GB2516375A - System, device and method for deploying and monitoring subsea cables - Google Patents

Abstract

A subsea cable monitoring arrangement comprises a monitor housing 300 coupled to a subsea cable 12, the monitor housing 300 containing an imaging device (e.g. camera) that relays image data of the touchdown point 100 of the cable 12, via a communication device, to a surface receiver. The monitor housing 300 comprises survey equipment mounted on a trolley, which runs freely on the cable 12. The trolley may be provided with a motor to move it along the cable 2. The trolley is tethered to an umbilical 22 which controls the position of the trolley, powers the survey equipment and provides a data link between the survey equipment and a cable-laying vessel 10. The umbilical 22 is contained and controlled by cable runners 18 which can run up and down the subsea cable 12. The cable runners 18 comprise: a body configured to be coupled to the cable 12 via runner elements (e.g. balls 202); a coupling ring 204 for engaging the umbilical 22; and a quick-release closure member. During installation of the cable 12 on the seabed, the monitor housing 300 is located close to a touchdown point 100 of the cable on the seabed and is retracted along the cable 12 as it is laid, image data being relayed to the surface receiver.

Description

SYSTEM! DEVICE AND METHOD FOR DEPLOYING AND MONITORING

SUBSEA CABLES

Field of the Invention

This invention is directed to the deployment of subsea cables and their subsequent monitoring, for example during installation. More particularly, but not exclusively, the invention relates to a system for attaching instrumentation to a housing, which is used to install subsea cables and a method of installing subsea cables.

Background of the Invention

As the marine energy industry (off-shore wind farms and wave farms) starts to grow, there is an increasing requirement to lay subsea power cables in areas of high tidal flow or regions with large waves.

Installers need to be sure that these subsea power cables are laid correctly to ensure the longevity of the power infrastructure. This can be best ensured if the installer has sight of the point at which the cable makes contact with the seabed, commonly known as the touchdown point.

Traditional techniques use systems that are not operable in highly dynamic marine environments, and as a result many cables are currently laid blind. This risks twists forming in the cable, over tensioning of the cable, or laying the cable such that it is suspended between two high points, such as across a trench, over a reef or between sand bars, so risking exposure to underwater currents which in turn can cause strumming of the cable and this can eventually lead to failure of the cable.

I

In such environments existing techniques also do not allow cable installers to know the precise location of the touchdown points that occur as the cable is laid.

In addition to the above problems this can also lead to problems subsequently when detailed knowledge of the precise position of the cable may be required.

Prior Art

European Patent Application EP-A-O 431 279 (Alcatel Stk) discloses a means for installing a longitudinal flexible body, such as a subsea fibre cable on a sea bed to from a vessel or cable ship. The means includes cable guiding means suspended substantially vertically from the vessel to a predetermined distance above the sea bed). The cable guiding means has a weight large enough to secure a substantially vertical position relatively to the vessel, thereby minimising the effect of sea currents on the cable being laid. t5

US Patent 4 384 808 (Yamamura et al) describes an underwater cable burying device comprising: a body, a travelling device provided on the body and a trenching device provided on the body. An arm extends from said body with a cable clamp member and a cable engaging member provided thereon.

The cable clamp member has two semi-cylindrical claws fixed on a support frame supported by the arm at its upper portions, which are made to open and close around a fulcrum by sliding a member vertically. The claws are formed horizontally at the lower side of the clamp member and pressure boards are arranged and biased by springs. The device is controlled from a mother ship through a control cable.

Many existing systems are not sufficiently compact or streamlined and cannot operate in more than 2 knots of current. This is primarily due to the fact that the umbilical is not supported and it therefore incurs a high degree of drag.

The present invention aims to address problems associated with prior art systems by providing a simple and cheap solution to laying cables in a controlled and predictable manner.

Summary of the Invention

According to a first aspect of the invention there is provided a system for deploying and monitoring a cable comprising: a monitor housing that has ballast, an imaging device for observing a subsea cable and a communication device for relaying image data from the imaging device to a surface receiver so as to assist in subsea cable installation, at least one cable runner is provided for retaining an umbilical adjacent the cable that is being laid, the umbilical relays image data from the imaging device, the at least one cable runner includes a cable body which is configured to be coupled to the cable by way of a coupling element that permits the cable runner to move along the length of the cable being laid, thereby permitting a user to deploy the housing in order to assist in laying the cable in a controlled manner.

