured to withstand all types of expected loads imposed thereon

In an area related to semisubmerged drilling platforms, there is a need by the military for an advanced base from which air, land and naval expeditionary forces can conduct operations complementary to, or independent of, host-nation support. Such a base could be located in international waters off an unfriendly or uncooperative country, or located with permission in the national waters of a cooperating country. Such a structure also must be capable of providing a tactical aviation operations and support base for conventional takeoff and landing aircraft It must be modular, allow for rapid, self-contained, at-sea assembly and disassembly, it must provide hangar and storage space, and it must be stable enough so that naval ships can load and unload Further requirements are stated in the Office of Naval Research of the U.S. Navy BAA 96-010 entitled "Mobile Offshore Bases, " incorporated herein by reference. Such base can be constructed over a deep ocean petroleum production site with refinery facilities on the base Summary of the Invention The problems associated with providing suitably engineered, cost effective and operable, generally stationary, floating structures which are stable and generally resistant to movement in unwanted sea states generated by high winds and ocean currents have been sought to be overcome by providing structures which have low reaction to wave force and wind and a center of gravity below a metacenter or center of buoyancy The embodiments of a floating structure in accordance with the present invention satisfies these requirements and is characterized by a plurality of substantially rigid, generally Y-shaped joints which are interconnected by leg members

The present invention provides simplified modular space frame structures utilizing improved Y-shaped components and joint members. Structural legs interconnect a plurality of these joints and can be modularized as flotation members or container members. Particular configurations of floating support structures for offshore drilling and production platforms made up of a Y-joint in accordance with the present invention with interconnecting legs are structurally uncomplicated, stable and are easily adapted for anchoring in the open sea by tension leg members or by conventional catenary anchor leg members, such as flexible chains, polyester taut cables or aramid ropes In accordance with one important aspect of the invention unique floating structures, particularly adapted for generally stationary placement offshore in the open ocean are provided which utilize modular Y-joints and which are otherwise made up of leg members interconnecting the Y- joints which also serve as flotation and fluid storage members together with the Y-joints

The present invention further provides plural embodiments of a unique offshore floating structure which is stable, compliant to movement due to high wave action or otherwise unwanted sea states or conditions, is easily fabricated at a shore-side yard or offshore and is also easily adapted for anchoring by tension leg or catenary anchor leg or taut anchor leg members The present invention further provides an improved Y-joint for use as a structural member in modular space frame structures having an inverted hip roof that acts as a keel, wherein a Y-shaped joint is formed of opposed branch members that are formed as channels which can be interconnected facing each other to provide the improved Y-shaped floats

The present invention still further provides an inflatable floatable structure made up of inflatable Y-shaped joints formed of flexible material, such as a fabric reinforced elastomeric material, and which are interconnected by unique connectors

Those skilled in the art will further appreciate the above-mentioned features and advantages of the invention together with other superior aspects thereof upon reading the detailed description which follows in conjunction with the drawings and claims Brief Description of the Drawing

FIG 1 is a perspective view of an improved semisubmerged floating structure in accordance with the invention for supporting an offshore platform.

FIG. 1 A is a plan view of the structure shown in FIG 1 ,

FIG. 2 and 2A are detail views of one of the Y-shaped joints and a portion of the interconnecting leg portions of the structure shown in FIGs 1 and IA,

FIG 3 is a perspective view of a rigid Y-shaped joint in accordance with an alternate embodiment of such joint of the invention;

FIG 3 A is a plan view of a metal plate having the outline of a chevron-shaped stamping from which the joint of FIG 3 can be made, FIG 4 is a schematic view of a valved, Y-shaped joint adapted for use with several embodiments of the floating structures in accordance with the invention,

FIG 5 is a perspective view of another embodiment of a semisubmerged, floating structure, particularly adapted for supporting a platform, in accordance with the invention,

FIG 6 is a schematic plan view of a landing strip pontoon comprised of a plurality of the platforms according to the present invention,

