NO339306B1 - Mooring arrangment and a chain stopper assembly - Google Patents

Description

MOORING ARRANGEMENT AND A CHAIN STOPPER ASSEMBLY

The following invention relates to a mooring arrangement forfloating vessels, and more particularly the arrangement coupling an anchor chain to the vessel. The invention is suitable both for mooring vessels that are moored at the same place for prolonged periods of time, e.g., over several years, such as production or storage vessels in the offshore oil and gas industry. However, the invention may also be used for mooring other types of vessels and for shorter periods of time, such as drilling vessels, workover platforms or other types of temporarily deployed floating vessels or structures that are frequently moved from site to site.

A common arrangement is shown in figure 1. This comprises a fairlead 21 attached to the side of the vessel 22 close to a bottom 23 of the vessel 22. It also comprises a chain stopper 24 arranged at a deck 25 level of the vessel. A chain 31 extends from a seabed anchor (not shown) through the fairlead 21 and to the chain stopper 24. The arrangement also comprises a chain-adjusting device 26, which in turn comprises a trolley 27 that is moveable on tracks 28. A chain winch 33 is placed in the trolley 27. Next to the trolley 27 is a chain container 30 for storing non-active pull chain. In particular for floating drilling platforms or workover platforms, a chain compartment can be situated within a leg of the platform.

The system comprises a plurality of fairleads 21 and chain stoppers 24. The trolley 27 is moveable between the chain stoppers 24 to tighten or slacken the chains according to needs. When a chain is to be, e.g., tightened, the trolley 27 will be brought to the chain stopper 24 holding this chain, a pull chain 22 stored in the chain container (there is one pull chain for each mooring chain) is fed over a turn down wheel 29 and connected to the mooring chain 31. Then the anchor winch 33 is activated, the chain stopper 24 released and the anchor

chain 31 is pulled to the required tension.

This process has to be repeated as the anchor chain slackens due to stretching of the chain, wear of the chain, displacement of the anchor of because the vessel is to be moved short distances without the need to change the anchor positions.

The multiple chains (typically, the vessel is moored by 5 or 6 chains arranged at 4 separate locations, such as one location at each side of the bow and one location at each side of the stem) should have substantially the same tension.

Consequently, the chains will have to be re-tensioned with intervals ranging from a few months to a year, depending on the age of the mooring system and local conditions.

If the moorings get too slack, the vessel will tend to move more. This is not only uncomfortable to the persons on board the vessel, but may also pose a risk to damaging equipment on board and if a heavy storm occurs, the vessel itself may be in danger of becoming ad rift.

It is of course possible to use one anchor winch for each chain, but this only serves to increase the costs and complicates the clearing of deck space when the winches are not in use.

The known arrangement of winch trolley and chain container is heavy and will increase the weight of the vessel and thereby reduce the loading capacity.

There is therefore a great need for a simpler arrangement for re-tensioning the mooring chains.

For both of the above discussed types of vessels or floating structures there is a need for an arrangement that occupies a smaller deck space and has a reduced

weight.

There is therefore a great need for a simpler mooring arrangement.

There is a great diversity of prior art in this field. In the following, some of this will be explained.

There are several examples of fairleads with chain stopper, such as described in US 7240633, US 200570241558, US 5441008, US 5845893, US 5934216, US 6435121, EP 1689636 and WO 2013/043049, . On the market, there are also fairleads with chain stopper sold under the brands Pusnes by the company MacGregor and BarLatch by the company Bardex.

Examples of chain stoppers in general are shown in WO2006/043821 and GB 1592884.

Although in these the chain stopper has been moved from a position at the deck level to an underwater position at the fairlead, these arrangements are nevertheless depending on an anchor winch and chain container on deck.

There is also known a removable fairlead from US 6148755. However, this only makes it easier to change the fairlead if it is worn or damaged, and does not solve the problem indicated with the arrangement described above.

