Patent Publication Number: US-7717762-B2

Title: Detachable mooring system with bearings mounted on submerged buoy

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based upon provisional application 60/794,469 filed on Apr. 24, 2006, the priority of which is claimed. 

   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 in  FIGS. 1 to 4 . 
     FIGS. 1A and 1B  illustrate 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 of  FIGS. 1A and 1B  provides 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 ( 56   a ) that is geostationary and in fluid communication with the flexible conductor, and an upper conductor pipe ( 56   b ), which is fixed to the vessel and in fluid communication with the lower conductor pipe ( 56   a ) 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 in  FIG. 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 2B  show a later version of a disconnectable turret mooring arrangement ( 71 ) design of FMC Technologies. The turret mooring arrangement ( 71 ) of  FIGS. 2A and 2B  is substantially similar to the turret mooring arrangement ( 51 ) of  FIGS. 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 ( 76   b ) in fluid communication with the flexible conductor, and an upper conductor pipe ( 76   a ), fixed to the vessel and in fluid communication with the lower conductor pipe ( 76   b ) 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 of  FIGS. 1A and 1B , where the buoy ( 61 ) abuts the keel of the moored vessel ( 52 ), in the arrangement of  FIGS. 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 skirt  90  is rotatively coupled to the lower bearing ( 78 ). This system typically is used when several large fluid conductors ( 88 ) are required. 
     FIGS. 3A and 3B  generally 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 4B  illustrate 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 art  FIGS. 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 art  FIGS. 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&#39;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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in detail hereinafter on the basis of the embodiments represented in the accompanying figures, in which: 
       FIG. 1A  is a side view in partial cross section of a disconnectable mooring system of prior art showing a mooring buoy connected to a vessel and a fluid transfer system; 
       FIG. 1B  is a side view in partial cross section of the prior art disconnectable mooring system of  FIG. 1A  showing the mooring buoy disconnected from the vessel in the process of mooring; 
       FIG. 2A  is a side view in partial cross section of a later disconnectable mooring system of prior art showing a mooring buoy connected to a vessel and a fluid transfer system; 
       FIG. 2B  is a side view in partial cross section of the prior art disconnectable mooring system of  FIG. 2A  showing the mooring buoy disconnected from the vessel in the process of mooring; 
       FIG. 3A  is a side view in partial cross section of a disconnectable subsurface buoy mooring system of prior art showing a mooring buoy connected to a vessel; 
       FIG. 3B  is a side view in partial cross section of the prior art disconnectable subsurface buoy mooring system of  FIG. 3A  showing the mooring buoy disconnected from the vessel; 
       FIG. 4A  is a side view in partial cross section of a disconnectable mooring system of prior art showing a mooring buoy with an onboard turret connected to a vessel; 
       FIG. 4B  is a side view in partial cross section of the prior art disconnectable mooring system of  FIG. 4A  showing the mooring buoy disconnected from the vessel; 
       FIG. 5A  is a side view of a floating cargo tanker ship moored to a disconnectable geostationary buoy according to an embodiment of the invention; 
       FIG. 5B  is a side view of the cargo tanker ship of  FIG. 5A  disconnected from the buoy of  FIG. 5A ; 
       FIG. 6A  is a side view of a floating production system moored by a detachable buoy according to an embodiment of the invention; 
       FIG. 6B  is a side view of the floating production system of  FIG. 6A  disconnected from the buoy of  FIG. 6A ; 
       FIG. 7A  is a side view of a floating LNG import/export terminal moored to a disconnectable geostationary buoy according to an embodiment of the invention; 
       FIG. 7B  is a side view of the LNG import/export terminal of  FIG. 7A  disconnected from the buoy of  FIG. 7A ; 
       FIG. 8  is a side view in partial cross section of a mooring and fluid transfer system according to a preferred embodiment of the invention; 
