GB2403976A

GB2403976A - Frame apparatus for deploying a sub-sea structure

Info

Publication number: GB2403976A
Application number: GB0316630A
Authority: GB
Inventors: Timothy William Grinsted; Michael John Watchorn
Original assignee: Engineering Business Ltd
Current assignee: Engineering Business Ltd
Priority date: 2003-07-16
Filing date: 2003-07-16
Publication date: 2005-01-19
Anticipated expiration: 2023-07-16
Also published as: GB2403976B; GB0316630D0

Abstract

Apparatus is disclosed for deploying a sub-sea mountable structure 9. The apparatus comprises a frame 1 including a plurality of seabed contacting support portions (3, Fig 1), means for attaching the structure to the frame, means for releasably attaching the frame to a deployment vessel 11 in a transport position, and means for lowering the frame with respect to the deployment vessel, from said transport position to a use position where the seabed contacting support portions are operatively brought into contact with the seabed 12. The apparatus further comprises means 6, 7 and 8 for lowering the structure with respect to the frame such that the structure is operatively brought to a use position on or adjacent the seabed. A method for the use of the apparatus is also disclosed.

Description

Marine Deployment Apparatus and Method The present invention relates to

apparatus and methods for deploying (i.e. placing in an intended position of use) and recovering equipment which is located in use on or near the seabed. Typically such equipment might be for extracting power from natural sources such as waves or tides, but the apparatus and method are in principle applicable to a wide range of sub-sea equipment.

Seabed mounted equipment is conventionally provided with a suitable foundation in which it is mounted. The equipment may be transported to its location of use either fully assembled or for assembly on site. Typical methods of deployment include: 1. Deployment from a floating vessel or jack-up vessel À- This method of deployment has several possible variations including deployment: À.

with cranes, A-frames or winches from a floating vessel or a jack-up vessel (the latter...

being well known in the art). The following procedures may conventionally be used: . . A: 1.1 a foundation is pre-installed onto the seabed using a suitable jack- up drilling barge. After installation of the foundations, the equipment to be located on the seabed is assembled and lifted with cranes onto the foundations using a suitable ' A floating or jack-up vessel. This technique has been used for the deployment of offshore wind turbines.

1.2 the foundation or base structure is incorporated into the structure of the seabed mounted equipment. Where suitable sea conditions are available, the seabed mounted equipment is assembled and lifted directly onto the seabed from a floating or jack-up vessel using onboard cranes.

2. Tow-out of buoyant structures 2.1 Typically means for providing buoyancy are attached to the equipment thereby enabling it to be towed out to an installation site. The buoyancy means may be incorporated into the equipment's structure or may be separately attached as a temporary feature for the purposes of deployment of the equipment. Once the equipment has reached the installation site, the buoyancy of the buoyancy means is reduced, e.g. by flooding tanks previously containing air, so that the equipment is submerged onto the seabed. If recovery of the equipment is required, such as for maintenance, air may be pumped into the tanks of the buoyancy means to displace water, thus raising the equipment from the seabed. This technique has been employed with a known wave power generator.

All the above prior art techniques have certain problems and disadvantages, typically due to one or both of physical and financial constraints. À. À À À À.

3.1. Deployment from a floating orjack-up vessel À .'..

The sites of use of seabed equipment such as for wave or tidal power generation are. . often in shallow water where challenging environmental conditions such as high À - ..

winds, large waves and strong tides are common. These environmental conditions make it difficult to deploy and recover the seabed mounted equipment, in particular by allowing only limited time periods where work can be undertaken. Such limited windows available for &e work frequently result in costly vessel stand-by time or a requirement for more expensive vessels which are better adapted to working in the prevailing conditions. For example, jack-up barges are expensive and can be difficult to use in locations where seabed conditions are unfavourable or strong currents occur.

Similarly, the equipment which is to be mounted on the seabed must be designed to withstand these arduous conditions, making the equipment larger and heavier than would otherwise be necessary. Consequently, the handling equipment required to lift the equipment necessitates vessels with suitably large capacity and craneage.

Suitable vessels can be difficult to obtain and can be costly in use.

Problems with the operation of the seabed mounted equipment, or routine maintenance, may require the equipment to be recovered to the sea surface from the seabed as the use of sub-sea maintenance techniques (such as divers) is limited by the environmental conditions. Again, recovery of the equipment requires the costly provision of a suitable vessel for what could be a minor problem with the equipment.

3.2. Tow-out of buoyant structures Where the seabed mounted equipment is provided with buoyancy means, the problem of recovery of the equipment may be reduced as the tanks of the buoyancy means can À.

be re-filled with air to raise the equipment to the surface. However, environmental: À . conditions also limit the opportunities to do this as the equipment when floating by À ...

virtue of the buoyancy means can become unstable in difficult sea conditions.

Furthermore, the time taken to empty and flood the buoyancy tanks can be lengthy, so..

that there is little certainty in having suitable environmental conditions for the required time period of the work. À 20..

According to a first aspect of the present invention, there is provided apparatus for deploying a sub-sea mountable structure comprising: a frame including a plurality of seabed contacting support portions; means for attaching the structure to the frame; means for releasably attaching the frame to a deployment vessel in a transport position; means for lowering the frame with respect to the deployment vessel from said transport position to a use position whereby the seabed contacting support portions are operatively brought into contact with the seabed; means for lowering the structure with respect to the frame whereby the structure is operatively brought to a use position on or adjacent the seabed.

According to a second aspect of the invention there is provided a deployment arrangement for deploying a sub-sea mountable structure comprising: a deployment vessel; a frame including a plurality of seabed contacting support portions; means for attaching the structure to the frame; means for releasably attaching the frame to the deployment vessel in a transport position; means for lowering the frame with respect to the deployment vessel from said transport position to a use position whereby the seabed contacting support portions are operatively brought into contact with the seabed; means for lowering the structure with respect to the frame whereby the structure is operatively brought to a use position on or adjacent the seabed.

In one preferred embodiment the structure is releasably attachable to the frame. À ...

However, the frame may be retained at the site of use with the structure attached thereto, if desired. .. . In another preferred embodiment, the apparatus or arrangement further comprise À means for raising the structure with respect to the frame, for recovery thereof from À A the seabed. Such means may preferably be the means for lowering the structure, operating in the reverse sense.

Preferably, the frame comprises a plurality of substantially upright support legs, each leg carrying at the lower end thereof a seabed contacting support portion. In preferred apparatus and arrangements according to the invention, the frame comprises four substantially upright legs. The substantially upright legs are preferably joined by a plurality of bracing members, specifically essentially horizontal braces and diagonally arranged cross-braces Preferably where the frame has four legs, the means for releasably attaching the frame to the deployment vessel in a transport position comprise means for mounting the frame such that two of said legs are disposed adjacent each side of the deployment vessel. s

Preferably the means for lowering the structure with respect to the frame comprise respective lowering means disposed within the frame adjacent each leg. The lowering means may conveniently comprise winches driving cables attachable to the structure. In further preferred embodiment guide means are provided adjacent said winch cables, said guide means operatively co-operating with the structure to limit the movement of the structure on lowering thereof substantially to a desired path.

According to a third aspect of the invention there is provided a method of deploying a Àe À sub-sea structure comprising the steps of: A. (i) providing a deployment vessel; À ..

(ii) providing an apparatus as claimed in any of claims 1 and 3 to 11; . (iii) attaching the frame to the deployment vessel; ..

(iv) attaching the structure to the frame; (v) transporting the frame and the structure on the deployment vessel to the site À of use of the structure; À . À . ' (vi) lowering the frame with respect to the deployment vessel such that the seabed contacting support portions contact the seabed while maintaining the structure in substantially fixed relation to the deployment vessel; (vii) detaching the frame from the deployment vessel and moving the deployment vessel away from the frame; and (viii) lowering the structure with respect to the frame into its position of use.

Preferably the method of this third aspect further comprises the steps of (ix) detaching the structure from the frame; (x) attaching the frame to the deployment vessel and removing the frame on the deployment vessel.

According to a fourth aspect of the invention there is provided a method of handling a seabed mounted structure, comprising: (i) providing apparatus as claimed in any of claims 1 and 3 to 11 disposed on the seabed with the structure attached thereto; (ii) raising the structure from its position on or adjacent the seabed to a predetermined location at or above the sea surface by use of the lifting means; (iii) retaining the structure in said desired location attached to said frame; and effecting repair or maintenance of the structure while the structure is retained in the predetermined location.

According to a fifth aspect of the invention there is provided a method of recovering a sub-sea structure to the sea surface comprising the steps of: (i) providing a deployment vessel; À.

IS (ii) providing an apparatus as claimed in any of claims 1 and 3 to 11; À À.

(iii) attaching the frame to the deployment vessel; - ...

(iv) transporting the frame to the site of the sub-sea structure and lowering the a. ; frame over the structure such that the seabed contacting support portions contact the seabed; À . (v) detaching the frame from the deployment vessel and moving the deployment À . . vessel away from the frame; (vi) attaching the structure to the frame; raising the structure with respect to the frame to a desired height.

For a better understanding of the invention and to show how the same may be carried into effect, reference will be made, by way of example only, to the following drawings, in which: Figure I is an isometric view of an apparatus according to the invention; Figure 2 is an isometric view of the apparatus of Figure 1 when supporting a wave power generating device; Figure 3 is a schematic side view of the apparatus of Figure 2 when mounted on a deployment vessel; Figure 4 is similar to Figure 3 showing the frame of the apparatus of the invention in a lowered condition; Figure 5 is a schematic side view of the apparatus after the deployment vessel has been moved away from the apparatus; and Figure 6 is a view similar to Figure 5 showing the wave power generating device in its lowered (use) position. À À À ..: Reletting now to the drawings, the apparatus of the invention comprises a frame 1 which in the illustrated embodiment has four substantially upright support legs 2 each..

of which terminates at its lower end with a seabed contacting support portion 3. The À - - legs 2 are joined together by a number of braces 4 and cross-braces 5 thereby to form a rigid structure. The frame 1 is provided for the deployment of a seabed mounted structure which in the illustrated embodiment is a wave power generator 9. The size and shape of the frame 1 is determined at least partly in accordance with the structure 9 to be deployed, so that the structure 9 can be appropriately attached to the frame 1.

In the illustrated embodiment, the frame 1 is generally square in cross section but other configurations are possible. For example the frame 1 may have a cross-section which is a rectangle, parallelogram, rhombus, trapezium or the like.

For deployment of the structure 9, the frame 1 is mounted on a deployment vessel 11.

The frame 1 is mounted on the vessel 11 such that it can be raised and lowered with respect to the vessel by suitable means such as winches and ropes or cables (not illustrated).

The structure 9 is, in use, attached to the frame 1 such that it may be raised and lowered with respect to the frame 1. To this end, the frame 1 is provided with a number of lifting devices 6 which are mounted close to each leg 2. Preferably the lifting devices 6 are rotary or linear winches and linear strand jacks are particularly convenient. The power supply and control equipment of these winches is not illustrated. Suitable equipment will be known to those of appropriate skill in the art.

The winches 6 move lift cable 7 which are attached in use to the structure 9. The frame 1 is also provided with guide means 8 which may be, for example, tensioned cables or rods, and which are disposed preferably close to the winch cables 7 and legs L 2. The guide means 8 co-operate with appropriate formations of the structure 9 to define the range of movement of the structure 9, i.e. to ensure that the structure 9 is able to move only along a desired upward and downward path, generally parallel to Àe the legs 2. Locking means such as latches or pins (not illustrated) may be provided to retain the structure 9 at a desired height with respect to the frame 1.

Referring in particular to Figure 3 to 6, in use, the frame 1 is mounted to a deployment vessel 11. For transporting the frame 1 to the site of use, the frame 1 is maintained in a raised condition with respect to the vessel 11 (Figure 3). The structure 9 is also mounted on the vessel 11 and may preferably be attached at this stage to the frame 1 via the lifting means 6, cables 7 and guide means 8 as described above. When the vessel 11 reaches the site of use, the frame 1 is lowered with respect to the vessel 11 until the seabed contacting support portions 3 contact the seabed 12. In this use condition, the frame 1 is thus securely mounted on the seabed 12 (Figure 4). As the frame 1 is lowered to the seabed 12, the structure 9 is maintained in substantially fixed relation to the vessel 11 by operation of the lifting means 6. After the frame 1 is positioned on the seabed 12, the structure 1 - if not already attached - is attached to the frame 1 by means of the cables 7 and guide means 8 and is raised with respect to the vessel 11 by means of the lifting means 6 and the vessel 11 is moved away from the frame 1 (Figure 5). The lifting means 6 and cables 7 are then used to lower the structure 9 to its operating position of use on or near the seabed 12 (Figure 6). In the operating position, the structure 9 may be locked by suitable means (e.g. latching means) to the frame 1 to improve the stability of its positioning.

Aner a period of operation, the structure 9 may develop a fault or may require planned maintenance, for example. The frame 1 enables the structure 9 to be raised to the sea surface simply and effectively by use of the lining means 6 and cables 7.

Once the structure 9 has been lined clear of the sea surface it is maintained in its elevated position by the frame 1 and the frame 1 provides a stable platform from which to carry out repairs and/or maintenance of the structure 9. Locking means such as latches or pins may be provided to secure the structure 9 to the frame 1 in its elevated position while work on the structure 9 is carried out.

In a variation of the invention, a given frame 1 may be used to deploy and/or recover a number of structures 9. In this case, the structure 9 is provided with seabed 12 engaging foundation parts, as is known in the art, and, after the structure has been placed on the seabed 12 it is released from the frame 1. The frame 1 is then recovered by the deployment vessel 11 for use elsewhere. For maintenance or repair of the structure 9, the frame 11 may be returned to the site of the structure 9 on the deployment vessel 11, lowered to the seabed 12 and re-attached to the structure Aner the vessel 11 has been moved away, the stricture 9 may be raised to the surface as previously described.

