Method for three tension applications of a mooring system having an anchor on the seabed

Abstract

A method for three tension applications of a mooring system having an anchor on the seabed, the method comprising: one or more moonpools (1) having a vertically extending through-channel, the ship (6) having an upper moonpool opening adjacent to the deck of the ship (6) and a bottom moonpool opening opening to the surrounding sea, the moonpool (1) comprising one or more chain stoppers (5), the ship (6) further comprising one or more tensioning winches (2), one or more chain handling winches (3), and one or more abandonment and recovery winches (4).

Description

Technical Field

[0001] The present invention relates to a method for applying tension three times to a mooring system having an anchor on the seabed, the method comprising a ship having one or more moonpools having a vertically extending through-channel having an upper moonpool opening proximate to the deck of the ship and a bottom moonpool opening opening to the surrounding sea, the moonpool being provided with one or more chain stoppers, and the ship further comprising one or more tensioning winches, one or more chain operating winches, and one or more abandonment and recovery winches.

Background Art

[0002] Known art is, for example, the "Stevtensioner" by Vryhof. The Stevtensioner® is basically a chain shortening clutch and has a mooring chain with one side connected and a reaction chain extending therethrough. A vertical pull can cause more than twice the pull of the horizontal leg. Repeatedly raising and lowering the Stevtensioner® in a yo-yo motion increases the load in the mooring chain until the required tension is achieved. Typically, 5 to 7 cycles are sufficient.

[0003] The Stevtensioner® requires the chain from end to end because there is a possibility that the tensioner may slip off the line and damage the rope.

[0004] International Publication No. 2020 / 040646 discloses a mooring tension applying configuration on a ship, comprising a moonpool having a vertically extending through-channel having an upper moonpool opening proximate to the deck of the ship and a bottom moonpool opening opening to the surrounding sea. A winch is located above the moonpool, a first anchor wire pendant extends from the winch into the sea beyond the stern of the ship, and a second anchor wire pendant extends from the winch through the moonpool into the sea.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The triangular floating facility is understood to be the most attractive way to propel floating wind power facilities. Depending on the size of the floater, the floater has one or more anchors at each corner (at an angular distance of approximately 120 degrees). The aim is to perform a "proof loading" of the three anchors in one operation by one ship.

[0007] The advantage compared to the already known technology is that it is a more efficient way to perform the "proof load" test. Since no reaction anchor is required, time and cost are saved. It is a safer operation by using one ship (in a narrow space) compared to three ships.

[0008] The advantage of the present invention is that all anchor lines are connected to the winch on the ship, thereby providing the possibility and flexibility to adjust the length of the anchor line during tensioning. If any of the anchor lines is "tension reduced", the tension can be adjusted.

[0009] The present invention also provides hook-up and cutting operations that save time.

[0010] Proof loading is performed simultaneously for all three anchors. The point of performing proof loading is to comply with the regulations by testing the anchor at a given load for at least 15 to 30 minutes to ensure that the anchor is properly fixed.

[0011] Floating wind power equipment requires a significantly higher load than oil and gas. For example, in the case of oil and gas, about 300 tons was the standard. However, floating wind power equipment can use larger drag anchors to which test tensions of, for example, up to 800 tons are applied.

[0012] Furthermore, the present invention can also be adapted to the removal of the reverse catenary for a suction anchor having the same mooring arrangement as the drag embedment anchor.

[0013] The present invention is not limited to drag anchors and may also be suitable for suction anchors / pile anchors, etc.