       FIG. 9A  is a side view in partial cross section of the mooring and fluid transfer system of  FIG. 8  showing the mooring buoy detached from the vessel and supported by a line as if being retrieved to the ship; 
       FIG. 9B  depicts in partial cross section an array of parts to be assembled onto the mooring buoy prior to disconnection from the vessel; 
       FIG. 10A  is an enlarged side view cross section of the structural connector and buoy bearing assembly of  FIG. 8 , showing the structural connector connected to the buoy bearing hub; 
       FIG. 10B  is an enlarged side view cross section of the structural connector and buoy bearing assembly of  FIG. 8 , showing the structural connector disconnected from the buoy bearing hub; 
       FIG. 11  is a cross section view taken along lines  11 - 11  of  FIG. 8  looking down on the mooring buoy and showing a circumferential arrangement of hydraulic actuators that operate the structural connector; 
       FIG. 12  is a cross section view taken along lines  12 - 12  of  FIG. 8  looking down on the mooring buoy and showing a circumferential arrangement of collet segments of the structural connector; 
       FIG. 13  is an enlarged side view exploded diagram of the buoy bearing assembly of  FIG. 8  as it would be installed on the buoy; 
       FIG. 14A  is an enlarged top view exploded diagram of the buoy bearing assembly of  FIG. 8  showing a segmented ring and bearing hub; 
       FIG. 14B  is an enlarged top view of completed assembly of  FIG. 14A  showing the segmented bearing ring assembled on the bearing hub; 
       FIG. 15  is a side view in partial cross section of an arrangement for sealing the opening at the structural connector when the buoy is disconnected therefrom; and 
       FIG. 16  is a side view in partial cross section of a mooring and fluid transfer system according to an alternative embodiment of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
     FIGS. 5A and 5B  illustrate an embodiment of the invention used for mooring a cargo tanker ship  1  that is adapted for transporting liquid or pressurized gas hydrocarbon products. Tanker  1  typically requires frequent connection and disconnection from the mooring system and may be equipped with bow thrusters  3  to aid the recurring mooring process. 
   Mooring system  4 , generally consisting of a geostationary buoy  5  that is detachably connectable to a structural connector  12  mounted to the bottom of the vessel  1 , 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 system  4  preferably includes a number of anchors  6  and anchor legs  7  that moor buoy  5  to the sea floor  9  so that the buoy is essentially geostationary. 
   The structural connector  12 , fixed to vessel  1 , is locked in axial engagement with the buoy but is free to rotate about the geostationary buoy. Mooring arrangement  4  provides 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 ship  1  by pipeline  11  on seafloor  9 , pipeline end manifold (PLEM)  10 , flexible conductor  8 , and fluid transfer system  13 , located on ship  1 . However, other fluid flow paths arrangements may be used as appropriate. 
     FIG. 5B  shows ship  1  disconnected from buoy  5 . Structural connector  12  remains on the ship. When the buoy  5  is completely detached from the vessel  1 , the buoy  5  is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level  2 . Unlike the mooring arrangements of  FIGS. 1-3 , the vessel  1  used with mooring system  4  does 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 6B  illustrate an embodiment of the invention used for mooring a floating production, storage, and offloading (FPSO) vessel  22 . Production system  21  may be installed on vessel  22 . 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 system  26 , generally consisting of a geostationary buoy  27  that is detachably connectable to a structural connector  28  mounted to the bottom of the vessel  22 , 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 system  26  preferably includes a number of anchors and anchor legs  23  that moor buoy  27  to the sea floor so that the buoy is essentially geostationary. 
   In  FIG. 6A , the structural connector  28 , fixed to vessel  22 , is locked in axial engagement with the buoy but is free to rotate about the geostationary buoy. Mooring arrangement  26  provides a fluid flow path between a subsea well  29  and the vessel when the vessel is moored to the buoy. Fluid is transported to FPSO  22  from the subsea well by a subsea manifold  24 , flexible conductor  30  and fluid transfer system  25 , located on FPSO  22 . However, other fluid flow paths arrangements may be used as appropriate. 