FIG 7 is a schematic end elevational view of a landing strip pontoon depicted in FIG 6,

FIG. 8 is a perspective schematic view of an inverted hip roof type pontoon unit utilizing cylindrical tanks as depicted in FIGs 6 and 7 for landing and launching aircraft,

FIG. 9 is a perspective view of yet another embodiment of a floating structure, also adapted for supporting an offshore platform;

FIG 9A is a detail section view taken in a downward direction above the bottom apex of FIG. 9; FIG. 10 is a section view showing a typical connection between Y-shaped joints of the type in FIG. 4;

FIG. 11 is a side elevational schematic view of a tanker storage structure with a platform in accordance with the invention which can be snugly mounted on top of the dodecahedron floating structure of Fig. 1 , FIG. 12 is a top plan schematic view of the floating structure depicted in FIG. 1 1 ,

FIG. 13 is a cross-sectional view of an interrupted thruster collar that can be used to connect the tanks and the Y-joint depicted in FIG. 11 ; and

FIG. 14 is an end elevational view of the joint depicted in FIG. 13 taken along line 14-14, and

FIG. 15 is a side elevational view of the joint depicted in FIG. 13 in a disconnected state. Description of the Preferred Embodiments

In the description which follows like parts are denoted throughout the specification and drawing with the same reference numerals, respectively. The drawing figures are not intended to be to scale and certain features and elements are shown in generalized or schematic form in the interest of clarity and conciseness. Referring to FIG. 1 there is illustrated one unique modular, semisubmerged, floating platform or structure in accordance with the present invention and generally designated by the numeral 20

Structure 20 can include an inflatable donut 21 abutting and attached to a central riser 34 and to the bottom of floating structure 20 to provide additional strength, stability, buoyancy and ballast Donut

21 can also be used as a hydrocarbon storage facility to add to the ballast of structure 20, which is particularly adapted to support an offshore exploration and/or production platform, generally designated by a numeral 22 that is used for drilling and production of hydrocarbon fluids from subterranean reservoirs disposed beneath a body of water 24. In the particular embodiment shown platform 22 is of generally rectangular configuration and includes a drill derrick 26 mounted thereon, a helicopter landing deck 26a, cranes 26b, living quarters 26c and other conventional components supported on the platform for carrying out drilling of wells, not shown, through a seabed 28

Platform 22 can also have a pentagonal shape, and the components of the platform can include those depicted in FIG. 1. In addition, a moon pool opening can be located through the platform below a centrally located derrick, and components such as generators, drawworks, cement

storage tanks, mud tanks and pipe storage racks, can be arranged around the moon pool opening Other arrangements (not shown) of a platform which are more suited for exploratory drilling can have a derrick mounted cantilevered out from one side of the platform

As shown in FIG 1, the entire structure 20 except for platform 22 is comprised of rigid Y- shaped joints 30 and interconnecting legs or leg members 32, as indicated A particular preferred embodiment of the structure 20, as shown in FIG 2, is one wherein the rigid Y-joints 30 each have arm portions 30a, 30b and 30c which are suitably connected to the leg members 32 or are integrally formed therewith In the embodiment of the Y-shaped joints 30 and leg members 32 for the structure 20 the arm portions 30a, 30b, and 30c are generally cylindrical tubular members suitably formed of tubular metal or fiber reinforced plastic composite segments joined to each other and to the leg members 32 The leg members 32 are also cylindrical tubes, as illustrated

A preferred embodiment of the Y-shaped joints 30 of structure 20 is one wherein the joint arm portions 30a, 30b and 30c extend away from each other at respective angles between any two arm portions of 108°, as indicated in FIG 2 The Y-joint 30 and the structure 20 can be formed with angles between the joint arm portions other than that indicated in FIG 2 However, when structure 20 is comprised of pentagonal frames utilizing Y-joints 30 and interconnecting leg members 32, it can enjoy a high degree of modularity in that the structure is basically comprised of the above-mentioned elements all suitably interconnected, such as by welding, by a threaded connection, or the like

