GB2585985A

GB2585985A - Mooring line tensioning tool

Info

Publication number: GB2585985A
Application number: GB2011395.7A
Authority: GB
Inventors: Shield John
Original assignee: Subsea Riser Products Ltd
Current assignee: Subsea Riser Products Ltd
Priority date: 2019-07-24
Filing date: 2020-07-23
Publication date: 2021-01-27
Anticipated expiration: 2040-07-23
Also published as: GB201910603D0; GB2585985B; GB202011395D0

Abstract

In an initial position, the two sections 12, 14 of a mooring line are not connected and the connector members 52, 54 are spaced apart, for example by 100m to 200m. The length of the mooring line sections are preselected such that the subsequent connection provides a pre-tensioned mooring line (10, Fig 1) at the required pre-tension. A mooring line tensioner 20 comprises a first engager 22 which engages with and grips/clamps a first connector/end 52 of a first section 12 of a mooring line. The mooring line tensioner comprises a second engager 24 which engages with and grips/clamps a second connector/end 54 of a second section 14 of the mooring line. A flexible tensioning line 40 is engaged around a pulley system 32, 34 provided on the engagers. An upper end of the tensioning line may be engaged with a winch which is arranged to wind the tensioning line on to a spool which pulls the two engagers towards each other until the connectors connect. Once the connectors are connected the mooring line tensioner is removable from a position around the now contiguous mooring line. An offshore assembly including the tensioner and a method of use are also disclosed.

Description

Mooring Line Tensioning Tool

FIELD OF THE INVENTION

The present invention relates to a mooring line tensioning tool, an assembly comprising a mooring line and a mooring line tensioning tool and a method of tensioning a mooring line.

BACKGROUND TO THE INVENTION

Mooring lines are typically used to secure offshore installations and structures in position relative to the seabed. In particular, such offshore structures and installations may include floating structures, floating platforms, for example Floating Production Storage and Offloading (FPSO) vessels, Mobile Offshore Drilling Units (MODU) etc. Such platforms/installations/structures generally have a number of mooring lines located around the periphery which extend downwardly to the seabed and the lower ends of each mooring line are attached to a respective anchor/pile. The position of these anchors/piles is held on the seabed and the anchors/piles inhibit or resist lateral movement along the seabed. In order to transfer this resistive force to the floating platform/installation, the mooring lines are typically pre-tensioned using a tensioner.

The term pre-tension refers to the tension existing in the mooring line prior to any increase or decrease in tension applied by the movement of the offshore installation from the neutral/stable position. In particular, once set by the tensioner, this pre-tension is not changed although the actual magnitude of the tension of the mooring line may change due to the movement of the offshore installation.

The mooring lines extend radially around the circumference of the floating platform/installation and the mooring lines all act together to retain the floating platform/installation in a stable position relative to the seabed. Such a pattern of mooring lines extending radially outwardly from around the periphery is able to -2 -effectively hold the floating installation in a stable position relative to the seabed. However, each mooring line will need to be installed to provide the required resistive force which is created through individually pre-tensioning each mooring line.

Accordingly, the floating platform/installation typically has a number of tensioners located around the periphery such that each mooring line has a respective tensioner from which the mooring line can pay in and pay out in order to set and adjust the tension. During the initial phase wherein the platform is being located in the correct position, the tensioners are used to set the individual pre-tension of each mooring line. These tensioners typically comprise either hydraulic jacks or a rotatable spool onto which the mooring line is hoisted in order to set the required length of mooring line down to the anchor/pile which will produce the required pre-tension in each mooring line. Chain jacks haul the chain through a few links at a time and these are more common for high tension. The pre-tension of the mooring lines can be easily calculated and set using such a system. However, the tensioners occupy significant valuable space on the platform/installation.

In addition, the tensioners may only be required during the initial set up/installation phase of the floating platform/installation. Once the required pre-tension is achieved in each mooring line and the platform is secured in position, the tensioners are no longer required. However, the tensioners remain on the deck of the floating installation/platform holding the set length of mooring line and continue to occupy valuable space on the deck of the platform/installation throughout the lifetime of the platform/installation. Furthermore, the tensioners are exposed to the elements throughout the lifecycle of the floating platform/installation even though they are not being actively used.

Alternatively, catenary mooring line systems can be used such that the physical weight of the mooring lines provide the anchoring forces to retain the floating platform/installation in position over the seabed. Catenary systems are also pre-tensioned, so experience the problems mentioned above. The catenary pre-tension sets the lateral stabilising force by lifting more chain off the seabed. In such -3 -systems, the weight of the catenary mooring line is utilised to further anchor and/or supplement the pre-tension to secure the installations. Such systems may not be as stable and/or these systems require catenary mooring lines of a significant length. Accordingly, catenary mooring systems may be primarily used in shallow water whereby the length of the required mooring lines is not excessive or problematic.

It is an aim of the present invention to overcome at least one problem associated with the prior art whether referred to herein or otherwise.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a mooring line tensioner comprising: a first engager for engaging a first connector member secured to a first section of a mooring line; a second engager for engaging a second connector member secured to a second section of a mooring line; a first pulley system mounted to the first engager; a second pulley system mounted to the second engager; a flexible member secured between the first pulley system and the second pulley system; the flexible member being arranged, in use, to move the first engager and first connector relatively towards the second engager and second connector until the first connector connects to the second connector thereby securing the first mooring line section to the second mooring line section; wherein, the mooring line tensioner is removable from a position around a contiguous mooring line formed by the connection of the first section of mooring line and the second section of mooring line.

