Abstract:
A mooring system for offshore vessels uses a chain stopper within a preset mooring line. The chain stopper has means for attaching a removable hydraulic chain jack actuator which may be used to stroke the chain through the stopper assembly while both the stopper and the mooring line remain under load.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/950,476 filed on Jul. 25, 2013, and now issued as U.S. Pat. No. 9,003,994 which claims the benefit of U.S. Provisional Application No. 61/675,650, filed on Jul. 25, 2012, and U.S. Provisional Application No. 61/678,889, filed on Aug. 2, 2012. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to floating vessels. More particularly, it relates to mooring systems for offshore vessels. 
     2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
     When mooring offshore floating vessels and buoys, there is need for a method and apparatus to adjust the length and tension of the mooring lines. This need arises during initial installation to provide the correct geometry and pretension for the mooring system, and later in the life of the system, to account for changes to the system, wear, or creep in the mooring lines or anchor system. In certain situations, the adjustment of length must be performed over the lower section of the mooring, below a spring buoy. In some cases, the spring-buoy-to-vessel distance must be kept as initially deployed in order to preserve the proper function of the system. 
     One mechanism for performing these adjustments is described in U.S. Pat. Nos. 6,983,714 and 7,059,262 entitled Method and Apparatus for Offshore Mooring. These patents describe the use of a chain stopper/chain wheel to enable the motive force for line tensioning to be applied from a boat above, and to adjust the length of line above the preset portion of the line. 
     GB2484840 describes the use of a subsea chain jack on a subsea buoy. Tensioning apparatus is provided for tensioning a tether extending between a first structure and second structure. A support bracket is provided for attaching the apparatus with respect to the first structure. A tether holding arrangement is provided for securing the tether with respect to the apparatus. A pivotable articulating member having a tether receiving channel therethrough is provided, the receiving channel having a longitudinal axis substantially aligned with a tether departure axis. A support socket is adapted to pivotably receive the pivotable articulating member such that movement of the tether departure axis away from alignment with the receiving channel longitudinal axis results in corresponding pivotal movement of the pivotable articulating member with respect to the socket. A method of installing a production buoy using such tensioning apparatus is also described. 
     U.S. Pat. No. 5,934,216 describes a method and apparatus for tensioning and deploying mooring chain. A set of inboard and outboard pawls are provided in the tensioner/stopper device which may include a fairlead. The pawls are spaced and operate in a manner that at least one pair of pawls grabs the chain at any given time. This is said to prevent accidental loss of the chain overboard. The chain is tensioned as the inboard pawls are engaged to the chain and actuated hydraulically to pull the chain inboard. Pulling inboard allows the outboard pawls to slide over at least one link and lock into place behind that link. The inboard pawls are stroked outboard over the next link to be grabbed, with the outboard pawls engaging the chain, the inboard pawls slide outboard to obtain another grip on a subsequent link and the process is repeated to conclude the tensioning. For deployment, the outboard pawls are retracted while the chain is retained by the inboard pawls. The inboard pawls are stroked outboard to pay out the chain. At that time, the outboard pawls grab the chain for temporary support as the inboard pawls are repositioned for the next cycle. 
     U.S. Pat. No. 7,421,967 describes a mooring system for securing a floating vessel to the sea floor that comprises a plurality of mooring legs, at least one of which includes separate first and second mooring lines. The first mooring line comprises a first end which is connected to the vessel and the second mooring line comprises a first end which is secured to the sea floor. The mooring system also comprises a connection and tensioning device which includes a body, a bore which extends through the body, a chain stopper for adjustably securing the first mooring line to the body, and a connector for connecting a second end of the second mooring line to the body. In use, a second end of the first mooring line is inserted into the bore and the first mooring line is pulled through the bore while the body is subject to an opposing pulling force. Once the first mooring line is pulled through the bore a desired distance, the chain stopper maintains the first mooring line in position relative to the body to thereby secure the vessel to the sea floor. 