WO 2013076461 shows an end termination for a mooring chain where a tubular arm is suspended to be able to swing about a link in one plane. At the lower end of the arm is a chain stopper. Above the link there is a chain tensioner. The tensioner is of a linear type. The tensioner can be removed between uses.

The tensioner of WO 2013076461 is depending on the employment of the chain stopper between each stroke of the tensioner. Consequently, the tensioning will take quite some time to complete.

Consequently, the present invention aims to simplify the mooring and re- tensioning of the anchor chains, save deck space and improve safety. This has been achieved by the arrangement defined in the subsequent claim 1.

By providing the mooring arrangement with an articulating joint that enables movement about two axes that are perpendicular to one another, the mooring arrangement can align with mooring forces in different directions, both in the horizontal plane and the vertical plane.

Preferably, the mooring arm comprises a frame that in turn is coupled to the articulating joint. This provides a sufficiently stiff arm that can accommodate the winch.

By providing the frame with a chain stopper that is arranged between the winch and the seabed anchor, the chain will be in tension only from the end of the mooring arm.

Alternatively, a chain stopper may be integrated in the winch.

In a preferred embodiment, the winch comprises at least one directly coupled hydraulic motor. This provides a compact and lightweight winch assembly.

In an alternative embodiment, the winch comprises at least one hydraulic motor and a reduction transmission. This provides a greater flexibility with regard to running speed and traction force of the winch.

Preferably, the motors are configured to act as both a static and dynamic brake. This reduces or removes the need for a separate brake arrangement.

Preferably, hydraulic lines are supplying hydraulic pressure from the vessel.

I one embodiment a chain storage compartment is arranged below the winch. Thereby is avoided a large chain storage compartment on board the vessel or

platform.

In another embodiment, said non-tensioned part of the anchor chain is hanging freely downwards into the sea. This is suitable if the vessel is permanently moored and the free-hanging chain part is not very long.

In another aspect, the invention provides a chain stopper, comprising a pair of locking arms that are hingedly attached to a stopper housing, so that they are moveable between a locked position and an unlocked position. The invention ischaracterized in thatit further comprises a set of lever arms that are hingedly attached to said locking arms and an actuator coupled to said set of lever arms, said, so as to move said locking arms between the locked and open positions, whereby said lever arms are moved to an over centre position when the locking arms are in the locked position. Thereby a fail-safe locking of the chain stopper is achieved.

Preferably, the set of lever arms comprises two lever arms, of which one is hingedly attached at a first end at the distal end of each of said locking arms, and hingedly attached to one another at a second end. This provides a simple linkage to move the locking arms.

Preferably, the over centre position is defined by said hinge at said second ends of said lever arms being situated beyond a line between said hinges at said first ends.

In a preferred embodiment, the actuator håving an elongated hole at one end, said elongated hole receiving a pin attached to one of said lever arms. This provides for a play that can be utilized by a quick release mechanism.

The chain stopper is preferably provided with a with quick release capability. A quick release capability is an advantage as the mooring can be slackened quickly if a situation occurs when the moored vessel or rig has to be moved urgently from the site. This may be because of a blow-out or similar incident. When the quick release of the chain stoppers has been activated, the anchor winches may be used to pull the vessel away from the site. Therefore the chain stopper has a quick disconnect actuator, said quick disconnect actuator håving a stroke length to push said set of lever arms out of said over centre position.

The invention will now be described, referring to the accompanying drawings, in which:

Figure 1 shows a mooring system according to prior art,

Figure 2 shows a section of a floating vessel utilizing the mooring arrangement of the present invention, Figures 3-15 show in longitudinal section a chain stopper with a quick release function according to the invention, and as a sequence of normal opening and closing as well as quick release:

Figure 3 shows the chain stopper in a completely closed state,

Figure 4 shows the chain stopper about to be opened and with the lever arms at the "tipping point",

Figure 5 shows the chain stopper in a partially open position,

Figure 6 shows the chain stopper in a fully open position and with the opening actuator at full stroke, Figure 7 shows the chain stopper in fully open position, but with the actuator partially retracted and ready to close the chain stopper,

