Detachable mooring system with bearings mounted on submerged buoy

A mooring system comprising a submerged buoy releasably connectable to a vessel keel having a combined axial/radial bearing. A segmented ring, fastened to the buoy, forms the bearing outer ring. An inner bearing hub slidingly carried on the bearing outer ring is connectable to a vessel structural connector. In a first embodiment, the structural connector includes an inner cylindrical sleeve coaxially movable within an outer cylindrical housing by circumferential actuators. The lower ends of the connector sleeve and connector housing capture plural collet segments circumpositioned therebetween that radially move in and out as the connector sleeve is moved axially within the connector housing. The lower ends of the collet segments extend downward into the bearing hub and releasably engage an interior groove therein, thereby dogging the bearing hub against the vessel. In a second embodiment, the bearing hub is simply bolted directly to a cylindrical connector member of the vessel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns detachable mooring systems for loading and offloading liquid petroleum product oil tankers, floating storage (FSO) vessels, floating production storage and offloading (FPSO) systems, floating vessels for natural gas offloading (for example, cryogenic liquefied natural gas (LNG) regas import terminals), and LNG transport vessels.

2. Description of the Prior Art

Numerous patents are known that pertain to disconnectable mooring systems, many of which provide a submerged buoy that can be detachably released from a floating vessel. For example, U.S. Pat. No. 5,651,708 issued to Borseth shows a detachable buoy with a geostationary part. The Borseth buoy has an outer body that is received in a recess in the bottom of the vessel, where the outer body is fixed to the vessel by locking wedges. Four other notable types of detachable mooring systems are known and are illustrated inFIGS. 1 to 4.

FIGS. 1A and 1Billustrate a disconnectable mooring system of a design of FMC Technologies and as illustrated by U.S. Pat. No. 5,240,446. The mooring system includes two basic parts—a geostationary buoy (61) that is detachably connectable to a turret assembly (53) that is disposed in the floating vessel. The buoy (61) is moored to the seabed by a number of anchor legs (63) that are connected to the buoy at anchor leg connectors (62), such that the buoy is generally geostationary.

The vessel (52) carries a turret assembly (53), which is revolvably disposed within the vessel hull and which opens to the sea near the keel elevation. The turret (53) includes a vertical turret shaft (59) and is supported by an upper axial bearing (57) and a lower radial bearing (58). The turret and bearings remain on the vessel when the buoy is disconnected therefrom. The lower end of the turret shaft (59) is equipped with a structural connector (60) that is designed and arranged to disconnectably mate with a connector hub (66) located at the upper surface of the buoy (61). Rubber fenders (64) are provided on the buoy to cushion the mooring process, and a water seal (67) is provided to maintain watertight integrity of the turret compartment in the vessel.

The turret mooring arrangement ofFIGS. 1A and 1Bprovides a fluid flow path between a subsea well or component and the vessel when the vessel is moored to the buoy. The fluid transfer system (FTS) (54) includes a flexible conductor (68) spanning the distance between the seabed and the buoy (61), a lower conductor pipe (56a) that is geostationary and in fluid communication with the flexible conductor, and an upper conductor pipe (56b), which is fixed to the vessel and in fluid communication with the lower conductor pipe (56a) via a fluid swivel (55).

When the buoy (61) is completely separated from the vessel (52), the buoy (61) is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level. As shown inFIG. 1B, the vessel is moored to the buoy by first recovering the submerged buoy upwards to the structural connector (60) by heaving in a retrieval line (65) with a winch system (not shown). The structural connector (60) is then locked in engagement with the connector hub (66), fixing the turret with the geostationary buoy and mooring the vessel (52) to the seabed. The vessel can freely weathervane about the geostationary turret in response to wind, waves and currents.