Referring again to FIGs 1 and 1 A, the structure 20 preferably includes a pentagonal space frame 33, which is disposed in a generally horizontal plane for supporting platform 22, and five dependent space frames 35 As shown in FIG 1 , the lowermost joints 30 of space frames 35 include means for connecting the structure 20 to plural flexible catenary or taut anchor legs or lines 36, respectively Each of the anchor lines 36 is connected to suitable anchor means 38 disposed on the seabed 28 As mentioned above, riser 34 is centrally located within structure 20 and extends from platform 22 to a wellhead in seabed 28 Further information about determining a suitable length for the anchor lines 36 can be obtained from the literature, such as the publication entitled "Semi- Submerged Modular Offshore Platform" by the present inventor presented at the International Offshore and Polar Engineering Conference, Osaka, Japan, April 12, 1994

FIG 2A shows one of the Y-joints 30 provided with a suitable transverse closure plate 39 across the cylindrical arm portion 30b and forming a connecting point 40 for one of the anchor lines 36 Each of the lowermost Y-joints 30 which are connected to anchor lines 36 are configured as shown in FIG 2A to have a watertight closure plate or bulkhead 39 disposed thereacross to close the tubular joint 30 and the leg members 32 so that these elements can be used to form flotation chambers

to provide requisite buoyancy for the structure 20. In fact, Y-joints 30 and leg members 32 can be constructed in accordance with known methods for constructing floating offshore platforms, including tension leg-type platforms and semi-submersible type platforms known to those skilled in the art. An important advantage of the present invention is its use of modular Y-joints 30 which can be prefabricated and erected with leg members 32 either on shore or using suitable work barges and/or floating drydock structures and the like in calm anchorages for assembling the structure 20. The depending leg members 32 of each of space frames 35 can include suitable floodable compartments or ballast tanks for ballasting structure 20 to maintain certain trim and freeboard conditions for platform 22, depending on sea conditions. Leg members 32 of the space frames 35 can also house certain equipment for structure 20, such as pumps and associated piping for flooding and deballasting in the aforementioned compartments or ballast tanks, not shown. Those skilled in the art will recognize that leg members 32 and Y-joints 30 can be constructed in such a way that branch arm portions 30a, 30b and 30c can be of various lengths to actually form part of or all of the leg members 32. For example, each arm of the Y-joint 30 can comprise approximately half the total length of a leg member 32 and the abutting ends of the aforementioned portions of leg members 32 can then be suitably secured together, such as by welding to form a water-tight tubular flotation structure

With reference to FIG. 3, another configuration of a hollow, tubular Y-joint which can be used in place of cylindrical tubular joints 30 for floating structures 20 and 50 is depicted at 1 12 Joint 112 is comprised of three channel members 96 that are welded together along weld lines 1 14 and 1 16 to define an enclosed interior space 1 15.

Each channel member 96 can be formed from a single piece of a substantially flat plate 101 , as depicted in FIG. 3A. Each channel 96 is formed as an integral part which is suitably bent to yield a web 97 and opposed flanges 99 and 100, and then also bent in a direction to form opposed branches or arm portions 96a and 96b Channel 96 is cut or stamped as a chevron plate 96c from a plate 101. Plate 96c has opposed flat branches 96d' and 96d", and gussets 96e' and 96e" are then removed Plural plates 96c may be cut from larger plate 101 and then further cut along coincident lines 102 and 104 leaving an integral web portion 106 therebetween. Plate 96c is then folded along a parallel fold line 108 for branch 96d' and parallel fold lines 1 10 for branch 96d" to form the channel. For a Y- joint 60 having angles between adjacent branches or arms 62, 64 and 66 of 108° the included angle between the branches 96d' and 96d" may be about 138°. A closure plate member 124, located at the juncture of the joint branches or arms, such as the arms 1 18, 120 and 122, closes the opening that results from the Chevron cut as shown in FIG. 3 A

Joint 46 may also be formed by four channel sections formed from four (4) chevron shaped plates (not shown) similar to channel sections 96, but having four branch portions

