SUBSEA CLEARING APPARATUS

Abstract

A subsea clearance apparatus (1) includes a chassis (2), fore and aft skids (3, 4) spaced along a principal axis (P) of the apparatus (1), and a pair of flanks (22a, 22b) with a plurality of tines (5) depending from the flanks (22a, 22b). The tines (5) are spaced transversely with respect to the principal axis (P) and pitched toward the fore of the apparatus (1). In use, the chassis (2) is spaced from the seabed (S) by the skids (3, 4) as the apparatus (1) is propelled therealong such that the tines (5) engage and deflect away from the principle axis (P) obstructions which are larger than a predetermined size and which protrude by a predetermined amount from the seabed (S).

Claims

1. A subsea clearance apparatus comprising a chassis, fore and aft supports spaced along a principal axis of the apparatus and one or more engaging elements depending from the chassis and arranged transversely with respect to the principal axis, wherein the chassis is spaced, in use, from the seabed by the supports as the apparatus is propelled therealong such that the engaging elements engage and deflect away from the principle axis obstructions which are larger than a predetermined size and/or which protrude by a predetermined amount from the seabed.

2. A subsea clearance apparatus according to claim 1, wherein the engaging elements comprise a plurality of tines which are spaced transversely with respect to the principal axis.

3. A subsea clearance apparatus according to claim 2, wherein the chassis comprises a pair of flanks and the tines depend from the flanks.

4. A subsea clearance apparatus according to claim 3, wherein the tines are angled or pitched toward the fore of the apparatus.

5. A subsea clearance apparatus according to claim 4, wherein the tines are configured such that they are spaced, in use, from the seabed.

6. A subsea clearance apparatus according to claim 5, wherein the space between the tines and the seabed is adjustable.

7. A subsea clearance apparatus according to claim 6, wherein the space is adjustable by adjusting the angle or pitch of the tines.

8. A subsea clearance apparatus according to claim 6, wherein the space is adjustable by adjusting the height of the fore and/or aft support.

9. A subsea clearance apparatus according to claim 3 comprising a cross-brace interconnecting the flanks.

10. A subsea clearance apparatus according to claim 9, wherein each flank comprises one or more modular segments for adjusting the swept width of the apparatus.

11. A subsea clearance apparatus according to claim 3, wherein the fore and aft supports each comprise a pair of skids on either side of the principal axis of the apparatus, the chassis comprising a pair of longitudinal members each having one of the fore skids mounted thereto and each aft skid being mounted to one of the flanks.

12. A subsea clearance apparatus according to claim 11, wherein each of the aft supports comprises a keel plate.

13. A subsea clearance apparatus according to claim 11, wherein each of the pair of fore supports is rotatable about a steering axis for steering the apparatus.

14. A subsea clearance apparatus according to claim 11, wherein each of the pair of fore supports is tiltable about an axis parallel, in use, with the seabed.

15. A subsea clearance tool according to claim 1, wherein the chassis comprises a hollow, floodable portion.

16. A subsea clearance tool according to claim 1 comprising a cradle configured to receive a remotely operated vehicle.

17. A method for clearing a seabed, the method comprising lowering a subsea clearance apparatus from a vessel to a seabed, propelling the apparatus along the seabed such that one or more engaging elements engage and deflect away from a principal propelling axis obstructions which are larger than a predetermined size and/or protrude by a predetermined extent from the seabed.

18. A method according to claim 17, wherein the engaging elements comprise tines and the method comprises maintaining the tines in a spaced relation relative to the seabed as the apparatus is propelled therealong.

19. A method according to claim 18 comprising adjusting the space between the tines and the seabed before, during or after the apparatus is propelled therealong.

20. A method according to claim 19 wherein the space between the tines and seabed is adjusted by adjusting the angle or pitch of the tines and/or the height of a chassis from which the tines depend.

21. A method according to claim 17, wherein the apparatus is steered while being propelled along the seabed by rotating one or more fore supports of the apparatus about respective steering axes.

22. A method according to claim 17 comprising at least partially flooding the apparatus before, during or after the apparatus is deployed to the seabed.

23. A method according to claim 17 comprising locating a remotely operated vehicle within a cradle of the apparatus before, during or after the apparatus is lowered to the seabed.

24. A method according to claim 23, wherein the remotely operated vehicle controls one or more actuators of the apparatus and/or relays data to a remote computer.

25. A method according to claim 17, wherein the apparatus is lowered using a crane.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0073] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

[0074] FIG. 1 is a plan view of an apparatus according to an embodiment of the invention;

[0075] FIG. 2 is a side elevation of the apparatus of FIG. 1;

[0076] FIG. 3 is a front elevation of the apparatus of FIGS. 1 and 2;

[0077] FIG. 4 is an enlarged view of part of FIG. 2 showing a selection of tines; and

[0078] FIG. 5 is an enlarged view of part of FIG. 1 showing a selection of tines.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0079] Referring now to the Figures, there is shown a subsea clearance apparatus 1 according to an embodiment of the invention. The apparatus 1 includes a chassis 2 formed of a plurality of hollow, floodable beams. The chassis 2 is supported by a pair of fore supports in the form of leading skids 3 and a pair of aft supports in the form of trailing skids 4, which are spaced from the leading skids 3 along the principal axis P of the apparatus 1. The apparatus 1 also includes a plurality of spaced tines 5 depending from the chassis 2 for engaging obstructions, such as boulders, on the seabed S.

[0080] The chassis 2 includes a pair of longitudinal members 21a, 21b located either side of and extending parallel to the principal axis P. A cross-brace 20 interconnects the longitudinal members 21a, 21b at a leading side of the apparatus 1 to provide a substantially U-shaped configuration. The longitudinal members 21a, 21b extend rearwardly of the cross-brace 20 and connect to a chevron-shaped tool portion 22. The tool portion 22 includes a pair of flanks 22a, 22b, which diverge from one another and from the principal axis P and are swept toward the aft of the apparatus 1.

[0081] Each flank 22a, 22b includes an end portion 23a, 23b, to which one of the trailing skids 4 is mounted, and an intermediate, modular extension portion 24a, 24b for selectively extending the effective length of the flanks 22a, 22b. The modular extension portions 24a, 24b are interconnected by cross-brace 24, which increases the strength and rigidity of the tool portion 22. The modular portions 24a, 24b are of equal length and increase the effective span W of the chassis 2 and, consequently, the swept area of the apparatus 1. The cross-brace 24 has a ladder-type structure which extends perpendicular to the principal axis P and is extendable in this embodiment to accommodate modular extension portions 23a, 23b of different lengths.

[0082] Each of the longitudinal members 21a, 21b includes a respective bridle connection 25 connecting to its leading end. Each bridle connection 25 is rotatable about a vertical pivot 25a and is connected to the end of a bridle line B. The bridle connection 25 transfers the pulling force from the tow line T via the bridle line B to the apparatus 1. The chassis 2 also has a lifting eye 26 for attachment to a lifting apparatus (not shown). The lifting eye 26 is located proximate the centre of gravity of the apparatus 1 to enable the entire apparatus 1 to be lifted from a single lifting point.

[0083] The apparatus 1 may also include a pair of tension adjusters (not shown), which may be in the form of winches. Each respective tension adjuster may be located within one of the bridle connections 25 and may be configured to reel in and pay out the respective bridle lines B so as to maintain substantially constant tension therein as the angle of tow varies. Each bridle connection 25 may have a sensor (not shown) for measuring the tension of a bridle line B attached thereto. Alternatively, the bridle lines B may be provided by portions of the same line to which the tow line T may be slidably connected, thereby to maintain the constant tension as the angle of tow varies.

[0084] The leading skids 3 are attached to the chassis 2 either side of the principal axis P, adjacent the leading end of a respective one of the longitudinal members 21a, 21b. Each of the leading skids 3 may be pivotable or rotatable with respect to the chassis about a steering axis 30 to facilitate steering of the apparatus 1. Each of the leading skids 3 is also tiltable about an axis 31 parallel to the seabed S, such that they can be canted upwardly and downwardly to accommodate surface irregularities of the seabed S.

[0085] Each leading skid 3 has a base plate 32 for contacting the seabed S and distributing the weight of the apparatus 1. Each skid includes a pair of leading edges 33 that converge to a leading apex, with a lip 34 extending from the leading edges 33. The lip 34 is inclined upwardly toward the fore of the apparatus 1. The taper of the leading edge 33 and the lip 34 forms a bow which deflects matter and obstructions out of the path of the skids 3 when the apparatus 1 is run along the seabed S. The leading skids 3 may also have a steering actuator, e.g. a hydraulic actuator (not shown), to rotate the skids 3 about the steering axis 30.

[0086] Alternatively, in a particularly preferred embodiment, the leading skids 3 may be attached to the chassis 2 via a steering frame (not shown). Each of the leading skids 3 may be fixed with respect to the steering frame and one another about their steering axis. The steering frame (not shown) may be pivotable or rotatable about a steering axis with respect to the chassis 2. The steering frame (not shown) may have one or more hydraulic cylinders (not shown) attached between itself and each of the leading skids 3. Each hydraulic cylinder may be a viscous damper.

[0087] Each trailing skid 4 includes a vertical plate 40 extending from a respective end portion 23a, 23b of one of the flanks 22a, 22b and a pair of base plates 41, which extend perpendicularly therefrom and rest on the seabed S to provide a flat, sliding contact with the seabed S. A keel plate 42 is attached by riveting to each vertical plate 40 in this embodiment and extends downwardly therefrom. Each keel plate 42 depends perpendicularly from the base plates 41 and penetrates, in use, into the seabed S to inhibit inadvertent lateral movement as the tines 5 engage obstructions.

[0088] In this embodiment, each of the leading skids 3 and each of the trailing skids 4 is rigidly connected to the chassis 2. However, it is also envisaged that one or more of the skids 3, 4 may be adjustably connected to the chassis 2. In such embodiments, the adjustable connection may be adjusted via one or more actuators, e.g. hydraulic actuators (not shown). Each actuator may be operable to adjust the height of the chassis 2 in the region of that actuator.

[0089] The tines 5 are spaced from one another along each of the flanks 22a, 22b so as to extend across the entire span W of the apparatus 1. The tines 5 depend from each flank 22a, 22b, are angled or pitched towards the fore of the apparatus 1 and extend parallel to each other and to the principle axis P. The spacing of the tines 5 along the flanks 22a, 22b is such that a gap Y is provided between adjacent tines 5. The tines 5 extend from a root at the chassis 2 to a reinforced tip 51. The reinforced tip 51 is of a material of greater wear resistance than a body 52 of the tines 5. In this embodiment, the angle of the tines 5 is adjustable relative to the chassis 2 using an actuator (not shown) in order to vary the distance X between the tips 51 of the tines 5 and the seabed S.

[0090] In this embodiment, the apparatus 1 also includes a support frame 6 extending from the cross-brace 20 and spanning the longitudinal members 21a, 21b. The support frame 6 has a cradle 61 for receiving and supporting an ROV. The support frame 6 includes a series of connections (not shown) for connecting the actuators to an ROV. An ROV may be received within the cradle 61 and connected to the connections to provide hydraulic inputs to the hydraulic actuators.

[0091] In this embodiment, the apparatus 1 is configured to be deployed to the seabed S and pulled therealong by a vessel (not shown) connected to the chassis 2 by the bridle lines B and tow line T. Any obstructions protruding from the seabed S a distance greater than the space X described between the tines 5 and the seabed S and having a width greater than the spacing Y described between adjacent tines 5 are deflected out of the path of travel of the apparatus 1.

