METHOD AND APPARATUS FOR TRANSPORTING CHAIN

Abstract

The invention relates to methods and apparatus for storing at least one chainon an offshore service vessel. The chain is stored in a carousel on the vessel which is driven to rotate while the chain is being loaded into the carousel.

Description

INTRODUCTION

The present invention relates to storage of chain such as mooring chain on an offshore service vessel used in the marine oil and gas industry. The invention also relates to transportation and installation of such chains, and to a storage apparatus.

Heavy metal chain is a vital element of most mooring installations offshore. The storage, transportation and installation of mooring chains offshore is conventionally performed by loading chain into bins or “chain lockers”. Chain lockers are large, cuboid structures and the chain or chains are loaded into the chain lockers one at a time. The order of recovery from these chain lockers is usually “first chain in/last chain out”, so selecting one particular chain from the chain locker can be difficult if the required chain is at the bottom of the pile.

To make recovery of a selected chain easier, a respective chain locker can be provided for each individual chain. However, providing a plurality of (smaller) lockers instead of one large locker restricts the length of chain that can be installed into each locker. Thus, any long chains might have to be split between two lockers, and this loading and unloading can be difficult to perform safely and efficiently.

According to a first aspect of the present invention there is provided a method of storing at least one chain on an offshore service vessel, the method comprising storing the chain on a rotatable carousel on the vessel, the carousel being driven to rotate while the chain is being loaded into the carousel.

“Offshore service vessel” means any vessel specialised for the exploration, development, or production phases of oil and gas at sea. Pipelaying vessels for handling flexible pipeline and umbilicals are commonly provided with carousels which can be adapted for chain transportation in the manner of the invention. A carousel is a storage chamber, generally cylindrical, which is mounted on bearings or rollers so as to rotate around a vertical axis as a flexible pipeline or other product is fed in or drawn out. Motors are provided to drive the rotation.

An advantage of using a carousel also for chain storage is that the chain can be laid flat on the base of the carousel, reducing the risk of twists or entanglement of the chain. This contrasts with loading a chain into a chain locker, where the chain is piled up on itself in the locker. Laying the chain(s) flat on the base of the carousel also reduces the centre of gravity of the chain(s), in comparison to chains piled up in chain lockers. This improves the stability of the vessel. A further advantage is that carousels can allow easy access to various different stored chains; not only to the last chain loaded therein. Also, in many cases, either end of the required chain can be accessed, provided that such access is not prevented by other parts of the same chain, or another chain, being on top of the two ends.

A further advantage of using a carousel is that the chain can be loaded into the carousel with accessories attached, for example, ballast clump weights, end assemblies and/or special connections.

In contrast, considering again the prior art, storing chain with attached accessories in a chain locker is not possible for two reasons. Firstly, a “gypsy” wheel (a pocketed wheel) is conventionally used to load mooring chain into a chain locker. Gypsy wheels are generally wheel-shaped, and have “pockets” which receive the chain. They function to pull the chain up from the deck and turn it through 90 degrees, letting it pile up in the chain locker under gravity. The chain fits quite snugly within the pockets of the gypsy wheel, without a great deal of clearance. Therefore, any accessories (appurtenances) must be detached from the chain before the chain is loaded into the gypsy wheel, in order for the chain to fit. Hence, the accessories must be stored separately from the chain lockers, and must be attached to the chain offshore. With some embodiments of the present invention, using a gypsy wheel can be avoided by using a crane to control the loading into/unloading of the chain from the carousel. The chain can be handled in sections by the crane, so that the loading/unloading is accomplished in a series of small steps.

Secondly, even without the problems caused by gypsy wheels, accessories cannot be stored together with the chain in chain lockers. Chain lockers being merely large bins, a chain loaded into a chain locker piles up on itself in an irregular way, with many u-turns and acute angles. Hence, any accessories would risk becoming damaged in the loading process and through being stored like this, with a large amount of weight crushing the lower, irregularly arranged parts of the chain.

In contrast, the carousel of the present invention can be used to lay out the chain in a regular circular/spiral path, without u-turns, acute angles or doubling-back, which provides much better protection for any attached accessories. Furthermore, to increase the protection further, packing material may be laid down around the accessories. Hence, the carousel allows provision for protection of sensitive components, such as ballast clump weights or other accessories, during and following loading.

Hence, the present invention has the advantage that accessories can be stored together with the chain, and do not have to be attached offshore.

Optionally, the carousel is located under the vessel's deck.