FIGS. 2A and 2Bshow a later version of a disconnectable turret mooring arrangement (71) design of FMC Technologies. The turret mooring arrangement (71) ofFIGS. 2A and 2Bis substantially similar to the turret mooring arrangement (51) ofFIGS. 1A and 1B. For example, the buoy (81) is moored to the seabed by a number of anchor legs (83) that are connected to the buoy at anchor leg connectors (82), such that the buoy is generally geostationary. The vessel (72) carries a turret assembly (73), which is revolvably disposed within the vessel hull and which opens to the sea near the keel. The turret assembly (73) includes a vertical turret shaft (79) and is supported by an upper axial bearing (77) and a lower radial bearing (78). The turret and bearings remain on the vessel when the buoy is disconnected. The lower end of the turret shaft (79) is equipped with a structural connector (80) that is designed and arranged to disconnectably mate with a connector hub (86) disposed at the upper surface of the buoy (81). A water seal (87) is provided to maintain watertight integrity of the turret compartment in the vessel. The fluid transfer system (FTS) (74) includes a flexible conductor (88) between the seabed and the buoy (81), a lower geostationary conductor pipe (76b) in fluid communication with the flexible conductor, and an upper conductor pipe (76a), fixed to the vessel and in fluid communication with the lower conductor pipe (76b) via a fluid swivel (75). When the buoy (81) is separated from the vessel (72), the buoy (81) is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level. A retrieval line (85) is provided for heaving the buoy to the vessel.

However, unlike the turret mooring arrangement ofFIGS. 1A and 1B, where the buoy (61) abuts the keel of the moored vessel (52), in the arrangement ofFIGS. 2A and 2B, the upper part of a buoy (81) is cone shaped and is brought into a cone shaped buoy receiving space (89). The structural connector (80) fastens the buoy (81) to the turret shaft (79). The turret shaft (79) is rotatively connected to the vessel (72) by the upper bearing (77). The skirt90is rotatively coupled to the lower bearing (78). This system typically is used when several large fluid conductors (88) are required.

FIGS. 3A and 3Bgenerally describe a subsurface buoy mooring system (101) such as that shown by Svensen in U.S. Pat. No. 4,892,495. A cone-shaped buoy (103) is rotatably received into a receptacle (108) formed in the vessel hull (111) and is secured inside a complementary turret receptacle (104) by latches (105). A radial bearing (106) and a vertically-oriented axial bearing (107) support turret (102). The axial bearing (107) abuts a bearing support surface (110). When the buoy (103) is disconnected from the vessel, the turret and the bearings remain on the vessel. The buoy (103) is moored to the seabed by a number of anchor legs (109) such that it is essentially geostationary. For simplicity, the fluid transfer system is not illustrated.

FIGS. 4A and 4Billustrate a type of mooring system (121) design of Advanced Production Loading (APL) AS of Norway and described in U.S. Pat. No. 5,468,166, among others. A buoy assembly (124) includes a buoy (128), upper and lower bearings (126,127), and a turret (125) that is rotatably supported by the bearings. The cone-shaped buoy (128) is non-rotatably secured into a complementary receptacle (137) formed in the vessel hull (122) by latches (134) that engage a groove (135) formed in the buoy.

The fluid transfer system (FTS) includes a flexible conductor (133) spanning the distance between the seabed and the buoy (128), a lower conductor pipe (132) that is geostationary and in fluid communication with the flexible conductor, and an upper conductor pipe (136), which is fixed to the vessel and in fluid communication with the lower conductor pipe (132) via a fluid swivel (123).

However, the buoy (128) is not geostationary; the buoy is attached to and rotates with the vessel hull (122) while the turret (125) remains geostationary. When the buoy assembly (124) is disconnected from the vessel (122), the bearings and the turret remain on the buoy. The lower end of the turret (125) forms a chain table or anchor leg frame (129) with anchor leg connectors (131). A number of anchor legs (130) connect the turret to the seabed so that the turret (125) is essentially geostationary. In this design the entire anchor leg system weight and loads are supported by the axial bearing (126). Because the APL buoy (128) is secured directly to the vessel (122), its buoyancy does not serve to reduce vertical bearing loads.