Ideally ballast is provided on the monitor housing, which is ideally supported on a movable trolley. The ballast counteracts the drag effect of strong currents and ensures that the trolley can be driven to a touchdown point which is where the cable comes into contact with the seabed.

Optionally a stabilisation mechanism is provided on the trolley for assisting an operator to locate the trolley and housing and so deploy and monitor the cable in a controllable manner, thereby improving the ability of the operator to locate precisely where the cable as it is being laid.

The stabilisation mechanism preferably includes active control devices and actuators so that data from motion sensors, provided on board the trolley, is used to stabilise the trolley.

The actuators on the trolley may be thrusters, such as propellers disposed on the trolley, in order to enable the operator to control the touchdown point of the cable.

These thrusters may be automatically controlled using data from a OPS beacon and coordinates from the designated cable route.

Ideally a plurality of cable runners is also provided and a means, on at least some of the cable runners, acts to retain the umbilical (or a tether) from a surface vessel to the housing, so as to prevent the cable from snagging.

Ideally the umbilical passes freely through coupling rings on the cable runners.

Coupling rings on the cable runners are orientated in the same plane as the cable runners to allow the umbilical to pass freely through the coupling ring.

The umbilical provides data and power and is ideally also used to lower and raise trolley. The umbilical is free to run through the coupling rings on the cable runners. In addition, there is a leash that controls the maximum spacing of the cable runners so as to link them together. The cable runners are fixed to the leash at a spacing of about 2 metre intervals.

Preferably the cable runners include a ring that at least partially surrounds the cable. The ring has mounted thereon runner elements for engaging the cable in a manner that allows free movement of the runners along the length of the cable.

The runner elements are ideally balls or wheels and the coupling element for the umbilical comprises a coupling ring mounted on the body of the cable runner.

A subsea cable monitoring system fitted to the monitor housing includes an imaging device and a communication device for relaying image data from the imaging device to a surface receiver where an operator is able to monitor the location of the cable and other subsea activity; retract and/or release the umbilical to the cable runner, in dependence upon the location of the cable with respect to a touchdown point. The monitoring system enables an operator to pay out more cable so that newly laid cable is placed in a desired location as seen and as required by the operator.

The housing is ideally in the form of a trolley that provides a mounting for the survey equipment and is free to move up and down the cable. The trolley may be driven down the cable via gravity or via a powered tracked system that grips to the subsea cable and uses it as traction surface.

The umbilical provides a connection to the survey equipment, power, and data feed to the vessel as well as a means of raising and lowering the survey equipment.

Cable runners that secure the electrical umbilical to the cable also act to prevent the cable from becoming fouled as well as reduce the amount of drag experienced by the umbilical from the flowing tide by holding the umbilical close to the cable that is being laid.

The system is streamlined to reduce drag and in a preferred embodiment enables observation of the cable touchdown point in flows up to 6 knots.

In use therefore the cable runner is dimensioned and arranged so as to permit the imaging device to be located as close as possible to the touchdown point of the subsea cable that is being laid. In this configuration the cable runner permits the imaging device to move in the direction the cable is being laid (or to be retracted as desired) thereby ensuring continuous monitoring of the seabed in the vicinity of the touchdown point.

An advantage of the aforementioned systems is that -even in very strong currents -and in conditions of turbidity (poor visibility), the imaging device is positioned sufficiently close to the touchdown point so that the precise location of the subsea cable is known.

Other aspects, features and embodiments of the invention are set out in the claims.

In general terms, one embodiment of a first aspect of the invention can provide a subsea cable monitoring system comprising: a subsea cable; a monitor housing containing an imaging device, the housing coupled to the cable; and a communication device for relaying image data from the imaging device to a surface receiver.

Preferably, the monitor housing is movably mounted on the cable. More preferably, the system further includes a trolley for mounting the monitor housing on the cable. The trolley may be strengthened by way of strengthening struts, cross bars, ribs or similar structures. In addition the trolley may be fitted with roll bars or rollers so as to add to its durability.

Suitably, the monitor housing is retractable along the cable, for example by means of a tether or the safety umbilical.

In another embodiment, the system further comprises a motor for displacing the monitor housing along the cable.

Preferably, the communication device comprises: an umbilical for connecting the imaging device to the surface receiver which is ideally a control room, aboard a vessel.

In an embodiment, the system further comprises a secondary communication device for determining a location of the monitor housing.

The system may further comprise a stabiliser for the monitor housing.