Optionally, the carousel may be a carousel of the vessel which is conventionally used to store flexible pipe and umbilicals. Hence, a large amount of additional equipment is not necessarily required to carry out the invention. Thus, such methods are efficient through duplication of use of pre-existing equipment.

Such carousels have a large base area, so that a large number of chains/length of chain, can be laid out directly on the base of the carousel. This also reduces the centre of gravity of the chain(s), and improves the stability of the vessel. This also avoids having to handle long chain lengths into two chain lockers.

Alternatively, the carousel may be located above the vessel's deck.

Typically, the method includes storing a plurality of chains in the carousel.

Hence, it is not necessary to provide a respective housing (e.g. chain locker) for each chain.

Optionally, the method includes positioning one or more dividers within the carousel, to separate different chains from each other.

This helps prevent the different chains from becoming entangled with each other, and also facilitates selection of a particular chain.

Additionally, the divider(s) may be used as an anchoring point to seafasten (fasten in a sufficiently seaworthy way) the chain for transit.

Rotating the carousel facilitates the loading process, as the carousel can be rotated as the chain is paid out, to lay down the chain in a circular or spiral path.

Typically, the method includes the step of laying down a plurality of chains in the carousel at different radial distances from the centre of the carousel.

This allows easy selection of a selected chain for installation, in contrast to having a number of chains piled on top of each other in a single chain locker. In some cases, the chains can be picked up by either end. Furthermore, laying the chains out at different radial distances (as opposed to on top of each other in chain lockers) reduces the centre of gravity of the chains, increasing the stability of the vessel.

Typically, the chain is loaded into the carousel under tension. For example, a wire can be attached between a leading end of the chain and a padeye (fixing ring) attached to the carousel, to fix the leading end of the chain relative to the carousel.

Optionally, such tension can be created by causing the path of the chain into the carousel to be inclined relative to the vertical, with the touchdown point of the chain being at a different circumferential position from the circumferential position of the chain as it enters the carousel.

For example, the circumferential position of the spooling device and/or the rotational position of the carousel can then be controlled to ensure that the touchdown point of the chain is circumferentially leading the rest of the chain (leading being defined in the direction of rotation of the carousel).

This keeps the chain under tension and prevents slack from being introduced into the chain, which could otherwise occur if the chain were allowed to drop directly downwards from the spool, without being under tension.

The weight of the chain typically also resists any dragging of the chain along the base of the carousel by the spooling device, and thus also helps to keep the chain in tension.

Optionally, the chain has at least one attached accessory which remains attached to the chain during the step of loading the chain into the carousel. This accessory/accessories could be, for example, ballast clump weights, end assemblies and/or special connections.

The method may include the step of adding protective packing material around the chain and attached accessory in the carousel. This provides additional protection for any fragile elements of the accessory/accessories.

Typically, the method includes the step of rotating the carousel in either rotational direction, as required.

Optionally, the method includes also storing at least one other type of product in the carousel in addition to the chain. The other type of product may optionally be flexible product, umbilicals and/or fibre or steel wire, but is not limited to these.

Typically, the method includes the step of transporting the chain in the carousel.

Optionally, the method includes the step of installing the chain offshore. In the following description, removing the chain from the carousel is described as part of the installation procedure.

Typically, the step of installing the chain includes rotating the carousel in a direction of rotation that is dependent on which end of the chain is to be installed first. For instance, if the trailing end of the chain in the loading process is to become the leading end for installation, the direction of rotation of the carousel for loading the chain into the carousel would typically be the opposite direction to that used for removing the chain from the carousel for installation. Hence, the path that the chain takes into and out from the carousel is reversed, by reversing the carousel direction. In contrast, if the leading end of the chain in the loading process is also to be the leading end for installation, the direction of rotation of the carousel for loading and installing the chain would typically be the same.

Optionally, the step of loading the chain into the carousel and/or the step of installing the chain (bringing it out of the carousel) may include using a crane to lower/raise the chain in sections. Hence, a gypsy wheel is not essential for loading/unloading the chain, although for lengths of simple chain a gypsy wheel presents an efficient solution for controlling the chain.

According to a second aspect of the invention there is provided the use of a rotatably driven carousel on board an offshore service vessel to store chain on the vessel.

According to a third aspect of the present invention there is provided apparatus for storing at least one chain on an offshore service vessel, comprising a carousel which is rotatably mounted on the vessel, a chain loading system adapted for loading the chain into the carousel and drive means for rotating the carousel as the chain is loaded into the carousel.