Preferably the flexible member comprises a cable. The cable may extend upwardly from the mooring line tensioner located subsea to an actuating mechanism located -4 -above sea level. The actuating mechanism may be located on a support vessel on the sea surface.

The actuating mechanism may comprise a winch. The winch may be arranged to 5 pay in and pay out the cable. The winch may comprise a spool about which the flexible member is wound.

Preferably the mooring line tensioner is movable between a closed position and an open position. Preferably in the closed position the first engager locates around and 10 engages the first connector and the second engager locates around and engages the second connector.

Preferably, in the closed position, the mooring line tensioner encompasses the mooring line and, in the open position, the mooring line tensioner provides a mouth portion which enables the mooring line tensioner to be detached from the mooring line. Preferably the mooring line tensioner comprises a hinge mechanism to enable the mooring line tensioner to (pivotally) move between the closed position and the open position.

The mooring line tensioner may comprise a release system to aid the movement of the mooring line tensioner from the closed position to the open position. The release system may comprise release ropes/wires located on the mooring line tensioner which are pulled to urge the mooring line tensioner to move from the closed position to the open position.

Preferably the first engager comprises a first jaw and a second jaw which are movable between an open position and a closed position. Preferably the first engager comprises a pivot/hinge mechanism to enable (pivotal) movement of the jaws between the closed position and the open position.

Preferably, for the first engager, a first release wire is secured to a first securement member on the first jaw and a second release wire is secured to a first securement -5 -member on the second jaw. The first securement member may be located along opposite lateral edges of the first engager and preferably with the hinge mechanism located centrally therebetween. Preferably an upper end of each wire is secured together and to a common operating wire. Preferably movement (and/or tension) in the common wire urges the two jaws to pivotally open about the hinge mechanism.

The first engager may comprise two pairs of release wires to urge the first engager from a closed position to an open position.

Preferably the second engager comprises a first jaw and a second jaw which are movable between an open position and a closed position. Preferably the second engager comprises a pivot/hinge mechanism to enable (pivotal) movement of the jaws between the closed position and the open position.

Preferably, for the second engager, a first release wire is secured to a first securement member on the first jaw and a second release wire is secured to a first securement member on the second jaw. The first securement member may be located along opposite lateral edges of the second engager and preferably with the hinge mechanism located centrally therebetween. Preferably an upper end of each wire is secured together and to a common operating wire. Preferably movement (and/or tension) in the common wire urges the two jaws to pivotally open about the hinge mechanism.

The second engager may comprise two pairs of release wires to urge the first engager from a closed position to an open position.

Preferably, in the closed position, the first jaw and the second jaw of the first engager are arranged to clamp (and/or engage with) the first connector.

Preferably the jaws of the first engager (simultaneously) move with the jaws of the second engager as the mooring line tensioner moves from the closed position to the open position. -6 -

Preferably the mooring line tensioner comprise an open channel into which the connector(s) and adjacent (attached) mooring line is locatable.

The first engager may comprise an open channel into which the first connector and preferably adjacent (attached) mooring line is locatable. The open channel may provide a mouth region into which the first connector and preferably adjacent (attached) mooring line is locatable. The open channel may be defined between two fixed (static) jaws which enable the first connector and preferably adjacent (attached) to be moved into and out of engagement with the first engager.

The second engager may comprise an open channel into which the second connector and preferably adjacent (attached) mooring line is locatable. The open channel may provide a mouth region into which the second connector and preferably adjacent (attached) mooring line is locatable. The open channel may be defined between two fixed (static) jaws which enable the second connector and preferably adjacent (attached) to be moved into and out of engagement with the second engager.

Preferably in the engaged position the open channel of the first engager locates around and engages the first connector and the open channel of the second engager locates around and engages the second connector.

Preferably the first engager comprises a sled to facilitate sliding movement of the 25 first engager over a surface and, more preferably, over a deck of a support vessel, and more preferably, for example, during initial deployment from the support vessel.

Preferably the first engager comprises a first end providing a passageway through which the first section of mooring line is extendable and wherein the passageway prevents the movement of the first connector therethrough. Accordingly, the first connector is engaged within the first engager and the first section of mooring line passes through the end of the first engager towards an end of the first section of -7 -mooring line secured to an anchor.

Preferably, in use, the first engager is moved away from the anchor to increase the tension in the first section of mooring line extending between the first engager and 5 the anchor.

Preferably the second engager comprises a first jaw and a second jaw which are movable between an open position and a closed position. Preferably the second engager comprises a pivot/hinge mechanism to enable (pivotal) movement of the 10 jaws between the closed position and the open position.

Preferably, in the closed position, the first jaw and the second jaw of the second engager are arranged to clamp (and/or engage with) the second connector.

Preferably the second engager comprises a sled to facilitate sliding movement of the second engager over a surface and, more preferably, over a deck of a support vessel, and more preferably, for example, during initial deployment from the support vessel.

Preferably the second engager comprises a first end providing a passageway through which the second section of mooring line is extendable and wherein the passageway prevents the movement of the second connector therethrough. Accordingly, the second connector is engaged within the second engager and the second section of mooring line passes through the end of the second engager towards an end of the second section of mooring line secured to an offshore installation/rig.

Preferably, in use, the second engager is moved away from the offshore installation to increase the tension in the second section of mooring line extending between the second engager and the offshore installation.

Preferably the flexible member is engaged within the first pulley system and the -8 -second pulley system to provide a mechanical advantage for the force between the two engagers relative to the tension in the section of flexible member extending away from the mooring line tensioner initiated by an actuating mechanism.