Most mooring systems are “turret” systems of one form or another which are familiar to those skilled in the art. Turrets are generally large and expensive structures that usually include large diameter upper and lower bearings. Many prior art disconnectable mooring systems also require a large (approximately 10 meters diameter or larger) cone shaped opening in the vessel bottom. Such structure mandates expensive vessel construction. Because there is a continuing requirement for lowering the cost of major components on floating production systems and loading/offloading cargo vessels, reduction of large, expensive mooring structures is advantageous. Furthermore, large openings in the vessel hull to accommodate mooring buoys cause significant drag and energy losses on those disconnectable cargo vessels when they are sailing long distances. As newer and larger high speed LNG carrier/regas vessels tend to have a narrow flat bottom near the bow at the optimum location for a buoy connection, a large hull opening is less desirable in these applications.

3. Identification of Objects of the Invention

A primary object of the invention is to provide a mooring buoy that remains geostationary with only an inner ring of a bearing mounted on the buoy that can be disconnectably connected to the ship.

Another primary object of this invention is to provide a detachable mooring system in which a bearing can be installed in or on the buoy that has a large radial mooring load capacity due to its unique arrangement. Detachable moorings having larger load capacity are desirable because hydrocarbon production and import/export terminals are moving into more hostile environments.

Another object of the invention is to provide a mooring system that requires a significantly smaller opening in the vessel with the capability to plug the opening so a virtually smooth ship bottom is achieved at the buoy connection point.

Another object of the invention is to provide an improved disconnectable mooring system that eliminates the need for the turret component of prior loading and offloading liquid petroleum product oil tankers, floating storage (FSO) vessels, floating production storage and offloading (FPSO) systems, floating vessels for natural gas offloading, and LNG transport vessels, thereby resulting in significant cost reductions.

Another object of the invention is to provide an improved detachable mooring system that can be released and recovered in high sea states and harsh conditions due to the arrangement of buoy to ship interface equipment.

Another object of the invention is to provide an adaptation of the invention that achieves the inherent cost and functional advantages of the new arrangement for mooring a vessel permanently installed at an offshore location.

SUMMARY OF THE INVENTION

The objects identified above, as well as other features and advantages of the invention are incorporated in a mooring and fluid transfer system including a submergible buoy that is moored to the sea floor so as to be generally geostationary. The buoy can be detached from a floating vessel. The buoy mounts adjacent the bottom of the vessel rather than having a substantial portion of the buoy being received into the vessel as disclosed by the prior artFIGS. 2-4. A combined bearing assembly that supports axial and radial loading is mounted on the buoy, rather than in the vessel as disclosed by the prior artFIGS. 1-3.

A cylindrical bearing hub, which forms an inner ring of a bearing assembly, is rotatively mounted to a segmented ring that forms the outer ring of the bearing assembly, which is ideally fastened to the buoy hull with bolts. The bearing hub can be releasably connected to the bottom of the vessel by a structural connector on board the vessel. The bearing assembly is structured so that radial bearing loads pass between the vessel and the buoy directly through the bearing hub, radial bushing segments, and a bushing seat formed in the buoy. The outer bearing ring and mounting bolts carry only axial loads; no radial loading passes through bolts. The multi-piece segmented structure of the outer bearing ring reduces bearing weight.

In a first embodiment, the vessel includes a structural connector which includes an inner cylindrical sleeve coaxially disposed in an outer cylindrical housing. The inner sleeve can be axially moved within the outer housing by a number of actuators which are circumferentially disposed between the sleeve and the housing. The lower ends of the connector sleeve and connector housing capture a number of collet segments circumpositioned therebetween that radially pivot in and out as the inner connector sleeve is moved axially up and down within the connector housing. To connect the mooring buoy to the vessel, the bearing hub of the buoy is placed axially adjacent the bottom of the connector housing of the vessel's structural connector. The lower ends of the collet segments extend downward into the interior of the bearing hub. The connector sleeve is moved downward by the actuators, which forces the lower ends of the collet segments to pivot radially outward. The ends of the collet segments then engage an interior groove in the bearing hub, thus dogging the bearing hub (and the buoy) against the connector housing of the vessel.