Optionally, the chain loading system comprises chain guide means, for controlling the radial distance of the chain touchdown point from the centre of the carousel.

Typically, the chain guide means comprises a spooling device.

Typically, the chain guide means comprises a chute, the position of which can be adjusted to control the touchdown point of the mooring chain.

Optionally, the orientation of the chute is adjustable. For example, the angle of the chute can be varied to direct the mooring chain to a radially inner, outer, or middle part of the carousel. This can be done by having a fixed upper end of the chute, and a lower end which is moveable in the radial direction with respect to the carousel.

Additionally or alternatively, the radial position of the chute with respect to the carousel is adjustable. Hence, the entire chute can move in the radial direction, instead of just a lower end thereof.

The apparatus may comprise a lay system for laying flexible pipe, provided with adaptations for chain handling. One such adaptation may be one or more pocketed wheels or “gypsy wheels”. Such wheels may be driven and/or passive in operation.

Alternatively, the chain guide means can include a moveable spooling arm, which can be moved to control the touchdown point of the chain.

In such cases, the chain guide means may also include a chute which has a width that increases towards a chute mouth, to permit the mooring chain to leave the chute in a selected one of a plurality of different directions, according to the position of the moveable spooling arm.

Alternatively, the chain guide means comprises a crane. A crane can be advantageous if an accessory/accessories is attached to the chain.

Optionally, the chain loading system includes a gypsy wheel.

Optionally, the apparatus includes attachment means, by which a chain can be attached to the carousel. Optionally, the attachment means comprises at least one padeye, which may be located on a base of the carousel.

Typically, the carousel is adapted to rotate in both rotational directions (clockwise and anti-clockwise), as required.

These and further features and advantages of the invention will be understood by the skilled reader from a consideration of the embodiment described below.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings, in which:

FIG. 1 shows a partially cut-away side view of an offshore service vessel with a mooring chain being loaded into a carousel, illustrating the principles of the invention;

FIG. 2 shows a plan view of the vessel of FIG. 1;

FIGS. 3 and 4 show plan views of the vessel of FIG. 1, showing two different methods of loading a mooring chain into the carousel of the vessel from the shore;

FIG. 5 shows an enlarged view of a compartment of the FIG. 1 vessel, showing the carousel and mooring chain in more detail;

FIG. 6 shows a plan view of the carousel of FIG. 5, and also shows two exemplary mooring chains located on the base of the carousel;

FIG. 7 shows a partially cut-away side view of the carousel of the vessel of FIG. 1, with a mooring chain being loaded into the carousel by a chain guide means according to a first embodiment of the invention;

FIG. 8 shows a plan view of the carousel of FIG. 7;

FIG. 9 shows a partially cut-away side view of the carousel of the offshore service vessel of FIG. 1, with a mooring chain being loaded into the carousel by a chain guide means according to a second embodiment of the invention;

FIG. 10 shows a plan view of the carousel of FIG. 9;

FIG. 11 shows a partially cut-away side view of the carousel of the vessel of FIG. 1, with a mooring chain being loaded into the carousel by a chain guide means according to a third embodiment of the invention;

FIG. 12 shows a plan view of the carousel of FIG. 11;

FIG. 13 shows a partially cut-away side view of the carousel of the vessel of FIG. 1, with a mooring chain and attached accessories being loaded into the carousel by a chain guide means according to a fourth embodiment of the invention; and

FIG. 14 shows a plan view of the carousel of FIG. 13.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

Referring to FIGS. 1 and 2, an offshore service vessel comprises a hull 100 with a superstructure 102, located forward of a larger working area. The vessel has various thrusters 104 to provide dynamic positioning (position holding) during operations of the vessel, for example pipe laying and mooring chain installation.

The vessel also has a deck 109. For the storage, transportation and installation of mooring chain, a carousel 110 is provided, located below the level of the deck 109, in a compartment 112. The compartment 112 has a floor 114 and its ceiling is the deck 109. A loading hatch 116 in the deck 109 provides access to the compartment 112. The loading hatch 116 is rectangular and has a length 117 (longer dimension) and a width 118 (shorter). The vessel also has a crane 120, which has a crane arm A and a hook H.

The carousel 110 will be described in use for the storage and transportation of chains, but can optionally also be used for the storage and dispensing of flexible product, as will be explained below. Indeed, in this embodiment, the vessel is substantially a pre-existing vessel and the carousel 110 is a carousel which is conventionally used for storage of flexible product such as pipe and umbilicals. However, in other embodiments, the carousel 110 could be used for the storage and dispensing of flexible product, and a further, additional carousel could be provided, above or below the deck 109, for mooring chain. Hence, the location of the carousel for the mooring chain is not an essential element of the invention.

