GB2354886A - Cable or pipe laying apparatus - Google Patents

Abstract

A cable or pipe 4 can be damaged by excessive bending when it exits the trenching and laying apparatus 1 at 6 or can be damaged as it enters the apparatus at 6 during initial deployment. To prevent or minimise this damage a device is inserted into the passage between plough share plates 10 and is either in the form of a bend limiting tube 12, Figure 2, or shaped body 20, Figure 7. Tube 12 may be formed from a number of semi-cylindrical sections of varying flexibility and body 20 may be formed from two halves. The device is held in position by depressor 11.

Description

2354886 CABLE OR PIPE LAYING MACHINES The invention relates to cable or

pipe laying machines such as trenching machines particularly those for burial of cables and pipelines in the sea bed or in a bed of 5 water.

Cable or pipe laying machines including trenching machines such as ploughs, mechanical cutters and j etters and the like are well known for use in protecting cable and pipelines under water. The cables or pipelines are buried in the sea bed to protect them from damage by, for example, fishing equipment or anchors. Typically these machines are operated from a vessel on the surface of the water, but may be operated by an underwater vessel such as a submarine or tractor. Such machines are typically fitted with soil cutting parts or jets that are arranged to dig into the sea bed and produce a trench that the cable or pipeline is placed into. The cable is generally stored in the surface vessel and passes through the water to the laying or trenching machine so as to be laid or placed in the trench.

Hitherto, damage has occurred to the cable or pipeline to be laid or trenched. Damage can occur in several ways, two in particular are as follows.

Damage can occur at the point of exit of the cable from the cable laying or trenching machine. Typically the cable exits between two spaced parallel share plates which support the share and which are upright in use. The surfaces around the cable exit in this as well as other types of trenching machines are usually narrow and have a small radius of curvature about which the cable can bend. The point of exit from the machine is at the back of the soil cutting parts and this is narrow to improve the action of the machine providing a narrow trench and a streamline-shaped trenching machine which presents less resistance to the soil. The risk of damage to the cable by excessive bending around the exit is particularly high during deployment of the machine. In particular, the heading of the machine during deployment cannot always be maintained. Thus, the cable, which is typically threaded into the machine on the I surface vessel, is no longer in line with the machine and this causes a bending moment in the cable at the front and more especially at the rear of the machine. Also, the machine may land on the sea bed on top of the cable.

Secondly, whilst there is an advantage in sliding the trenching machine down the cable during deployment, this is often not carried out because of the risk of damage to the cable in sliding it the wrong way through the machine. The risk of damage is particularly acute at the normal point of exit of the machine (which becomes the entrance to the machine in this deployment operation). However, deployment in this way is advantageous in that the length of cable left untrenched on the sea bed is minimised.

It is an object of the present invention to alleviate the above problems. The invention relates to all machines for laying cable, pipeline, wire or other elongate items, whether or not these are laid in a trench, and the term "cable" should be interpreted to include all such items.

According to the invention there is provided a cable laying apparatus comprising:

a first cable passage through which a cable can pass; a device having means for connecting with the first cable passage; the device comprising a second cable passage through which a cable can pass; an inner surface of the second cable passage being adapted to limit the radius of curvature of a cable in at least one direction.

Preferably, the radius of curvature is limited at the exit of the first cable passage.

Preferably the radius of curvature is limited beyond the exit of the first cable passage.

Preferably, the means for connecting with the first cable passage is an insert for at least partially inserting into the first cable passage.

2 Preferably, the device is detachable from the first cable passage.

Preferably, the device is adapted to be retained by the apparatus once detached from the first cable passage, for example, by the provision of one or more connecting 5 means such as a line or link.

Preferably, the device comprises two or more parts so as to be positionable about the cable.

Preferably, the device is buoyant in water such as buoyant plastic or wood.

Preferably, the radius of curvature of an inner surface of the second cable passage is significantly greater than the radius of curvature presented to a cable at the exit of the first cable passage in at least one plane. Thus, the radii of curvature may be the same 15 or less than existing surfaces in some planes.

Preferably, the radius of curvature of an inner surface of the second cable passage being adapted to limit a bend in a cable in more than one direction or in all directions.

Preferably, the radius of curvature of the inner surface of the second cable passage is fixed in one or more directions.

Preferably, the radius of curvature of the inner surface of the second cable passage is 25 variable in all directions.

Preferably, the device comprises a flexible tube. The tube may optionally be circular in internal and/or external cross-section. The tube may comprise a spiral.

Preferably, the flexibility of the tube varies along its length.

3 Preferably, the tube becomes more flexible towards a rearward end of the tube relative to the first passage.

Preferably, the tube is of greater flexibility towards a forward end of the tube relative 5 to the first passage.

Preferably, the device is in sections at least two sections being of differing flexibility.

Preferably, sections are arranged such that the flexibility of the device may be varied 10 longitudinally and/or laterally throughout its extent.

Preferably, sections of differing flexibility oppose one another along the length of the device.

Preferably, the sections are substantially semi-cylindrical.

Preferably, the apparatus comprises a movable depressor for retaining the device in the first cable passage.

Preferably, the device comprises an enlarged section for retaining the device in the first cable passage.

Preferably, the first cable passage comprises a passage between spaced share plates. 25 Preferably, the device comprises one or more wings which extend laterally relative to the first cable passage, one or more wings carrying an inner surface adapted to limit the radius of curvature of the cable.

4 In one embodiment, a trenching machine comprising a cable or pipeline bend limiting and protecting device fitted to the point of exit of a cable or pipeline from the machine is provided.

Preferably, this device is used during deployment of the machine, but is detachable from the machine after deployment to the sea bed, Preferably, the bend limiting device is attached to the machine so that after deployment it is releasable from the deployment position, but remains attached to the machine, for example by use of rigid arm or link or a line or cable or the like. Thus, the device can be recovered with the machine and not lost.

Specific embodiments of the invention will now be described with reference to cable ploughs, by way of example only, as illustrated in the accompanying figures.

Figure I shows in elevation a typical plough during deployment positioned just above the sea bed.

Figure 2 shows the same plough as Figure I fitted with a bend limiting device according to the invention.

Figure 3 shows a close-up view of a bend limiting device in accordance with the invention (the insert is a cross-sectional view of a clamp block used to help secure the bend limiting device in the plough).

Figure 4 shows an exploded view of the bend limiting device of Figure 3.

Figure 5 shows an elevation of a plough similar to that in Figure I fitted with an alternative bend limiting device.

Figure 6 shows a rear view of the plough of Figure 5.

Figure 7 shows an enlarged elevation of the bend limiting device of Figures 5 and 6.

Figure 8 shows an enlarged rear view of the alternative bend limiting device of 5 Figures 5 and 6.

Figure 9 shows a plan view of the plough shown in Figures 5 and 6.

Figure 10 shows an enlarged plan view of the alternative bend limiting device of Figures 5 and 6.

In Figure 1, the plough generally indicated by I is lowered to the sea bed 2 by means of lift and towrope 3 from the support ship (not shown). Cable 4 to be buried under sea bed 2 has been threaded into the plough already whilst on the support ship. The plough I comprises a chassis 7 to which is attached a bellmouth 8 for receiving the cable during trenching and share 9 for ploughing a trench. The rearmost part of share 9 comprises spaced parallel share plates 10. Cable 4 passes through the plough entering at the bellmouth 8 during ploughing and exiting behind ploughshare 9 at exit 6. Umbilical control cable 5 supplies power control etc to the plough. The cable is retained in the share 9 by depressor I I during ploughing, During deployment by lowering the plough on towrope 3, the orientation of the plough may not remain in line with the plane of the cable 4. This can result in two problems. Firstly, during deployment rear opening 6 becomes the entrance for the cable in the plough and bellmouth 8 the exit. If the orientation of the plough and cable are not in line then as the cable enters opening 6 it bends around the edges of share plates 10. Secondly, after deployment and at commencement of ploughing, the cable exits the plough at an angle to the plough if the orientation of the plough does not remain in line with the plane of the cable. The cable then exits the plough around the edges of the share plates 10 at 6. These share plates have small bend radii at these edges and cable damage can result. Also, as the plough contacts the sea bed 6 during deployment, it is possible for cable 4 to be trapped between the share 9 and the sea bed and therefore be damaged.

In Figure 2 a plough is shown fitted with a device 12 according to the invention. The bend limiting and/or protection device 12 is in the form, in this embodiment, of a flexible tube that is attached to the plough whilst the plough is being deployed. Bend limiting tube 12 may be connected directly or indirectly to the cable passage through the plough. Preferably tube 12 is inserted between plates 10 and held in place by a depressor 11. As the plough is lowered, the cable or pipeline 4 passes through tube 12. In this case the depressor 11 is the same as that used to position the cable within the ploughshare during trenching. Depressor I I is pivotally attached to chassis 7 of plough 1. Tube 12 is constructed in a way that allows it to be fitted to the cable without an end of the cable being available. For example, tube 12 is formed in two halves along its length and joined together about cable 4 with clamping devices spaced along its length. Alternatively, the tube may be formed in a spiral to allow it to be fitted to the cable. The tube may be in one or more sections and the sections may differ in stiffness, construction and/or means of attachment to the cable. Tube 12 therefore provides a sheath about the cable 4 at exit 6 of plough 1. The flexible tube allows the cable to bend to a certain degree about exit 6. Thus, tube 12 provides an enlarged bend radii vis-A-vis the much smaller radii at the edges of plates 10 at the rear plough exit 6. Damage caused by the smaller bend radii of the edges of plates 10 at exit 6 is therefore much reduced. Also, tube 12 extends beyond opening 6 and directs cable 4 away from it. Therefore tube 12 is directed away from the underside of the plough and in particular the ploughshare 9. The likelihood of cable being trapped is therefore reduced.

Once on the sea bed, the depressor I I may be lifted slightly to release the bend limiting tube 12 and it is left behind as the plough is towed forward. The tube 12 may then provide useful protection for the cable and be left in position.

Alternatively, the tube may be recovered later or indeed made from a material that degrades, dissolves or disperses in sea water. As will be shown in Figure 3, the bend 7 limiting tube 12 may extend further forward into or beyond the plough or indeed further behind the plough to provide greater protection along the cable length.

Latches, pins or clamps (not shown) may retain the device as an alternative or addition to the depressor. Use of the depressor is advantageous because additional modification to the plough is not always required.

The tube 12 may be graded in stiffness or flexibility along its length either in a stepped or continuous manner. One example of how stepped grading in flexibility may be achieved is shown in Figures 3 and 4. Here tube 12 comprises 8 pieces 12A to 12H. Each piece is half cylindrical in cross-section and has either a recess 13 or a projection 14 for telescopically engaging with a neighbouring piece. Sections 12B, 12C and 12G are semi-rigid whereas sections 12A, 12D, 12E, 12F and 12H are of standard rigidity, being more flexible than pieces 12B, 12C and 12G. Typically, the differing pieces are made from polyurethane of differing rigidities, although other plastics or materials can be used.

Being of half cylindrical cross-section the pieces can be clamped about the cable 4 with cable ties spaced along its length or other means. After use during plough deployment the tube can be left in place on the cable.

Sections 12A to 12H are of differing lengths so that the joins at 13, 14 are staggered providing a stronger structure. By providing two semi-rigid sections 12B and 12C on one side and only one 12G on the other, a tube 12 of graded rigidity is provided.

Near the heel of depressor 11, tube 12 is semi-rigid comprising opposing semi-rigid sections 12G and 12B and 12C. Moving out from this central section semi- rigid pieces 12B and 12C oppose more flexible pieces 12F and 12H. Further out still more flexible sections 12A, 12E and 12D and 12H oppose each other providing greater flexibility still. Whilst this embodiment shows more flexibility towards both the ends of the tube this is optional although greater flexibility at the exit of cable 4 from tube 12 to that near the cable exit of the plates 10 is clearly desirable to provide a larger bend radii at the cable exit from tube 12. A rebate 15 on the ploughward end 8 of tube 12 allows a clamping or wedging block 16 to be positioned about the tube. The clamping or wedging block 16 is shaped to fit, optionally with a close fit, within ploughshare plates 10 and, preferably, to engage depressor 11. Block 16 thus prevents rotation of the tube and also helps to prevent jamming of tube 12 on release 5 of the depressor 11.

Flexibility in sections 12D and 12H helps maximise the bend radius at the exit of tube 12 in all directions in which the cable can bend. Furthermore, the length of the tube beyond exit 6 essentially moves the cable exit of the plough away from point 6 at the exit of share plates 10.