Claims

Claims 1. Apparatus for deploying a sub-sea mountable structure

comprising: a frame including a plurality of seabed contacting support portions means for attaching the structure to the frame means for releasably attaching the frame to a deployment vessel in a transport position means for lowering the frame with respect to the deployment vessel from said transport position to a use position whereby the seabed contacting support portions are operatively brought into contact with the seabed; means for lowering the structure with respect to the frame whereby the structure is operatively brought to a use position on or adjacent the seabed.
2. Deployment arrangement for deploying a sub-sea mountable structure À; comprising: ' À À9 a deployment vessel; ,., a frame including a plurality of seabed contacting support portions; .. À . means for attaching the structure to the frame; means for releasably attaching the frame to the deployment vessel in a transport position; À '..

means for lowering the frame with respect to the deployment vessel from said transport position to a use position whereby the seabed contacting support portions are operatively brought into contact with the seabed; means for lowering the structure with respect to the frame whereby the structure is operatively brought to a use position on or adjacent the seabed.
3. Apparatus as claimed in claim I or arrangement as claimed in claim 2 wherein the structure is releasably attachable to the frame.
4. Apparatus as claimed in claim 1 or 3, or arrangement as claimed in claim 2 or 3 further comprising means for raising the structure with respect to the frame, for recovery thereof from the seabed.
S. Apparatus as claimed in claim 1 or 2 to 40r arrangement as claimed in any of claims 2 to 4 wherein the frame comprises a plurality of substantially upright support legs, each leg carrying at the lower end thereof a seabed contacting support portion.
6. Apparatus or arrangement as claimed in claim 5 comprising four substantially upright legs.
7. Apparatus or arrangement as claimed in claim 6 wherein the substantially upright..

legs are joined by a plurality of bracing members. . .
8. Apparatus or arrangement as claimed in claim 6 or 7 wherein the means for À.

releasably attaching the frame to the deployment vessel in a transport position Hi.

comprise means for mounting the frame such that two of said legs are disposed....

adjacent each side of the deployment vessel.

20,,. .,
9. Apparatus or arrangement as claimed in any of claims 6 to 8 wherein the means for lowering the structure with respect to the frame comprise respective lowering means disposed within the frame adjacent each leg.
10. Apparatus or arrangement as claimed in claim 9 wherein the lowering means comprise winches driving cables attachable to the structure.
11. Apparatus or arrangement as claimed in claim 10 further comprising guide means adjacent said winch cables, said guide means operatively cooperating with the structure to limit the movement of the structure on lowering thereof substantially to a desired path.
12. A method of deploying a sub-sea structure comprising the steps of (i) providing a deployment vessel; (ii) providing an apparatus as claimed in any of claims 1 and 3 to 11; (iii) attaching the frame to the deployment vessel; (iv) attaching the structure to the frame; (v) transporting the frame and the structure on the deployment vessel to the site of use of the structure; (vi) lowering the frame with respect to the deployment vessel such that the seabed contacting support portions contact the seabed while maintaining the structure in substantially fixed relation to the deployment vessel; (vii) detaching the frame from the deployment vessel and moving the deployment vessel away from the frame; and.

(viii) lowering the structure with respect to the frame into its position of use. . . À À
13. A method as claimed in claim 12 further comprising the steps of À À. : (ix) detaching the structure from the frame; A: (x) attaching the frame to the deployment vessel and removing the frame on the....

deployment vessel.

20....
14. A method of handling a seabed mounted structure, comprising: (i) providing apparatus as claimed in any of claims 1 and 3 to 11 disposed on the seabed with the structure attached thereto; (ii) raising the structure from its position on or adjacent the seabed to a predetermined location at or above the sea surface by use of the lifting means; (iii) retaining the structure in said desired location attached to said frame; and (iv) effecting repair or maintenance of the structure while the structure is retained in the predetermined location.
15. A method of recovering a sub-sea structure to the sea surface comprising the steps of: (i) providing a deployment vessel; (ii) providing an apparatus as claimed in any of claims 1 and 3 to 11; (iii) attaching the frame to the deployment vessel; (iv) transporting the frame to the site of the sub-sea structure and lowering the frame over the structure such that the seabed contacting support portions contact the seabed; (v) detaching the frame from the deployment vessel and moving the deployment vessel away from the frame; (vi) attaching the structure to the frame; (vii) raising the structure with respect to the frame to a desired height.
16. A structure or assembly substantially as hereinbefore described with reference to any of Figures 1 to 6. . .
17. A method substantially as hereinbefore described with reference to any of Figures 1to6.