Further carousels and storage space (not shown) may also be provided, which can additionally or alternatively be used for flexible product, or other equipment.

FIG. 1 shows (schematically) a mooring chain 332 being loaded onto the carousel 110 from the deck 109, through the loading hatch 116.

FIGS. 3 and 4 show two variations of how the mooring chain can be loaded into the carousel 110 from the shore. In FIG. 3, the vessel is moored by ropes/chains 118 to a dock 120. The mooring chain 332 is stored on the dock, is brought onto the deck 109, and is then guided through a turn of 90 degrees so that it enters the loading hatch 116 from a direction parallel to the width 118 of the loading hatch 116. In FIG. 4, the procedure is similar except that the mooring chain 332 enters the loading hatch 116 from a direction parallel to its length 117.

Referring now to FIGS. 5 and 6, the schematic view of the mooring chain 332 and the carousel 110 is shown in more detail. The carousel 110 comprises a base 312, an outer cylindrical wall 314, and an inner cylindrical wall, which forms a hub 316 of the carousel 110. The outer cylindrical wall 314 is provided at the radially outermost extent of the base 312. The base 312, the outer cylindrical wall 314 and the hub 316 together define a body 317 of the carousel 110, in which mooring chain can be stored.

The base 312 is located on a support plate 319, which includes an upwardly-extending hub support 318 at its centre, which also corresponds with the centre of the base 312.

The hub support 318 has an upper bearing surface, on which the base 312 is directly mounted. Also between the base 312 and the support plate 319 various bearings 320 (e.g. slide bearings or roller bearings) which are located radially outwards of the hub support 318. Hence, the body 317 of the carousel 110 is rotatably mounted on the support plate 319. The support plate 319 is, in turn, located on the floor 114 of the compartment 112.

As shown in FIG. 6 (but not FIG. 5), a divider 322 can be provided within the body 317 of the carousel 110. The divider 322 divides a radially inner volume of the body 317 from a radially outer volume. The divider 322 comprises posts or bollards 324, arranged in a circular path on the base 312 and which are linked together by ropes 326 to form a fence-like structure.

The position of the divider 322 is not necessarily fixed where it is shown in FIG. 6, and could be located closer to, or further away from, the hub 316, or moveable to adjust the relative sizes of the inner and outer storage volumes. Furthermore, in some embodiments, a plurality of dividers 322 could be used, at different radii from the hub 316. For example, two dividers could be used to provide three separate volumes within the body 317 of the carousel 110, and similarly if even more separate volumes are required.

Typically, the divider(s) 322 may be used to separate different mooring chains from each other. However, it is also possible to store other flexible product one side of a divider and mooring chain(s) on the other side of the divider. Hence, in this way, the carousel 110 could be used for the storage and dispensing of both mooring chain and flexible product.

Also shown in both FIGS. 5 and 6 are various mooring chains. In FIG. 6, a first mooring chain 328 is shown laid out on the base 312 at a radially inner position, next to the hub 316. The mooring chain 328 is laid out in a spiral configuration, starting in contact with the hub 316, and gradually increasing in radius, such that after one circumference (circuit) of the hub 316 has been completed, a second circuit starts, not on top of the first circuit, but also on the base 312 at a slightly increased radius.

The first mooring chain 328 has a lead wire 334 attached to a leading end 328a of the chain 328. The lead wire 334 is fixed to a padeye (not shown) on the body 317 of the carousel, typically on the base 312. This fixes the leading end 328a in position. The first mooring chain 328 also has a trailing wire 336 attached to a trailing end 328b of the chain 328.

Also shown in FIG. 6 is a second mooring chain 330, which is located at a radially outer position, next to the outer cylindrical wall 314. The second mooring chain 330 extends along a portion of the outer cylindrical wall 314. Hence, the mooring chains 328, 330 are laid down in the carousel 110 at different radial distances from the centre of the carousel 110. Both of the mooring chains 328, 330 are laid flat on the base 312 of the carousel 110, which keeps the centre of gravity of both chains 328, 330 as low as possible.

The second mooring chain 330 has a lead wire 338 attached to a leading end 330a of the chain 330. The lead wire 338 is fixed to a padeye (not shown) on the body 317 of the carousel, typically on the base 312. This fixes the leading end 330a in position. The second mooring chain 330 also has a trailing wire 340 attached to a trailing end 330b of the chain 330.

Typically both chains 328, 330 will be longer than shown, and will vary in size; FIG. 6 is merely illustrative of the concept. If the first mooring chain 328 was longer, it might cover the entire area of the base 312 between the hub 316 and the divider 322. Furthermore, once this area has been covered, the chain 328 could be laid out, still in a spiral form, on top of the already-laid down chain 328, in a second vertical layer, and so on, if third, fourth, etc. layers are required. The same applies to the second mooring chain 330.

Optionally, more than two chains can be stored in the carousel 110, either with or without additional dividers 322. Optionally, enough dividers 322 would be provided to separate each chain from the others.

FIG. 5 shows the exemplary mooring chain 332 (which could be the first mooring chain 328, the second mooring chain 330, or a further mooring chain) being loaded into the carousel 110, using a chain loading system 342 (shown schematically). The chain loading system 342 is adapted for loading mooring chain into the carousel.

The chain loading system 342 comprises chain guide means 344, for controlling the radial distance of the chain touchdown point from the centre of the carousel 110. The chain guide means 344 comprises a spooling device, which is moveable to different radii relative to the rotational axis of the carousel 110, to lay down the chain 332 at a selected radius. In FIG. 5, the chain guide means 344 is moveable in a direction that is parallel to the length 117 of the loading hatch 116 (the direction perpendicular to the plane of view of FIG. 5). The chain 332 in FIG. 5 is in front of the hub 316 (“in front” defined by reference to the viewing axis) and is not inside the centre of the hub 316.

A schematic example of the novel method of storing mooring chain will now be explained with reference to FIGS. 5 and 6. The method in this example comprises storing a pair of mooring chains on a carousel 110 on the vessel.

The method may include positioning dividers within the carousel 110, to separate different mooring chains from each other. In FIGS. 5 and 6, a single divider 322 is used, to separate two mooring chains from each other. The divider 322 (or plurality of dividers if required) is typically installed in the body 317 of the carousel 110 before loading any mooring chains into the carousel 110, although this is not essential.

Typically, part of the chain loading system is used to raise the mooring chain from the deck up to the chain guide means 344, with which it is engaged. Referring to FIG. 5, the mooring chain 332 (which at this stage in the method is the first mooring chain 328) is fed into the body 317 of the carousel 110 by the chain loading system 342. The chain guide means 344 is set to a selected radial distance from the hub 316 (e.g. adjacent to the hub 316 in this example). The chain loading system 342 then lowers the leading end 328a of the chain 328 onto the base 312.

The lead wire 334 attached to the leading end 328a of the chain 328 can now (or earlier in the method) be fixed to a padeye (not shown) on the body 317 of the carousel, typically on the base 312. This fixes the leading end 328a in position.

As the chain 328 lands on the base 312, the body 317 of the carousel 110 is progressively rotated relative to the support plate 319, to present an uncovered part of the base 312 to the following links of the chain 328 as they land on the base 312. Also, at the same time, the chain guide means 344 is moved very gradually in the radially outward direction (towards the viewer of FIG. 5). The combined result of the rotation of the base 312 and the movement of the chain guide means 344 is that the chain 328 is laid down in a spiral path around the hub 316 as shown in FIG. 6.

Typically, the circumferential position of the chain guide means 344 and/or the rotational position of the carousel 110 is controlled to ensure that the touchdown point of the chain 328 is circumferentially leading the rest of the chain (leading being defined in the direction of rotation of the carousel 110). The touchdown point of the chain 328 is typically one or two metres in advance of the chain 328 at the chain guide means 344. This is possible because the leading end 328a of the chain 328 has already been fixed to the carousel 110.

Hence, tension is created in the chain 328 by causing the path of the chain into the carousel to be inclined relative to the vertical, with the touchdown point of the chain being at a different circumferential position from the circumferential position of the chain 328 as it enters the carousel 110. This helps ensure that the chain 328 is kept under tension as it is paid out, which prevents slack from being introduced into the chain 328. Hence, the mooring chain 332 is loaded into the carousel 110 under tension.

The weight of the mooring chain 328 also resists any dragging of the chain 328 along the base 312 by the chain guide means 344, and thus also helps to keep the chain 332 in tension.