The lengths of the branches or arm portions of the Y-joints 60 and 1 12 may be virtually any which are suitable or necessary to build the structure associated therewith and formed thereby In the structure of FIG 8, for example, the respective branches or arms 62, 64 and 66 extend the entire length of the beam spans required of these members, as illustrated Although such an arrangement is not required, certain advantages may result from providing the Y-shaped joints 60 in this manner to simplify erection of the structure associated with the joints As mentioned previously, the joints 30, 46, 60 and 112, as well as components described herein not otherwise specified, may be fabricated of metal suitable for the particular application, such as structural steels or aluminums Alternatively, the Y-shaped joints may also be fabricated of certain composite or reinforced plastic materials suitable for structural purposes depending on the application and the environment to which the structure is to be exposed Conventional engineering materials may be utilized in this regard

Referring now to FIG 4, a Y-shaped joint 146 generally of the type shown in U S patent 4,288,947, incorporated herein by reference, is shown in greater detail Joint 146 is characterized by three separate branch portions 146a, 146b and 146c which are suitably integrally joined together and form angles with respect to each other of 120°, 108° and 120°, as shown in FIG 4 These angles are measured from the central axes of each of the branch portions 146a, 146b and 146c, as illustrated Each of the branch portions of the joint 146 is provided with a suitable transverse bulkhead 160 having a remotely controllable fluid control valve 162 interposed therein as shown The distal ends of the branch portions 146a, 146b and 146c are provided with coupler members 164, which comprise frustoconical tapered sleeves The tapered coupler members 164 include transverse shoulder portions 164a and spaced apart circumferential grooves 164b and 164c formed therein, respectively The tapered members 164 are preferably integrally formed with the branch portions 146a, 146b and 146c, respectively, in the embodiment of the Y-shaped joint, as shown in FIG 4 Alternatively the coupler members 164, and alternate embodiments described below may be formed separate from and then bonded to tubular branch portions 146a, 146b and 146c

Each of the leg portions 148 of the space frames of the floating structures 210 and 151 can be made up of a structure as shown in FIG 10, respectively Referring to FIG 10, for example, interconnected legs or branch portions of two adjacent Y-shaped joints 146 are shown and each designated by numeral 146a, respectively The tapered coupler members or sleeves 164 of each branch portion 146a are shown connected to a coupler member 170 comprising an elongated cylindrical sleeve having opposed coaxial tapered bores 172 and 174 formed therein Transverse

shoulder portions 172a and 174a are formed in the member 170 and cooperate with and engage the transverse shoulder portions 164a of the sleeves 164. Spaced apart circumferential grooves 172c, 172d, 174c and 174d are also formed in the tapered bores 172 and 174, respectively The coupler tapered surfaces, the surfaces 164a and grooves 164b and 164c and the surfaces 172, 172a, 174, 174a and grooves 172c, 172d, 174c and 174d can be machine finished

Resilient cylindrical O-ring type seal and connector members 176 and 178 are disposed in the cooperating sets of grooves, as shown in FIG. 10. By way of example, one of the ring members 176 is disposed in cooperating grooves 172c and 164b and one of the ring members 178 is disposed in the cooperating grooves 164c and 172d When a coupler sleeve 164 is inserted in a bore of a coupler member 170, it is locked in place as shown in FIG. 10 by the engagement of the ring members 176 and 178 in registration with the respective sets of grooves as shown and described. In this way, a simplified interconnection of the Y-shaped joints 146 can be carried out using a coupler arrangement as shown and described in conjunction with FIG. 10. The coupler sleeves 164 include axial bores 165 which communicate with the interior chambers 161 of the branch portions 146a of the Y-shaped joints 146, respectively. A connecting bore portion 171 interconnects the tapered bores 172 and 174 to provide a continuous passage for pressure fluid during inflation and deflation of the Y-shaped joints and the connecting leg portions.