     U.S. Pat. No. 5,809,925 describes a chain stopper wherein a mooring chain is guided for movement through the frame of the chain stopper along a pair of upright rails, with vertical links of the chain received between the rails and horizontal links of the chain riding on top of the rails. A pawl is swingably mounted on the frame above the rails with inner legs of the pawl engaging a horizontal link of the chain at opposite sides of an adjacent vertical link. The pawl has outer legs which extend downward to a release pin. The release pin has grooves positioned to receive the bottom ends of the outer legs and prevent the pawl from moving in a direction which will allow loosening of the chain, unless the release pin is freed for rotation through an angle of about 90 degrees. The release pin is connected to a trigger assembly including a spinner block which is normally held against rotation by a trigger finger. Movement of the trigger finger frees the spinner block and thereby allows the release pin to move from a pawl-engaging to a pawl-released position. The force of the chain on the inner legs of the pawl swings the pawl automatically as the chain loosens by sliding along the rails. The spinner block rotates freely, with no mechanism restraining it or the release pin. 
     U.S. Pat. No. 4,862,821 describes a mechanism for tensioning a moving chain. In an anchoring system for a floating vessel which includes an anchor line comprising chain cable, a chain locker and a windlass having a chain wheel that conveys the chain cable during paying out from the chain locker, a mechanism is positioned between the chain locker and chain wheel to back-tension the chain during paying out. The mechanism has an axis along which the chain is passed with every second links oriented in a given plane. Paired brake shoes are positioned to either side of the plane and define braking surfaces of sufficient extent along the axis of chain movement that a given chain link and an immediately succeeding link of similar orientation can be simultaneously engaged during their movement to provide a continuous retarding effect. One pair of braking shoes is pivotally mounted on an appropriate support structure and urged with hydraulic cylinders towards the other pair thereby causing the brake shoes to engage the opposing faces chain link. The pressure of hydraulic fluid applied to the cylinders is adjusted to back-tension the chain sufficiently that sudden shocks to the windlass otherwise occasioned by tilting and jumping of chain links during conveyance over the chain wheel are avoided. Non-standard links and irregularities in the chain link surfaces such as weld lines are accommodated by contraction of the hydraulic cylinders and deflection of the pivoting brake shoes. 
     U.S. Pat. No. 4,936,710 describes a mooring line tensioning and damping system. The floating structure comprises one or more catenary mooring cables for anchoring the structure to the seabed. An extensible dynamic tensioner system is provided for maintaining a predetermined dynamic tension in each mooring cable, as the structure responds to cyclic wave forces, and for increasing the natural periods of oscillation of the pitch, roll, heave, surge, sway, and yaw motions of the moored floating structure by reducing the spring stiffness of the mooring system. A motion damping system is coupled between the dynamic tensioner system and the structure for damping the linear and angular displacements of the structure relative to the tensioned cables. The damping system selectively applies frictional forces against a movable member in the tensioner system. The movable member does not move relative to the cables. 
     U.S. Pat. No. 6,602,019 describes a device for fixing, tensioning or pulling an extensible traction element such as a cable. The device has two supports which can be moved in relation to each other in a transverse direction to the axis of the traction element. Several clamping jaws are mounted in displaceable fashion in pairs opposite each other on said supports. The clamping jaws have surfaces which grasp the traction element. When strain is placed on the traction element, the clamping jaws are displaced linearly at increasing distances except for the rear pair, in such a way that the clamping force can be evenly distributed over a great length, despite the extension of the traction element. This is said to allow, for example, steel cables with a high traction force to be tensioned without damaging the cable. 
     International Publication No. WO 2013/043049 describes a device for tensioning anchor chains, in particular mooring legs of off-shore vessels and installations, comprising a frame carrying connectors for holding together lower and upper portions of the chain to be tensioned. The frame further carries a tensioning mechanism for pulling at least one portion of the chain towards the other portion of the chain while the device is submerged. 
     BRIEF SUMMARY OF THE INVENTION 
     An in-line mooring connector and tensioner according to the invention comprises a chain stopper assembly that may be used to connect a chain to another line and a removable chain jack assembly which may be used to tension and adjust the chain that passes through the in-line mooring connector and tensioner. The in-line mooring connector and tensioner may be deployed between a chain and another line, and used to facilitate the adjustment of the overall length of the mooring by adjustment of the active length of the chain. 
     The removable chain jack may be configured such that it may be inserted over a tensioned chain when the locking pawls are oriented such that they are in-line with the cylinders. This allows adjustment to be performed without pulling the mooring line out of its normal geometry as would be required by a winch-actuated line to an auxiliary surface vessel. 