Preferably the flexible member is engaged within the first pulley system and the second pulley system to increase (by a multiple of) the tension in the section of flexible member between the first engager and the second engager initiated by the actuating mechanism (winch).

Preferably the first pulley system and the second pulley system provide a gearing system to multiply the tension (provide a mechanical advantage) in the flexible member to a greater force between the first engager and the second engager.

Preferably the flexible member extends between the first pulley system (and/or the 15 first engager) and the second pulley system (and/or the second engager) a plurality of times and more preferably 8 or 10 times.

Preferably the first pulley system comprises a plurality of first pulley wheels. The first pulley system may comprise 4 or 5 pulley wheels.

The first pulley wheels may be mounted on (or to rotate about) a common axle (and/or a common axis).

The first pulley wheels may be mounted along a distal end of the first engager.

The first pulley wheels may be spaced apart adjacently along a lateral extent of the first engager.

Preferably the second pulley system comprises a plurality of second pulley wheels. 30 The second pulley system may comprise 4 or 5 pulley wheels.

The second pulley wheels may be mounted on (or to rotate about) a common axle -9 - (and/or a common axis).

The first second wheels may be mounted along a distal end of the first engager.

The second pulley wheels may be spaced apart adjacently along a lateral extent of the second engager.

Preferably a tension created in the flexible member is arranged to move the first engager towards the second engager and to move the mooring line tensioner from an unconnected position to a connected position.

Preferably the path(s) (or route) of the flexible member extending between the first engager (and/or first pulley system) and the second engager (and/or the second pulley system) guides the first engager towards the second engager and prevents (and/or inhibits) relative rotation of the first engager and the second engager.

Preferably, in the connected position, the tension in the flexible member extending between the first engager (and/or first pulley system) and the second engager (and/or second pulley system) maintains the first engager and second engager in the connected position. Preferably in the connected position a proximal end face of the first engager located adjacent to a proximal end face of the second engager.

The mooring line may comprise a chain.

The mooring line may be arranged to extend between an anchor and a floating installation. An upper (first) end of the second section of mooring line may be connected to the floating installation. A lower (second) end of the mooring line may provide the second connector. A lower (first end) of the first section of mooring line may be connected to the anchor. An upper (second) end of the first section of mooring line may provide the first connector.

The floating installation may be held in a stable position by a plurality of contiguous pre-tensioned mooring lines.

The connector may comprise a male member and a female member.

The male member may be arranged to automatically latch within the female member. The male member may comprise lugs which are arranged to automatically latch against a latching flange provided within the female member.

The connector may comprise a chain joining device. The chain joining device may comprise a H-link or a shackle or a subsea mooring connector.

The mooring line tensioner is arranged to guide the male member into engagement with the female connector.

The mooring line tensioner may comprise communication means to enable remote operation of the mooring line tensioner (from the vessel on the surface). The communication means may be arranged to receive control signals from a remote control.

The remote control may comprise hydraulic control from the surface and/or via a remotely operated vehicle (ROV) (hot stab) and/or via ROV plugs in hydraulics.

The communication means may comprise an acoustic transceiver. A first acoustic transceiver may be mounted on the first engager and a second acoustic transceiver 25 may be mounted on the second engager.

The communication means may enable the mooring line tensioner to be engaged to and/or disengaged from the first connector member and/or the second connector member and/or (the first/second sections of) the mooring line; and may provide the locking and unlocking functions of the connector (chain connection device).

The communication means may control one or motors mounted on the mooring line tensioner.

The communication means may control one or (hydraulic) pistons mounted on the mooring line tensioner.

According to a second aspect of the present invention there is provided an offshore assembly comprising a mooring line and a mooring line tensioner, the mooring line tensioner comprising: a first engager for engaging a first connector member secured to a first section of a mooring line; a second engager for engaging a second connector member secured to a second section of a mooring line; a first pulley system mounted to the first engager; a second pulley system mounted to the second engager; a flexible member secured between the first pulley system and the second pulley system; the flexible member being arranged, in use, to move the first engager and first connector relatively towards the second engager and second connector until the first connector connects to the second connector thereby securing the first mooring line section to the second mooring line section; wherein, the mooring line tensioner is removable from a position around a contiguous mooring line formed by the connection of the first section of mooring line and the second section of mooring line.

According to a third aspect of the present invention there is provided a method of pre-tensioning a mooring line, the method comprising using a mooring line tensioner comprising: a first engager for engaging a first connector member secured to a first section of a mooring line; a second engager for engaging a second connector member secured to a second section of a mooring line; a first pulley system mounted to the first engager; a second pulley system mounted to the second engager; a flexible member secured between the first pulley system and the second pulley system; the method comprising pulling the flexible member to move the first engager and first connector relatively towards the second engager and second connector until the first connector connects to the second connector thereby securing the first mooring line section to the second mooring line section; and removing the mooring line tensioner from a position around a contiguous mooring line formed by the connection of the first section of mooring line and the second section of mooring line.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only, with reference to the drawings that follow, in which: Figure 1 is a side schematic view of a mooring line from a floating installation showing a part of a preferred embodiment of a mooring line tensioner prior to tensioning of the mooring line.

Figure 2 is a side schematic view of a mooring line from a floating platform during tensioning by a preferred embodiment of a mooring line tensioner.

Figure 3 is a side schematic view of a mooring line from a floating platform in a tensioned configuration with a preferred embodiment of a mooring line tensioner still in position around the contiguous mooring line.

