GB2364358A

GB2364358A - Plough for laying elongate articles

Info

Publication number: GB2364358A
Application number: GB0112437A
Authority: GB
Inventors: Timothey William Grinstead
Original assignee: Engineering Business Ltd
Current assignee: Engineering Business Ltd
Priority date: 2000-05-22
Filing date: 2001-05-22
Publication date: 2002-01-23
Anticipated expiration: 2021-05-22
Also published as: GB0112437D0; GB2364358B; GB0012279D0

Abstract

A plough for laying elongate articles such as cables or pipes has a plough share which excavates a trench in which the elongate article is buried. The plough comprises a guide 20, preferably in the form of a bellmouth, having an entrance and an exit for the elongate article, wherein the guide 20 can be moved to alter its inclination and/or the height of the guide entrance relative to the plough share. The mechanism for moving the guide 20 is preferably coupled to means for moving a rear skid 23 which raises and lowers the plough share, such that lowering the skid 23 causes the guide 20 to be lowered and/or inclined. This allows smoother entry of the cable at lower trenching depths, particularly when the elongate articles includes a larger diameter body 22.

Description

2364358 A PLOUGH BACKGROUN-D,TO THE INVENTION This invention relates to

ploughs, especially those used 5 to bury cable or pipe in the seabed.

Submarine cables or pipelines are often buried to protect them from damage by, for example, fishing equipment or anchors. Submarine ploughs are commonly used to bury 10 them. Typically, these ploughs are towed via a towrope by a vessel on the surface of the water, but may be towed by an underwater tractor. They are fitted with a share that is shaped to dig into the seabed under the action of the towing force and produce a trench into which the cable or 15 pipe is directed. An important aspect of the design of cable ploughs is the way they accommodate larger diameter bodies in the cable, forexample repeaters or joints.

Hitherto, submarine ploughs have been operated 20 successfully in many types of seabed and over great distances, but they sometimes experience problems when passing larger diameter bodies, particularly at the point where the cable and body enter the plough. Typically, the plough will have a guide having an entrance that faces 25 toward the front of the plough and receives the cable or pipe to be buried. However, the entry.point of the cable into the guide may, under some operating conditions, be high enough above the seabed for there to be a risk that a larger diameter body may not easily enter the guide.

30 This can be a serious disadvantage resulting in a high risk of damage to the cable or the larger diameter body.

t I SUMMARY OF THE INVENTION

It is the object of the present invention to improve the operation of cable and pipeline ploughs under these circumstances.

According to the present invention, there is provided a plough adapted for burying an elongate flexible element, the plough comprising a plough share, a guide having an 10 entrance and an exit, the entrance facing toward the front of the plough for receiving the element to be buried, means for directing the element from the exit of the guide into a trench excavated by the share and means for moving the guide relative to the plough share between 15 first and second positions that differ from one another in the inclination or the height of the entrance to the guide relative to the plough share.

As will readily be understood, this effectively deals 20 with the problem of the entry point of the flexible element being high enough above the seabed for there to be a risk that a larger diameter body may not easily enter the guide, by providing for the guide to be lowered or inclined in the appropriate circumstances.

It is preferred that the first and second positions differ from one another in the inclination and the height of the entrance to the guide relative to the plough share, such that the relatively higher of those two 30 positions of the entrance to the guide is also the relatively less inclined. This ensures that the 2.

advantages of lowering the guide and the advantages of _L inclining the guide can be achieved together.

Typically, the cross-sectional area of the entrance to 5 the guide will be s larger than that of the exit from the guide. A conventional bellmouth fulfils this requirement.

often, the plough will be supported on one of more skids that can be moved relative to the plough share between 10 positions that differ from one another in the height of the skid relative to the plough share. This allows the trenching depth to be controlled, but will result in the height of the guide relative to the seabed being increased if, for example, the skids are lowered to 15 reduce the trenching depth. Accordingly, it is preferred that the means for moving the guide and the means for moving the skid are coupled, such that lowering the skid causes the guide to be lowered and/or inclined. Automation of the adjustments to the guide is a 20 convenience.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described by way of example with reference to the accompanying drawings in which: figure 1 shows a side view of a conventional cable plough. figure 2 shows a side view of the plough in figure 1 operating at normal working trench depth.

13 figure 3 shows a side view of the plough in figure 1 operating at normal working trench depth with a cable body entering. figure 4 shows a side view of the plough in figure I operating at reduced trench depth with a cable body entering.

figure 5 shows a side view of -a plough f itted with the invention at normal working trench depth.

figure 6 shows a side view of a plough fitted with 10 the invention at reduced depth with a cable body entering.

DETAILED DESCRIPTION

As shown in figures 1 and 2, a seabed cable plough 15 includes a chassis 1, a share 3 and support skids 2. The skids 2 support the plough on the seabed 6 and the share 3 penetrates the seabed as the plough is towed by a ship via towrope 5. The skids 2 are adjustable hydraulically to set the trenching depth of the plough. Cable 7 enters 20 the plough at bellmouth 12 and exits underground at the back of the plough 8. The plough may be fitted with a control and monitoring system and a hydraulic power pack, allowing the operators on the ship to operate it via an umbilical 14.

In figure 3, the plough is shown at a normal operating trench depth, with a larger diameter cable body 16 entering the bellmouth 12. It can be seen that at this operating position of the plough that the body enters 30 easily into the bellmouth. In figure 4, the plough is shown operating at a reduced trench depth with a larger diameter cable body 18 entering the bellmouth 12, which is now at an elevated position above the seabed as a result of -the reduced trenching depth of the plough. It can be seen that the body 18 may take up an attitude that 5 could result in damage to the cable or body by excessive bending at the entry to bellmouth 12.

In figures 5 and 6, a plough similar to that shown in the previous figures is shown. It is fitted with a hydraulic 10 power pack and control system and adjustable rear skids 23. It is also fitted with a moveable cable guiding bellmouth 20. In figure 5 the moveable bellmouth 20 is shown raised, allowing the plough to operate at a lower position in the seabed, where the cable is buried deeper.

15 A cable body 22 is shown entering the plough. In figure 6, the moveable bellmouth is shown in a lowered position 21, allowing smoother entry of the cable and body 24.

The lower position shown in figure 6 is a position at 20 whichthe bellmouth is both lower and more inclined with respect to the plough and thus the plough share. This is achieved by articulating the bellmouth about a pivot 30 at the rear of the bellmouth. Attaching the bellmouth to the plough chassis at another pivot 31, above the 25 articulating pivot 30, is a hydraulic ram 32. This is operated by remote control using a hydraulic actuator.

The hydraulics operating the bellmouth an the hydraulics operating the skids may be coupled, for example in a 30 closed loop, so that lowering the skid causes the guide to be lowered and/or inclined.

S

Claims

I. A plough adapted for burying an elongate flexible element, the plough comprising a plough share, a guide 5 having an entrance and an exit, the entrance facing toward the front of the plough for receiving the element to be buried, means for directing the element from the exit of the guide into a trench excavated by the share and means for moving the guide relative to the plough 10 share between first and second positions that differ from one another in the inclination or the height of the entrance to the guide relative to the plough share.
2. A plough according to claim 1 in which the first and is second positions which differ from one another in the inclination and the height of the entrance to the guide relative to the plough share, such that the relatively higher of those two positions of the entrance to the guide is also the relatively less inclined.
3. A plough according to claim 1 or claim 2 in which the cross-sectional area of the entrance to the guide is larger than that of the exit from the guide.

25
4. A plough according to any one of claims 1-3 further comprising a supporting skid and means for moving the skid relative to the plough share between positions that differ from one another in the height of the skid relative to the plough share.

LO
5. A plough according to claim 4 in which the means for moving the guide and the means for moving the skid are coupled, such that lowering the skid causes the guide to be lowered and/or inclined.
6. A plough according to any preceding claim that is a submarine cableor pipe- line-burying plough.
7. A plough substantially as described herein with 10 reference to figures 5 and 6 of the accompanying drawings.

-7