     An in-line mooring connector and tensioner according to the invention allows for tensioning and re-tensioning mooring lines without a vessel-mounted tensioning system. 
     A chain tensioning system according to the invention may include:
         Structural frame and fixed stopper assembly for each mooring line   Removable chain jack assembly with movable stopper assembly   Hoses and hose reel assembly for operating the chain jack   Hydraulic power unit and controls for operating the chain tensioning system   Applicable ROV interfaces and tooling       

    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  is a schematic drawing of an in-line mooring connector and tensioner according to the invention connected to an FPSO and a work boat. 
         FIG. 2A  is a front elevation of an in-line mooring connector and tensioner according to a first embodiment of the invention. 
         FIG. 2B  is a cross-sectional view of the in-line mooring connector and tensioner illustrated in  FIG. 2A  taken along line  2 B- 2 B in  FIG. 2A . 
         FIG. 2C  is an isometric view of the in-line mooring connector and tensioner illustrated in  FIG. 2A . 
         FIG. 2D  is an exploded view of the in-line mooring connector and tensioner of  FIG. 2A  showing the chain jack being connected to the mooring connector. 
         FIG. 2E  is a side view of a hydraulically-actuated chain stopper in the closed position. 
         FIG. 2F  is a side view of the chain stopper shown in  FIG. 2E  in the open position. 
         FIG. 3A  is a front elevation of an in-line mooring connector and tensioner according to a second embodiment of the invention. 
         FIG. 3B  is a cross-sectional view of the in-line mooring connector and tensioner illustrated in  FIG. 3A  taken along line  3 B- 3 B in  FIG. 3A . 
         FIG. 3C  is an isometric view of the in-line mooring connector and tensioner illustrated in  FIG. 3A . 
         FIG. 3D  is an exploded view of the in-line mooring connector and tensioner of  FIG. 3A  showing the chain jack being connected to the mooring connector. 
         FIG. 4A  is a front elevation of an in-line mooring connector and tensioner according to a third embodiment of the invention. 
         FIG. 4B  is a cross-sectional view of the in-line mooring connector and tensioner illustrated in  FIG. 4A  taken along line  4 B- 4 B in  FIG. 4A . 
         FIG. 4C  is an isometric view of the in-line mooring connector and tensioner illustrated in  FIG. 4A . 
         FIG. 4D  is an exploded view of the in-line mooring connector and tensioner of  FIG. 4A  showing the chain jack being connected to the mooring connector. 
         FIG. 5A  is a front elevation of an in-line mooring connector and tensioner according to a fourth embodiment of the invention. 
         FIG. 5B  is a side view of a mechanically-actuated chain stopper in the closed position. 
         FIG. 5C  is a side view of the chain stopper of  FIG. 5B  in the open position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention may best be understood by reference to the exemplary embodiments illustrated in the drawing figures. 
       FIG. 1  shows a vessel  22  floating on surface  20  of the sea. In the illustration, vessel  22  is a disconnectable, turret-moored FPSO. Subsea risers  28  are attached at buoy  26 , which may be connected to a rotatable turret  24 . Vessel  22  may weathervane about turret  24 . 
     Buoy  26  (and turret  24  when connected) are moored to the seabed  18  by a plurality of mooring lines  46 . For clarity, only a single mooring line is shown in  FIG. 1 , but it should be understood that, in practice, a spread mooring system having at least three mooring lines would be used to position buoy  26  (and hence turret  24  and vessel  22 ). 
     Upper mooring line  46  connects between buoy  26  and spring buoy  30  which may support the lower portions of the mooring line. 
     An adjustment chain  32  is provided between spring buoy  30  and the anchor line  12  for adjusting the overall length of mooring line  46  (and hence the position of vessel  22 ). Adjustment chain  32  is comprised of an upper tensioned portion (at  32 ) and a lower, excess, slack portion  34 . Adjustment chain  32  passes through, and is movably fixed to in-line mooring connector and tensioner  10  which is attached at connector  48  to anchor line  12  which may be a polyester line or any other suitable material. At its lower end, anchor line  12  is attached to ground chain  14  with connector  50 . Ground chain  14  is secured to anchor  16  embedded in seafloor  18 . Anchor  16  may be any suitable securing device. 