Figure 4 is a side schematic view of a mooring line from a floating platform in a tensioned configuration and with a preferred embodiment of a mooring line tensioner being retrieved by a vessel.

Figure 5 is a side view of a preferred embodiment of a mooring line tensioner with two connectors of a mooring line in an unconnected position.

Figure 6 is a plan view of a preferred embodiment of a mooring line tensioner with 5 two connectors of a mooring line in an unconnected position.

Figure 7 is an end view of a preferred embodiment of a mooring line tensioner with two connectors of a mooring line in an unconnected position.

Figure 8 to Figure 18 show sequential schematic perspective views of a preferred embodiment of a mooring line tensioner being used to pre-tension a subsea mooring line.

Figure 19 is a perspective view of a support vessel during the initial deployment of a preferred embodiment of a mooring line tensioner located along a mooring line.

Figure 20 to Figure 25 show perspective views of a preferred embodiment of a mooring line tensioner being used to pre-tension a subsea mooring line.

Figure 26 is a perspective view of another embodiment of a mooring line tensioner 20 with two connectors of a mooring line in an unconnected position.

Figure 27 is a side view of another embodiment of a mooring line tensioner with two connectors of a mooring line in an unconnected position.

Figure 28 is a perspective view of another embodiment of a mooring line tensioner connecting two connectors of a mooring line.

Figure 29 is a side view of another embodiment of a mooring line tensioner connecting two connectors of a mooring line.

Figure 30 is a perspective view of another embodiment of a mooring line tensioner.

Figure 31 is a perspective view of a third preferred embodiment of a mooring line tensioner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As mentioned above, offshore installations (floating installations/rigs) may be retained in position through the use of a number of anchors and/or piles (not shown) located on the seabed. The term anchor will be used for the specific description although it should be appreciated that the anchoring function could be provided by a pile or similar device.

Pre-tensioned mooring lines extend from the offshore installation to the respective anchors located on or in the seabed. One aim of the present invention is to provide an easy system to apply the required pre-tension in each mooring line and also to prevent or restrict the tensioning equipment (winch) remaining in position on the deck of the offshore installation for a prolonged period and potentially for substantially the life of the offshore installation. The present invention effectively relates to a concept for a subsea winch for re-joining mooring lines after they have been disconnected.

Briefly, a mooring line 10 comprises a first section 12 and a second section 14 each having a respective connector member 52, 54 at an end thereof. The connection/completion of this connector 50 forms a contiguous mooring line 10 extending upwardly from an anchor/pile on the sea bed to an upper end secured to the offshore installation 2. In order to complete this connection easily, a mooring line tensioner 20 is used.

In an initial position, the two sections 12, 14 of mooring line are not connected and the connector members 52, 54 are spaced apart, for example by 100m to 200m.

The length of the mooring line sections 12, 14 are preselected such that the subsequent connection provides a pre-tensioned mooting line 10 at the required pre-tension.

The mooring line tensioner 20 comprises a first engager 22 which engages with and grips/clamps the first connector/end of the first section 12 of mooring line. The mooring line tensioner 20 comprises a second engager 24 which engages with and grips/clamps the second connector/end of the second section 14 of mooring line. A flexible (tensioning) line 40 is engaged around a pulley system 32, 34 provided on the engagers 22, 24. An upper end of the tensioning line 40 is engaged with a winch which is arranged to wind the tensioning line 40 on to a spool which pulls the two engagers 22, 24 towards each other until the connector members 52, 54 connect.

The pulley system is arranged to multiply the tension applied to the tensioning line for the pulling force for the two engagers 22, 24 since the pulley system effectively creates multiple sections of the tensioning line 40 passing between the engagers 22, 24. In some embodiments there may be 8 or 10 sections of the tensioning line 40 extending between the two engagers 22, 24 which thereby provides a mechanical advantage and multiplies the tensile force/pulling force in the tensioning line 40 by a factor of 8 or 10 for the urging force pulling the two engagers 22, 24 together.

In this connected position, the mooring line tensioner 20 opens since it is formed with hinged/pivotal jaws which thereby provides an open region through which the now connected/completed contiguous mooring line 10 can be disengaged from the mooring line tensioner 20. Finally, the mooring line tensioner 20 can be retrieved and the pre-tensioned mooring line 10 is complete and all auxiliary apparatus no longer required can be removed and does not remain in situ and/or occupy unnecessary valuable space.

As shown in Figure 1 to Figure 4, the preferred embodiment of a mooring line tensioner 20 comprises a subsea tensioner which is arranged to connect two sections 12, 14 of a mooring line 10 to provide a pre-tensioned mooring line 10.

Once connected, the subsea mooring line tensioner 20 is removed from the completed mooring line 10 such that there is no tensioning apparatus simply left in situ which would be redundant. Furthermore, such a system does not unnecessarily occupy the valuable deck space on the offshore installation 2.

The mooring line 10 is provided with a first section of mooring line 12 and respective first connector 52 and a second section of mooring line 14 and respective second connector 54. In the preferred embodiment, the mooring line 10 comprises a chain although other types of mooring line 10 could be used. Furthermore, in the preferred embodiment, the connector 50 comprises an automatic latching and locking connector 50 having a male connector 54 and a female connector 52. The male connector 54 is guided into the female connector 52 and lugs automatically latch the male connector 54 within the female connector 52. The connector 50 may be automatically locked in place. Alternatively, the connector 50 may be actuated in order to be locked.

The connector may comprise any type of chain joining device, such as a H-link, 15 shackle and/or a subsea mooring connector.

The mooring line tensioner 20 comprises a first engager 22 which is secured to the first connector 52 and a second engager 24 which is secured to the second connector 54. Initially the two connectors 52, 54 are spaced apart with no pre-tension in either section 12, 14 of the mooring line 10. The overall completed length of mooring line 10 is calculated such that the mooring line 10 will have the required pre-tension once the two sections 12, 14 are connected. The mooring line tensioner 20 is arranged to move the two connectors 52, 54 until the connector 50 is formed and imparts the required pre-tension in the mooring line 10. The pre-tension is effectively transmitted through the completed connector 50.

Once the connectors 52, 54 are locked together, the mooring line tensioner 20 can be removed from around the completed mooring line 10/connector 50. In a preferred embodiment, the mooring line tensioner 20 moves from a closed (enclosing) position to an open position in order to form a mouth section whereby the mooring line tensioner 20 can be removed from the contiguous mooring line 10.

The specific mechanisms and method of use of the preferred embodiment will now be described in more detail. A specific arrangement for a preferred embodiment of a mooring line tensioner is shown in Figures 5-7 and a corresponding sequence showing the operation of the mooring line tensioner and installation of a pre-tensioned mooring line 10 is shown in Figures 8-18.

As shown in Figure 5, Figure 6 and Figure 7, the mooring line tensioner 20 comprises the first engager 22 and the second engager 24 which are arranged to facilitate the connection of the two sections 12, 14 of the mooring line 10 to form a completed and contiguous pre-tensioned mooring line 10. In particular, the completed mooring line 10 may extend between an offshore installation 2 and a subsea anchor (not shown). Prior to completion, the required length of mooring line 10 may be calculated since this length will thereby provide the required pre-tension. The individual lengths of the first section 12 and the second section 14 of the mooring line 10 are calculated by the separation distance of the respective anchor and the offshore installation 2.

The first section 12 of mooring line 10 is connected at a first end to the anchor located on the seabed and the second free (unconnected) end of the first section 12 of mooring line 10 is provided with the female connector 52. Similarly, the second section 14 of mooring line 10 is connected at a first end to the offshore installation 2 and the second free end of the second section 14 of mooring line 10 is provided with the male connector 54.

Accordingly, once the connector 50 is completed the two sections 12, 14 of the mooring line 10 form a contiguous mooring line 10 with the required pre-tension. Since the required pre-tension may be relatively high, the force required to move the respective end connectors 52, 54 to a connected position will likewise be relatively high. However, the present invention provides a pulley system to facilitate the movement of the two connectors 52, 54 towards each other and to the connected position. It should be noted that the system may need to gather up 100m to 200m of chain and a pulley system is able to provide this capability and a system using hydraulic cylinders or turnbuckles may not be able to provide this capability. The pulley system is arranged to significantly reduce the winch tension in pulling the two engagers 22, 24 together and may be arranged to reduce the winch tension to 1/10 or 1/8 of the line tension.

The first engager 22 is provided with a first pulley system 32 and the second engager 24 is provided with a second pulley system 34. A cable 40 is engaged and extends to between the two pulley systems 32, 34. A free end of the cable 40 extends away from the mooring line tensioner 20 and to a winch or similar drive unit whereby the tension in the cable 40 can be controlled.

As shown in Figure 5, Figure 6 and Figure 7, the first pulley system 32 comprises a number of individually spaced apart pulley wheels and the second pulley system 34 also provides a number of individually spaced apart pulley wheels. In the preferred embodiment, each pulley system 32, 34 comprise four laterally spaced apart and adjacent pulley wheels which are axially mounted. In particular, the rotatable pulley wheels for each pulley system 32, 34 are mounted on a respective common axle. The axle for the first pulley system 32 is located at a distal end of the first engager 22 and the axle for the second pulley system 34 is mounted at a distal end of the second engager 24. A proximal end of the first engager 22 is arranged to locate opposite and adjacent to a proximal end of the second engager 24 when the mooring line tensioner 20 is in a connected configuration.

Accordingly, the cable 40 extends over a first pulley wheel of the first pulley system 32 and extends over and around a first pulley wheel of the second pulley system 34 and then returns to the second pulley wheel of the first pulley system 32 and to the second pulley wheel of the second pulley systems 34 and so on and so forth. Accordingly, this multiple routing for the cable 40 provides a mechanical advantage. In particular, the force to move the cable 40 is only a fraction of that generated between the two engagers 22, 24. In the preferred embodiment, the cable 40 extends eight times between the two engagers 22, 24. This thereby creates an urging force between the two engagers 22, 24 of eight times that applied to the cable by the actuating mechanism. It will be appreciated that other multipliers may easily be provided by adjusting the number and/or arrangement of the pulley wheels on each engager 22, 24.

In some embodiments the cable (tensioning line) 40 extends upwardly from the first engager 22 which locates on the first section of mooring line 12 connected to the anchor. However, in some embodiments, the cable (tensioning line) 40 extends upwardly from the second engager 24 which locates on the second section 14 of mooring line connected to the floating offshore installation 2. For example, Figure 1 shows the cable 40 or tensioning line extending upwardly from the second engager 24 whereas Figure 8 shows the cable 40 or tensioning line extending upwardly from the first engager 22.

Since the cable 40 is taut and engaged around aligned pulley wheels on the first and second engagers 22, 24, the intervening cable sections between the engagers 22, 24 is maintained in tension. Accordingly, as the two engagers 22, 24 are moved from a spaced apart configuration towards the connected configuration (where the connectors 52, 54) engage, the relative movement of the first engager 22 towards the second engager 24 is guided such that relative rotation between the two engagers 22, 24 is prevented. Accordingly, alignment means on each engager 22, 24 will readily cooperate at the connecting position. The alignment means may comprise cooperating projecting members/lugs and sockets on opposing faces (at the proximal ends) of the two engagers 22, 24. An aim of this alignment and cooperating mechanism is to enable the two engagers 22, 24 to function as a single unit once in the connected configuration.

Further subsequent movement and manipulation of the two engagers 22, 24 can be easily controlled if the two engagers 22, 24 function as a single unitary component. However, in some embodiments the two engagers 22, 24 may be connected to lifting slings separately as will be described later. Such an arrangement may the movement of the engagers clear of the connector as they flair out because of the lifting sling angel.

-20 -The embodiments in which the two engagers function as a single unitary component aids with the disengagement of the mooring line tensioner 20 and the subsequent retrieval of the mooring line tensioner 20 as will be described in due course. Due to this guided movement, once the first connector 52 is latched to the second connector 54, the two engagers 22, 24 similarly engage and this engagement aids the subsequent retrieval of the mooring line tensioner 20.

Once the two engagers 22, 24 are in the connected configuration and the two connectors 52, 54 are latched, a locking actuator may be operated to physically lock the male connector 54 to the female connector 52. The operation may be controlled subsea by a ROV 6 which may manually manipulate the locking actuator.

With the connector 50 in a locked position and the two engagers 22, 24 operating as a single component, the mooring line tensioner 20 is actuated to move from an engaged position to a disengaged position around the connector 50. The first and second engagers 22, 24 move to an open position with respective jaws of each engager 22, 24 opening from around the respective connector 52, 54. In this open configuration, the mooring line tensioner 20 no longer encompasses the connector/mooring line 10 and provides a mouth portion for the relative extraction of the mooring line 10 from within the mooring line tensioner 20. This enables the mooring line tensioner 20 to be removed from around the completed mooring line 10. Once open and disengaged, the mooring line tensioner 20 can be easily retrieved using the cable 40 which is connected to the winch on the support vessel 4 or a second work wire, or by connecting the slings to the original pulley.

Figure 19 shows a deployment vessel 4 in which the mooring line tensioner 20 is located on the deck and the vessel 4 may comprise an anchor handling tug vessel (AHTV). As can be seen, the first section 12 of mooring line will be deployed into position and will be followed by the intermediate section of cable 40 which initially separates the first section 12 of the mooring line from the second section 14 of the mooring line. The first section 12 of mooring line will drag the first engager 22 from the deck.

At this stage, the separation distance between the first engager 22 and the second engager 24 may be increased as the first section 12 and the first engager 22 are lowered into position from the deck. The engagers 22, 24 may be arranged to have a 100m separation distance. Eventually, at the chosen separation distance for the first engager 22 and the second engager 24, the intermediate section of cable 40 will drag the second engager 24 and the second section 14 of mooring line from the deck and into position. The upper end of the second section 14 of the mooring line can then be secured in position on the floating offshore installation prior to closing the gap between eth two engagers 22, 24 to gradually apply the pre-tension.

As previously mentioned, once in this configuration, the winch on board the deployment vessel 4 may be used to pull the two engagers 22, 24 towards each other and to eventually connect the corresponding connectors 52, 54. In this connected configuration, the mooring line tensioner 20 can be retrieved by the vessel 4 and subsequently used for pre-tensioning further mooring lines.

Figure 20 to Figure 25, show further detailed views of another embodiment of a mooring line tensioner 20 for applying a pre-tension in a subsea mooring line 10. In this embodiment, the mooring line tensioner 20 is retrieved through the use of lifting wires 70. These wires 70 are omitted form Figure 20 and Figure 21 for clarity.

The engagers 22, 24 include a number of lifting eyes 72 located on the upper surface. In particular, each engager 22, 24 includes four lifting eyes each of which is secured to a section of a lifting wire 70. These sections of lifting wires 70 extend upwardly where they are connected to a further section of a main lifting wire. The sections of lifting wires 70 may be coupled together in pairs which may aid the operation (especially the remote disconnection) of the mooring line tensioner 20, as described later.

The sequence of operation for this embodiment of the mooring line tensioner 20 is -22 -effectively the same as previously described. Following the subsea deployment from the vessel 4, the cable 40 is used to pull the two engagers 22, 24 together, as shown in Figure 20 and Figure 21. The tension in the cable 40 is sufficient to maintain the two engagers 22, 24 in a closed and effectively engaged position and separate engaging components are not required to physically link the two engagers 22, 24 together. Once the engagers 22, 24 are secured together, the section of cable 40 extending from the mooring line connector 20 to the winch may be slackened off and the tool 20 subsequently opened prior to retrieval.

The two engagers 22, 24 have lifting wires 70 secured on an upper surface, as shown in Figure 22 and Figure 23. These lifting wires enable the mooring line tensioner 20 to be easily retrieved by the deployment vessel 4.

In one embodiment previously described, the ROV operated a screw to flair the engagers 22, 24 out to clear the connector 50, and the residual tension in the winching line 40 is enough to keep the engagers 22, 24 effectively stuck together.

However, in this embodiment, lifting wires 70 have been added which will help separate the two halves of each engager 22, 24, so they can be jockeyed free of the connector 50. The main tensioning line 40 may still be used to lift the mooring line tensioner 20 back to surface as a unit, and this secondary lifting arrangement may not be needed.

