GB2357134A - A cable or pipe laying plough - Google Patents

Abstract

This invention relates to ploughs particularly those used to bury cable or pipe in the bed of the sea or other water. The invention comprises a cable laying plough having a first cable passage through which a cable 7 can pass and a cable exit 8A and an extension assembly 31 comprising a member moveable between a retracted and an extended position relative to the first cable passage so that when extended the cable exit 8A of the plough is moved to a lower position relative to a base 9 of the plough. The extension assembly 31 is preferably extended and retracted by hydraulic rams 32,41.

Description

2357134 APLOUGH This invention relates to ploughs, particularly those used

to bury cable or pipe in the sea bed or in a bed of water.

Cable or pipeline machines, such as ploughs, are a well known method of protecting cable and pipelines under water. Cables or pipelines are buried in the sea bed to protect them from damage by, for example, fishing equipment or anchors.

Typically these ploughs are towed via a tow rope by a vessel on the surface of the water, but may be operated by an underwater vessel such as a sub-marine or tractor.

Such ploughs are typically fitted with a soil engaging share that is shaped to dig into the sea bed under the action of the lowing force and produce a trench that the cable or pipe is placed into.

Hitherto, these ploughs have been operated successfully in many types of sea bed and over great distances, but sometimes they experience problems if hard sea bed or rock is encountered. Under these circumstances, the plough may not move forward evenly if the share encounters hard sea bed or rock. The plough may ride up over the rock or hard sea bed. When this occurs, the plough inclines forward at an angle with the result that the position of the cable exit through which the cable or pipe leaves the back of the plough is higher than the front of the share which digs the trench. This accentuates the effect of the plough riding up, and can result in inadequate burial of the pipe or cable. Two effects occur, firstly the depth of the trench produced by the plough is reduced because the plough is pushed upwards and secondly, the pipe or cable is not laid at the bottom of the trench produced by the plough. This can be a serious disadvantage resulting in a high risk of damage to the cable or pipe.

The invention relates to all ploughs or trenching machines for laying pipeline, cable, wire or other elongate items or the like and the term "cable' should be interpreted to include all such items.

I It is an object of the current invention to alleviate these problems by improving the burial of cable under these circumstances.

According to the invention there is therefore provided a cable laying plough comprising a first cable passage through which a cable can pass having a cable exit, a cable passage extension assembly comprising an extension, the extension being moveable between a retracted and an extended position relative to the first cable passage, whereby when the extension is in an extended position, the cable exit from the plough is in a lower position relative to a base of the plough than the cable exit of the first cable passage.

Preferably the cable exit of the first cable passage is adjacent to the base of the plough when the extension is in a retracted position; Preferably the extension slidably co-operates with the first cable passage.

Preferably the extension is located within the first cable passage when in a retracted position.

Preferably the extension is connected to the first cable passage.

Preferably the extension assembly comprises means for pivotally moving the extension relative to the first cable passage.

Preferably the extension is pivotally connected to the first cable passage by two or more pivoting links.

Preferably the at least two pivoting links are at an angle to one another; 2 Preferably the extension moves relative to the first cable passage via resilient means whereby the extension is urged into an extended position.

Preferably extension is movable in response to changes in the position of the plough relative to the material to be ploughed.

Preferably the extension is moved relative to the first cable passage by means of a hydraulic jack.

Preferably the plough comprises means for retaining the cable within the extension.

Preferably a cable depressor is provided connected to the extension.

Preferably the extension comprises two laterally spaced plates.

Preferably the plates are substantially parallel.

Preferably the extension is U-shaped in cross-section; Preferably, the invention provides a sub-sea pipeline or cable plough provided with a moveable cable protecting and/or guiding device fitted behind the plough share, the device being moveable from the normal operating position to a position generally below such that the cable is guided to the bottom of the trench cut by the plough. Preferably, a resilient arrangement such as a spring and/or an automatic control system moves the protecting and/or guiding device in response to the pitch angle of the plough. Preferably, the response is more or less immediate following the change in the pitch angle of the plough.

A specific embodiment of the invention will now be described by way of example only with reference to the a ecompanying figures.

3 Figure I shows a side view of a conventional cable plough.

Figure 2 shows a side view of the plough of figure I riding over a rock.

Figure 3 shows a side view of a plough according to the invention.

Figure 4 shows a side view of an extension device fitted to the plough shown in figure 3.

Figure 5 shows a cross-section of the share and extension device at A-A in figure 3.

Figure 6 shows a side view of the plough in figure 3 riding over a rock.

In figure I a sea bed cable plough is made up of a chassis I at a forward end of which are latterly spaced support skids 2. Skids 2 support the plough on sea bed 6.

At the rear of chassis I is a share 3. The share 3 penetrates the sea bed as the plough is towed by a ship (not shown) via a tow rope 5.

Skids 2 are adjustable by cylinders 4 to set the trenching depth of share 3 of the plough.

A cable 7 to be laid enters the plough at bellmouth 12. The cable passes between laterally spaced generally parallel side plates 10 of share 3 and exits between these plates underground at the back of the plough 8. A cutter I I fixed to plates 10 provides a share point 21 which cuts the trench. The base of the plough 9 is formed, in this embodiment, by a plate tranversely joining the share plates 10.

The plough may be fitted with a control and monitoring system and a hydraulic power pack 13 allowing the operators on a ship to operate it via umbilical 14. The plough is shown in a normal operating position. Share point 21 cuts a trench to a depth x and in normal circumstances cable 7 exits the plough at cable exit 8 to be laid in the trench also substantially at depth x.

4 In figure 2, the plough is shown riding up over a rock 20 buried in sea bed 6.

The share point 21 engages the rock and is impeded in its travel. The towing force continues to pull the plough forward so that the plough takes up a forward pitch angle. This results in the cable exit Position 8, between plates 10, being at a depth y, in other words laid to a less deep depth than depth x cut by the share point 2 1.

In figures 3-5, a plough according to the invention is fitted with a cable guiding and protecting extension assembly broadly indicated by 3 1. The assembly comprises, in this embodiment, a member of U-shaped cross-section having laterally spaced, substantially parallel extension plates 43 which are slidably located in between plates 10 of share 3. Whilst plates 43 are substantially parallel and fit closely inside plates 10, this need not be the case. Indeed, part 40 may only operate behind the side plates 10 of share 3. Member 40 may be of other cross- sectional shape and/or it may be a tube or the like, flat plates 43 being replaced by curved plates or members, for example.

Extension assembly 31 is mounted at the back of the plough by pivoting links 33 and 34. Links 33 and 34 are pivotally connected to and extend between share plates 10 and extension member 40. Extension assembly 31 is moved in a controlled manner by hydraulic cylinder 3 2 also connected between share plate 10 and extension member 40. The extension and retraction motion of assembly 31 could be by means of sliders instead of or as well as links 33, 34. The links 33, 34 are shown not parallel in figures 3 and 6 as this can give an optimwn path of movement, for example, a certain proportion of rearward movement as well as a certain proportion of downward movement relative to the base of the plough. The links may be parallel in some embodiments.

In figures 4 and 5, the extension device also comprises an optional cable depressor 42 which holds the cable down in position between extension plates 43.

Depressor 42 pivots relative to the cable enclosing member 40 and the control of a hydraulic jack 41. The depressor 42 is connected to and fitted inside member 40, which in turn moves inside side plates 10 of share 3. Alternatively, depressor 42 may be fitted to the chassis or to plates 10 although in this case, it is preferably arranged to be extendable in its own right so that the heel of depressor 42 is located near exit 8A of cable enclosing member 40. Other means for locating the cable in the member 40 may be provided other than a depressor 42, for example member 40 may be tubular. Here the depressor is elongate and resiliently mounted to push the cable to the exit 8A of member 40. Other means for locating the cable in the member 40 may be provided other than depressor 42, for example member 40 may be tubular. Here, the depressor is elongate and resiliently mounted to push the cable towards the exit 8A of member 40.