[0092] Prior to deployment of the apparatus, the hollow chassis members 20, 21a, 21b, 22a, 22b, 23a, 23b, 24a, 24b are empty or at least partially empty. The bridle lines B are connected to the bridle connection 25 at one of their ends and to the tow line T at a common point at the other of their ends. The apparatus 1 is connected to a vessel crane (not shown) at lifting eye 26 and the apparatus 1 is lifted from the vessel by the crane. The apparatus 1 is then placed into the sea such that the hollow chassis members 20, 21a, 21b, 22a, 22b, 23a, 23b, 24a, 24b fill with water as the apparatus is lowered to the seabed S.

[0093] The apparatus 1 is lowered such that the contact surfaces 32 and 41 of the leading and trailing skids 3, 4 contact the seabed S, causing minimal disruption thereto. The chassis 2 includes water inlet ports (not shown) for admitting water therein at a predetermined rate. In some embodiments, the water inlet ports may be selectively opened and closed using valve means to control the speed at which the chassis 2 is flooded, thereby controlling the decent of the apparatus 1 to the seabed S. Once on the seabed S, flooding of the hollow chassis members 20, 21a, 21b, 22a, 22b, 23a, 23b, 24a, 24b is complete.

[0094] An ROV is received by the cradle 61 and connected to the hydraulic system via the connections. The hydraulic actuators of the tines 5 are operated by the ROV so as to adjust the distance X between the tines 5 and the seabed S. The apparatus 1 is then pulled by a vessel via the tow line T to carry out the clearing operation. While the apparatus 1 is being towed, a controller on the surface can send steering signals to the ROV. The bridle connection 25 transfers the pulling force from the tow line T via the bridle line B to the apparatus 1. As the angle of tow varies, the bridle lines B pivot about vertical pivot 25a so as to affect steering by virtue of a change in direction of force.

[0095] In a preferred embodiment, the bridle lines B are connected to the steering frame (not shown). As the angle of tow varies, the steering frame (not shown) is rotated or pivoted about its steering axis. The leading skids 3, fixed with respect to the steering frame (not shown) and one another rotate by virtue of rotation of the steering frame (not shown) so as to effect steering of the apparatus. The hydraulic cylinders connected between the steering frame (not shown) and each leading skid 3, dampens any shock loading imparted to the steering frame (not shown) due to sudden change of angle of tow or take up in bridle line B tension.

[0096] Alternatively, the ROV can operate hydraulic actuators associated with the leading skids 3 so as to rotate the skids about their respective steering axis and steer the apparatus 1. The ROV may operate hydraulic actuators connected between the steering frame (not shown) and leading skids 3.

[0097] In embodiments which include a sensor in each of the bridle connections 25, the tension in the bridle lines B is monitored. As the apparatus 1 is steered or the vessel changes the angle of tow and unequal bridle line tensions are measured, a controller fed by the sensors operates the winches in order to equalize the bridle line tensions.

[0098] As the apparatus 1 is pulled along the seabed S, any obstructions in the path of the leading skids 3 are deflected out of the path thereof by the leading edge 33 and the lip 34. In addition, any obstructions protruding from the seabed S by a distance greater than the space X between the tines 5 and the seabed S and having a width greater than the space Y described between adjacent tines 5, are deflected out of the path of the apparatus 1. Once the clearing operation is complete the ROV operates a ballast pump (not shown) to evacuate water from the hollow chassis members 20, 21a, 21b, 22a, 22b, 23a, 23b, 24a, 24b. The vessel crane then retrieves the apparatus 1 to the surface.

[0099] It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. For example, the apparatus need not include tines 5 and may instead include one or more engaging elements having a different configuration. The tines 5 or other engaging element(s) may be fixed to the chassis 2. The skids 3, 4 may be replaced with rollers or any other suitable support means. Whilst not stated above, the tines 5 could be configured to engage the seabed S, although this is preferably avoided to minimise the impact to the seabed S. In some embodiments, the apparatus 1 may include one or more buoyancy tanks. The one or more buoyancy tanks may be floodable or ballastable. It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.