     In-line mooring connector and tensioner  10  contains a removable chain jack which may be installed and retrieved by one or more work lines  60  from deck-mounted crane  62  on vessel  40 . Installation and retrieval of the removable chain jack may be assisted by a remotely operated vehicle (ROV)  36  controlled from workboat  40  via umbilical  38 . Workboat  40  may be an Anchor Handling Vessel (AHV) or any such suitable vessel. In certain embodiments, hydraulic lines from hydraulic power unit (HPU)  44  on vessel  40 , data sensor lines and other control and power means may connect to in-line mooring connector and tensioner  10  via umbilical  42 . In this way, in-line mooring connector and tensioner  10  may be remotely cycled from vessel  40  to pay out or take in adjustment chain  32 . 
     As illustrated in  FIG. 1 , the system of the present invention permits length and/or tension adjustment of mooring line  46  at a safe distance from vessel  22  and turret  24 . This decreases the chances of interference with risers  28  or vessel  22 . 
     An in-line mooring connector and tensioner according to a first embodiment of the invention is shown in  FIGS. 2A, 2B, 2C and 2D . In-line mooring connector and tensioner  200  comprises chassis  210  which forms the frame of the mooring connector portion of the device—i.e., the portion which remains subsea and within the mooring line. Mooring line attachment fitting  212  is affixed to the lower end of chassis  210  and may be used to connect in-line mooring connector and tensioner  200  to an anchor line secured to the ocean floor. 
     Adjustment chain  214  is routed through in-line mooring connector and tensioner  200 . The upper portion (at  214 ) is connected (directly or indirectly) to the vessel or other floating device being moored and is normally under tension. The lower or excess portion  218  is slack and may, in use, hang vertically from in-line mooring connector and tensioner  200  (see  FIG. 1 ). Excess chain portion  218  may be directed to chain exit  216  by means of chain exit ramp  220 . In other embodiments element  220  may be a rotating wheel, sprocket or the like. In certain embodiments, element  220  may include means for sensing the movement of chain  214 ,  218 . 
     Chain stopper  224  is attached to chassis  210  and acts to lock chain  214  when in the closed position. Locking pawls (or “dogs”)  228  bear against a link of chain  214  positioned within chain stopper  224  and transmit a compressive load from chain  214  to chassis  210 . In the embodiment illustrated in  FIGS. 2A-2D , chain stopper  224  is moved from the open (unlocked) position to the closed (locked) position (and vice versa) by hydraulic actuator  226 . Linkage  227  may be provided to ensure that locking pawls  228  move equally. Hydraulic actuator  226  may be connected to an ROV or may be connected to a hydraulic power unit on a support vessel by an umbilical line  42  (as illustrated in  FIG. 1 ). 
     Chain jack connector  222  is provided at the end of chassis  210  opposite anchor line attachment fitting  212 . In the illustrated embodiment, connector  222  is a collar-type connector that permits sliding engagement of a removable chain jack. 
     Removable chain jack  230  comprises base plate  236  having U-shaped opening  238  sized and configured to slidingly engage connector  222  on the upper end of chassis  210  and permit the passage of chain  214  therethrough. 
     A pair of hydraulic cylinders  232  having double-acting actuators [piston rods]  234  retractably extending therefrom are mounted on base plate  236  such that they are arrayed on opposite sides of chassis  210  when chain jack  230  is installed. Hydraulic line connectors  252  may be attached to an ROV or to an umbilical line  42  leading to a hydraulic power unit on an attending surface vessel (as illustrated in  FIG. 1 ). 
     Moveable plate  240  is attached to actuators  234  with piston rod connectors  244  and piston rod caps  242 . Moveable plate  240  also has U-shaped opening  241  to permit the passage of chain  214  therethrough. 
     Second chain stopper  246  is mounted to base plate  240  and includes locking pawls  247  which may be moved between the opened and closed positions by hydraulic actuator  248 . In other embodiments, the chain stoppers  246  and  224  may be opened and closed by other means known in the art. 
     Pad eyes  250  may be provided at various locations on chain jack  230  to provided attachment means for work lines  60  and the like for maneuvering chain jack  230  into position on chassis  210  and retrieving it when the tensioning operation is completed (see  FIG. 1 ). 
     In operation, chain stopper  246  may be opened (while chain stopper  224  remains closed, preventing movement of chain  214 ) and moveable plate  240  extended (as shown in phantom in  FIG. 2A ). Actuators  234  may be sized such that their full extension corresponds to an integral number of chain links. When moveable plate  240  is fully extended (which may be detected by a position sensor [not shown] or, alternatively, by monitoring the flow or pressure of hydraulic fluid in cylinders  232 ), chain lock  246  may be closed and chain lock  224  may be opened. In certain embodiments, moveable plate  240  may be slightly retracted so as to relieve the chain tension on chain stopper  224  prior to opening chain stopper  224 . When chain stopper  224  is fully open (as may be detected by one or more position sensors and/or fluid flow to actuator  226 ), moveable plate  240  may be retracted. 
     When moveable plate  240  is fully retracted, chain stopper  224  may be closed and chain stopper  246  opened. As described previously, actuators  234  may be slightly extended to relieve the load on chain stopper  246  prior to opening it. 
     This cycle may be repeated a selected number of times in order to achieve the desired level of tension in adjustment chain  214 . The process may be automated. Sensors in chassis  210 —e.g., strain gauges, or the like—may be used to determine the mooring line tension. This tension can also be determined from the hydraulic pressure in the chain jack when static with no hydraulic fluid flowing. 
     When the desired chain tension is achieved, chain stopper  246  may be locked in the open position and chain jack  230  removed from chassis  210  with lift lines guided by an ROV and retrieved. Because chain jack  230  is retrievable, it can be serviced and maintained on the surface. 
     It will be appreciated by those skilled in the art that the above-described process may be reversed to pay out chain  214 . 
     An in-line mooring connector and tensioner according to a second embodiment of the invention is shown in  FIGS. 3A, 3B, 3C and 3D . In-line mooring connector and tensioner  300  comprises chassis  310  which forms the frame of the mooring connector portion of the device—i.e., the portion which remains subsea and within the mooring line. Mooring line attachment fitting  312  is affixed to the lower end of chassis  310  and may be used to connect in-line mooring connector and tensioner  300  to an anchor line secured to the ocean floor. 
     Adjustment chain  314  is routed through in-line mooring connector and tensioner  300 . The upper portion (at  314 ) is connected (directly or indirectly) to the vessel or other floating device being moored and is under tension. The lower or excess portion  318  is slack and may, in use, hang vertically from in-line mooring connector and tensioner  300  (see  FIG. 1 ). Excess chain portion  318  may be directed to chain exit  316  by means of chain exit ramp  320 . In other embodiments element  320  may be a rotating wheel, sprocket or the like. In certain embodiments, element  320  may include means for sensing the movement of chain  314 ,  318 . 
     Chain stopper  324  is attached to chassis  310  and acts to lock chain  314  when in the closed position. Locking pawls (or “dogs”)  328  bear against a link of chain  314  positioned within chain stopper  324  and transmit a compressive load from chain  314  to chassis  310 . In the embodiment illustrated in  FIGS. 3A-3D , chain stopper  324  is moved from the open (unlocked) position to the closed (locked) position (and vice versa) by hydraulic actuator  326 . Hydraulic actuator  326  may be connected to an ROV or may be connected to a hydraulic power unit on a support vessel by an umbilical line  42  (as illustrated in  FIG. 1 ). 
     Chain jack connector  322  is provided at the end of chassis  310  opposite anchor line attachment fitting  312 . In the illustrated embodiment, connector  322  is a spline-type connector that permits sliding engagement of a removable chain jack. 
     Removable chain jack  330  comprises splined connector  323  on housing  337  sized and configured to slidingly engage slotted connector  322  on the upper end of chassis  310 . Base plate  336  may include generally U-shaped opening  338  to permit the passage of chain  314  therethrough. Opening  338  may include elements to assist in orienting chain  314 . 
     A pair of hydraulic cylinders  332  having double-acting actuators [piston rods]  334  retractably extending therefrom are attached at a first end to moveable plate  340  and, at an opposing second end, to cylinder plate  354 . Hydraulic line connectors  352  may be attached to an ROV or to an umbilical line  42  leading to a hydraulic power unit on an attending surface vessel (as illustrated in  FIG. 1 ). 