In a second embodiment, the bearing hub is simply bolted directly to a cylindrical connector member of the vessel.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

FIGS. 5A and 5Billustrate an embodiment of the invention used for mooring a cargo tanker ship1that is adapted for transporting liquid or pressurized gas hydrocarbon products. Tanker1typically requires frequent connection and disconnection from the mooring system and may be equipped with bow thrusters3to aid the recurring mooring process.

Mooring system4, generally consisting of a geostationary buoy5that is detachably connectable to a structural connector12mounted to the bottom of the vessel1, is adapted to temporarily moor the vessel, allowing the vessel to weathervane around the point of mooring under the influence of wind, waves and currents while it is being loaded. Mooring system4preferably includes a number of anchors6and anchor legs7that moor buoy5to the sea floor9so that the buoy is essentially geostationary.

The structural connector12, fixed to vessel1, is locked in axial engagement with the buoy but is free to rotate about the geostationary buoy. Mooring arrangement4provides a fluid flow path between a subsea well, pipeline, or component and the vessel when the vessel is moored to the buoy. The cargo is transported to or from ship1by pipeline11on seafloor9, pipeline end manifold (PLEM)10, flexible conductor8, and fluid transfer system13, located on ship1. However, other fluid flow paths arrangements may be used as appropriate.

FIG. 5Bshows ship1disconnected from buoy5. Structural connector12remains on the ship. When the buoy5is completely detached from the vessel1, the buoy5is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level2. Unlike the mooring arrangements ofFIGS. 1-3, the vessel1used with mooring system4does not carry a turret assembly revolvably disposed within the vessel hull. Neither axial bearings nor radial bearings remain on the vessel when the buoy is disconnected therefrom.

FIGS. 6A and 6Billustrate an embodiment of the invention used for mooring a floating production, storage, and offloading (FPSO) vessel22. Production system21may be installed on vessel22. This type system does not require frequent or rapid disconnection from the buoy. Disconnection and reconnection of this type system generally is done in fairly calm water conditions, but may occur in deteriorating weather conditions from an approaching hurricane. Advantages of quicker construction, less capital expense, and rapid offshore installation of the mooring system are provided by the invention.

Mooring system26, generally consisting of a geostationary buoy27that is detachably connectable to a structural connector28mounted to the bottom of the vessel22, is adapted to moor the vessel, allowing the vessel to weathervane around the point of mooring under the influence of wind, waves and currents. Mooring system26preferably includes a number of anchors and anchor legs23that moor buoy27to the sea floor so that the buoy is essentially geostationary.

InFIG. 6A, the structural connector28, fixed to vessel22, is locked in axial engagement with the buoy but is free to rotate about the geostationary buoy. Mooring arrangement26provides a fluid flow path between a subsea well29and the vessel when the vessel is moored to the buoy. Fluid is transported to FPSO22from the subsea well by a subsea manifold24, flexible conductor30and fluid transfer system25, located on FPSO22. However, other fluid flow paths arrangements may be used as appropriate.

FIG. 6Bshows FPSO22disconnected from buoy27. Structural connector28remains on the vessel. When the buoy27is completely detached from the vessel22, the buoy27is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level. Unlike the mooring arrangements ofFIGS. 1-3, the vessel22used with mooring system26does not carry a turret assembly about which the vessel can revolve. Neither axial bearings nor radial bearings remain on the vessel when the buoy is disconnected therefrom.