Figure 8 shows the chain stopper in a partially closed state,

Figure 9 shows the chain stopper about to be fully closed and with the lever arms at the "tipping point", Figure 10 shows the chain stopper I completely closed state and with the actuator fully retracted, Figure 11 shows the chain stopper in a completely closed state and idling position for both normal opening and quick release (this figure is identical to figure 3), Figure 12 shows the chain stopper about to be opened by a quick release actuator and with the lever arms at the "tipping point", Figure 13 shows the chain stopper during the quick release opening

sequence as the lever arms have just passed the "tipping point",

Figure 14 shows the chain stopper partially open during quick release, and

Figure 15 shows the chain stopper fully open during quick release.

The arrangement of the present invention is shown in figure 2. The arrangement comprises an elongate mooring arm 1 that is attached to the side of a vessel 2 close to the upper deck 3 of the vessel. The attachment close to the upper deck 3 is convenient for a platform or other floating structure that is temporarily deployed and frequently moved. For a vessel that is more or less permanently moored, the arrangement will conveniently be attached substantially doser to the bottom of the vessel.

The arrangement 1 comprises a bracket 4 that is fixedly attached to the vessel 2, such as by welding or bolting. A frame 5 is hingedly attached to the bracket 4. The frame 5 can articulate in the vertical plane through a hinge 6 and in a plane transverse to the vertical plane through a hinge 7. A hydraulic cylinder (not shown) may be coupled between the bracket 4 and the frame 5. The cylinder can lift the frame 5 upwards to facilitate the installation of an anchor chain 8, as will be explained later.

The frame 5 comprises two tubular beams 9 and 10 that are connected at each end. The beams 9, 10 can of course have other cross-sections than tubular, but a tubular cross-section is the most convenient with regard to corrosion protection.

Approximately midway between the ends of the beams 9, 10 is fixedly attached an anchor winch 11. The anchor winch is directly driven by two hydraulic motors that are coupled to the winch 11, one on each side. At the distal end of the frame is arranged a chain stopper 12. The chain stopper 12 may be of a type known per se in the field, or may be of the novel type that is to be explained in connection with figures 3-6.

Below the mooring arrangement 1 and attached to the side of the floating vessel or structure a chain compartment 13 may be arranged. The chain compartment is convenient if the floating structure is a platform or the like, which is to be frequently moved. If the vessel is permanently moored, the chain compartment can be dispensed with and the chain may be allowed to hang freely downward towards the seabed.

Now the function of the arrangement of the invention will be explained.

The coupling of the arrangement 1 of the invention to the anchor chain 8 can be done in various ways. A convenient way is to feed an anchor chain down to the arrangement 1 from the deck of the vessel while the frame is articulated upwards by the cylinder (not shown). The chain can be led over the anchor winch 11 and fed through the chain stopper 12. Thereafter it can be connected subsea with an anchor chain attached to an anchor that has been deployed on the seabed. Alternatively, a lead wire can be fed through the arrangement and used to pull the anchor chain up through the chain stopper 12 to the winch 11.

As soon as the anchor chain has been laid over the winch, the winch 11 is ready to pull in the anchor chain 8. The non-tensioned part 8a of the anchor chain 8 that has been pulled in by the winch may be allowed to hang over the winch 11 and downwards into the sea or into the chain compartment 13. Consequently, there is no need to pull the chain 8a up to the deck for storage.

When the anchor chain 8 is to be re-tensioned, this can be done simply by releasing the chain stopper 12 (by use of an ROV, a diver or by remotely operating a hydraulic cylinder and then running the anchor winch 11. There is no need to put any equipment on the deck. Consequently, the deck space is permanently freed for the use by other types of equipment.