Optionally a means for measuring tension in the subsea cable is also provided and ideally this measures tension at or close to the surface of the water. In a tidal flow the surface tension may be very different from the tension at the seabed. When slack forms in the cable at the seabed loops may form which can result in damage to the inner cores of the cable. Therefore a device for determining tension is able to provide a signal to an operator in order to modify one or more parameters for laying the cable.

A separate system may be used to monitor cable tension at the surface (this tension will be different to that at the seabed).

In an embodiment, the systems further comprise a means for controlling an aspect of the imaging device in response to received image data. For example a different resolution or background light or strobe effect may be selected.

Likewise the orientation or buoyancy of the housing or another feature of the housing may be altered so as to have an effect on the delivery path or displace the cable being laid to a desired touchdown location.

One embodiment of another aspect of the invention can provide a cable runner for a subsea cable system, the runner comprising: a body configured to be coupled to a cable; and a coupling element for engaging an umbilical to be coupled to the cable, wherein the body is configured to be movable along the cable.

Optionally the stabiliser may be active, making use of signals received from motion sensors.

This cable runner provides a means for allowing a movable monitor housing and umbilical to move along the cable during installation, and for securing the umbilical and preventing damage andIorfouling of the umbilical.

Preferably, the cable runner has a body comprising a ring that at least partially surrounds the cable, the ring having mounted thereon runner elements for engaging the cable to allow movement along the cable. More preferably, the runner elements are balls or wheels.

Suitably, the coupling element for the umbilical comprises a coupling ring mounted on the body. In an embodiment, the coupling element comprises a fixture for removably fastening the umbilical to the runner.

One embodiment of a third aspect of the invention can provide a method of installing a subsea cable, comprising the steps of: coupling a plurality of cable runners to the cable, the cable runners being movable along the cable; engaging an umbilical with a coupling element on one or more cable runners; connecting a monitor to a subsea installation end of the umbilical; and during installation of the cable on the seabed, retracting the umbilical, thereby withdrawing the monitor and moving the cable runners along the length of the cable being laid by way of the umbilical.

The present invention provides a means of attaching a camera and a beacon to the subsea cable and arranging that equipment so that operators on board the cable installation vessel can view the cable touchdown and the area in the vicinity of that point in real time. The beacon provides a GPS position reference of the touchdown point.

The embodiment may include an altimeter, which enables the distance from the seabed to be measured. This data is fed back to a computer for processing which in turn controls winch or trolley motors for retracting or paying out a line or leash 7 and so automatically maintains a safe distance between the trolley (monitor housing) and the seabed.

A further embodiment of the invention provides a method of monitoring a seabed during subsea cable installation, comprising the steps of: movably mounting a monitor housing, containing an imaging device, to a subsea cable; and during installation of the cable on the seabed: retracting the monitor housing along the cable as the cable is laid; and relaying image data from the imaging device to a surface receiver.

The above aspects and embodiments may be combined to provide further aspects and embodiments of the invention.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Brief Description of the Drawings

Figure 1 is a diagram illustrating a subsea cable installation and monitoring system according to an embodiment of the invention; Figure 2 is a diagram illustrating a cable runner according to an embodiment of the invention; Figure 3 is a diagram illustrating a monitor housing according to one embodiment of the invention; Figures 4a illustrates how induced tension in cable is created in the direction of travel of the cable laying vessel; and Figure 4b illustrates how induced tension in cable is created due to drag from tide in a different direction of travel of the cable laying vessel and how this can cause slack in the cable at the seabed and very high tension at the surface so giving rise to twisting or kinking of the cable.

Detailed Description of Preferred Embodiments of the Invention Referring to the Figures there are shown embodiments of the present invention which is used in conjunction with a cable laying vessel 10 to lay underwater cable 12.

The system has an imaging device 14 (Figure 3) supported within a housing 300 which when deployed is located on or near a sub-sea cable 12 as close as possible to a touchdown point 100, so that the seabed touchdown point 100 can be monitored remotely during installation.

A cable runner 18 (shown in greater detail in Figure 2) allows movement of the monitor 20 in the housing 16 along the cable 12 that is being laid. An umbilical 22 is secured to cable runners 18 and the umbilical 22 relays image data from the imaging device 14 to a control room and operator in the vessel 10 on the surface.

The present invention provides a system for enabling a camera or imaging device 14 and a communication device that transmits images to operators enabling them to observe and deploy the system in a controllable manner.

The sub-sea cable 12 is thereby located by operators on board a cable installation vessel 10 precisely as they are able to view the touchdown point 100 and the location of the cable 12 in the vicinity of the touchdown point 100 in real time and control the location of deployment of the cable even in strong currents.