     FIG. 6B  shows FPSO  22  disconnected from buoy  27 . Structural connector  28  remains on the vessel. When the buoy  27  is completely detached from the vessel  22 , the buoy  27  is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level. Unlike the mooring arrangements of  FIGS. 1-3 , the vessel  22  used with mooring system  26  does 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 7B  illustrate an embodiment of the invention used with an LNG import/export terminal  35  including an LNG regas ship  36  that loads or offloads LNG cargo through flexible conductor  41 . Mooring system  37 , generally consisting of a geostationary buoy  38  that is detachably connectable to a structural connector  45  mounted to the bottom of the vessel  36 , 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 system  37  preferably includes a number of anchors  39  and anchor legs  40  that moor buoy  38  to the sea floor  42  so that the buoy is essentially geostationary. 
   In  FIG. 7A , the structural connector  45 , fixed to vessel  36 , is locked in axial engagement with the buoy but is free to rotate about the geostationary buoy. Mooring arrangement  37  provides 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 ship  36  by pipeline  44  on seafloor  42 , pipeline end manifold (PLEM)  43 , flexible conductor  41 , and fluid transfer system  46 , located on vessel  36 . However, other fluid flow paths arrangements may be used as appropriate. 
     FIG. 7B  shows LNG carrier ship  36  disconnected from buoy  38 . Structural connector  45  remains on the ship. When the buoy  38  is completely detached from the vessel  36 , the buoy  38  is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level. Unlike the mooring arrangements of  FIGS. 1-3 , the vessel  36  used with mooring system  37  does 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. 8  illustrates the improved mooring and fluid transfer system  151  of the invention in partial cross-section according to a preferred embodiment. Detachable buoy  162  is rotatively fastened to the keel  166  of vessel  152  by bearing hub  167 , buoy bearing  170 , and structural connecter  161 . Rubber fenders  165  are provided on buoy  162  to cushion the mooring process, and a water seal  168  is provided to maintain watertight integrity of the vessel fluid transfer system (FTS) compartment. Buoy  162  is geostationarily moored above the sea floor by anchor legs  164  and anchor leg connectors  163 . Center post  184  serves the dual purpose of driving swivel torque tube  158  and providing the attachment point for pulling head  182  as shown in  FIG. 9 . 
   A flexible fluid conduit  169  is suspended by buoy  162  to provide a fluid flow path between a subsea well, pipeline or component and vessel  152 , when moored to buoy  162 . Bend restrictor  174  is preferably disposed about flexible conduit  169  at the buoy/conduit interface to prevent bend radii of flexible conduit  169  smaller than allowable limits. Flexible conductor  169  connects to the vessel fluid transfer system (FTS)  153 . The fluid path of FTS  153  includes fluid swivel  154 , upper flexible conductor  155 , conductor elbow  156 , isolation valve  173 , and geostationary conductor  171 . Conductor water seal  172  is provided to maintain watertight integrity of the vessel FTS compartment. The axial geostationary part of swivel  154  is attached to buoy  162  by torque tube  158 . The weight of swivel  154  and the geostationary fluid conductors  156 ,  173 ,  171  and  169  are carried by swivel bearing  159 . A swivel rotary drive  160  is also provided. 
     FIG. 9A  illustrates mooring buoy  162  detached from vessel  152  and supported by hawser  176 , as if being retrieved to the ship. Fluid swivel  154  has been moved aside on trolley  186 . A fixed retrieval guide unit  177  centers line  176  and provides for centralized alignment of pulling head  182  as buoy  162  approaches vessel bottom  166 . Retrieval guide unit  177  includes a central guide sleeve  179  and rubber shock absorber elements  178  to allow impact loading by pulling head  182 . Guide sleeve  179  and shock absorbers  178  are disposed within a cylindrical guide housing  180 . Guide housing  180  has an upper flange  300  that vertically supports retrieval guide unit  177  on connector cover  191  when installed. Retrieval guide unit  177  is secured in place by guide latches  181 , which are ideally fastened to connector cover  191 . After buoy  162  is fully connected, retrieval guide  177  is removed in preparation for lifting conductors  169 ,  171 , and  173  toward swivel  154 . 