The rotation of the base 312 and the radial movement of the chain guide means 344 is continued until the chain 328 has been fully laid out. If the chain 328 covers the entire area of the base 312 between the hub 316 and the divider 322 before being fully laid out, a second layer of the chain 328 can be loaded on top of the first layer, also in a spiral configuration, and so on. Hence, the chain 328 can be of any length.

After sufficient turns of the carousel, the trailing end of the chain will be reached. The trailing wire 336 is used to support the trailing end 328b as it is lowered into the carousel 110.

After the first chain 328 has been fully laid out, the radial position of the chain guide means 344 is adjusted (moved radially outward, in this example). The chain loading system 342 is then used to lay down the second mooring chain 330 into the body 317 of the carousel 110, on the radially outer side of the divider 322. This is done using a method very similar to that described above for the chain 328. Hence, the two mooring chains are laid down in the carousel at different radial distances from the centre of the carousel 110, on either side of the divider 322.

Optionally, the method can include fastening (seafastening) one or both mooring chains to the divider 322, by any suitable means. Optionally, packing can be put down around the chains (and any attached accessories) to provide additional protection.

Various alternative methods and apparatus for loading a chain into the carousel will now be explained with reference to FIGS. 7 and 8; FIGS. 9 and 10; FIGS. 11 and 12; and FIGS. 13 and 14, which are all variations on the generic method of FIGS. 5 and 6. All that varies in these alternative examples is the chain loading system.

In the example of FIGS. 7 and 8, a chain loading system 342a includes a pocketed wheel known in the art as a gypsy wheel 346a, mounted on the deck 109. The chain loading system 342a also includes a chain guide means 344a, which includes a chute 348a (best shown in FIG. 8) and a moveable spooling arm 350. The chute 348a is shaped like half a pipe, and is mounted on the deck 109, with a mouth M of the chute 348a being above the loading hatch 116. The chute 348a increases in width in the direction towards its mouth M, and also curves downwards slightly at the mouth M, leading the chain 332 into the compartment 112. The moveable spooling arm 350 is mounted on the vessel at a fixed end, articulated and activated by hydraulic rams. The arm 350 carries a wheel arrangement 351 at its free end. The wheel arrangement 351 is adapted to engage the chain 332, by insertion partway into one of the chain links. The moveable spooling arm 350 is adapted to move the wheel arrangement 351 in the plane parallel to the base 312.

In use, the chain 332 is paid out by the gypsy wheel 346a at a controlled rate, passes over the chute 348a, through the loading hatch 116 into the compartment 112, where it lands on the base 312 of the carousel 110. The spooling arm 350 can be moved as required to control the touchdown point of the mooring chain 332.

FIG. 8 shows two different possible (alternative) positions of the chain 332. A first chain path P1 follows the contour of the hub 316, and is caused by having moved the spool arm 350 to a radially inward position. The chain 332 is diverted by the spool arm 350 along the radially inner edge of the chute 348a, and from there, continues radially inwards to a touchdown position close to the hub 316.

A second, alternative chain path P2 follows the contour of the outer cylindrical wall 314, and is caused by having moved the spool arm 350 to a radially outer position. The chain 332 is diverted by the spool arm 350 along the radially outer edge of the chute 348a, and from there, continues radially outwardly to a touchdown position close to the outer cylindrical wall 314.

Hence, moving the spooling arm 350 controls the path of the chain 332. The spooling arm 350 would typically be moved when beginning a new chain 332, to lay the new chain down at a different radius. The spooling arm 350 can also be moved whilst a chain is being laid out, to cause the chain to fall into a spiral rather than a circular path.

Referring to FIGS. 9 and 10, an alternative chain loading system 342b includes a gypsy wheel 346b which is mounted on the deck 109 directly above the loading hatch 116. The chain loading system 342b also includes an alternative chain guide means, in the form of an elongate chute 348b. The chute 348b may be tubular, or in the form of a half-pipe.

An upper end of the chute 348b is swivel-mounted on the vessel, so that the orientation of the chute 348b is adjustable in a plane parallel to the base 312. The chute 348b is not shown in elevation, but has an incline to allow the chain 332 to slide down under gravity. The chute 348b can point around a large arc. Three possible orientations of the chute 348b are shown in FIG. 10. An inward pointing orientation can be used to direct the chain 332 along an inner, radial path, adjacent to the hub 316, and an outwardly pointing orientation can be used to direct the chain 332 to lie adjacent to the outer cylindrical wall 314, and a spectrum of intermediate positions can be used for all radii in between. As with the previous examples, the orientation of the chute 348b can be adjusted as the chain 332 is laid out, to cause the chain 332 to fall into a spiral path. The rest of the method has been described above with reference to FIGS. 5 and 6.