     Cylinder plate  354  may comprise generally U-shaped opening  358  to permit passage of chain  314  when chain jack  330  is installed onto chassis  310 . As shown in  FIG. 3D , opening  358  may be configured to orient chain  314  in the desired direction. Hinged gate  360  may be provided to close opening  358 , thereby securing chain  314  within opening  358 . Gate  360  may be equipped with a locking device operated by gate lock actuator  362  (see  FIG. 3B ). Gate lock actuator  362  may be configured for operation by an ROV. 
     Base plate  336  is attached to actuators  334  with piston rod connectors  344  and piston rod caps  342 . Base plate  336  also has U-shaped opening  338  to permit the passage of chain  314  therethrough. Base plate  336  is also attached to housing  337  on the side opposite connector  323 . 
     Second chain stopper  346  is mounted to moveable plate  340  and includes locking pawls  347  which are moved between the opened and closed position by hydraulic actuator  348 . In other embodiments, the chain stoppers  346  and  324  may be opened and closed by other means known in the art. 
     Pad eyes  350  may be provided at various locations on chain jack  330  to provide attachment means for work lines  60  and the like for maneuvering chain jack  330  into position on chassis  310  and retrieving it when the tensioning operation is completed (see  FIG. 1 ). 
     In operation, chain stopper  346  may be opened (while chain stopper  324  remains closed, preventing movement of chain  314 ) and moveable plate  340  extended (as shown in phantom in  FIG. 3A ). Actuators  334  may be sized such that their full extension corresponds to an integral number of chain links. When moveable plate  340  is fully extended (which may be detected by a position sensor [not shown] or, alternatively, by monitoring the flow or pressure of hydraulic fluid in cylinders  332 ), chain lock  346  may be closed and chain lock  324  may be opened. In certain embodiments, moveable plate  340  may be slightly retracted so as to relieve the chain tension on chain stopper  324  prior to opening chain stopper  324 . When chain stopper  324  is fully open (as may be detected by one or more position sensors and/or fluid flow to actuator  326 ), moveable plate  340  may be retracted—i.e., moved closer to base plate  336 . 
     When moveable plate  340  is fully retracted, chain stopper  324  may be closed and chain stopper  346  opened. As described previously, actuators  334  may be slightly extended to relieve the load on chain stopper  346  prior to opening it. 
     This cycle may be repeated a selected number of times in order to achieve the desired level of tension in adjustment chain  314 . The process may be automated. Sensors in chassis  310 —e.g., strain gauges, or the like—may be used to determine the mooring line tension. This tension can also be determined from the hydraulic pressure in the chain jack when static with no hydraulic fluid flowing. 
     When the desired chain tension is achieved, chain stopper  346  may be locked in the open position and chain jack  330  removed from chassis  310  with lift lines guided by an ROV and retrieved. Because chain jack  330  is retrievable, it can be serviced and maintained on the surface. 
     It will be appreciated by those skilled in the art that the above-described process may be reversed to pay out chain  314 . 
     An in-line mooring connector and tensioner according to a third embodiment of the invention is shown in  FIGS. 4A-4D . In-line mooring connector and tensioner  400  comprises chassis  410  that forms the frame of the device and which remains subsea and within the mooring line. Flanged reinforcing rails  411  are provided on either side of chassis  410  to strengthen it. 
     Chain jack cavity  431  in the central portion of chassis  410  may be open to the front and/or the back of chassis  410  and is sized and configured to accommodate removable chain jack  430 . Mooring line attachment fitting  412  is affixed to the lower end of chassis  410  and may be used to connect in-line mooring connector and tensioner  400  to an anchor line secured to the ocean floor. 
     Adjustment chain  414  is routed through in-line mooring connector and tensioner  400 . The upper portion (at  414 ) is connected (directly or indirectly) to the vessel or other floating device being moored and is normally under tension. The lower or excess portion  418  is slack and may, in use, hang vertically from in-line mooring connector and tensioner  400  (see  FIG. 1 ). Excess chain portion  418  may be directed to chain exit  416  by means of chain exit ramp  420 . In other embodiments element  420  may be a rotating wheel, sprocket or the like. In certain embodiments, element  420  may include means for sensing the movement of chain  414 ,  418 . 