As will be appreciated from the foregoing description, each leg 148 of floating structure 210, for example, can be made up of a coupler member 170 and cooperating respective branch portions of Y joints 146. An alternate embodiment of a connection between adjacent Y-shaped joints 146 (not shown) has modified branch portions of the joints to include tapered, externally threaded coupler members 164e on each of the branch portions 146a, 146b and 146c.

Each Y-shaped joint 146 can include a fluid fill and vent valve connected to the joint suitably connected to a source of pressure fluid, such as compressed air, via a supply conduit. Each valve can be remotely controllable to provide for pressurizing the joints, including the portions thereof forming the legs, by valving pressurized fluid, such as compressed air, into a joint base and then into each of the branch portions. The Y-shaped joints 146 can be formed of a fabric reinforced flexible polymer material, su. h as urethane coated polyvinyl chloride, which is durable and airtight The coupler members 17< 170a, for example, can also be formed of the same or a similar material. The Y-shaped joints 30, 43, 130 and 146 and the connecting leg of each of the associated floating structures can be adapted to provide temporary storage of production fluids, such as crude oil, for example, prior to transferring such fluids to a tanker or via pipeline to a shore side facility.

The components described herein may be fabricated of metal suitable for the particular application, such as structural steels or aluminum. Alternatively, the joint may also be fabricated of certain composite or reinforced plastic materials suitable for structural purposes depending on the application and the environment to which the structure is to be exposed. Referring now to FIG. 5, there is shown a modified floating structure, generally designated by the numeral 50, which is an inverted structure of the floating structure 20 such that the bottom pentagonal space frame 33 forms a submerged generally horizontal portion of the structure 50 with upwardly extending leg members 32 formed by the space frames 35 terminating at uppermost Y-joints 30 having arm portions 30c" adapted to support a deck or platform structure, generally designated by the numeral 52. The platform or deck 52 can also be adapted to be operable as a drilling and/or production platform, and includes a suitable derrick 26 mounted thereon and centered over a moon pool opening 27 formed in the platform, as shown. Other structure and apparatus, useful in drilling and producing hydrocarbon fluids, can be disposed on the platform 52 in a conventional manner. The platform 52 is suitably secured to the upwardly projecting arm portions 30c" of the Y-joints 30, by welding or with other appropriate fastening means such as bolts.

The structure 50 is also adapted to form flotation chambers within the leg members 32 of the space frames 33 and 35 in substantially the same manner as the structure 20 in FIG. 1 Suitable compartments or ballast tanks can be provided in the leg members 32 of the space frame 33 to add stability to the structure when floating in the sea. The structure 50 can be anchored to the seabed by conventional tension leg members or risers

54 connected to respective ones of the Y-joints 30 of the space frame 33, as illustrated and anchored to the seabed in a conventional manner, not shown. In addition to the anchor means provided by the tension legs or risers 54, the structure 50 is moored by flexible anchor lines or catenary anchor leg chains 56, four being illustrated in FIG 5, and connected to respective ones of Y-joints 30 as shown and to the seabed by suitable anchor means, not shown. Another anchoring means is a vertical riser storage caisson, which could also be incorporated with a moon pool opening.

Since a semi-submerged, moored structure is essentially an inverted pendulum subject to wave forces, resulting from wind, gravity, earthquake, temperature and pressure variations, as well as ocean currents, natural frequency of the floating structure can be adjusted by shifting and varying the weights on the platform, or by adjusting the riser system to achieve an optimum intact or damaged stability. Some of this technology is disclosed in the Steddum U S patent No 3,982,492 and the Newby et al. Patent No. 4, 169,424, incorporated herein by reference

Those skilled in the art will appreciate from the foregoing description that a unique semi- submersible, movable, floating structure can be fabricated using the Y-joint described above and preferably formed of interconnected space frames such as the space frames 33 and 35 The frames 33 and 35, when constructed of hollow tubular members, either circular or of other cross-sectional configurations, can form a unique floating structure which is easily fabricated and has a high degree of stability when held stationary by anchor means of the type described herein

Referring now to FIG 9, another embodiment of a floating structure in accordance with the invention is illustrated and generally designated by the numeral 42 The floating structure 42 is of a generally inverted pyramidal configuration and is made up of four Y-shaped joints 43 at the respective corners of a space frame 44 Each of the Y-shaped joints 43 is formed to have hollow tubular segments or arms in the same manner as the joints 30 and can include branch portions 45, 47 and 49 The branch portions 45 and 47 interconnect with other Y-joints 43 and the branch portions 49 descend to a quadrajoint 46 at the tip of the floating structure 42, as shown The floating structure 42 can be anchored by a hollow tubular tension leg or riser member 48 and by catenary anchor leg members 51 extending from each Y-shaped joint 43 The floating structure 42 is adapted to support a platform 53 thereon above the surface of the sea 24. The Y-joints 43 are formed with respective angles A, B and C between the respective branch portions wherein the angle A between branch portions 45 and 47 is 90°, the angle B between branch portions 47 and 49 is 60° and the angle C between branch portions 45 and 49 is 60° Y-shaped joints 43 can be constructed in substantially the same manner as Y-shaped joints 30 and depending legs 49 can be configured to form flotation and ballast chambers for floating structure 42

In a modification of structure 42, interconnecting legs 49 can be covered by an outer skin 57, see FIG. 9 A, and an inner skin 61 to form a closable space 63 which can serve as a flotation chamber for structure 42 Another pyramidal floating structure (not shown) can be configured in the form of a tetrahedron having four Y-shaped joints similar to Y-shaped joints 30, but having angles between their respective branch portions of 60° rather than the angle of 108° as shown for the structure 20 Cylindrical tubular leg members interconnect the Y-joints, and are all of equal length forming a generally horizontally disposed space frame and three dependent arms. The lowermost Y-joint can be connected to a hollow tubular riser or tension leg which in turn can be connected to a subsea wellhead or blowout prevention system, such as system 48a depicted in FIG 9 A catenary or taut anchor legs can extend from each of the Y-joints, except the lowermost Y-joint which is connected to a riser This floating structure has a triangular space frame disposed generally horizontally for

supporting a platform thereon, and includes triangular depending space frames depending from the horizontally disposed space frame

Another structure as mentioned above that is similar in conceptual shape with FIG 1 is depicted in FIGs 1 1 and 12 as floating structure 202. Structure 202 is comprised of a substructure or base 204 and a superstructure 206 Essentially, structure 202 is comprised of a plurality of Y- joints schematically shown at 208, each of which interconnects three cylindrical tanks 210 (see also FIG 8) The Y-joints are described herein below. Tanks 206 are preferably made of a stainless steel or carbon steel material which can withstand the salinity and forces of the ocean environment, but also could be made of some composite materials and fiber reinforced plastics Tanks 210 of substructure 204 form a plurality of depending pentagonal space frames 212 and an upper pentagon shaped, horizontal space frame 214 that together form a truncated dodecahedron Structure 204 is one half of a full dodecahedron and thus has only 5 sides and a top The overall shape of base 204 provides for a greater number of submerged tanks 210 which contain a plurality of anchor legs 36 and risers 54 that secure structure 204 to the seabed When one side of the pentagon-shaped space frame has exemplary dimensions of about 200 feet in length, the overall diameter of substructure 204 would be about 500 feet

Superstructure 206 is comprised of a horizontal, planar pentagonal space frame 216, which as shown in FIG 12 is similar to, but larger than horizontal space frame 214 of base 204 Superstructure 206 is also comprised of five space frames 218 (see FIG 1 1) which are angled outwardly from the vertical Whereas the centerlines of tanks 210 that form the depending arms of base 204 converge on a point above structure 202, the centerlines of tanks 210 that form the depending arms of superstructure 206 converge at a point below base 204