Referring to FIGS. 11 and 12, an alternative chain loading system 342c includes a gypsy wheel 346c which is mounted on the deck 109. The chain loading system 342c also includes an alternative chain guide means 344c, in the form of a chute 348c on a linear spooling drive (not shown). The gypsy wheel 346c is aligned so that the chain 332 coming from the gypsy wheel 346c is parallel to the length 117 of the loading hatch 116.

The spooling drive and chute 348c sits partially in the loading hatch 116 or just above it, and the chute 348c is moveable in a direction parallel to the length 117 of the loading hatch 116. The linear spooling drive may for example comprise a carriage driven along support rails extending along the length of hatch 116, the carriage in turn supporting chute 348c at a desired position.

As the length 117 of the loading hatch 116 runs substantially in the radial direction of the carousel 110, this means the chute 348c is adjustable in radial position with respect to the carousel. The range of movement of the chute 348c is indicated by the arrow X in FIGS. 11 and 12. As shown in FIG. 11, the selected position of the chute 348c corresponds to a selected radius for the chain touchdown point on the base 312. The range of touchdown radii is shown by arrow Y in FIG. 11. Thus, the radial position of the chute 348c is adjustable to adjust the path of the mooring chain 332 being laid down, e.g. in a spiral path, or for a second chain to be laid down at a different radial position from a first chain.

In each of these examples the chain is maintained in tension to control its touchdown and coiling.

FIGS. 13 and 14 show a method and apparatus for handling a mooring chain 332a with attached accessories 360. The accessories 360 may be ballast clump weights, end assemblies and/or special connections, or other types of accessories, for example.

Since a chain with accessories 360 cannot be handled by a gypsy wheel (because the accessories 360 are too bulky to fit in the wheel), the crane hook H of the crane 120 is used to lower the chain 332a into the carousel 110 in stages. FIG. 14 shows the first chain 328, the installation of which has already been explained with reference to FIG. 5, and the chain 332a. The chain 332a has been laid out on the base 312 adjacent to the outer perimeter of the divider 322, “hugging” the outer perimeter. In this embodiment, the chain guide means is therefore provided by the crane 120 and the hook H, the hook H being moveable to adjust the touchdown position of the chain 332a.

To increase the protection of the accessories 360, packing material (not shown) may be laid down around the accessories 360. Hence, sensitive components can be protected during and following loading.

Thus, this example allows attached accessories 360 to loaded into the carousel 110 together with the mooring chain 332a. This is advantageous because the accessories 360 do not have to be stored separately from the chain 332a on the vessel, and do not need to be attached to the chain 332a offshore.

Any of the above methods can also include the step of transporting the mooring chain(s), by moving the vessel, with the mooring chain located in the carousel. The chain may be transported to an installation site for deployment into the sea, or may be recovered from the sea and transported to another location.

Any of the above methods can also include the step of installing a mooring chain. Since the chains 328, 330 are laid down at different radial distances, a particular chain 328, 330 can be easily selected and pulled out of the carousel 110 for installation. The same equipment used to load the chains 328, 330 will be used in unloading and installing the chains 328, 330.

The chains 328, 330 shown in FIG. 6 can be picked up by either end, as both ends are accessible and are not covered up by further chains/parts of the same chain. Typically, the installation procedure is very similar to the chain-loading procedure, but in reverse. Thus, the chain loading system 342 is also used in the process of picking up and installing the mooring chains. A crane 120, gypsy wheel 346, or other equipment can be used to hoist the chain up from the body 317 of the carousel 110, as required.

As with the loading process, the carousel 110 is rotated to facilitate the removal of the chain from the carousel 110. If the trailing end of the chain in the loading process is to become the leading end for installation, the direction of rotation of the carousel 110 for loading in the chain would typically be the opposite direction to that used for installation. Hence, the path that the chain takes into and out from the carousel is reversed, by reversing the carousel direction. Both ends need not be accessible, so that the chain can be layered in the carousel if its length requires. Membranes may be deployed to separate the layers if appropriate.

In contrast, if the leading end of the chain in the loading process is to also be the leading end for installation, the direction of rotation of the carousel for loading and installing the chain would typically be the same.

Once the chain has been selected and pulled out of the carousel 110, the rest of the installation procedure is carried out, as is conventional. The mooring chain may, for example, be installed between a floating rig and the seabed, to anchor the floating rig in position. However, the invention is not limited to any particular end use of the mooring chain.