     Chain stopper  424  is attached to chassis  410  within chain stopper housing  470  and acts to lock chain  414  when in the closed position. Locking pawls (or “dogs”)  428  bear against a link of chain  414  positioned within chain stopper  424  and transmit a compressive load from chain  414  to chassis  410 . In the embodiment illustrated in  FIGS. 4A-4D , chain stopper  424  is moved from the open (unlocked) position to the closed (locked) position (and vice versa) by hydraulic actuator  426 . Hydraulic actuator  426  may be connected to an ROV or may be connected to a hydraulic power unit on a support vessel by an umbilical line  42  (as illustrated in  FIG. 1 ). 
     Base plate  436  may include generally U-shaped opening  438  sized and configured to slidingly engage collar connector  422  on the lower end (in  FIG. 4A ) of housing  470 . Generally U-shaped opening  438  is sized and positioned to permit the passage of chain  414  therethrough. 
     A pair of hydraulic cylinders  432  having double-acting actuators [piston rods]  434  retractably extending therefrom are attached at a first end to base plate  436 . Hydraulic line connectors  452  may be attached to an ROV or to an umbilical line  42  leading to a hydraulic power unit on an attending surface vessel (as illustrated in  FIG. 1 ). 
     Movable plate  440  is attached to actuators  434  with piston rod connectors  444  and piston rod caps  442 . Movable plate  440  also has U-shaped opening  441  to permit the passage of chain  414  therethrough. 
     Second chain stopper  446  is mounted to moveable plate  440  and includes locking pawls  447  which are moved between the opened and closed position by hydraulic actuator  448 . In other embodiments, the chain stoppers  446  and  424  may be opened and closed by other means known in the art. 
     Pad eyes  450  may be provided at various locations on chain jack  430  to provided attachment means for work lines  60  and the like for maneuvering chain jack  430  into position within chassis  410  and retrieving it when the tensioning operation is completed (see  FIG. 1 ). 
     In operation, chain stopper  446  may be closed (while chain stopper  424  is opened, preventing movement of chain  414 ). Moveable plate  440  may be extended slightly to relieve the load on chain stopper  424  to facilitate its opening. Moveable plate  440  may then be extended fully (as shown in phantom in  FIG. 4A ). Actuators  434  may be sized such that their full extension corresponds to an integral number of chain links. When moveable plate  440  is fully extended (which may be detected by a position sensor [not shown] or, alternatively, by monitoring the flow or pressure of hydraulic fluid in cylinders  432 ), chain lock  424  may be closed and chain lock  446  may be opened. In certain embodiments, moveable plate  440  may be slightly retracted so as to relieve the chain tension on chain stopper  446  prior to opening chain stopper  446 . When chain stopper  446  is fully open (as may be detected by one or more position sensors and/or fluid flow to actuator  426 ), moveable plate  440  may be retracted—i.e., moved closer to base plate  436 . 
     If another cycle is to be performed, chain stopper  446  may be closed when moveable plate  440  is fully retracted, and chain stopper  424  opened. As described previously, actuators  434  may be slightly extended to relieve the load on chain stopper  424  prior to opening it. 
     This cycle may be repeated a selected number of times in order to achieve the desired level of tension in adjustment chain  414 . The process may be automated. Sensors in chassis  410 —e.g., strain gauges, or the like—may be used to determine the mooring line tension. This tension can also be determined from the hydraulic pressure in the chain jack when static with no hydraulic fluid flowing. 
     When the desired chain tension is achieved, chain stopper  446  may be locked in the open position and chain jack  430  removed from chassis  410  with lift lines attached to pad eyes  450  and guided by an ROV and retrieved. Because chain jack  430  is retrievable, it can be serviced and maintained on the surface. 
     It will be appreciated by those skilled in the art that the above-described process may be reversed to effect pay out chain  414 . 