Means for Solving the Problems

[0014] According to the present invention, there is provided a method for applying tension to a mooring system having an anchor on the seabed, the ship comprising one or more moonpools having a vertically extending through-channel having an upper moonpool opening adjacent to the deck of the ship and a bottom moonpool opening opening to the surrounding sea, the moonpool comprising one or more chain stoppers, the ship further comprising one or more tensioning winches, one or more chain operating winches, and one or more abandonment and recovery winches, the method comprising: -a) Deploying a first anchor line having a proof loading chain connected to a first anchor at a first position on the seabed, the anchor being deployed from the stern of the ship and embedded in the seabed using the bollard pull from the ship; -b) By repeating step a), deploying a second anchor line having a proof loading chain connected to a second anchor at a second position and deploying a third anchor line having a proof loading chain connected to a third anchor at a third position; -c) moving the ship so that while the first anchor line is connected to a tensioning winch and extends over the stern of the ship, it picks up the second and third anchor lines through the moon pool of the ship; -d) at the position for picking up the second anchor line, · deploying a pick-up wire having a hook connectable from a abandonment and recovery winch through the moon pool; · connecting the pick-up wire from the anchor to the proof loading chain; · recovering the pick-up wire together with the proof loading chain through the moon pool and engaging a chain stopper to take over the load from the proof loading chain; · connecting the proof loading chain to the chain from the chain operating winch; -e) moving the ship to the position for picking up the third anchor line and repeating step d) for the third anchor line; -f) applying tension to the first anchor line and applying tension to all three proof loading chains of the three anchor lines; -g) performing a proof loading test on the tripod mooring system; -h) adjusting both the payout and retrieval of the proof loading chain using the chain operating winch in case of non-uniform embedment / tension of the anchors; including.

[0015] The anchor can be embedded in the seabed using a bollard pull from the ship, or the anchor can be embedded in the seabed using a tensioning winch, or a combination thereof.

[0016] The anchor is preferably installed together with a bottom chain connected to the proof loading chain by chain links.

[0017] After the first anchor is embedded in the seabed, an initial embedding test can be performed.

[0018] The proof loading test of the tripod mooring system can be performed using a final tension application of up to 800 te.

[0019] The proof loading test of the tripod mooring system can be performed using a final tension application of more than 800 te.

[0020] The anchors can be deployed into their respective target boxes and aligned with their respective mooring line passages.

[0021] In step d) of the method, the proof loading chain can be retrieved through the moon pool until the first chain link passes through the chain stopper, after which the chain stopper is engaged, taking over the load from the chain catenary of the proof loading chain and disconnecting the connection hook.

[0022] The extra length of the proof loading chain can be held in the chain locker, and the chain is sent downward from the locker through the chain operating winch towards the proof loading chain in the chain stopper. Thereafter, the chain from the locker is connected to the proof loading chain using chain links.

[0023] When performing tension application, the ship can move closer towards the anchor connected to the tension application winch, and all three proof loading chains are aligned towards their respective target boxes.

[0024] The mooring system can be assumed to be a tripod mooring system having three anchors on the seabed.

[0025] The method for applying tension to a mooring system can be repeated for a six-legged mooring system having, for example, six anchors on the seabed.

[0026] The anchors on the seabed can be arranged with a spread of approximately 118 - 122 degrees, preferably approximately 120 degrees.

Brief Description of the Drawings

[0027] Here, with reference to the following figures, embodiments of the present invention will be described as mere examples.

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Embodiment for Carrying out the Invention

[0028]

Explanation of Reference Numerals

[0029] 1 Moon pool (plural available) 2 Tension winch 3 Chain operation winch 4 Abandonment and recovery (A&R) winch 5 Chain stopper 6 Ship 7 Chain locker 8 Chain from the anchor 9 Chain to the locker 10 Drag embedment anchor 11 ROV operation hook 12 Pulley for A&R winch 13 Chain connection part 14 Seabed 15 Proof load chain 16 Chain link 17 Bottom chain 18 Anchor target box 19 Mooring line target box 20 Wire from the tensioning winch 21 Work remotely operated vehicle (WROV)

[0030] Figure 1. The first step in the three tensioning operations is for the vessel 6 to install the first drag embedment anchor 10. The vessel 6 deploys the anchor 10 from the stern of the vessel 6 and lands it on the seabed 14. The anchor 10 is installed together with its bottom chain 17 connected to the proof load chain 15 by any type of chain link 16. The first anchor is embedded using a bollard pull from the vessel 6, typically 150 - 300 te, but may be embedded in the seabed 14 using the tensioning winches 2, or a combination thereof. This is called the initial embedment. The aim is to ensure that the anchor 10 is embedded and prepared for the final tensioning to apply a force up to, for example, 800 te.