A beacon 24 provides a GPS position reference of the touchdown point 100 of the cable 12 at regular intervals so enabling accurate coordinates to be obtained for records and for charts. A digital record of these is stored in a computer (not shown) on the vessel 10.

Referring to Figure 1 the system includes a trolley 26 that provides a mounting for monitoring or survey equipment, including the imaging device 14. The trolley 26, which is ideally loaded or able to be loaded with heavy weights or ballast, moves up and down the cable 12 on wheels, sliders or by way of a drive device.

An umbilical 22 provides a connection to monitoring or survey equipment, as well as power and a data feed to/from the vessel 10. Optionally a tether 28 is provided which is connected to the vessel as well as to a winch (not shown) or other retrieval system.

Cable runners 18 (shown in Figure 2) secure the umbilical 22 to the cable 12 that is being laid, thereby preventing the umbilical 22 from becoming fouled or damaged by the tide. Optionally the tether 28 may be similarly secured to the cable 12. This is illustrated in Figures 4a and Figure 4b. In Figure 4b beneficial aspects of the invention are understood as it appreciated how an operator is able to view on a display (not shown) images and data obtained from the imaging device 14 and survey equipment, in a control room on the vessel 10 and observe at close range a camera field of view and to manipulate a cable deployment system (not shown) on the vessel 10 and, in combination with the tension in the cable 12, locate the precise touchdown point of the cable 1; even in heavy seas and strong currents.

In an alternative embodiment monitoring equipment, including the trolley and imaging device 14, may be detachable and re-attachable to the cable 12, so that the monitoring equipment can be moved in stages, rather than continuously along the length of the cable 12.

In another embodiment of the system, the trolley 26 and imaging device 14 may be made buoyant (for example using compressed air tanks and buoyancy system (not shown) in order to lift a snagged cable by inflating underwater buoyancy tanks. The trolley 26 is tethered to the vessel 10 optionally by a tether 28 or by the umbilical 22 or by both. Cable runners 18 are connected one to another by way of the umbilical 22 and the cable runners 18 are mobile with respect to and free to move along the length of the cable 12 thereby ensuring the umbilical does not snag with any obstructions or debris in the water.

An alternative system may include an imaging device movable along the cable fitted with a wireless transceiver. In embodiments using an umbilical 22 to relay image data from the imaging device 14 to the surface receiver, the umbilical 22 may also act as the tether for the imaging device 14 and/or trolley 26 and/or other monitoring equipment, thereby for example permitting equipment to be retracted along the cable 12 by the umbilical 22.

Figure 1 is a diagram illustrating a monitoring and installation system according to one particular embodiment of the invention. Figure 1 depicts survey equipment 40 mounted to a trolley 26 which runs freely along the length of a subsea cable 12. The survey equipment 40 comprises an imaging device 14, such as a video camera or the like, and shows the field of view marked as an eye or >. Survey equipment 40 may also include other cable installation equipment such as gyroscopes, welding and cutting machinery, shovels and pumps; however none of these are depicted.

The trolley 26 has wheels engaging the cable 12 to allow the trolley 26, and thus the survey equipment 40 to move along the cable 12. The trolley 26 is provided with a drive motor and brake mechanism 42, to provide a means to move the trolley 26 along the cable 22, either alone or in addition to retraction by the umbilical 22.

The trolley 26 is stabilised by a stabilising system (not shown) and is connected to the umbilical 22. The umbilical 22 controls the position of the trolley 26, powers the survey equipment 40 and provides a data link between the survey equipment 40 and the installation vessel 10.

The umbilical 22 is contained and controlled by cable runners 18 which are free to run up and down the subsea cable 12 thereby preventing the umbilical 22 from snagging with the vessel 10 or being dragged away by strong currents or the tide.

During an installation, the cable 12 is laid on the seabed, at a series of touchdown points 100. The survey equipment 40 views each touchdown point and relays image data via the umbilical 22 to the installation vessel, where the operator uses the image data to check the touchdown point and if necessary re-orientate the cable.

Once the cable has been laid at this touchdown point, the survey equipment 40 is retracted, for example by retracting the umbilical 22, along the cable 12 towards the vessel 10 by means of the trolley 22 moving along the cable 12. The cable runners 18 allow the umbilical 22 to move alongside and close to the cable 12, and the cable runners 18 are either gathered in by the retraction of the umbilical 22 moving them back up the length of the cable 22. Alternatively the cable runners 18 are either gathered in by the trolley 26 as it moves back up the cable 12. The cable runners 18 therefore both allow a movable imaging device 14 to be mounted on the cable 12 and the umbilical 22 supplies the imaging device 14 (and any lighting) with power and relays data to the operator whilst securing it to the cable 12.

Figure 2 illustrates in detail an example of the cable runner 18. The cable runner 18 is formed as a ring 200 for surrounding the cable 12 to be laid. A hinge 206 allows opening of the ring 200 for installation around the cable 12. A clasp 208 secures the ring 200 in place around the cable 12.

In the example shown in Figure 2, the ring 200 is a stainless steel formed from an approximately 10mm round bar. The hinge 206 has width 25.4mm and an open length 50.8mm. The thickness of the ring is around 0.9mm. A hinge bar diameter is about 2.3mm and its knuckle is 12.7mm.

To allow the cable runner 18 to move freely along the cable 12, synthetic plastics or composite balls 202 are threaded onto the ring 200. These contact the cable 12 as they rotate around the ring 200, allowing free movement of the cable 18 runner along the cable 12. In this example, the balls are 30mm diameter, with 12mm holes to accommodate the ring 200.

Cable runners 18 are ideally kept at a reasonable minimal spacing (typically around 2m apart) in order to control the umbilical 18. Optionally cable ties (not shown) may be used in order to connect the cable runners 18 to the umbilical 18 but an alternative connection may be used that achieves the same objective and is quick to deploy and remove.

Cable runners 22 have one or more coupling rings 204 attached to their outer edge. The umbilical 22 can therefore be threaded through the coupling rings 204, of consecutive cable runners 18, in order to secure the umbilical 22 or tether 28 to the cable 12, but in a manner as to still allow movement of the cable runners 18 along the cable and if necessary movement of the tether 28 through the coupling ring(s) during, for example, retraction of the imaging device and/or trolley 26.

Ideally the coupling rings are orientated in the same plane as the cable runner 18 so as to allow the umbilical 22 to pass freely through the coupling ring 204. In an alternative, the umbilical 22 may be formed so that it can pass freely through the coupling rings 204 in spite of an obtuse feed angle. Therefore when the umbilical 22 is retracted so as to retract the trolley 26, along the cable 12, the cable runners remain substantially in the same relative orientation along the cable 12, until they are collected up, so ensuring that the coupling rings 204 are in register, the umbilical 22 is free to move through the coupling rings and thereby avoiding snagging of the umbilical 22. Other embodiments can permit a tether to be used to pull and lower the trolley 26; controlling its ascent and descent.

In other embodiments the means for allowing the cable runner 18 to move along the cable 12 may be different. For example, the ring bar 200 may have a set of wheels mounted on it, for contacting the cable and allowing the runner to move as they rotate. Alternatively, a set of runners could be mounted on the inside of the ring bar, to slide along the surface of the cable to allow the runner assembly to move.

In other embodiments other means or devices for securing the umbilical 22 to the cable runner 18 may be used, such as clasps or other fasteners, or loops or other enclosures allowing free movement of the umbilical 22.

Figure 3 illustrates an example of a monitor housing 300 in which various instruments are housed. The housing 300 comprises a series of connected plates 302, 304 and 306 forming a box shape assembly, which in this embodiment is formed from stainless steel and a low drag cowling 317 is provided to shield components and to minimise the effect of strong currents. A load pin 350 connects the umbilical 22 to the housing 300. A hinge is provided between two of the plates to allow access to the interior of the housing, for example to install the monitor or imaging device 14. The hinge 314 enables quick and straightforward attachment of the trolley 26 to, and detachment of the trolley 26 from, the cable 12 (not shown).

A forward facing imaging device (camera) 14a is ideally mounted on the trolley 26 below a light 320. Other cameras may be used and may be located on the lateral side and or underside of the housing. A pair of stainless steel guides 316 of dimensions 3OxlOx5mm is disposed between plates 310 and 312, and stainless steel clasps 318 secure the plates one to another.

Ballast 320 is provided on a ballast stabiliser 326 so as to ensure the housing 300 is maintained in a generally upright state. An altimeter 326 is located below a motor and a brake mechanism 326 which presses on the cable being laid and in conjunction with rollers 327 drives the housing forwards and backwards along the cable 12.

On one side of the housing 300 is located an ultra-short base line (USBL), transponder 333 which acts as a beacon to assist in locating the housing 300 as part of an underwater positioning system that uses a vessel mounted transceiver to enable the operator to pinpoint the position of the housing and so have knowledge of the location of the cable 12.

Figure 4a shows cable runners holding the umbilical 22 close to the submarine cable, in a tidal flow in the direction of travel of the vessel 10. In this configuration drag forces on the cable from tides on the umbilical 22 are minimised due to shielding from the submarine cable thereby enabling survey instrumentation (not shown) to approach to within a few metres (typically 4 metres) of the so-called touchdown point without any mechanical propulsion.

Referring now to Figure 4b which illustrates how touchdown monitoring, during strong tidal flow, is required to prevent the cable 12 from looping back on itself and kinking or snagging. Drag forces from the tidal flow cause the cable 12 to become taught along its length and at the surface, but relatively slack around the vicinity of the seabed. Slackness in the cable 12, at the seabed, can result in loops or kinks forming, which if subsequently pulled tight, can damage, weaken or break cores within the cable 12. The survey equipment monitors the cable in real time during high tidal flows to help avoid loops from forming.

It will be appreciated by those skilled in the art that the invention has been described by way of example only, and that a variety of alternative approaches may be adopted without departing from the scope of the invention, as defined by the appended claims.

Claims (19)

1. Claims 1. A system for deploying and monitoring a cable comprising: a monitor housing that has ballast, an imaging device for observing a subsea cable and a communication device for relaying image data from the imaging device to a surface receiver so as to assist in subsea cable installation, at least one cable runner is provided for retaining an umbilical adjacent the cable that is being laid, the umbilical relays image data from the imaging device, the at least one cable runner includes a cable body which is configured to be coupled to the cable by way of a coupling element that permits the cable runner to move along the length of the cable being laid, thereby permitting a user to deploy the housing in order to assist in laying the cable in a controlled manner.
2. 2. A system according to Claim 1, wherein a stabilisation mechanism is provided on a trolley in which the housing is located, and the stabilisation mechanism includes at least one active control devices and at least one actuator so that data from motion sensors is used to stabilise the trolley.
3. 3. A system according to Claim I or Claim 2, wherein the monitor housing in use is connected to and is movable with respect to the cable.
4. 4. A system according to Claim 2 or 3, wherein a means is provided to retract the monitor housing along the cable.
5. 5. A system according to Claim 4, wherein the means to retract the monitor housing comprises a motor and winch.
6. 6. A system according to any preceding claim, further comprising a secondary communication device for determining the location of the monitor housing.
7. 7. A system according to any preceding claim, further comprising a stabiliser for the monitor housing.
8. 8. A cable runner for use with the system according to any preceding Claim wherein the cable runner comprises a body configured to surround the cable; a coupling element enabling engagement of the umbilical to the cable; and a quick release closure member.
9. 9. A cable runner according to Claim 8 wherein the closure member is arranged to be smooth and lie flat so as to prevent it from snagging with the cable or the umbilical.
10. 10. A cable runner according to Claim 8 or 9, wherein the body of the cable runner comprises a ring for at least partially surrounding the cable, the ring has mounted thereon runner elements for engaging the cable to allow movement along the cable.
11. 11. A cable runner according to Claim 13, wherein the runner elements are balls or wheels.
12. 12. A cable runner according to any of Claims 8 to 11, wherein the coupling element for the umbilical comprises a coupling ring mounted on the body.
13. 13. A cable runner according to Claim 12, wherein the plane of the coupling ring is in the same plane as the plane of the body.
14. 14. A cable runner according to any of Claims 8 to 13, wherein the coupling element comprises a fixture for removably fastening the umbilical to the runner.
15. 15. A method of installing a subsea cable, comprising the steps of: coupling a plurality of cable runners to the cable to be laid, the cable runners being movable along the cable; engaging an umbilical with a coupling element on each of the cable runners; connecting a monitor to a subsea installation end of the umbilical; during installation of the cable on the seabed, monitoring the location of the cable close to a touchdown point; and retracting the umbilical, thereby withdrawing the monitor and moving the cable runners along the cable with the umbilical.
16. 16. A method of monitoring a seabed during subsea cable installation, comprising the steps of: movably mounting a monitor housing, containing an imaging device, to a subsea cable; and during installation of the cable on the seabed, locating the monitor close to a touchdown point; and retracting the monitor housing along the cable as the cable is laid; and relaying image data from the imaging device to a surface receiver.
17. 17. A system for deploying and monitoring a cable substantially as herein described with reference to the Figures.
18. 18. A cable runner substantially as herein described with reference to Figure 2.
19. 19. A method of installing a subsea cable substantially as herein described with reference to the Figures.