Abstract:
A disconnectable rigid mooring system for attaching a ship to a tower structure includes a yoke releasably connected to a yoke head. The yoke head is pivotally attached to the tower structure and the yoke is arranged and designed to attach to the ship. The yoke and the yoke head each have a mating connector portion arranged and designed to connect the yoke to the yoke head. When the connector portions are engaged and locked, the yoke is securely attached to the yoke head, allowing a rigid interconnection between the ship and the tower structure. During normal operations and in normal sea states, the yoke remains connected to the yoke head pivotally attached to the tower structure. In the event of predicted abnormally high sea states, the yoke may be disconnected from the yoke head by the ship and be secured to the ship and removed prior to the abnormally high sea state event. The yoke and yoke head are provided with alignment guides and mechanisms which permit the yoke and yoke head to be properly aligned during the connect and disconnect procedures.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a rigid mooring system for use in attaching a floating vessel or ship to a tower structure attached to the sea floor. More particularly, the invention relates to a tower mooring system comprising a rigid tower yoke assembly having a yoke releasably attached to a yoke head via a connector allowing removal of the yoke by the ship in the event of predicted abnormally high sea states. 
         [0003]    2. Description of the Related Art 
         [0004]    Typical tower yoke mooring systems are permanent mooring systems where the floating vessel cannot leave for a storm. The typical tower yoke, single point mooring system includes a “soft yoke” for mooring a floating vessel directly to a fixed tower. A turntable is fastened to the tower, typically with a roller bearing, to allow the floating vessel to freely weathervane about the fixed tower. A yoke is connected to the turntable with pitch and roll joints to allow the vessel to pitch and roll. The yoke includes a large ballast tank adapted to be filled with water to provide the necessary restoring force to minimize vessel motions. Two mooring links suspend the ballast tank from a support structure mounted on the floating vessel. 
         [0005]    Product, such as oil or gas for example, is transferred from the tower across swivels located on the turntable and through hoses from the turntable to the vessel. The tower includes deck space for a manifold and other equipment. Access to the tower can be made via walkways from the vessel and on the yoke. 
         [0006]    However, some tower yoke mooring system applications in shallow water are needed in areas potentially subjected to large storms or extreme sea states such as hurricanes or typhoons, during which the floating vessel will leave the area. For purposes of safety and to survive the extreme sea states it is desirable that the tower yoke be disconnectable from the tower structure. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention includes a disconnectable tower yoke for a large storm environment. The disconnectable tower yoke allows the yoke to be removed from the tower structure and remain with the floating vessel when disconnecting for a large storm. In a preferred embodiment, the disconnection takes place at a yoke head with a hydraulic connector. The yoke head includes a trunnion for pivotal movement relative to the tower structure. Preferably, a conical interface at the yoke to yoke head connection allows for alignment and connection of the yoke to the yoke head. A pull-in line attached to the yoke head trunnion housing serves as a guide for the yoke and yoke head during vessel pull-in and connection. 
         [0008]    The preferred embodiment of the present invention further includes a frame, attached to the mooring support structure of the vessel, containing a motion compensated winch that allows for the yoke to be supported by the vessel and allows for reconnection of the yoke to the yoke head. Hoses and flow lines are disconnected at the tower structure and transferred to the vessel prior to disconnection. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    The various aspects and advantages of the preferred embodiment of the present invention will become apparent to those skilled in the art upon an understanding of the following detailed description of the invention, read in light of the accompanying drawings which are made a part of this specification and in which: 
           [0010]      FIG. 1  is an elevation view showing a floating vessel or ship moored to a tower via a tower yoke; 
           [0011]      FIG. 2  is a plan view of the yoke; 
           [0012]      FIG. 3  is an elevation view showing a connection between a turntable and a yoke head; 
           [0013]      FIG. 4  is an elevation view showing a preferred embodiment of the invention in which the yoke and yoke head are in a disconnected condition; 
           [0014]      FIG. 5  is a cross-sectional view of the preferred embodiment showing the yoke and yoke head in a disconnected condition; and 
           [0015]      FIG. 6  is a cross-sectional view showing the yoke and the yoke head in a connected condition, with the hydraulic connector engaged in the upper half of the figure and disengaged in the lower half of the figure. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    The preferred embodiment of the present invention will now be discussed with reference to the drawings.  FIG. 1  shows a tower  10  including a jacket structure  12  fixedly attached to the sea floor F, typically via piling. The tower  10  also includes a plurality of decks  14  mounted on the jacket structure  12  at various elevations above the water level L, typically mean water level, and a vertical support column  16 . It is understood by those of skill in the art that the decks  14  are arranged and designed to support various equipment, including manifolds, etc. A turntable  18  is fastened to the support column  16 , with a turntable bearing  28  ( FIG. 5 ), preferably a roller bearing, to allow a floating vessel V moored to the tower  10  to freely weathervane about the tower  10 . Preferably, one or more decks, including a hose deck  19 , are located above the turntable  18  and rotate with the turntable  18 . 