The winch is preferably driven by at least one, preferably two, directly coupled hydraulic motors. However, it is also possible to use at least one smaller hydraulic motor that is coupled to the winch wheel by a reduction gear transmission. In both cases, the motor is configured to act as both a static and a dynamic brake. It is possible to use the motor to hold the anchor chain in tension without the use of a chain stopper, but it is preferred to use a mechanical chain stopper as this may reduce the strain on the winch and the risk of slackening if the hydraulic pressure in the motor should fail.

A novel chain stopper 12 with quick release capability will now be explained, referring to figures 3-15. In the following description, the distal end or direction is outwards from the vessel and downwards to the sea, while the proximal end or direction is towards the vessel and generally upwards away from the sea.

The chain stopper 12 comprises a pair of locking arms 14, 15, which are arranged in opposition to one another. The arms 14, 15 are hingedly attached to a stopper housing 16 at hinges 17, 18. The hinges 17, 18 are arranged away from the distal end of the mooring arrangement.

A set of lever arms 19, 20 are hinged between the outer ends of the locking arms 14, 15 at a respective hinge 43, 44 (best shown in e.g. figure 6). A corresponding set of lever arms (not shown) are hingedly arranged between the locking arms at the other side of the locking housing 16, so that a pair of lever arms 19 are parallel and a pair of lever arms 20 are parallel. Both sets of lever arms 19, 20 are hingedly attached to one another at a hinge 40.

A pair of hydraulic cylinders 41 (only one shown) is arranged between the stopper housing 16 and each of the hinges 40. At the end attached to the hinges 40 the cylinder has an elongated hole 42, which provides some play when the cylinder is actuated. A pin 47 fixed to the lever arm 19 extends through the elongated hole 42.

At the position of the hinges 43, 44 an elongated hole 45, 46 (see e.g. figure 5) is formed in each one of two side plates of the locking housing 16. The locking arms 14, 15 being arrange between these side plates. These holes 45, 46 limit the movement of the locking arms 14, 15. The final element is a quick release actuator 50, which function will be explained in due course. The quick release actuator 50 has a piston rod 51 with a roller 52 at its distal end. The roller abuts the edge of the lever arm 19. As for the actuators 41, there are also a pair of quick release actuators 50, one acting against each of the lever arms 19 in the pair of lever arm.

The chain stopper 12 is in the closed position in figure 3. In this position the lever arms 19, 20 are "over centre", i.e. the hinge 44 is distal of a line between the hinges 43 and 40, so that when the chain tries to push the locking arms 14, 15 apart, the hinge 40 will be pushed further towards the hinge 18 and hence tighten the locking of the locking arms 14, 15. Thereby the locking arms will be held firmly in the locked position. When the lock is to be opened during normal operation, the hydraulic actuators 41 are extended. As the pin 47 is situated at the inner end of the elongated hole 47, the actuator will immediately start pushing the lever arm 19 and the hinge 40 away from the hinges 17, 18. As shown in figure 4, the hinge 40 has been pushed to the "tipping point", when it is on the same line as the line between the hinges 43, 44.

In figure 5, the hydraulic actuator 41 has pushed the hinge 40 somewhat distal of the line between the hinges 43, 44 and the locking arms 14, 15 have started to move apart. In figure 6 the hinge 40 has been pushed distal as far as possible, so that the hinges 40, 44 and 18 are on the same line. The locking arms 14,15 are now in the open position and the chain is free to move through the chain stopper 12.

When the chain stopper 12 is to be closed, the actuator 41 is retracted. After being retracted for some distance, the pin is situated at the distal end of the hole 42. From there on the actuator pulls the lever arm 19 backwards towards the proximal end of the mooring arrangement, as shown in figure 8. In figure 9, the lever arms 19, 20 have reached the "tipping point" again and are about to be moved "over centre". In figure 10, the hinge 40 has been moved over centre and the locking arms 14, 15 are locked safely. When this over centre position has been reached, the hydraulic actuator 41 is extended again until the pin 47 is at the proximal end of the elongate hole 42, as shown in figure 11.