FIGS. 7A and 7Billustrate an embodiment of the invention used with an LNG import/export terminal35including an LNG regas ship36that loads or offloads LNG cargo through flexible conductor41. Mooring system37, generally consisting of a geostationary buoy38that is detachably connectable to a structural connector45mounted to the bottom of the vessel36, is adapted to moor the vessel, allowing the vessel to weathervane around the point of mooring under the influence of wind, waves and currents. Mooring system37preferably includes a number of anchors39and anchor legs40that moor buoy38to the sea floor42so that the buoy is essentially geostationary.

InFIG. 7A, the structural connector45, fixed to vessel36, is locked in axial engagement with the buoy but is free to rotate about the geostationary buoy. Mooring arrangement37provides a fluid flow path between a pipeline or component and the vessel when the vessel is moored to the buoy. Fluid is transported to or from LNG carrier ship36by pipeline44on seafloor42, pipeline end manifold (PLEM)43, flexible conductor41, and fluid transfer system46, located on vessel36. However, other fluid flow paths arrangements may be used as appropriate.

FIG. 7Bshows LNG carrier ship36disconnected from buoy38. Structural connector45remains on the ship. When the buoy38is completely detached from the vessel36, the buoy38is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level. Unlike the mooring arrangements ofFIGS. 1-3, the vessel36used with mooring system37does not carry a turret assembly revolvably disposed within the vessel hull. Neither axial bearings nor radial bearings remain on the vessel when the buoy is disconnected therefrom.

FIG. 8illustrates the improved mooring and fluid transfer system151of the invention in partial cross-section according to a preferred embodiment. Detachable buoy162is rotatively fastened to the keel166of vessel152by bearing hub167, buoy bearing170, and structural connecter161. Rubber fenders165are provided on buoy162to cushion the mooring process, and a water seal168is provided to maintain watertight integrity of the vessel fluid transfer system (FTS) compartment. Buoy162is geostationarily moored above the sea floor by anchor legs164and anchor leg connectors163. Center post184serves the dual purpose of driving swivel torque tube158and providing the attachment point for pulling head182as shown inFIG. 9.

A flexible fluid conduit169is suspended by buoy162to provide a fluid flow path between a subsea well, pipeline or component and vessel152, when moored to buoy162. Bend restrictor174is preferably disposed about flexible conduit169at the buoy/conduit interface to prevent bend radii of flexible conduit169smaller than allowable limits. Flexible conductor169connects to the vessel fluid transfer system (FTS)153. The fluid path of FTS153includes fluid swivel154, upper flexible conductor155, conductor elbow156, isolation valve173, and geostationary conductor171. Conductor water seal172is provided to maintain watertight integrity of the vessel FTS compartment. The axial geostationary part of swivel154is attached to buoy162by torque tube158. The weight of swivel154and the geostationary fluid conductors156,173,171and169are carried by swivel bearing159. A swivel rotary drive160is also provided.

FIG. 9Aillustrates mooring buoy162detached from vessel152and supported by hawser176, as if being retrieved to the ship. Fluid swivel154has been moved aside on trolley186. A fixed retrieval guide unit177centers line176and provides for centralized alignment of pulling head182as buoy162approaches vessel bottom166. Retrieval guide unit177includes a central guide sleeve179and rubber shock absorber elements178to allow impact loading by pulling head182. Guide sleeve179and shock absorbers178are disposed within a cylindrical guide housing180. Guide housing180has an upper flange300that vertically supports retrieval guide unit177on connector cover191when installed. Retrieval guide unit177is secured in place by guide latches181, which are ideally fastened to connector cover191. After buoy162is fully connected, retrieval guide177is removed in preparation for lifting conductors169,171, and173toward swivel154.

FIG. 9Bdepicts the array of parts to be assembled onto buoy162prior to buoy disconnection. After torque tube158is retracted from engagement with center post184(seeFIG. 8), cover183is lowered into position on post184. Pulling head182with attached line176is then lowered and locked onto post184.