A plurality of outer anchor lines 36 are connected at one end to one of the lower Y-joints 208 and are anchored at the other end with anchors 38 to the seabed Structure 202 is also anchored to the seabed with a plurality of conventional tension risers 54 connected to respective ones of tanks 210 or the interconnecting Y-joints 208 that form horizontal space frames 214 and 218

With the proper ballast and buoyancy tanks, structure 202 will float partially submerged with respect to a water line 218 that intersects base 204 This configuration provides a maximum amount of stability and a maximum amount of freeboard for superstructure 206 The skeleton of a large floating structure 270 that can support operations of large aircraft is schematically depicted in FIG 6 Structure 270 is comprised of a plurality of individual inverted roof frame units 272 that are anchored by three tension risers at the keel In addition each frame unit 272 is individually anchored to the seabed with a plurality of conventional tension risers 54 (see FIG 7)

CT/US97/08149

- 12 - that together form a guyed anchor mooring system. A landing strip would be formed by attaching a plurality of planar sheets (not shown) of conventional decking such as that used on naval aircraft carriers, on top of frame units 272. Frame units 272 are connected side by side to each other and to anchoring structures 202 with simple locking connectors (not shown) An exemplary size of structure 270 would be 600 feet wide by 6000 feet long with individual frame units 272 being 200 feet wide by 600 feet long Thus, 30 frame units 272 would be required

With reference now to FIGs 8 and 7, a frame unit 272 is depicted in greater detail Frame unit 272 has a horizontal space frame 274 that is comprised of six horizontal tanks 210 interconnected with 6 Y-joints 208. The third leg of Y-joint 208 is attached to a depending leg made of a tank 210 The six depending legs are connected at three Y-joints 208 with a two segmented keel 276 Each segment of keel 276 is comprised of a tank 210. Keel 276 is anchored to the seabed with a plurality of tension risers 54

FIG 8 depicts the interconnecting Y-joints 208 in greater detail Each Y-joint 208 is comprised of a plenum 280 and three legs 282. Each leg 282 is a cylindrical tube made of a rigid material such as a stainless steel The angles between legs 282 will depend upon the location of Y- joint 208, but in most locations it will be 60 degrees. Adjacent legs are connected together by welding, such as shown at 284.

Joint 208 is depicted in greater detail in FIGs. 13, 14 and 15. Interrupted thruster collars 282' and 282" are joined in a butting relationship and have a weld bead 284 completely around the joint Leg 282' has a male end with three protruding, centrally disposed tapered blades to be fitted to a female end 282" Collar 282" is a female end with protruding, centrally disposed tapered slots and axially aligned socket portion 286 which includes a central bore 288 that has a size and shape corresponding to the outer surface of a stub portion so that the latter can be received in central bore 288. Bore 288 is tapered so that there is a tight fit with the stub portion. Joint 208 is one of many ways the Y-joint can be connected to a leg.

The aforedescribed Y-shaped joints 30, 43 and 130 and the interconnecting legs associated with each can also be constructed of reinforced plastic or composite materials as well as materials which are generally flexible and require internal inflation to form a rigid joint and interconnecting leg portion Accordingly, the Y-shaped joints of the present invention may be constructed in accordance with the teaching of my U S Patent 4,288,947. Still further, the joints 30 and 43 can be formed of a flexible fabric reinforced elastomeric material which would require constant inflation pressure to maintain the rigidity of the structure but the structure can be deflated to aid in towing to and from its working position In this regard, the inflatable joints 30 and the interconnecting leg members 32, for

example, can be connected to a platform structure which itself is a buoyant vessel. The platforms 22, 22a and 22b, for example, can comprise barge-like vessels which would be suitably buoyant to move to and from a work site but operable to be positioned above the surface of the sea 24 at the target location and supported by their structures, respectively, once the structures are inflated to a suitable working pressure which would form the rigid joints and the interconnecting legs. After operations are completed such structures can be removed with minimum impact on the environment

Although preferred embodiments of the present invention have been described in detail herein, those skilled in the art will recognize that various substitutions and modifications can be made to the invention without departing from the scope and spirit of the appended claims.