Modifications and improvements can be incorporated without departing from the scope of the invention. For example, the size, dimensions and location of the carousel for mooring chain are not essential to the invention and can be varied. As already stated above, it is not essential to use a carousel of the type usually used for storage and dispensing of flexible product. Optionally, a plurality of small carousels could be used, instead of one large carousel.

The offshore service vessel can be of any shape and design, and is not limited to the exemplary vessel of FIG. 1. Apart from that the offshore service vessel must have a carousel, none of the other equipment described in relation to FIG. 1 is essential to the invention. Equally, the offshore service vessel may also include additional equipment and may be designed for additional tasks not described above. The phrase “offshore service vessel” is not used in any limiting sense, so that construction vessels are included, for example.

In some methods, the chain guide means 344 is not adjusted whilst the chain is being laid out, so that the chain is laid down in a circular path, instead of a spiral path. For chain lengths shorter than one circuit of the base 312 at that particular radius, this will make no difference. For longer chain lengths, a second circular layer laid on top of a first circular layer may in any case fall off the first layer and onto the carousel base 312. More orderly spooling is thus preferred.

Claims

1. A method of storing at least one chain on an offshore service vessel, the method comprising storing the chain in a rotatable carousel on the vessel, the carousel being driven to rotate while the chain is being loaded into the carousel.

2. A method as claimed in claim 1, wherein the carousel is located under the vessel's deck.

3. A method as claimed in claim 1, including storing a plurality of chains in the carousel.

4. A method as claimed in claim 3, including positioning at least one divider within the carousel to separate different chains from each other.

5. A method as claimed in claim 4, including using the divider as an anchoring point to seafasten the chain for transit.

6. A method as claimed in claim 1, including storing a plurality of chains in the carousel, and wherein the method includes laying down the chains in the carousel at different radial distances from the centre of the carousel.

7. A method as claimed in claim 1, wherein the chain is loaded into the carousel under tension.

8. A method as claimed in claim 7, wherein tension is created by causing the path of the chain into the carousel to be inclined relative to the vertical, with the touchdown point of the chain being at a different circumferential position from the circumferential position of the chain as it enters the carousel.

9. A method as claimed in claim 1, wherein the chain is a mooring chain and has at least one attached accessory which remains attached to the chain during loading the chain into the carousel.

10. A method as claimed in claim 9, including adding protective packing material around the chain and attached accessory in the carousel.

11. A method as claimed in claim 1, including rotating the carousel in both rotational directions.

12. A method as claimed in claim 1, including also storing at least one other type of product in the carousel in addition to the chain.

13. A method as claimed in claim 1, including transporting the chain in the carousel.

14. A method as claimed in claim 1, including installing the chain offshore.

15. A method as claimed in claim 1, wherein installing the chain includes rotating the carousel in a direction of rotation that is dependent on which end of the chain to be installed first.

16. (canceled)

17. Apparatus for storing at least one chain on an offshore service vessel, comprising a carousel which is rotatably mounted on the vessel, a chain loading system adapted for loading the chain into the carousel and drive means adapted for rotating the carousel as the chain is loaded into the carousel.

18. Apparatus as claimed in claim 17, wherein the chain loading system comprises chain guide, for controlling the radial distance of a chain touchdown point from the centre of the carousel.

19. Apparatus as claimed in claim 18, wherein the chain guide comprises a spooling device.

20. Apparatus as claimed in claim 18 wherein the chain guide comprises a chute, the position of which can be adjusted to control the touchdown point of the chain.

21. Apparatus as claimed in claim 20, wherein the orientation of the chute is adjustable.

22. Apparatus as claimed in claim 20 wherein the radial position of the chute with respect to the carousel is adjustable.

23. Apparatus as claimed in claim 18 wherein the chain guide includes a moveable spooling arm which can be moved to control the touchdown point of the chain.

24. Apparatus as claimed in claim 23, wherein the chain guide also includes a chute which has a width that increases towards a chute mouth to permit the chain to leave the chute in a selected one of a plurality of different directions according to the position of the moveable spooling arm.

25. Apparatus as claimed in claims 17 wherein the chain loading system also includes a gypsy wheel.

26. Apparatus as claimed in claim 18, wherein the chain guide comprises a crane.

27. Apparatus as claimed in claims 17 including an attachment by which a chain can be attached to the carousel.

28. Apparatus as claimed in claims 17 wherein the carousel is adapted to rotate in both rotational directions.