       FIG. 5A  shows a fourth embodiment of the invention. In-line mooring connector and tensioner  500  is similar to the second embodiment illustrated in  FIGS. 3A-3D . However, the embodiment shown in  FIG. 5A  has three sets of chain stoppers—two in removable chain jack  530  (stopper  546  on movable plate  540  and stopper  580  on base plate  536 ) and a third ( 524 ) housed in chassis  510  that normally remains subsea. In operation, chain stopper  524  (the “permanent” chain stopper) may be opened at the beginning of the tensioning operation, remain open for the duration of the operation, and subsequently closed upon completion of the operation. In this way, the chain stoppers that must be repeatedly cycled during the tensioning operation (i.e., chain stoppers  546  and  580 ) are those that are on removable chain jack  530  which can be retrieved and serviced on the surface. Permanent chain stopper  524  need only be cycled once during the entire procedure. Because chain stopper  524  normally remains subsea, it is more likely to become fouled by marine organisms and/or corroded. This may adversely affect its ease of movement and hence increase the cycle time of the device if it must be operated on each stroke of the chain jack (as in the embodiment illustrated in  FIGS. 3A-3D ). 
     Chain stopper  524  may be of the same type as chain stoppers  546  and  580 —i.e., hydraulically operated via an umbilical line from a surface vessel or via a hydraulic line connected to an ROV. Alternatively, chain stopper  524  may be mechanically actuated. One particular type of mechanically actuated chain stopper is illustrated in  FIGS. 5B and 5C . 
     Chain stopper  524  is equipped with a rack-and-pinion type mechanical actuator  584  which comprises toothed rack  586  and geared pinion  588 . Pinion  588  may have a hex head (or other such connector) to engage a rotatable driver on an ROV. Rack  586  may be driven in or out of housing  587  by rotating pinion  588 . This action moves linkage  590  which is connected to locking pawls  592 . Linkage  590  ensures that locking pawls  592  move equally. 
     An in-line mooring connector and tensioner according to the invention may be used in the following applications:
         Mooring line installation to initially pull in the spring buoy chain.   Construction stretch removal from the polyester to pull in and pay out the spring buoy chain for applying an initial set to the polyester ropes.   Mooring tension adjustment to correct for vessel position or riser load changes.   Mooring tension adjustment for polyester rope creep over time and to rotate the chain link on the fixed stopper.   Mooring chain paying out and pulling in permit removal of a polyester test insert if required (additional temporary chain will be added to permit this).       

     The structural frame of the in-line mooring connector and tensioner may contain the permanent chain stopper that remains subsea for the life of the mooring line. The interface to the chain jack may be configured to permit ease of installation of the chain jack using work wire to support the chain jack and ROV assistance to maneuver and lock in position on the structural frame. 
     A hydraulic umbilical from an AHV may provide the source of hydraulic power for operating the chain jack cylinders and the chain stopper cylinders if used. Hydraulic cylinders on the permanent chain stopper may be designed to be replaceable by an ROV. An ROV installation tool may be provided for subsea intervention of the cylinders. 
     Load monitoring may be implemented on the chain jack via pressure transmitters at the actuating cylinders. If the permanent chain stopper is hydraulically actuated, it may be configured so that no hydraulic pressure is needed during a static hold under load. The system may be designed such that, upon loss of hydraulic pressure, the grip on the chain is maintained. 
     The chain jack of an in-line mooring connector and tensioner according to the invention may be hydraulically driven and operated by a control console during normal paying in and paying out operations. The system may contain all necessary valving to automatically sequence the unit through the working cycle without operator intervention. It may also have manual override for control of the individual functions. The operator may have visibility of the operation from an ROV-mounted camera. 
     The system may further be provided with:
         A control console.   A load cell to provide pulling load indication during installation operations.   An encoder measuring total and partial chain paid-in/out.   A flow control device to control the pull speed.   An adjustable speed facility during paying in and paying out operations.       

     In cases where lower mooring line  12  is polyester, it may also be necessary to readjust the length of the mooring line due to creep of the material over time. In that case, the in-line mooring connector and tensioner may be used to incrementally tension the line to maintain the proper pre-tension and mooring geometry. 
     Practice of the invention allows the use of a chain jack mid-span in a mooring line. It allows tension adjustments to be performed without pulling the mooring line out of its normal geometry as would be required by a winch-actuated line to an auxiliary surface vessel. The invention also permits use of a chain jack to act on a tensioned line by side entry. 
     Although particular embodiments of the present invention have been shown and described, they are not intended to limit what this patent covers. One skilled in the art will understand that various changes and modifications may be made without departing from the scope of the present invention as literally and equivalently covered by the following claims.