FIGS. 10A and 10Bare enlarged side view cross sections of structural connector161and buoy bearing assembly170, connected and disconnected respectively, andFIGS. 11 and 12are top view cross sections of structural connector161looking down at lines11,12ofFIG. 8. Structural connector161preferably includes a cylindrical connector housing192connected to a cylindrical retainer ring193by bolts301. Retainer ring193includes an upper flange302that vertically supports structural connector161on a lip303of a cylindrical vessel structural bulkhead304. Housing192is secured in place by a cylindrical rim305that extends downwardly from connector cover191, which in turn is bolted to the cylindrical vessel bulkhead304by bolts306. Housing192has an integral internal shelf307formed therein, the interior circumference308of which acts as a lower guide for movable connector sleeve189to slide axially therein. Connector cover191includes a downwardly extending ring313that fits within the interior of connector sleeve189and provides an upper guide for connector sleeve189to slide within.

The upper surface309of housing shelf307supports a circular hydraulic pressure manifold187thereon. Manifold187supplies pressurized hydraulic fluid to a plurality of hydraulic piston/cylinder actuators188that are circumferentially arranged about connector sleeve189and seated on manifold187. Preferably, twelve actuators188are used, but any suitable number may be used. The upper ends of actuators188are connected to connector sleeve189at an integral external upper flange310. Below shelf307, a plurality of circumferentially arranged collet segments190are captured between a lower interior lip311of housing192and a lower exterior lip312of connector sleeve189. Ideally, two dozen collet segments190are used, but any suitable number may be used.

Each collet segment190has a profile that vertically captures it between lips311,312of connector housing192and connector sleeve189, respectively, yet forces the lower end of the collet segment190to pivot radially in and out as connector sleeve189is moved up and down axially within housing192by actuators188. The lower end of each collet segment190has a radially-outward facing lip314that engages an interior groove315of buoy bearing hub167. Thus, when connector sleeve189is moved downwardly, lip312forces the lower ends of collet segments190to pivot radially outward, thereby securely dogging buoy bearing hub167against housing192. Alternatively, when connector sleeve189moves upwardly, the lower ends of collet segments190pivot radially inward, thereby disconnecting bearing hub167from the vessel.

Although connector161is described and illustrated herein as being generally cylindrical, it is not limited to a cylindrical configuration. For example, octagonal, hexagonal, or even a square-shaped structural connector161may be used. Also, although the movable connector sleeve189is preferred to be coaxially disposed within housing192, it may be disposed coaxially outside of housing192, if desired.

Bearing hub167is rotatively captured by buoy bearing assembly170so that hub167can rotate with respect to buoy162when the buoy is connected to the seabed and the hub167is connected to the connector161. A water seal168prevents water ingress into the structural connector compartment after the buoy162is connected to the vessel.

FIG. 13is an enlarged side view exploded diagram illustrating buoy bearing assembly170as it is completely constructed for installation on buoy162.FIG. 10Bshows a side view cross section of the assembled and mounted bearing assembly170ofFIG. 13.FIGS. 14A and 14Bare a top view exploded diagram and a plan view of bearing assembly170, respectively. Referring toFIGS. 10B,13,14A, and14B collectively, bearing hub167is rotatively captured in a tongue and groove arrangement by bearing ring203. Bearing hub167slidingly rotates within segmented bearing ring203by means of upper and lower axial bushing segments206,207and radial bushing segments208. Upper and lower bushing segments206,207are captured between bearing ring203and bearing hub167. Bearing ring203is manufactured in segments and is dimensioned so that when the segments are assembled they form a true circular ring that fits closely into pilot bore205(FIG. 13) yet allow a circumferential gap211(FIG. 10B) between bearing ring203and bearing hub167. Gap211minimizes any sliding contact between hub167and ring203even after wear of radial bushing208. Bearing ring segments203preferably include alignment pins216and alignment pin holes217(FIG. 14A) to maintain proper alignment during assembly. Joining plates204are used to hold bearing ring segments203together during assembly, and they also assure alignment and flatness at the segment joints within bearing ring203. Radial bushing segments208circumferentially fit outside the lower portion of bearing hub167at radial bushing209and fit within radial bushing seat210of the bearing module200on buoy162. Bushing segments206,207,208,209are preferably made of non-metallic low-friction bushing material, such as Orkot brand or a similar material. Such materials are readily available for submerged service exposed directly to the seawater. The sliding bearing surfaces of bearing ring203, bearing hub167, and bearing module200that are in contact with bushing segments206,207,208, and209are made of non-corrosive wear resistant materials such as stainless steel or Inconel. Grease suitable for use in salt water may advantageously be applied between bushings208,209and between segments206and207and surfaces of hub167. Bearing assembly170is mounted to the bearing module200on buoy162by threaded studs or other fasteners202.