[0031] The vessel 6 comprises at least a tensioning winch 2, one or more moonpools 1, a chain handling winch 3, a chain stopper 5, and a abandonment and recovery winch 4.

[0032] Figure 2. After the initial embedment of the first anchor line, two other anchor lines are deployed using the same method.

[0033] The anchors are deployed within their respective target boxes 18 and aligned with their respective mooring line passages 19. This is the configuration on the seabed before connecting all the anchor lines to the vessel.

[0034] The first anchor line embedded in the initial test may remain connected to the vessel 6 and the tensioning winch 2, but the vessel is moving towards the two other anchor lines for recovery through the moonpool 1.

[0035] Figure 3. To accommodate the movement of the vessel, the tensioning winch pays out its wire 20.

[0036] When in position for picking up the first anchor line through the moon pool, the abandonment and recovery winch 4 deploys its wire having an ROV connectable hook 11 through the moon pool 1.

[0037] Figure 4. When the wire from the abandonment and recovery winch 4 and the ROV connectable hook 11 descend to the seabed and come near the proof load chain 15 for the anchor 10, the ROV 21 can execute the connection and prepare for the recovery of the anchor line to return to the ship 6.

[0038] Figure 5. The abandonment and recovery winch 4 retrieves its wire and the proof load chain 15 through the moon pool 1 until the first chain link passes through the chain stopper 5. Then the chain stopper 5 is engaged, where it is receiving the load from the chain catenary of the proof load chain 15.

[0039] The ROV connection hook 11 is cut here. The extra length of the proof load chain is held in the chain lockers 7, 9. This chain is sent downward from the locker 7 through the chain operating winch 3 towards the proof load chain 15 in the chain stopper 5. Here, the chain from the locker 7 is connected to the proof load chain 15 using the chain link 13. The chain operating winch 3 can now adjust both the payout and retrieval of the proof load chain 15 in case of uneven embedding / tension of the anchor 10.

[0040] Figure 6. The ship 6 is moving towards the pick-up points of the remaining two proof load chains 15 with the wire 20 of the tension winch 2 connected to the first anchor.

[0041] The ship 6 comes to a position where it recovers one anchor line at a time through the moon pool 1 using the abandonment and recovery winch 4.

[0042] Figure 7. The second proof loading chain 15 is recovered using the same method.

[0043] Figure 8. The third proof loading chain 15 connected to the third anchor 10 is recovered to the ship 6 through the moon pool 1. Here, all three proof loading chains 15 are recovered to the ship 6, and the final proof loading of the anchor can be started. This is performed by pulling in the wire 20 using the tensioning winch 2.

[0044] Figure 9. When performing tensioning, the ship 6 moves closer towards the anchor 10 connected to the tensioning winch 2. All three proof loading chains start to align towards their respective target boxes 19.

[0045] Figure 10. This figure shows the configuration during the final proof load test of the tripod mooring system.

[0046] Figure 11. The configuration mounted on the ship 6 during the final proof loading of all three anchors 10.

[0047] The chain operation winch 3 enables adjustment of the chain length in case of uneven embedment or tension in the line. The extra - length proof loading chain is stored in the chain locker 7 mounted on the ship 6.

[0048] The method according to the invention is disclosed as being used with a tripod mooring system. However, the method can also be used, for example, in a six-leg mooring system having six anchors 10 on the seabed 14 by simply repeating the operation twice.

Claims

1. A method for applying tension to a mooring system having an anchor on the seabed, the method comprising: a ship (6) having one or more moonpools (1) with a vertically extending through-channel having an upper moonpool opening proximate to the deck of the ship (6) and a bottom moonpool opening opening to the surrounding sea, the moonpool (1) comprising one or more chain stoppers (5), the ship (6) further comprising one or more tensioning winches (2), one or more chain operating winches (3), and one or more abandonment and recovery winches (4), wherein the method comprises: - a) deploying a first anchor line having a proof loading chain (15) connected to a first anchor (10) at a first location on the seabed (14), the anchor (10) being deployed from the stern of the ship (6) and embedded in the seabed (14) using a bollard pull from the ship (6); - b) by repeating step a), deploying a second anchor line having a proof loading chain (15) connected to a second anchor (10) at a second location and deploying a third anchor line having a proof loading chain (15) connected to a third anchor (10) at a third location; - c) moving the ship (6) so as to pick up the second anchor line and the third anchor line through the moonpool (1) of the ship (6) while the first anchor line is connected to the tensioning winch (2) and extends over the stern of the ship; - d) at a position for picking up the second anchor line, · deploying a pickup wire having a hook (11) connectable through the moonpool (1) from the abandonment and recovery winch (4); · connecting the pickup wire to the proof loading chain (15) from the anchor (10); · recovering the pickup wire together with the proof loading chain (15) through the moonpool (1) and engaging the chain stopper (5) to take over the load from the proof loading chain (15); - connecting the proof load chain (15) to the chain from the chain operating winch (3); - e) moving the vessel (6) to a position for picking up the third anchor line and repeating step d) for the third anchor line; - f) applying tension to the first anchor line and applying tension to the proof load chains of all three of the three anchor lines; - g) performing a proof load test on the tripod mooring system; - h) adjusting both the payout and retrieval of the proof load chain (15) using the chain operating winch (3) if there is non-uniform embedding / tension of the anchor (10); A method comprising the above steps. **Claim 2** The method according to claim 1, wherein the anchor (10) is embedded in the seabed (14) using a bollard pull from the vessel (6), or the anchor (10) is embedded in the seabed (14) using the tensioning winch (2), or a combination thereof. **Claim 3** The method according to claim 1, wherein the anchor (10) is installed together with a bottom chain (17) connected to the proof load chain (15) by a chain link (16). **Claim 4** The method according to claim 1, wherein an initial embedding test is performed after the first anchor (10) is embedded in the seabed. **Claim 5** The method according to claim 1, wherein the proof load test on the tripod mooring system is performed using a final tension application of a force up to 800 te. **Claim 6** The method according to claim 1, wherein the proof load test on the tripod mooring system is performed using a final tension application of a force of 800 te or more. **Claim 7** The method according to claim 1, wherein the anchors (10) are deployed within their respective target boxes (18) and aligned with their respective mooring line passages (19). **Claim 8** In step d), the proofloading chain (15) is recovered through the moonpool (1) until the first chain link passes through the chain stopper (5), after which the chain stopper (5) is engaged, taking over the load from the chain catenary of the proofloading chain (15), and the connecting hook (11) is severed, the method according to claim 1.

9. The extra length of the proofloading chain is held within the chain lockers (7, 9), and the chain is sent downward from the locker (7) through the chain operating winch (3) towards the proofloading chain (15) within the chain stopper (5), and thereafter the chain from the locker (7) is connected to the proofloading chain (15) using a chain link (13), the method according to claim 8.

10. When applying tension, the ship (6) moves closer towards the anchor (10) connected to the tensioning winch (2), and all three proofloading chains are aligned towards their respective target boxes (19), the method according to claim 7.

11. The mooring system is a tripod mooring system having three anchors (10) on the seabed (14), the method according to claim 1.

12. The method for applying tension to the mooring system is repeated for a hexapod mooring system having six anchors (10) on the seabed (14), the method according to claim 11.

13. The anchors (10) on the seabed (14) are arranged with a spread of approximately 118 - 122 degrees, preferably approximately 120 degrees, the method according to claim 1.

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