         [0017]    The floating vessel V is moored to the tower  10  via a yoke  24 .  FIG. 2  shows a plan view of a yoke  24 . Typically, the yoke  24  is formed primarily from tubular members. As shown in  FIG. 2 , the yoke  24  is generally triangular in shape when viewed in plan view. The yoke  24  includes a large ballast tank  26  adapted to be filled with water or other ballast to provide the necessary restoring force to minimize motions of the vessel V when connected to the tower  10 . The yoke  24  includes a pair of legs  25  angled towards each other. Each leg  25  has one end connected to the ballast tank  26  and a second end connected to a yoke coupler  30 . In the preferred embodiment, the yoke  24  is arranged and designed to be connected to and disconnected from a yoke head  20  while on location. Preferably, the yoke coupler  30  is a conical section for alignment and connection with the yoke head  20  as best shown in  FIG. 4 . 
         [0018]    In the preferred embodiment, the yoke head  20  is mounted to the turntable  18  via a pair of trunnions  23  for pivotal movement relative to the turntable  18  as shown in  FIGS. 3-5 . Referring to  FIG. 5 , the pair of trunnions  23  extend outwardly from a trunnion housing  22 . A pull-in line  38  attached to the trunnion housing  22  of the yoke head  20  serves as a guide for the yoke  24  and yoke head  20  during vessel V pull-in and connection. 
         [0019]    As shown in  FIG. 5 , a yoke head conical section  32  is connected to the trunnion housing  22 , preferably via a roll bearing  40 . The yoke head roll bearing  40  allows the head conical section  32  to rotate relative to the trunnion housing  22 . 
         [0020]    In the preferred embodiment the yoke head conical section  32  is arranged and designed to cooperate and interface with the yoke conical section  30 . This interface includes two conical machined surfaces: an inner surface  34  on the yoke conical section  30  (female) and an outer surface  36  on the head conical section  32  (male) as shown in  FIG. 5 . The conical sections  30  and  32  at the ends of the yoke  24  and the yoke head  20 , respectively, allow for guidance during connection and allow for load transfer from the yoke  24  to the yoke head  20 . 
         [0021]    In the preferred embodiment as shown in  FIG. 5 , a hydraulic connector  50  is positioned inside of the yoke head conical section  32  and is actuated from the tower side by accumulators and telemetry controlled valves. Accumulators and telemetry controlled valves are well known to those skilled in the art. The hydraulic connector  50  has a stationary housing  52  mounted within the head conical section  32 . The stationary housing  52  is preferably a substantially cylindrical housing having a bore  54  therethrough. The stationary housing  52  includes an outwardly facing shoulder  56  and one or more line guides  58  within the bore  54 . The pull-in line  38  extends through the bore  54  and between the one or more line guides  58 . The hydraulic connector  50  also includes a movable sleeve  60  extending around the outwardly facing shoulder  56 . The movable sleeve  60  includes an inwardly directed flange  62  at one end and a band  64  at an opposite end. The band  64  contacts one or a plurality of pivot fingers  66 . One or more actuators  68 , preferably hydraulic cylinders, are positioned between and connected to the outwardly facing shoulder  56  of the stationary housing  52  and the inwardly directed flange  62  of the movable sleeve  60 . Preferably, when more than one actuator  68  is used, all of the actuators are controlled by a singular control to provide simultaneous operation and movement of the movable sleeve  60 . 
         [0022]    A mating hub  70  of the hydraulic connector  50  is mounted within the yoke conical section  30  by means of an adapter  72 . Preferably, the mating hub  70  and the adapter  72  are annular members having a common bore  74  extending therethough. Preferably, one or more line guides  58  are mounted within the common bore  74 . The pull-in line  38  extends through the common bore  74  and between the one or more line guides  58 . 
         [0023]      FIG. 5  shows the yoke  24  and the yoke head  20  in a disconnected condition and  FIG. 6  shows the yoke  24  and the yoke head  20  in a connected condition, with the hydraulic connector  50  engaged in the upper half of the figure and disengaged in the lower half of the figure for exemplary purposes. When the hydraulic connector  50  is engaged, it provides a preload to the conical structural interfaces  34  and  36 . With reference to  FIG. 5  and the lower half of  FIG. 6 , the rod of the actuator  68  is extended such that the band  64  of the movable sleeve  60  allows the pivot fingers  66  to pivot outwardly. Upon engagement of the end of the stationary housing  52  with the end of the mating hub  70  and the engagement of the conical structural interfaces  34  and  36 , the actuators  68  are actuated to move the movable sleeve  60  in the direction of the mating hub  70  until the pivot fingers  66  are forcibly inserted into the mating hub recess  76  as shown in the upper half of  FIG. 6 . With the pivot fingers  66  forcibly inserted in the mating hub recess  76 , the yoke  24  is securely connected to the yoke head  20 . Preferably, secondary mechanical locks (not shown) in line with the actuators  68  keep the connector locked without the need of hydraulic pressure. Secondary mechanical locks may be interference sleeve locks such as the Bear-Loc™ locking device, manufactured by Wellman Dynamics Machining and Assembly Inc. of York, Pa. 
         [0024]    Referring to  FIG. 1 , the floating vessel V is equipped with a support structure  100  preferably including a pair of mooring links  102 . The mooring links  102  are connected to the support structure via upper U-joints  118 . Lower U-joints  120  connect the mooring links  102  to the ballast tank  26  of the yoke  24 . The support structure  100  with the pair of mooring links  102  are arranged and designed to suspend the ballast tank  26  of the yoke  24 . A motion compensated winch or lifting device  110  is mounted on a cantilevered section  104  of the mooring support structure  100 . The motion compensated winch  110  may be located elsewhere on the mooring support structure  100  or vessel V and the line  112  reeved through sheaves located on the mooring support structure  100  and cantilevered structure  104 . The motion compensated winch  110  is arranged and designed to support the yoke  24  during disconnection and reconnection. A mooring connection winch  106  on the vessel V is arranged and designed to pull the vessel V to the tower  10  and provide guidance for the structural connection of the yoke  24  to the yoke head  20 . Preferably, the rope or cable  108  of the mooring connection winch  106  is connected to the pull-in line  38  attached to the trunnion housing  22  of the yoke head  20 . 
         [0025]    Still referring to  FIG. 1 , during normal operations with the vessel V moored to the tower  10 , one or more hoses or flow lines  114  and cables  116  from the vessel V to the tower  10  are typically connected for process flow. The link arms  102  are connected to the ballast tank  26  of the yoke  24  and support the ballast tank  26  above the water level L. In the event of excessive environmental conditions anticipated at the tower location, the following procedures are permitted as a result of the preferred embodiment of the present invention. 
         [0026]    Initially, the hoses or flow lines  114  and cables  116  are disconnected at the tower interface and retrieved to the vessel V and stored for transportation. An alternative configuration allows the hoses  114  and cables  116  to be disconnected at the vessel V and stored on the hose deck  19  of the tower  10 . Referring to  FIG. 1 , a winch line  112  of the motion compensated winch  110  is attached to the yoke  24  to suspend the yoke coupler  30  end of the yoke  24  after disconnection from the yoke head  20 . A cylinder  42 , preferably a hydraulic cylinder ( FIG. 4 ), attached to the trunnion housing  22  of the yoke head  20  and to the tower turntable  18  orients the yoke head  20  in a near horizontal orientation (or at the proper angle) during disconnection of the yoke  24 , while the yoke  24  is disconnected and during reconnection of the yoke  24 . The hydraulic cylinders  68  of the hydraulic connector  50  inside the yoke head  20  are actuated to move the movable sleeve  60  from the position shown in the upper half of  FIG. 6  to the position shown in the lower half of  FIG. 6 , allowing the yoke  24  to disconnect from the tower structure  10  at the yoke head  20  while being supported by the motion compensated winch  110  and the mooring links  102  of the vessel support structure  100 . The yoke  24  is stored and pulled against fenders of the vessel V and the yoke coupler end  30  is fastened to the cantilevered structure  104  for sailing of the vessel V. 
         [0027]    During reconnection of the yoke  24  to the yoke head  20 , the motion compensated winch  110  is attached to the yoke  24  to suspend the yoke coupler  30  end of the yoke  24 . The pull-in line  38  attached to the inside of the trunnion housing  22  is retrieved, and the pull-in line  38  or winch cable  108  of the mooring connection winch  106  is inserted through the mating hub  70  of the yoke  24 . The pull-in line  38  is connected to the winch cable  108  of the mooring connection winch  106 . The vessel V is pulled towards the tower  10  for connection. The pull-in line  38  extends through the plurality of line guides  58  inside the connector  50  and mating hub  70 , providing for initial guidance of the yoke head  20  and yoke  24  for connection. Final guidance is obtained by the mating conical surfaces  34  and  36  of the yoke  24  and yoke head  20 , respectively, in addition to the connector  50  and hub  70  interface. The trunnion cylinder  42  supports the yoke head  20  for alignment and reconnection. The mooring links  102  and the yoke lifting device  110  support the yoke  24  for alignment and reconnection. Once the mating conical surfaces  34  and  36  are completely engaged, the hydraulic cylinders  68  are actuated to structurally connect the connector  50  to the mating hub  70 . The vessel is now moored. The trunnion cylinder  42  is then disengaged from the yoke head  20  and the yoke lifting device  110  is disengaged from the yoke  24 . Preferably, the winch cable  108  of the mooring connection winch  106  is also disconnected from the pull-in line  38  in preparation for the next yoke disconnection. 
         [0028]    Preferably, the disconnection takes place at the yoke head  20  which allows the yoke  24  to be transported with the vessel V. This leaves the tower  10  and the yoke head  20  attached to the tower  10  to survive the large storm. The hydraulic connector  50  is placed at the yoke/yoke head disconnection interface to allow for quick disconnection under load. Preferably, the yoke disconnection interface is located as close to the yoke head roll bearing  40  as possible. The yoke  24  is suspended by a motion compensated winch  110  and attached to the vessel V for evasion of the storm. 
         [0029]    While preferred embodiments of the present invention have been illustrated in detail, it is apparent that modifications and adaptations of the preferred embodiment will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.