An advantage of the bearing assembly170is the prevention of radial loading of the studs202. The radial load path passes directly through the radial bushing seat210, radial bushing segment208and segment209of bearing hub167. Segmented bearing ring203carries only the axial forces and moment loads acting on buoy162. A second advantage is minimization of weight of the bearing components by providing a two-or-more-piece segmented bearing ring203. This feature eliminates additional bolted or keyed joints that require additional parts.

Although a bearing assembly170is described where bearing ring203forms the tongue and bearing hub167includes the groove in the tongue and groove capturing arrangement, an opposite bearing arrangement may be used. In other words, bearing hub167may have a circumferential tongue (not illustrated) instead of a circumferential groove, which is received into a groove (not illustrated) formed in the interior of bearing ring203.

FIG. 15shows an arrangement for sealing the central opening of connector161when buoy162is disconnected. Guide unit177remains in place inside connector sleeve189of structural connector161. Guide unit177is raised to a position flush with the vessel bottom166and is secured by a guide latch236. Plug235is lowered and secured into guide unit177to complete the flush bottom arrangement. Seal237around the upper circumference of plug235prevents water entry into the vessel FTS compartment. Other seals (not shown) prevent water entry through structural connector161.

FIG. 16illustrates a mooring and fluid transfer system220according to an alternative embodiment of the invention that is suitable for applications requiring only infrequent disconnection of the vessel152from the mooring buoy224. A lower cost mooring system is provided by the arrangement ofFIG. 16as compared to that ofFIG. 8, et al. Unlike the mooring and fluid transfer system151ofFIGS. 8-15having a quick-disconnect structural connector161, the mooring and fluid transfer system220ofFIG. 16simply has a cylindrical connector member221that is fastened directly to bearing hub201of the disconnectable buoy224by fasteners223. The fastener may be disconnected for separation of the buoy224from connector member221and vice-versa. Connector member221has a lower internal flange222that forms a seat for the upper end of bearing hub201. A connector retaining ring230secures connector member221to the cylindrical vessel structural bulkhead304. Bearing hub201ofFIG. 16is similar to bearing hub167ofFIG. 10B, except that it substitutes a circumferential pattern of threaded holes along the top of the hub to receive threaded studs223in place of the internal groove315that is engaged by collet segments190. Ideally, bearing assembly170is structured and functions identically for both embodiments. Buoy224supports the static weight of anchor legs164, although in some cases it may be desirable and readily possible also to support the weight of fluid conductors169and fluid transfer system153on the buoy.

The Abstract of the disclosure is written solely for providing the United States Patent and Trademark Office and the public at large with a way to determine quickly from a cursory reading the nature and gist of the technical disclosure, and it represents solely a preferred embodiment and is not indicative of the nature of the invention as a whole.

While some embodiments of the invention have been illustrated in detail, the invention is not limited to the embodiments shown; modifications and adaptations of the above embodiment may occur to those skilled in the art. Such modifications and adaptations are in the spirit and scope of the invention as set forth herein: