Chain tensioners for mooring offshore floating structures

Abstract

The present invention relates to a subsea tensioner (30), a marine tensioner (130) and an in-line tensioner (230) for tensioning an anchor chain (20) in a mooring arrangement, said tensioner comprising a chain roller (32) having a sprocket supported on a first support shaft (42) in a housing (34), a first part of the housing arranged to receive the anchor chain (20) encircling the chain roller (32) and a second part of the housing (34) having an attachment for an anchor line (16) or to a floating structure (12), said first and second parts of the housing (34) facing in opposite directions. The present invention further discloses a system and method for mooring a floating structure.

Description

[Technical field]

[0001] The present invention relates to mooring of offshore floating structures such as oil and gas installations, wind turbine foundations, and fish farming cages. Subsea tensioners, vessel tensioners, and in-line tensioners are provided for tensioning anchor lines in mooring devices. The present invention further discloses a system and method for mooring the floating structures. [Background technology]

[0002] In-line tensioners are known which are placed in the water as part of the anchor line, and also tensioners which are attached directly to the floating structure.

[0003] In-line tensioners used with bollard pulls have the advantage that they can be connected and tightened relatively quickly. The disadvantages are that breaks occur in the anchor rope during tightening, i.e. the tension is reduced after the tightening is completed. The in-line tensioner rotates 180° after tightening and thus causes a twist in the anchor rope. The chain end may sag below the in-line tensioner after tightening, which may lead to chain fatigue. The in-line tensioner acts as an extra lump of weight in the anchor rope. It has high fuel consumption during tightening and thus a poor environmental profile. In case of large anchor spreads, it cannot be tightened by vertical lifting. The in-line tensioner has to be handled on the deck of the anchor handling vessel.

[0004] In-line tensioners used with winch pulls have the advantage that tensioning can be done with a winch without using a bollard pull and thus have a good environmental profile. The disadvantages are that an extra line has to be connected to the lower chain, which would involve extra marine work. Lift forces can be generated on the anchor. Breaks can occur in the anchor line during tightening, i.e. the tension drops after tightening is completed. The in-line tensioner will rotate 180° after tightening, thus causing a twist in the anchor line. The chain end may sag below the in-line tensioner after tightening, which can lead to chain fatigue. The in-line tensioner acts as an extra lump of weight in the anchor line. The in-line tensioner has to be handled on deck of the anchor handling vessel.

[0005] Marine tensioners used with bollards (in-line tensioners mounted on floating structures) have the advantages of relatively quick connection and tightening start, no breaks in the anchor lines during tightening, no extra mass weight in the middle of the anchor lines, and no handling of the marine tensioners on deck in anchor handling vessels. The disadvantages are that the chain end has to be hoisted to the marine tensioner or hoisted upwards along the legs of the floating structure, which involves extra marine work. The tightening of the active anchor line is smaller than that of the two passive anchor lines, and therefore the tension of the passive anchor lines drops slightly after tightening is finished. It has high fuel consumption during tightening and therefore a poor environmental profile.

[0006] A vessel tensioner used with a winch pull has the advantages that there is little or no breakage of the anchor line during tightening and there is no extra lump weight in the middle of the anchor line. Tightening can be done with a winch without using a bollard pull, thus having a good environmental profile. There is no handling of the vessel tensioner on the deck of the anchor handling vessel. The disadvantages are that the chain end has to be hoisted to the vessel tensioner or hoisted upwards along the leg of the floating structure, which involves additional marine work. The tightening of the active anchor line is weaker than the tightening of the two passive anchor lines, therefore the tightening of the passive anchor line drops slightly after the tightening is completed. An extra line has to be connected to the lower chain, which involves extra marine work.

[0007] EP 3251943 A1 discloses a mooring tensioning device for a floating structure or vessel, the mooring tensioning device comprising an anchor, a mooring line extending to the floating structure, a fairlead chain stopper device arranged on the floating vessel, an underwater pulley device and a towing unit on the anchor handling vessel. The mooring line is attached at a first end to the anchor and at a second end to the towing unit on the anchor handling vessel, the mooring line extending from the anchor through the fairlead chain stopper device on the floating structure. The fairlead chain stopper device comprises a chain stopper interacting with the mooring line and a chain pulley guiding the mooring line through the fairlead chain stopper device.

[0008] EP 3251942 A1 discloses a similar system for a mooring tensioning device for a floating structure or vessel, comprising an anchor, a mooring line, a mooring tensioner and a working line. The mooring tensioner has a tensioning pulley. The mooring line is attached at a first end to the anchor and at a second end to the mooring tensioner, the working line is attached at a first end to the floating structure and extends over the tensioning pulley, and the working line is attached at a second end to a towing unit on an anchor handling vessel.

[0009] US2020377178A1 discloses a tensioning system for mooring lines of a floating structure. The mooring lines include separate first and second mooring line sections, with a first end of the second mooring line section attached to the floating structure and a first end of the first mooring line section attached to an anchorage embedded in the seabed. A tensioner configured to act on the mooring lines includes a body having a housing and an inlet unit for inserting the second end of the first mooring line section into the housing of the body. The body includes an opening for passing the second end of the first mooring line section from the inlet unit through the housing along the redirecting element. The tensioning system includes a stabilizing platform fixed to the body. At least a portion of the stabilizing platform protrudes laterally from the body of the tensioner.

[0010] Delmar&Vryhof, Stevadjuster (https: / / www.youtube.com / watch?v=nsKIV38diPY) is a solution for chain adjustment, pre-tensioning moorings, and connecting or disconnecting anchor lines.

[0011] Furthermore, reference is made to International Publication No. 2020046127 (A1), International Publication No. 2018025018 (A1), and International Publication No. 2020165568 (A1), which show the general state of the art in the art. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention, in one embodiment, is directed to a subsea tensioner for tensioning anchor and mooring lines on the seabed.

[0013] The principle is that it is possible to tighten the anchor lines with the help of an anchor handling vessel, e.g. using a bollard pull, i.e. there is no need to mount an anchor winch on the floating structure. It is possible to tighten both the active and the passive anchor lines on opposite sides of the floating structure, e.g. by placing a tensioning unit on the seabed close to the anchor. With three anchor lines, which seems to be a typical configuration for floating wind turbines, the same tightening is obtained in the two opposing anchor lines as in the active lines.

[0014] The subsea tensioning unit is a subsea tensioner that can be mounted on a runner, skid or toboggan so that it can slide along the seabed during tightening. When the anchor chain end connected to the anchor handling vessel is pulled, the reaction force of the active anchor line extending to the floating structure is doubled. This means that such a strong bollard pull is not needed for the anchor handling vessel (AHT), which is also important to achieve high tension while removing the "stretch" of the fiber rope of the anchor line. The angle of the tensioning wire from the anchor handling vessel is adjusted to obtain a small lift on the subsea tensioner, which releases the pressure against the seabed during tightening.

[0015] After tightening, the excess length of the anchor chain can be laid on the seabed, which is static and not exposed to dynamic loads as in alternative solutions where the tensioning unit is located further up on the anchor line (in-line tension) or in solutions where it is directly attached to the floating structure.

[0016] Other embodiments of the present invention are directed to marine tensioners and in-line tensioners.

[0017] All three chain tensioners eliminate the need for an on-board floater winch as tensioning is performed by an external vessel. The tensioners are targeted at permanently moored floating structures, particularly but not limited to floating offshore wind, offshore aquaculture, and oil and gas industry floating structures.

[0018] The chain tensioner is designed with few moving parts, safe operation and a focus on requiring minimal maintenance and failure modes over the product's life.

[0019] The solution of the invention is easy to reconnect later if it turns out that the anchor lines need to be retightened.

[0020] The anchor chain from the anchor is locked in a chain tensioner. [Means for solving the problem]

[0021] The above mentioned object is achieved by a subsea tensioner, a system for mooring a floating structure and a method for mooring a floating structure as disclosed in the independent claims.

[0022] According to a first embodiment of the present invention, there is provided a subsea tensioner for tensioning an anchor chain in a mooring arrangement, the subsea tensioner being positionable on the seabed adjacent to an anchor, the subsea tensioner comprising a chain roller having a sprocket supported on a first support shaft in a housing. A first part of the housing is arranged to accommodate an anchor chain connected to the anchor and encircling the chain roller, and a second part of the housing has an attachment for an anchor line extendable to a floating structure on the water surface, the first part of the housing facing in opposite directions. A spring-loaded locking pawl is arranged in the housing and supported on a second support shaft in the first part of the housing, the locking pawl being engageable with a chain link of the anchor chain before the anchor chain leaves the chain roller, the locking pawl being arranged to press the chain link against one of the sprockets on the chain roller to lock the anchor chain, the sprocket being the sprocket on the chain roller facing the second part of the housing.

[0023] The housing is connected to one or more subsea skids to allow the subsea tensioner to slide along the seabed during tensioning of the anchor chain. The housing may be hinged to the subsea skids to allow angular adjustment of the housing.

[0024] The locking pawl may be a single spring-loaded locking pawl that automatically locks every other chain link that passes over the sprocket of the chain roller.

[0025] The housing may comprise spaced apart locking plates forming said first part of the housing and comprising a first support shaft supporting a chain roller having a sprocket and a second support shaft supporting said locking pawl, the locking plates being joined together to form said second part of the housing and comprising attachments for anchor ropes.

[0026] The first support shaft for the chain rollers may be arranged vertically above a second support shaft for the locking pawl.

[0027] The chain roller may include a central groove for accommodating the wire.

[0028] The first and second parts of the housing are preferably horizontally opposed and the inlet in the first part of the housing for the anchor chain from the anchor and the attachment for the anchor line in the second part of the housing are linearly opposed.

[0029] The pawl may be connected to an actuator that applies the spring force, the actuator being releasable to allow the pawl to disengage from a sprocket on a chain roller.

[0030] The system for mooring a floating structure of the present invention comprises the subsea tensioner disclosed in relation to the first embodiment of the present invention, - a floating structure located on the water surface and at least partially submerged; - one or more passive anchor lines extending from the floating structure through the water to the seabed and moored to the seabed; at least one active anchor line extending from the floating structure through the water to a subsea tensioner disposed on the seabed adjacent to the anchor; the passive anchor line and the active anchor line extend in different directions in the water; and - comprising an anchor chain extending from the anchor to a chain roller in the subsea tensioner and encircling the chain roller; The anchor chain is arranged so that it is tensioned in the water in a direction opposite to the direction of the active anchor line.

[0031] One end of the anchor chain, which is wrapped around a chain roller in the subsea tensioner, can be connected to a tension wire from the anchor handling vessel.

[0032] The tension wire may be connected to a bollard or winch on the anchor handling vessel and arranged to be tensioned by the anchor handling vessel pulling away from the floating structure.

[0033] The tension wire may be connected to a winch of the anchor handling vessel and arranged to be tensioned by actuating the winch of the anchor handling vessel to pull the tension wire away from the floating structure.

[0034] The anchor may be a subsea drag buried anchor.

[0035] The inventive method for mooring a floating structure using the anchor handling vessel and the subsea tensioner disclosed in relation to the first embodiment of the present invention comprises: - mooring one or more passive anchor lines extending between the floating structure and the seabed to the seabed; - deploying a subsea tensioner on the seabed adjacent to the anchor, and connecting an active anchor line extending from the floating structure through the water to the subsea tensioner to the subsea tensioner; the passive anchor line and the active anchor line extend in different directions in the water; and - connecting an anchor chain extending from the anchor to and encircling a chain roller in a subsea tensioner to a tensioning wire from an anchor handling vessel; The anchor chain is tensioned in the water in a direction opposite to that of the active anchor line by pulling on the tension wire.

[0036] The method may include sliding the subsea tensioner along the seabed during tensioning of the anchor chain.

[0037] The method may further comprise the steps of connecting the tensioning wire to a bollard or winch on the anchor handling vessel and tensioning the anchor chain by pulling it away from the floating structure.

[0038] The method may further include the steps of connecting the tension wire to a winch on the anchor handling vessel and actuating the winch to pull the tension wire away from the floating structure.

[0039] The anchor chain may be locked in a subsea tensioner. The method may include unlocking the anchor chain in the subsea tensioner using the ROV to manually operate a locking pawl in the subsea tensioner.

[0040] According to a second embodiment of the present invention there is provided a marine tensioner for tensioning an anchor chain in a mooring arrangement, said marine tensioner connectable to a floating structure, said marine tensioner comprising a chain roller having a sprocket supported on a first support shaft in a housing. A first part of the housing is arranged to accommodate the anchor chain encircling the chain roller, and a second part of the housing has an attachment to the floating structure, said first part and said second part of the housing facing in opposite directions. A spring loaded locking pawl is arranged in the housing and supported on a second support shaft in the first part of the housing, the locking pawl being engageable with a chain link of the anchor chain before the anchor chain leaves the chain roller, the locking pawl being arranged to press the chain link against one of the sprockets on the chain roller to lock the anchor chain, said sprocket being the sprocket on the chain roller facing the second part of the housing.

[0041] The marine tensioner's locking pawl may be a single spring-loaded locking pawl that automatically locks every other chain link that passes over the sprocket of the chain roller.

[0042] In the marine tensioner, the first support shaft of the chain roller may be arranged vertically above the second support shaft of the locking pawl.

[0043] The first and second parts of the marine tensioner housing are preferably horizontally opposed and the inlet for the anchor chain in the first part of the housing and the attachment in the second part of the housing are linearly opposed.

[0044] The pawl of the marine tensioner may be connected to an actuator that applies the spring force, the actuator being releasable to allow the pawl to disengage from a sprocket on a chain roller.

[0045] According to a third embodiment of the present invention there is provided an in-line tensioner for tensioning an anchor chain in a mooring arrangement, said in-line tensioner being connectable to a floating structure, said in-line tensioner comprising a chain roller having a sprocket supported on a first support shaft in a housing. A first part of the housing is arranged to accommodate the anchor chain encircling the chain roller, and a second part of the housing has an attachment for the support chain extending to the floating structure, said first part and said second part of the housing facing in opposite directions. A spring loaded locking pawl is arranged in the housing and supported on a second support shaft in the first part of the housing, the locking pawl being engageable with a chain link of the anchor chain before the anchor chain leaves the chain roller, the locking pawl being arranged to press the chain link against one of the sprockets on the chain roller to lock the anchor chain, said sprocket being the sprocket on the chain roller facing the second part of the housing.

[0046] The in-line tensioner pawl may be a single spring-loaded pawl that automatically locks every other chain link that passes over the sprocket of the chain roller.

[0047] In an in-line tensioner, the first support shaft for the chain rollers may be arranged vertically above a second support shaft for the locking pawl.

[0048] The first and second parts of the in-line tensioner housing are preferably horizontally opposed and the inlet for the anchor chain in the first part of the housing and the attachment in the second part of the housing are linearly opposed.

[0049] The pawl of an in-line tensioner may be connected to an actuator that applies the spring force, the actuator being releasable to allow the pawl to disengage from a sprocket on a chain roller.

[0050] Marine tensioners and in-line tensioners can be part of systems and methods similar to those disclosed above.

[0051] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which: [Brief description of the drawings]

[0052] [Figure 1] FIG. 1 shows an exemplary mooring device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged view of detail A of FIG. [Diagram 3] FIG. 3 is an enlarged view of detail B of FIG. 2. [Figure 4] FIG. 2 is an enlarged view of detail C of FIG. [Figure 5-6] FIG. 2 shows a subsea tensioner according to a first embodiment of the present invention connected to an anchor chain and an active anchor rope extending to a floating structure. [Figure 7-8] FIG. 2 shows a subsea tensioner according to the invention connected to an anchor chain and a fiber rope of an active anchor rope. [Figure 9-11] 1A-1D are perspective, side and top views of a subsea tensioner according to the present invention; [Figure 12-13] 1A-1D are cross-sectional views of a subsea tensioner according to the present invention in a locked and unlocked position; [Figure 14] FIG. 4 is a schematic diagram of an exemplary mooring arrangement having a marine tensioner according to a second embodiment of the present invention. [Figure 15] FIG. 15 shows the marine tensioner of FIG. 14 connected to a floating structure and through which the anchor chain of the anchor line passes. [Figure 16] FIG. 1 is a perspective view of a marine tensioner according to the present invention; [Figure 17-18] 1 is a cross-sectional view of a marine tensioner according to the present invention in a locked and unlocked position; FIG. [Figure 19] FIG. 13 is a schematic diagram of an exemplary mooring arrangement having an in-line tensioner according to a third embodiment of the present invention. [Figure 20] FIG. 20 shows the in-line tensioner of FIG. 19 connected to a floating structure and through which the anchor chain of the anchor rope passes. [Figure 21] FIG. 1 is a perspective view of an in-line tensioner according to the present invention. [Figure 22-23] 1A-1C are cross-sectional views of an in-line tensioner according to the present invention in a locked and unlocked position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] The present invention comprises three essentially similar chain tensioners for tensioning mooring lines, which are tensioners based on the same technology. A first embodiment is shown in Figures 1 to 13 showing a subsea tensioner, a second embodiment is shown in Figures 14 to 18 showing a marine tensioner, and a third embodiment is shown in Figures 19 to 23 showing an in-line tensioner. The difference between the three chain tensioners is their connection to and position in the mooring line.

[0054] Figure 1 is a schematic diagram of a mooring system according to the invention with a seabed tensioner 30. On the right hand side, a floater in the form of a floating structure 12 is shown (e.g. a floating wind turbine floating on the water surface 24 and partially submerged). Passive anchor lines 18, partially shown by dotted lines, run from the floating structure 12 through the water to the seabed 14, to which the passive anchor lines 18 are moored, for example by using anchors (not shown). The passive anchor lines 18 are connected to the floating structure and run in different directions, for example at an angle of 120° to each other.

[0055] Connected to the opposite side of the floating structure 12 is an active anchor line 16 which extends downward from the floating structure 12 through the water to the seabed 14 and is connected to a subsea tensioner 30 located on the seabed 14 adjacent to an anchor 22, for example of the drag buried anchor type. As better shown in Figures 2 and 3, an anchor chain 20 extends from the anchor 22 to a chain roller 32 in the subsea tensioner 30 and loops around the chain roller 32. The anchor chain 20 is tensioned in the water in the opposite direction to that of the active anchor line 16 by pulling on the end of the anchor chain 20 which loops around the chain roller 32 in the subsea tensioner 30. This will be explained in more detail.

[0056] In the mooring system according to the present invention, it is possible to simultaneously tighten the entire length of all three anchor ropes 16, 18. In addition, after the floating structure has been anchored for a long period of time, the anchor ropes can be easily retightened.

[0057] A typical anchor rope 16 as shown in Figure 1 may comprise a top chain that starts from the floating structure 12 and is connected in the water to an upper fiber rope and a clamp chain. The clamp chain is further connected to an intermediate fiber rope that is connected to a subsea buoy 26, as shown in Figure 4 showing detail C of Figure 1. The lower fiber rope extends from the subsea buoy 26 to a lower chain that is connected to a subsea tensioner 30. The fiber rope 16', for example the lower fiber rope, may be directly connected to the subsea tensioner 30, as shown in Figures 7 and 8. The term "anchor rope" is used hereinafter to collectively disclose all or part of the anchor rope as described.

[0058] 1 shows an anchor handling vessel (AHT) on the water surface 24. A tension wire 50 extends downward through the water to the subsea tensioner 30, and one end of the anchor chain 20 that has been wound around a chain roller 32 in the subsea tensioner 30 is connected to the tension wire 50 from the anchor handling vessel 10.

[0059] The anchor chain 20 is tensioned in the water in a direction opposite to that of the active anchor line 16 by pulling the end of the anchor chain 20 around a chain roller 32 in a subsea tensioner 30 .

[0060] The tensioning wire 50 is preferably connected to a bollard or winch on the anchor handling vessel 10 and is tensioned by pulling the anchor handling vessel 10 away from the floating structure 12. The anchor handling vessel can therefore quickly connect and start tightening. Furthermore, the tensioning wire 50 multiplies the force of the anchor line in relation to the pulling force of the anchor handling vessel 10.

[0061] However, tensioning could be done using a winch instead of a bollard pull, for example using a reaction anchor attached to the anchor handling vessel. The tensioning wire 50 is then connected to a winch on the anchor handling vessel 10 and tensioned by operating the winch on the anchor handling vessel 10 and pulling the tensioning wire 50 away from the floating structure 12.

[0062] In the mooring system of the present invention it is possible to avoid breaking of the active anchor rope 16 during tightening. Moreover, the tightening force does not change after the anchor-handling vessel releases the force.

[0063] Figures 5 and 7 show the situation when there is no tension from the anchor handling vessel 10. The active anchor rope 16 and the anchor chain 20 from the anchor 22 are collinear with each other. When there is tension from the anchor handling vessel by pulling on the tension wire 50, the subsea tensioner 30 changes angle slightly as there is a force pulling on the end of the anchor chain 20, as shown in Figures 6 and 8.

[0064] The present invention allows the fiber rope 16 ′ to be connected directly to the subsea tensioner 30 because the attachment point 36 is located high enough that the fiber rope 16 ′ does not contact the seabed 14 .

[0065] 9 to 13 are detailed views of the submarine tensioner 30 according to the first embodiment of the present invention.

[0066] The subsea tensioner 30 includes a chain roller 32 disposed within a housing 34 .

[0067] The housing 32 is further connected to one or more subsea skids 38, allowing the subsea tensioner 30 to slide along the seabed 14 during tensioning of the anchor chain 20. Hinging the housing 32 to the subsea skids 38 allows for angular adjustment of the housing 34.10. Having a hinged skid 38 that can slide along the seabed 14 allows the tension to be adjusted in response to reaction forces from the anchor line.

[0068] The housing 34 further comprises spaced apart locking plates 34a, 34b which form a first part of the housing and which comprise a first support shaft 42 supporting the chain roller 32 with the sprockets 32a-32n and a second support shaft 44 supporting the locking pawl 40. The first support shaft 42 and the second support shaft 44 may be arranged vertically one above the other, i.e. on the same vertical axis. The locking plates 34a, 34b are joined together to form a second part of the housing 34 which includes an attachment 36 for the active anchor rope 16.

[0069] The first part of the housing 34 receives and accommodates the anchor chain 20 going from the anchor 22 around the chain roller 32, and the second part of the housing 34 can be connected to the active anchor line 16 extending to the floating structure 12 on the water surface 24. The first and second parts of the housing 34 are in opposite orientations as shown, i.e. in opposite horizontal orientations with respect to the seabed 14, as is evident for example from FIG. 2. Thus, the inlet in the first part of the housing 34 for the anchor chain 20 from the anchor 22 and the attachment 36 for the anchor line 16 in the second part of the housing 34 are linearly opposite when the anchor chain 20 in the subsea tensioner 30 is not tensioned by the anchor handling vessel 10, i.e. when it is in the installed and moored position, as shown for example in FIGS. 5 and 7.

[0070] At least one locking pawl 40 is disposed adjacent to and directly below the chain roller 32 for locking or releasing the anchor chain 20. The locking pawl 40 is, for example, a single spring-loaded locking pawl that automatically locks every other chain link passing through the sprocket of the chain roller 32. An actuator 46 (for example, a spring-loaded cylinder) may be disposed adjacent to the locking pawl 40 in the housing 34 and connected to an actuator arm 40a on a first portion of the locking pawl 40. The spring force of the actuator acts on the actuator arm 40a to pivot the locking pawl 40 about the support shaft 44 into engagement with the sprocket 32a of the chain roller 32. The spring force may be applied by other means, such as hydraulic or pneumatic pressure, but using a spring is a simple and easy option.

[0071] A second portion of the locking pawl 40 has a concave abutment surface 40b for engaging and abutting the chain link 20a of the chain 20, which presses the chain link 20a against the sprocket 32a of the chain roller 32. The horizontal chain link is located between the two sprockets, towards the chain roller 32. The vertical chain link is held by the locking pawl 40, as shown in FIG.

[0072] The sprocket 32 ​​a to which the chain link 20 a is locked is the sprocket on the chain roller 32 that faces the second portion of the housing 34 .

[0073] 12, the locking pawl 40 locks against the chain link 20a to the left (in the drawing) of the support shaft 42 that supports the chain roller 32, so that locking occurs after approximately a quarter revolution of the chain roller 32. The first free chain link (to the right of the locking pawl) is the vertical chain link that allows angular movement of the chain 20.

[0074] During tensioning of the mooring line, the locking pawl 40 therefore has a ratcheting function making the locking mechanism fail-safe. The ratcheting function is achieved by spring-loading the locking pawl 40 so that it presses against the chain 20 and automatically supports the nearest chain link 20a in case of a fault or when the required tension is achieved.

[0075] The design of all chain tensioners 30, 130, 230 allows the chain exit point to be tangential to the chain roller 32, both during tensioning and after external forces from the vessel are disconnected. This eliminates the need for a bending shoe at the exit point of the chain tensioner, eliminating damage to the chain during the tensioning operation. Eliminating the need for a bending shoe also results in better control of forces during tensioning, since no extra frictional forces or other aspects are generated from the chain passing over the bending shoe.

[0076] Such a solution consists of fewer moving parts and does not require synchronization as with the double pawl. If the locking pawl 40 needs to be opened, for example by changing the anchor chain, this can be done manually or with the help of an ROV, which can disengage the locking pawl 40 from the anchor chain 20, i.e. by hydraulic power source.

[0077] When the pawl 40 needs to be opened, there is an interface 48 that allows the ROV to connect and power the actuator 46. The actuator 46 normally uses spring force to pull the pawl into a locked position, but when pressure is applied, it can open the pawl 40. To open the pawl 40, tension in the line needs to be released to ensure that pressure on the pawl 40 from the chain 20 is released.

[0078] The arrangement of the chain rollers with sprockets 32, the pawls 40, the support shafts 42, 44, and the actuator 46 are similar for the subsea tensioner 30, the marine tensioner 130, and the in-line tensioner 230.

[0079] In an alternative embodiment, the subsea tensioner 30 of the present invention may have a chain roller 32 with a central groove to accommodate additional wire.

[0080] The chain tensioner of the present invention provides a tensioner that is self-locking during tightening with the pawl 40. The pawl is simple and does not require synchronization as with dual pawls.

[0081] The anchor may be a subsea drag buried anchor, or any suitable type of anchor.

[0082] A second embodiment is shown in Figures 14-18, showing a vessel tensioner 130. The vessel tensioner 130 is pivotally connected to the hull of the floating structure 12. The anchor line 16 extends from an anchor on the seabed, and an anchor chain 20, which is part of the anchor line 16, extends through the vessel tensioner 130 and is connected to the vessel 10 by a tension wire 50. Similarly, a passive anchor line (same as the anchor line 18 shown above) extends downward from the floating structure 12 through the water to the seabed 14, to which the passive anchor line is moored, for example by using an anchor (not shown). The passive anchor lines are connected to the floating structure and extend in different directions, for example at an angle of 120° to each other.

[0083] The anchor chain 20 is tensioned in the water in a direction opposite to that of the active anchor line 16 by pulling the end of the anchor chain 20 around the chain roller 32 in the marine tensioner 130 as described above.

[0084] The tensioning wire 50 is preferably connected to a bollard or winch on the anchor handling vessel 10 and is tensioned by the anchor handling vessel 10 pulling it away from the floating structure 12.

[0085] The arrangement of the chain rollers 32 with sprockets, the pawls 40, the support shafts 42, 44, and the actuators 46 are similar to those described above. The housing 134 is somewhat different, i.e., more elongated in shape, and is hingedly and pivotally connected to the hull of the floating structure 12, as can be seen, for example, in FIG. 16 showing the hinge connection 138.

[0086] As shown in Figure 17, when the anchor chain 20 is pulled through the marine tensioner 130, the pawl 40 engages with the chain link 20a of the anchor chain 20 in a similar manner as described above. Figure 18 shows the pawl 40 disengaged from the chain 20.

[0087] A third embodiment is shown in Figures 19-23, which shows an in-line tensioner 230. The in-line tensioner 230 is connected to the floating structure 12 by a support chain 216. The anchor line 16 extends from an anchor on the seabed, and the anchor chain 20, which is a part of the anchor line 16, extends through the in-line tensioner 230 and is connected to the ship 10 by a tension wire 50. Similarly, a passive anchor line (same as the anchor line 18 shown above) extends downward from the floating structure 12 through the water to the seabed 14, and the passive anchor line is moored to the seabed 14, for example by using an anchor (not shown). The passive anchor lines are connected to the floating structure and extend in different directions, for example at an angle of 120° to each other.

[0088] The anchor chain 20 is tensioned in the water in a direction opposite to that of the active anchor rope 16 by pulling the end of the anchor chain 20 around the chain rollers 32 in the in-line tensioner 230 as described above.

[0089] The tensioning wire 50 is preferably connected to a bollard or winch on the anchor handling vessel 10 and is tensioned by the anchor handling vessel 10 pulling it away from the floating structure 12.

[0090] The arrangement of the chain rollers 32 with sprockets, the pawl 40, the support shafts 42, 44, and the actuator 46 are similar to those described above. The housing 234 is somewhat different, namely, it is more elongated in shape.

[0091] As shown in Figure 22, when the anchor chain 20 is pulled through the in-line tensioner 230, the pawl 40 engages with the chain link 20a of the anchor chain 20 in a similar manner as described above. Figure 23 shows the pawl 40 disengaged from the chain 20.

[0092] Once tensioned, the ship-facing portion of the mooring line becomes passive until it is next necessary to tension or disconnect the mooring line. For ship tensioners, the line is cut and the remainder is placed in the wheel. For in-line tensioners, whether the chain needs to be cut depends on the mooring design. After tensioning, in-line tensioners invert due to the position of their centre of gravity, so that the excess chain hangs vertically below the tensioner.

Claims

1. A subsea tensioner (30) for tensioning an anchor chain (20) in a mooring arrangement, the subsea tensioner (30) being positionable on the seabed (14) adjacent to the anchor (22), the subsea tensioner comprising a chain roller (32) having a sprocket supported on a first support shaft (42) in a housing (34); A subsea tensioner (30), wherein a first part of the housing is arranged to receive an anchor chain (20) connected to the anchor (22) and wrapped around the chain roller (32), and a second part of the housing (34) has an attachment (36) for an anchor line (16) extendable to a floating structure (12) above the water surface (24), the first and second parts of the housing (34) facing in opposite directions, a spring-loaded locking pawl (40) is disposed in the housing (34) and supported on a second support shaft (44) of the first part of the housing (34), the locking pawl (40) is engageable with a chain link (20 a) of the anchor chain (20) before the anchor chain (20) leaves the chain roller (32), the locking pawl (40) is arranged to press the chain link (20 a) against one of the sprockets (32 a) on the chain roller (32) to lock the anchor chain (20), the sprocket (32 a) being the sprocket on the chain roller (32) facing the second part of the housing (34).

2. 2. The subsea tensioner (30) of claim 1, wherein the housing (32) is connected to one or more subsea skids (38) to enable the subsea tensioner (30) to slide along the seabed (14) during tensioning of the anchor chain (20).

3. The subsea tensioner (30) of claim 2, wherein the housing (32) is hinged to the subsea skid (38) to allow angular adjustment of the housing (34).

4. 2. The subsea tensioner (30) of claim 1, wherein the pawl (40) is a single spring-loaded pawl that automatically locks every other chain link that passes over the sprocket of the chain roller (32).

5. 2. The subsea tensioner (30) of claim 1, wherein the housing (34) comprises spaced apart locking plates (34a, 34b) forming the first portion of the housing and comprising the first support shaft (42) supporting the chain roller (32) with the sprocket and the second support shaft (44) supporting the locking pawl (40), the locking plates (34a, 34b) being joined together to form the second portion of the housing (32) and comprising the attachment (36) for the anchor line (16).

6. 2. The subsea tensioner (30) of claim 1, wherein the first support shaft (42) for the chain roller (32) is disposed vertically above the second support shaft (44) for the locking pawl (40).

7. The subsea tensioner (30) of claim 1, wherein the chain roller (32) includes a central groove for receiving a wire.

8. 2. The subsea tensioner (30) of claim 1, wherein the first and second parts of the housing (34) are horizontally oriented in opposite directions, and an inlet in the first part of the housing (34) for the anchor chain (20) from the anchor (22) and an attachment (36) for the anchor line (16) in the second part of the housing (34) are linearly opposed.

9. 2. The subsea tensioner (30) of claim 1, wherein the pawl (40) is connected to an actuator (46) that applies the spring force, the actuator (46) being releasable to allow the pawl (40) to disengage from the sprocket (32a) on the chain roller (32).

10. A system for mooring a floating structure (12), comprising a subsea tensioner (30) according to any one of claims 1 to 9, a floating structure (12) above the water surface (24) and at least partially submerged in the water; one or more passive anchor lines (18) extending from the floating structure through the water to the seabed (14) and anchored to the seabed (14); at least one active anchor line (16) extending through the water from the floating structure to a subsea tensioner (30) disposed on the seabed (14) adjacent to the anchor (22); The passive anchor lines and the active anchor lines (18, 16) extend in different directions in the water, and An anchor chain (20) extends from the anchor (22) to a chain roller (32) in the subsea tensioner (30) and wraps around the chain roller (32); The system, wherein the anchor chain (20) is arranged to be tensioned in the water in a direction opposite to that of the active anchor line (16).

11. 11. The system of claim 10, wherein the subsea tensioner (30) comprises one or more subsea skids (38) that allow the subsea tensioner (30) to slide along the seabed (14) during tensioning of the anchor chain (20).

12. The system according to claim 10, wherein one end of the anchor chain (20) wrapped around the chain roller (32) in the subsea tensioner (30) is connectable to a tensioning wire (50) from the anchor handling vessel (10).

13. 13. The system of claim 12, wherein the tensioning wire (50) is connected to a bollard or winch on the anchor handling vessel (10) and arranged to be tensioned by the anchor handling vessel (10) pulling away from the floating structure (12).

14. The system described in claim 12, wherein the tensioning wire (50) is connected to a bollard or winch on the anchor handling vessel (10) and arranged to be tensioned by actuating the winch on the anchor handling vessel (10) to pull the tensioning wire (50) away from the floating structure (12).

15. Anchor handling vessel (10) and A method for mooring a floating structure (12) using a subsea tensioner (30) according to any one of claims 1 to 9, comprising the steps of: mooring one or more passive anchor lines (18) extending between the floating structure and the seabed (14) to the seabed (14); deploying the subsea tensioner (30) on the seabed (14) adjacent to an anchor (22) and connecting an active anchor line (16) to the subsea tensioner (30), the active anchor line (16) extending from the floating structure through the water to the subsea tensioner (30); The passive anchor lines and the active anchor lines (18, 16) extend in different directions in the water, and connecting an anchor chain (20) extending from the anchor (22) to a chain roller (32) in the subsea tensioner (30) and encircling the chain roller (32) to a tensioning wire (50) from the anchor handling vessel (10); The anchor chain (20) is tensioned in water in a direction opposite to that of the active anchor line (16) by pulling the tension wire (50).

16. The method of claim 15, comprising sliding the subsea tensioner (30) along the seabed (14) during tensioning of the anchor chain (20).

17. 16. The method according to claim 15, comprising the steps of connecting the tensioning wire (50) to a bollard or winch on the anchor handling vessel (10) and tensioning the anchor chain (20) by pulling it away from the floating structure (12).

18. 16. The method of claim 15, comprising the steps of connecting the tension wire (50) to a winch on the anchor handling vessel (10) and operating the winch to pull the tension wire (50) away from the floating structure (12).

19. The method of claim 15, comprising locking the anchor chain (20) in the subsea tensioner (30).

20. 20. The method of claim 19, comprising unlocking the anchor chain (20) in the subsea tensioner (30) using an ROV to manually operate a locking pawl (40) in the subsea tensioner (30).

21. A marine tensioner (130) for tensioning an anchor chain (20) in a mooring arrangement, said marine tensioner (130) connectable to a floating structure (12), said marine tensioner (130) comprising a chain roller (32) having a sprocket supported on a first support shaft (42) in a housing (134); A marine tensioner (130), wherein a first portion of the housing (134) is arranged to receive the anchor chain (20) encircling the chain roller (32), and a second portion of the housing (134) has an attachment (136) to the floating structure (12), and the first and second portions of the housing (134) face in opposite directions, 13. A marine tensioner (130), characterized in that a spring-loaded locking pawl (40) is disposed in the housing (134) and supported on a second support shaft (44) of the first part of the housing (134), the locking pawl (40) is engageable with a chain link (20 a) of the anchor chain (20) before the anchor chain (20) leaves the chain roller (32), the locking pawl (40) is arranged to press the chain link (20 a) against one of the sprockets (32 a) on the chain roller (32) to lock the anchor chain (20), the sprocket (32 a) being the sprocket on the chain roller (32) facing the second part of the housing (134).

22. 22. The marine tensioner (130) of claim 21, wherein the locking pawl (40) is a single spring-loaded locking pawl that automatically locks every other chain link that passes over the sprocket of the chain roller (32).

23. 22. The marine tensioner (130) of claim 21, wherein the first support shaft (42) for the chain roller (32) is disposed vertically above the second support shaft (44) for the locking pawl (40).

24. 22. The marine tensioner (130) of claim 21, wherein the first and second portions of the housing (134) are horizontally oriented in opposite directions, and an inlet for the anchor chain (20) in the first portion of the housing (134) and the attachment (136) in the second portion of the housing (134) are linearly opposed.

25. 22. The marine tensioner (30) of claim 21, wherein the locking pawl (40) is connected to an actuator (46) that applies the spring force, the actuator (46) being releasable to allow the locking pawl (40) to disengage from the sprocket (32a) on the chain roller (32).

26. An in-line tensioner (230) for tensioning an anchor chain (20) in a mooring system, said in-line tensioner (230) connectable to a floating structure (12), said in-line tensioner (230) comprising a chain roller (32) having a sprocket supported on a first support shaft (42) in a housing (234); an in-line tensioner (230), wherein a first portion of the housing (234) is arranged to receive the anchor chain (20) encircling the chain roller (32), and a second portion of the housing (234) has an attachment (236) for a support chain (216) extending to the floating structure (12), the first portion and the second portion of the housing (234) facing in opposite directions; a spring-loaded locking pawl (40) is disposed within the housing (234) and supported on a second support shaft (44) of the first portion of the housing (234), the locking pawl (40) is engageable with a chain link (20 a) of the anchor chain (20) before the anchor chain (20) leaves the chain roller (32), the locking pawl (40) is arranged to press the chain link (20 a) against one of the sprockets (32 a) on the chain roller (32) to lock the anchor chain (20), the sprocket (32 a) being the sprocket on the chain roller (32) facing the second portion of the housing (234).

27. 27. The in-line tensioner (230) of claim 26, wherein the pawl (40) is a single spring-loaded pawl that automatically locks every other chain link that passes over the sprocket of the chain roller (32).

28. 27. The in-line tensioner (230) of claim 26, wherein the first support shaft (42) for the chain roller (32) is disposed vertically above the second support shaft (44) for the locking pawl (40).

29. 27. The in-line tensioner (230) of claim 26, wherein the first and second portions of the housing (234) are horizontally oriented in opposite directions, and an inlet for the anchor chain (20) in the first portion of the housing (234) and the attachment (236) in the second portion of the housing (234) are linearly opposed.

30. 27. The in-line tensioner (230) of claim 26, wherein the pawl (40) is connected to an actuator (46) that applies the spring force, the actuator (46) being releasable to allow the pawl (40) to disengage from the sprocket (32a) on the chain roller (32).

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