In Figures 5 to 10, the plough is fitted with an alternative device in accordance with the invention. Here bend limiting device 20 is in the form of a shaped body with cable bend limiting surfaces 22, 23 and 24 that are of adequate radius to protect the cable. Whilst the radius of curvature of these surfaces is fixed (unlike the inner surfaces of tube 12), these do allow the cable to bend to a limited degree in all directions (up, down, side to side, front to rear). The device 20 has an extended insertion portion 21 which slots into the space between ploughshare plates 10. Depressor 11, or another means, may retain the device in this position. As can be shown in Figures 6 and 8 (rear views) the cable can leave the plough at a side angle without damage from the share plates 10.

Once on the sea bed, the depressor I I may be lifted slightly to release the bend limiting device (12 or 20) and it is left behind as the plough is towed forward. The device may be recovered later or it can be made from a material that degrades, dissolves or disperses in sea water. The device, particularly device 20, may be made in two parts, for example, with a split at 36 as shown in Figure 8 so that it may be placed around the cable with ease. The two halves of the bend limiting device 20 can be attached to the plough with one or more links or lines allowing it to be attached to the plough after use in such a way that prevents its loss but does not impede plough operation during ploughing. Advantageously, the parts may be buoyant for example 9 a buoyant plastic or wood so that once used they float in water above the plough, or if unattached float to the surface for recovery. Alternatively, the bend limiting device may be made from material that breaks up or wears away as the plough moves forward or it could be left in place to provide cable protection. 5 P71538GB

Claims (24)

1. A cable laying apparatus comprising: a first cable passage through which a cable can pass; 5 a device having means for connecting with the first cable passage; the device comprising a second cable passage through which a cable can pass; an inner surface of the second cable passage being adapted to limit the radius of curvature of a cable in at least one direction.

2. An apparatus according to Claim I in which the means for connecting with the first cable passage is an insert for at least partially inserting into the first cable passage.

3. An apparatus according to Claim I or 2 in which the device is detachable 15 from the first cable passage.

4. An apparatus according to Claim 3 in which the device is adapted to be retained by the apparatus once detached from the first cable passage.

5. An apparatus according to any preceding claim in which the device comprises two or more parts so as to be positionable about the cable.

6. An apparatus according to any of Claims 3 to 5 in which the device is buoyant in water such as buoyant plastic or wood.

7. An apparatus according to any preceding claim in which the radius of curvature of the second cable passage is significantly greater than the radius of curvature at the exit of the first cable passage in at least one plane.

11

8. An apparatus according to any preceding claim in which the radius of curvature of the inner surface of the second cable passage is limited in more than one direction or in all directions,

9. An apparatus according to any of Claims I to 7 in which the radius of curvature of the inner surface of the second cable passage is fixed in one or more directions.

10. An apparatus according to any of Claims I to 7 in which the radius of 10 curvature of the inner surface of the second cable passage is variable in all directions.

11. An apparatus according to any preceding claim in which the device comprises flexible tube.

12. An apparatus according to Claim I I in which the flexibility of the tube varies along its length.

I I An apparatus according to Claim 12 in which the tube becomes more flexible towards a rear-ward end of the tube relative to the first passage.

14. An apparatus according to any of Claims 11 to 13 in which the tube is of greater flexibility towards a forward end of the tube relative to the first passage.

15. An apparatus according to any of Claims 12 to 14 in which the device is in sections at least two sections being of differing flexibility.

16. An apparatus according to Claim 15 in which sections of differing flexibility oppose one another.

17. An apparatus according to Claims 15 or 16 in which one or more sections are substantially semi -cylindrical.

12

18. An apparatus according to any preceding claim comprising a movable depressor for retaining the device in the first cable passage.

19. An apparatus according to any preceding claim in which the device comprises an enlarged section for retaining the device in the first cable passage.

20. An apparatus according to any preceding claim in which the first cable passage comprises a passage between spaced share plates. 10

21. An apparatus according to any preceding claim in which the device comprises one or more wings which extend laterally relative to the first cable passage, one or more wings carrying an inner surface adapted to limit the radius of curvature of the cable. 15

22. An apparatus according to any preceding claim in which the device comprises plastic, such as Polyurethane, or wood or the like.

23. A cable laying apparatus substantially described herein with reference to 20 and/or as illustrated in Figures 2-10.

24. A device for use with a cable laying apparatus substantially as described herein with reference to and/or as illustrated in Figures 2- 10. 25 P71538GB 13