However, Figure 24 and Figure 25 show the disconnection and lifting sequence with the lifting wires 70. The lifting wires 70 are just stowed on the tool 20 during the tensioning and then hooked up by the ROV at the top (nearly at top of frame) using an ROV hook.

As mentioned above, the stowed lifting lines are not shown in the pre-connection figures (Figure 20 and Figure 21). Similarly, the main tensioning line 40 is not shown in Figure 24 and Figure 25, and this tensioning line 40 is slackened off during initial lifting but could still be used for retrieving the mooring line tensioner tool 20.

-23 -Further embodiments of the mooring line tensioner 120 will be described with particular reference to Figure 26 to Figure 30 and Figure 31. The mooring line tensioner 120 comprises a first engager 122 which is secures to the first connector 52 and a second engager 124 which is secures to the second connector 54. Initially the two connectors 52, 54 are spaced apart. As described above, the mooring line tensioner 120 is arranged to move the two connectors 52, 54 until the connector 50 is formed and imparts the required pre-tension in the mooring line 10. The pretension is effectively transmitted through the completed connector 50.

In these embodiments, the mooring line tensioner 120 does not include a pivotal or hinged mechanism in order to engage around the mooring line 10/connectors 52, 54. The engagers 122, 124 are provided with respective mouth regions 123, 125 or fixed/static jaws along a lower face of the mooring line tensioner 120. These mouth regions 123, 125 enable the connectors 52, 54 to be secured within the respective engager 122, 124 without manipulating and articulating jaw components. Accordingly, such a mooring line tensioner 120 is simple and easy to reliably locate around the respective connectors 52, 54.

Each mouth region 123, 125 may comprise a linear channel section defined along a lower face of the engager 122, 124 such that the engager 122, 124 can be placed over the respective connector 52, 54 and adjacent mooring line 10. Accordingly, the tool (mooring line tensioner 120) is no longer split / hinged compared to the first embodiment, and it just drops over the top of the mooring line 10.

The mooring line tensioner 120 includes a pulley system 132, 134 which functions as previously described with the tensioning line 40 pulling and urging the two engagers 122, 124 towards each other until the connectors 52, 54 latch to form the completed connector 50 along the mooring line.

Once the completed connector 50 has been created, the mooring line tensioner 120 can be removed and retrieved. Again, the fixed/static jaws forming the mouth regions 123, 125 enables this procedure to be completed without having to manipulate and articulate (move) any jaw members on the engagers 122, 124.

In some embodiments, for example as shown in Figure 31, the mooring line tensioner 120 comprises communication means to enable operational signals to be communicated to the mooring line tensioner 120. In particular, operational signals can be sent to enable the mooring line tensioner to be controlled remotely which may prevent the use of an ROV for operating the tool 120.

The mooring line tensioner 120 may include acoustic receiving means to receive the control signals. The first engager 122 may have a first acoustic transceiver 127 mounted thereon. The second engager 124 may have a second acoustic transceiver 129 mounted thereon.

These communication modules 127, 129 may enable remote control of the lock function, if required, and to release the winch from the mooring line 10 once the connector 50 is locked. The communication modules 127, 129 may comprise modems which are commercially available. Typical actuation would be either motors supplied by batteries, or a hydraulic valve which discharges accumulators into pistons to achieve each of these functions.

In yet further embodiments of the present invention there may be an electric and/or hydraulic umbilical to achieve the same operation of the mooring line tensioner 120.

In summary, these embodiments of the mooring line tensioner tool 120 provides a tool 120 which does not have a hinged design, and also provides an acoustic option for operation to prevent the use of an ROV for operational functions.

The present invention may be used in a mooring line 10 with a 400t maximum line 30 tension applied, in a 1000m maximum water depth and/or with 150m maximum pull in length. An ROV is used subsea to unlock the mooring line tensioner 20 and the connector 50 may have an optional automatic lock capability or comprise an ROV -25 -operated lock. The cable 40 may comprise 50mm UHMPE Dyneema work wire with a breaking strength of greater than 190t, a maximum load of 50t at 400t mooring line tension based on an 8:1 pulley reduction although a greater reduction is possible. The mooring line comprises a chain (R4 147mm chain) which may be a stud less chain with a minimum breaking load (MBL) of 1950t. The connector may comprise a Rocksteady connector produced by Subsea Riser Products Limited. This connector may similarly have a 1950t MBL.

Overall, the present invention provides a solution with a relatively low capital cost and with minimum disruption to the mooring design. The section of mooring line can be disconnected and re-adjusted and the system uses an in-line DNV/ABS certified connector.

Claims

CLAIMS1. A mooring line tensioner comprising: a first engager for engaging a first connector member secured to a first section of a mooring line; a second engager for engaging a second connector member secured to a second section of a mooring line; a first pulley system mounted to the first engager; a second pulley system mounted to the second engager; a flexible member secured between the first pulley system and the second pulley system; the flexible member being arranged, in use, to move the first engager and first connector relatively towards the second engager and second connector until the first connector connects to the second connector thereby securing the first mooring line section to the second mooring line section; wherein, the mooring line tensioner is removable from a position around a contiguous mooring line formed by the connection of the first section of mooring line and the second section of mooring line.
2. A mooring line tensioner according to Claim 1 in which the flexible member comprises a cable and the cable is arranged to extend upwardly from the mooring line tensioner located subsea to an actuating mechanism located above sea level and wherein the actuating mechanism is located on a support vessel on the sea surface.
3. A mooring line tensioner according to Claim 2 in which the actuating mechanism comprises a winch which is arranged to pay in and pay out the cable and wherein the winch comprises a spool about which the flexible member is wound.
4. A mooring line tensioner according to Claim 1 or Clam 2 in which the mooring line tensioner is movable between a closed position and an open position.
-27 - 5. A mooring line tensioner according to Claim 4 in which, in the closed position, the first engager locates around and engages the first connector and the second engager locates around and engages the second connector.
6. A mooring line tensioner according to Claim 4 or Claim 5 in which, in the closed position, the mooring line tensioner encompasses the mooring line and, in the open position, the mooring line tensioner provides a mouth portion which enables the mooring line tensioner to be detached from the mooring line.
7. A mooring line tensioner according to Claim 6 in which the mooring line tensioner comprises a hinge mechanism to enable the mooring line tensioner to move between the closed position and the open position.
8. A mooring line tensioner according to any one of Claim 4 to Claim 7 in which the mooring line tensioner comprises a release system to aid the movement of the mooring line tensioner from the closed position to the open position.
9. A mooring line tensioner according to Claim 8 in which the release system comprises release wires located on the mooring line tensioner which are pulled to urge the mooring line tensioner to move from the closed position to the open position.
10. A mooring line tensioner according to Claim 1 or Claim 2 in which the mooring line tensioner comprise an open channel and wherein the first engager comprises an open channel into which the first connector and adjacent attached mooring line is locatable and in which the open channel is defined between two fixed jaws and the second engager comprises an open channel into which the second connector and adjacent attached mooring line is locatable and in which the open channel is defined between two fixed jaws.
11. A mooring line tensioner according to any preceding claim in which the first engager comprises a first end providing a passageway through which the first -28 -section of mooring line is extendable and wherein the passageway prevents the movement of the first connector therethrough.
12. A mooring line tensioner according to Claim 11 in which the first connector is engaged within the first engager and the first section of mooring line passes through the end of the first engager towards an end of the first section of mooring line secured to an anchor.
13. A mooring line tensioner according to Claim 12 in which, in use, the first engager is moved away from the anchor to increase the tension in the first section of mooring line extending between the first engager and the anchor.
14. A mooring line tensioner according to any preceding claim in which the second engager comprises a first end providing a passageway through which the 15 second section of mooring line is extendable and wherein the passageway prevents the movement of the second connector therethrough.
15. A mooring line tensioner according to Claim 14 in which the second connector is engaged within the second engager and the second section of mooring 20 line passes through the end of the second engager towards an end of the second section of mooring line secured to an offshore installation.
16. A mooring line tensioner according to Claim 15 in which, in use, the second engager is moved away from the offshore installation to increase the tension in the 25 second section of mooring line extending between the second engager and the offshore installation.
17. A mooring line tensioner according to any preceding claim in which the flexible member is engaged within the first pulley system and the second pulley system to provide a mechanical advantage for the force between the two engagers relative to the tension in the section of flexible member extending away from the mooring line tensioner initiated by an actuating mechanism.
-29 - 18. A mooring line tensioner according to any preceding claim in which a tension created in the flexible member is arranged to move the first engager towards the second engager and to move the mooring line tensioner from an unconnected position to a connected position.
19. A mooring line tensioner according to Claim 18 in which the path of the flexible member extending between the first engager and the second engager guides the first engager towards the second engager and prevents relative rotation of the first engager and the second engager.
20. A mooring line tensioner according to any preceding claim in which, in a connected position, the tension in the flexible member extending between the first engager and the second engager maintains the first engager and second engager in the connected position.
21. A mooring line tensioner according to any preceding in which the connector comprises a male member and a female member and in which the male member is arranged to automatically latch within the female member.
22. A mooring line tensioner according to Claim 21 in which the mooring line tensioner is arranged to guide the male member into engagement with the female connector.
23. A mooring line tensioner according to any preceding claim in which the mooring line tensioner comprises communication means to enable remote operation of the mooring line tensioner and wherein the communication means is arranged to receive control signals from a remote control.
24. An offshore assembly comprising a mooring line and a mooring line tensioner, the mooring line tensioner comprising: a first engager for engaging a first connector member secured to a first -30 -section of a mooring line; a second engager for engaging a second connector member secured to a second section of a mooring line; a first pulley system mounted to the first engager; a second pulley system mounted to the second engager; a flexible member secured between the first pulley system and the second pulley system; the flexible member being arranged, in use, to move the first engager and first connector relatively towards the second engager and second connector until the first connector connects to the second connector thereby securing the first mooring line section to the second mooring line section; wherein, the mooring line tensioner is removable from a position around a contiguous mooring line formed by the connection of the first section of mooring line and the second section of mooring line.
25. A method of pre-tensioning a mooring line, the method comprising using a mooring line tensioner comprising: a first engager for engaging a first connector member secured to a first section of a mooring line; a second engager for engaging a second connector member secured to a second section of a mooring line; a first pulley system mounted to the first engager; a second pulley system mounted to the second engager; a flexible member secured between the first pulley system and the second pulley system; the method comprising pulling the flexible member to move the first engager and first connector relatively towards the second engager and second connector until the first connector connects to the second connector thereby securing the first mooring line section to the second mooring line section; and removing the mooring line tensioner from a position around a contiguous mooring line formed by the connection of the first section of mooring line and the -31 -second section of mooring line.