If a quick release of the chain stopper is needed, the quick release actuator 50 is extended. As shown in figure 11, the roller 52 bots against the edge of the lever arm 19 when the lever arm is in its extreme proximal position. This will also prevent the arm 19 from advancing further in the proximal direction. As shown in figure 12, the quick release actuator 50 has moved the arm 19 to the "tipping point". This is allowed because the pin 47 can advance along the elongate hole 42. In figure 13, the arm 19 has advanced even further in the distal direction. It is now out of the over centre position and an outward force on the locking arms 14,15 may push the arms 14, 15 apart. Figure 14 shows that the locking arms 14, 15 is about to be pushed apart. The chain will now unhindered push the arms away from each other until they assume the fully open position shown in figure 15.

Claims (14)

1. Mooring arrangement (1) for a floating vessel or structure (2), comprising at least one anchor chain(8) coupled to a subsea anchor, said anchor chain being coupled to an anchor winch (11),characterised in thatthe winch (11) is fixedly attached to an elongate mooring arm (1), said mooring arm (1) being coupled to an attachment (4) on the vessel or structure (2) via an articulating joint (6, 7), that the anchor chain (8) extends from the anchor over the winch (11), and that the non-tensioned part (8a) of the anchor chain (8), i.e. the chain part (8a) remote from the anchor, is hanging downwards outside of the vessel or structure (2) side , and that the winch (11) comprises at least one directly coupled hydraulic motor or at least one hydraulic motor and a reduction transmission.

2. Mooring arrangement according to claim 1,characterised in thatthe articulating joint (6, 7) enables movement about two axes that are perpendicular to one another.

3. Mooring arrangement according to claim 1 or2,characterised in thatthe mooring arm (1) comprises a frame (5) that in turn is coupled to the articulating joint (6, 7).

4. Mooring arrangement according to claim 3,characterised in thatthe frame (5) has a chain stopper (12) arranged between the winch (11) and the seabed anchor.

5. Mooring arrangement according to any of the preceding claims, characterised in thata chain stopper (12) is integrated in the winch (11).

6. Mooring arrangement according to any of the preceding claims,characterised in thatthe motor is configured to act as both a static and dynamic brake.

7. Mooring arrangement according to any of the preceding claims,characterised in thatit comprises hydraulic lines supplying hydraulic pressure from the vessel (2).

8. Mooring arrangement according to any of the preceding claims,characterised in thata chain storage compartment (13) is arranged below the winch (11).

9. Mooring arrangement according to any of the preceding claims 1-7,characterised in thatsaid non-tensioned part (8a) of the anchor chain (8) is hanging freely downwards into the sea.

10. A chain stopper assembly, comprising a pair of locking arms (14, 15) that are hingedly attached to a stopper housing (16), so that they are moveable between a locked position and an unlocked position,characterised in thatit further comprises a set of lever arms (19, 20) that are hingedly attached to said locking arms (14, 15) and an actuator (41) coupled to said set of lever arms (19, 20), said, so as to move said locking arms (14, 15) between the locked and open positions, whereby said lever arms (19, 20) are moved to an over centre position when the locking arms (14, 15) are in the locked position.

11. Chain stopper assembly according to claim 10,characterised in thatsaid set of lever arms (19, 20) comprises two lever arms, of which one is hingedly attached at a first end (43, 44) at the distal end of each of said locking arms (14, 15), and hingedly attached to one another at a second end (40).

12. Chain stopper assembly according to claim 11,characterised in thatsaid over centre position is defined by said hinge (40) at said second ends of said lever arms (19, 20) being situated beyond a line between said hinges (43, 44) at said first ends.

13. Chain stopper assembly according to any of the claims 10-12,characterisedin that said actuator håving an elongated hole (42) at one end, said elongated hole receiving a pin(47) attached to one of said lever arms (19).

14. Chain stopper assembly according to any of the claims 10-13,characterisedin that it further comprises a quick disconnect actuator (50), said quick disconnect actuator (50) håving a stroke length to push said set of lever arms (19, 20) out of said over centre position.winch