During ploughing, when the plough is tilted the base 9 is no longer parallel to the sea bed. In these circumstances, the front part of plough base 9, share point 2 1, is lower relative to the sea bed than the cable exit 8 from between plates 10. Extension of jack 32 lowers the cable exit 8A of assembly 31 by moving extension member 40, as seen in figure 6, relative to plough base 9. Preferably, the extension assembly 31 is lowered sufficiently so that the plough share point 21 and cable exit 8A can be located at substantially the same level despite the tilting of base 9 so that cable 7 can be laid at the base of the trench dug by point 2 1. If the tilting is too severe, this may not be possible. Nevertheless, use of the extension device would result in cable being laid at a deeper depth in the trench than without it.

In figure 6, the plough is shown riding upon a buried rock 50. The cable enclosing extension member 40 has been extended under control of cylinder 32 so that it positions cable 7 in the bottom of the trench made by share point 2 1, thus ensuring maximum protection from the reduced trench depth. The actuating cylinder 32 may be connected to a hydraulic accumulator or other device to allow it to operate as a spring, holding the extension member 40 at the bottom of the trench automatically. Alternatively, or in addition, a resilient means such as a spring can be used to hold extension member 40 at the bottom of the trench automatically. The extension member 40 may be extendable to a continuous range of positions or it may 6 be extendable in steps. Cylinder 32 may also be driven in response to changes in the pitch of the plough, either manually or automatically. The pitch of the plough would be monitored in these circumstances. It is preferred that the mounting of extension 31 is such that it can retract under excess forces from contact with the trench side and/or bottom so as to reduce the chances of damage. Retraction could be automatic if the pressure is too great or as a result of hydraulic oil being forced into an accumulator or passed pressure relief valve.

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Claims (17)

1. A cable laying plough comprising:

a first cable passage through which a cable can pass having a cable exit; a cable passage extension assembly comprising an extension, the extension being moveable between a retracted and an extended position relative to the first cable passage; whereby when the extension is in an extended position, the cable exit from the plough is in a lower position relative to a base of the plough than the cable exit of the first cable passage.

2. A plough according to Claim I in which the cable exit of the first cable passage is adjacent to the base of the plough when the extension is in a retracted position.

3. A plough according to Claim I or 2 in which the extension slidably co operates with the first cable passage.

4. A plough according to any preceding claim in which the extension is located within the first cable passage when in a retracted position.

5. A plough. according to any preceding claim in which the extension is connected to the first cable passage.

6, A plough according to any preceding claim in which the extension assembly comprises means for pivotally moving the extension relative to the first cable passage.

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7. A plough according to Claim 5 or 6 in which the extension is pivotally connected to the first cable passage by two or more pivoting links.

8. A plough according to Claim 7 in which at least two pivoting links are at an angle to one another.

9. A plough according to any preceding claim in which the extension moves relative to the first cable passage via resilient means whereby the extension is urged into an extended position.

10. A plough according to any preceding claim in which te extension is movable in response to changes in the position of the plough relative to the material to be ploughed.

11. A plough according to any preceding claim in which the extension is moved relative to the first cable passage by means of a hydraulic jack.

12. A plough according to any preceding claim comprising a means for retaining the cable within the extension.

13. A plough according to Claim 12 in which a cable depressor is provided connected to the extension.

14. A plough according to any preceding claim in which the extension comprises two laterally spaced plates.

15. A plough according to Claim 14 in which the plates are substantially parallel.

16. A plough according to any preceding claim in which the extension is U shaped in cross-section.

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17. A plough substantially as described herein Vith reference to and/or as illustrated in figures 3-6.