     FIG. 9B  depicts the array of parts to be assembled onto buoy  162  prior to buoy disconnection. After torque tube  158  is retracted from engagement with center post  184  (see  FIG. 8 ), cover  183  is lowered into position on post  184 . Pulling head  182  with attached line  176  is then lowered and locked onto post  184 . 
     FIGS. 10A and 10B  are enlarged side view cross sections of structural connector  161  and buoy bearing assembly  170 , connected and disconnected respectively, and  FIGS. 11 and 12  are top view cross sections of structural connector  161  looking down at lines  11 ,  12  of  FIG. 8 . Structural connector  161  preferably includes a cylindrical connector housing  192  connected to a cylindrical retainer ring  193  by bolts  301 . Retainer ring  193  includes an upper flange  302  that vertically supports structural connector  161  on a lip  303  of a cylindrical vessel structural bulkhead  304 . Housing  192  is secured in place by a cylindrical rim  305  that extends downwardly from connector cover  191 , which in turn is bolted to the cylindrical vessel bulkhead  304  by bolts  306 . Housing  192  has an integral internal shelf  307  formed therein, the interior circumference  308  of which acts as a lower guide for movable connector sleeve  189  to slide axially therein. Connector cover  191  includes a downwardly extending ring  313  that fits within the interior of connector sleeve  189  and provides an upper guide for connector sleeve  189  to slide within. 
   The upper surface  309  of housing shelf  307  supports a circular hydraulic pressure manifold  187  thereon. Manifold  187  supplies pressurized hydraulic fluid to a plurality of hydraulic piston/cylinder actuators  188  that are circumferentially arranged about connector sleeve  189  and seated on manifold  187 . Preferably, twelve actuators  188  are used, but any suitable number may be used. The upper ends of actuators  188  are connected to connector sleeve  189  at an integral external upper flange  310 . Below shelf  307 , a plurality of circumferentially arranged collet segments  190  are captured between a lower interior lip  311  of housing  192  and a lower exterior lip  312  of connector sleeve  189 . Ideally, two dozen collet segments  190  are used, but any suitable number may be used. 
   Each collet segment  190  has a profile that vertically captures it between lips  311 ,  312  of connector housing  192  and connector sleeve  189 , respectively, yet forces the lower end of the collet segment  190  to pivot radially in and out as connector sleeve  189  is moved up and down axially within housing  192  by actuators  188 . The lower end of each collet segment  190  has a radially-outward facing lip  314  that engages an interior groove  315  of buoy bearing hub  167 . Thus, when connector sleeve  189  is moved downwardly, lip  312  forces the lower ends of collet segments  190  to pivot radially outward, thereby securely dogging buoy bearing hub  167  against housing  192 . Alternatively, when connector sleeve  189  moves upwardly, the lower ends of collet segments  190  pivot radially inward, thereby disconnecting bearing hub  167  from the vessel. 
   Although connector  161  is 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 connector  161  may be used. Also, although the movable connector sleeve  189  is preferred to be coaxially disposed within housing  192 , it may be disposed coaxially outside of housing  192 , if desired. 
   Bearing hub  167  is rotatively captured by buoy bearing assembly  170  so that hub  167  can rotate with respect to buoy  162  when the buoy is connected to the seabed and the hub  167  is connected to the connector  161 . A water seal  168  prevents water ingress into the structural connector compartment after the buoy  162  is connected to the vessel. 
     FIG. 13  is an enlarged side view exploded diagram illustrating buoy bearing assembly  170  as it is completely constructed for installation on buoy  162 .  FIG. 10B  shows a side view cross section of the assembled and mounted bearing assembly  170  of  FIG. 13 .  FIGS. 14A and 14B  are a top view exploded diagram and a plan view of bearing assembly  170 , respectively. Referring to  FIGS. 10B ,  13 ,  14 A, and  14 B collectively, bearing hub  167  is rotatively captured in a tongue and groove arrangement by bearing ring  203 . Bearing hub  167  slidingly rotates within segmented bearing ring  203  by means of upper and lower axial bushing segments  206 ,  207  and radial bushing segments  208 . Upper and lower bushing segments  206 ,  207  are captured between bearing ring  203  and bearing hub  167 . Bearing ring  203  is manufactured in segments and is dimensioned so that when the segments are assembled they form a true circular ring that fits closely into pilot bore  205  ( FIG. 13 ) yet allow a circumferential gap  211  ( FIG. 10B ) between bearing ring  203  and bearing hub  167 . Gap  211  minimizes any sliding contact between hub  167  and ring  203  even after wear of radial bushing  208 . Bearing ring segments  203  preferably include alignment pins  216  and alignment pin holes  217  ( FIG. 14A ) to maintain proper alignment during assembly. Joining plates  204  are used to hold bearing ring segments  203  together during assembly, and they also assure alignment and flatness at the segment joints within bearing ring  203 . Radial bushing segments  208  circumferentially fit outside the lower portion of bearing hub  167  at radial bushing  209  and fit within radial bushing seat  210  of the bearing module  200  on buoy  162 . Bushing segments  206 ,  207 ,  208 ,  209  are 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 ring  203 , bearing hub  167 , and bearing module  200  that are in contact with bushing segments  206 ,  207 ,  208 , and  209  are 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 bushings  208 ,  209  and between segments  206  and  207  and surfaces of hub  167 . Bearing assembly  170  is mounted to the bearing module  200  on buoy  162  by threaded studs or other fasteners  202 . 
   An advantage of the bearing assembly  170  is the prevention of radial loading of the studs  202 . The radial load path passes directly through the radial bushing seat  210 , radial bushing segment  208  and segment  209  of bearing hub  167 . Segmented bearing ring  203  carries only the axial forces and moment loads acting on buoy  162 . A second advantage is minimization of weight of the bearing components by providing a two-or-more-piece segmented bearing ring  203 . This feature eliminates additional bolted or keyed joints that require additional parts. 
   Although a bearing assembly  170  is described where bearing ring  203  forms the tongue and bearing hub  167  includes the groove in the tongue and groove capturing arrangement, an opposite bearing arrangement may be used. In other words, bearing hub  167  may 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 ring  203 . 
     FIG. 15  shows an arrangement for sealing the central opening of connector  161  when buoy  162  is disconnected. Guide unit  177  remains in place inside connector sleeve  189  of structural connector  161 . Guide unit  177  is raised to a position flush with the vessel bottom  166  and is secured by a guide latch  236 . Plug  235  is lowered and secured into guide unit  177  to complete the flush bottom arrangement. Seal  237  around the upper circumference of plug  235  prevents water entry into the vessel FTS compartment. Other seals (not shown) prevent water entry through structural connector  161 . 
     FIG. 16  illustrates a mooring and fluid transfer system  220  according to an alternative embodiment of the invention that is suitable for applications requiring only infrequent disconnection of the vessel  152  from the mooring buoy  224 . A lower cost mooring system is provided by the arrangement of  FIG. 16  as compared to that of  FIG. 8 , et al. Unlike the mooring and fluid transfer system  151  of  FIGS. 8-15  having a quick-disconnect structural connector  161 , the mooring and fluid transfer system  220  of  FIG. 16  simply has a cylindrical connector member  221  that is fastened directly to bearing hub  201  of the disconnectable buoy  224  by fasteners  223 . The fastener may be disconnected for separation of the buoy  224  from connector member  221  and vice-versa. Connector member  221  has a lower internal flange  222  that forms a seat for the upper end of bearing hub  201 . A connector retaining ring  230  secures connector member  221  to the cylindrical vessel structural bulkhead  304 . Bearing hub  201  of  FIG. 16  is similar to bearing hub  167  of  FIG. 10B , except that it substitutes a circumferential pattern of threaded holes along the top of the hub to receive threaded studs  223  in place of the internal groove  315  that is engaged by collet segments  190 . Ideally, bearing assembly  170  is structured and functions identically for both embodiments. Buoy  224  supports the static weight of anchor legs  164 , although in some cases it may be desirable and readily possible also to support the weight of fluid conductors  169  and fluid transfer system  153  on 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: