GB2027781A

GB2027781A - Improvements in or Relating to Underwater Operations

Info

Publication number: GB2027781A
Application number: GB7921617A
Authority: GB
Original assignee: Vickers Ltd
Current assignee: Vickers Ltd
Priority date: 1978-04-25
Filing date: 1979-06-21
Publication date: 1980-02-27
Also published as: AU4626279A; BR7902548A; JPS54151296A; IT7922166A0; NO791366L; ES479918A1; FR2424371A1

Abstract

Underwater operations are carried out by placing an object (22, 23) at a desired position underwater by pulling it down through the water to an anchoring point 14 and then moving the object from the anchoring point to the desired position. The object may be mounted on a carrier (21) and the apparatus comprising the object and the carrier may be pulled down by a winching device (1, 8, 12) secured to an underwater structure 30 and comprising a winch (11) and a connector 14 for engagement with a connector (27) of the carrier. The object may be equipment for cutting, turning, joining or moving an underwater pipe (30). <IMAGE>

Description

SPECIFICATION Improvements In or Relating to Underwater Operations This invention relates to the placing of an object at a desired position underwater.

In the field of underwater engineering it is often necessary to transfer equipment of substantial weight to the seabed. Hitherto, the method for achieving this has most commonly been by means of a heavy lift vessel using either dynamic positioning or anchors to hold the vessel in the correct position. This method has some obvious disadvantages. Thus, it is costly, it can only be carried out during limited weather and water conditions, and it is not very suitable for accurately placing equipment at great depths.

Furthermore, as the depth of water increases, divers cannot be used and therefore a surface controlled system aided by cameras must be employed.

It is an object of the present invention to provide a system of placing an object on the seabed which system capitalises on the availability of a submersible craft which can monitor and control the operation in water beyond the operational depth of a diver and which avails itself of power stored in batteries on board the submersible which means that no physical connection is required between the surface craft and the object at the seabed.

According to one aspect of the present invention there is provided a method of placing an object in a desired position under water, which method comprises (i) securing one end of a line to the object and the other end of the line to an anchoring point in the vicinity of said desired position, (ii) reducing the length of the line until the object is drawn to the anchoring point, and (iii) moving the object from the anchoring point to the desired position.

According to another aspect of the present invention there is provided an apparatus for carrying out the foregoing method, which apparatus comprises in combination:- (a) a carrier, (b) the object mounted on the carrier, (c) a device having means for securing it at the anchoring point, (d) a line linking the device and the carrier, (e) a means of reducing the length of the line so as to draw the carrier to the device at the anchoring point, (f) a means of connecting the carrier and the device together at the anchoring point, and (g) a means of moving the object with respect to the anchoring point to place the object at the desired position.

The object may be equipment for carrying out an underwater operation at said desired position when actuated by means of a diver or vessel located externally of the object and in order to facilitate the relocation of the equipment so that it operates at that position, the equipment is preferably moveable with respect to the carrier.

Accordingly, the present invention also provides an apparatus for carrying out an operation at a desired position on an underwater structure, which comprises (a) equipment for carrying out the operation, (b) a carrier for supporting the equipment and for hauling down from the water surface to the vicinity of the underwater structure, and (c) a means of connecting the carrier to the structure when in said vicinity, the equipment being moveably mounted with respect to the carrier so that it may be moved to said desired position when the carrier is connected to said structure.

The device for locating at the anchoring point preferably incorporates a winch and the anchoring point may be the seabed or a suitable rock on the seabed, or some other underwater structure, for example a pipe, on the seabed, the arrangement being such that the length of the line may be reduced by actuation of the winch by means of a diver or vessel located externally of the device.

Accordingly the present invention also provides a device for use in juxtaposing an underwater structure and an apparatus located at the water surface and comprising a carrier and equipment for effecting an operation on the structure, which device comprises (a) a means of securing the device to the structure (b) a winch for hauling the apparatus down from the surface into juxtaposition with the structure, and (c) a connector for engagement with the carrier so as to form a connection between the device and the carrier when the apparatus is in juxtaposition with the structure.

The device and/or the carrier preferably comprise(s) articulated members and a means of moving the members with respect to one another so that the equipment can be readily relocated with respect to the underwater structure when the device and the carrier are connected together so that the equipment can operate at the desired position on the structure. In the case where the device comprises articulated members it is preferred that a first of these members incorporates the means of securing the device to the structure, a second of the members includes the connector and a third of the members includes the winch and is located between the first and second members and articulated thereto.

The operation effected on the structure in accordance with the present invention may consist of moving the structure across the seabed in the case where the structure is, for example, a pipe. In this case, the equipment which the apparatus includes may comprise moveable legs (optionally individually operable) so that by suitably actuating the legs, by means of a diver or submerged vessel, the structure may be lifted and moved across the seabed. In alternative embodiments, in the case where the structure is a pipe, the operation effected by the equipment may be a pipe turning or pipe cutting operation or a pipe-joining operation. In these cases, the equipment which the apparatus includes will be respectively, a pipe turning machine, a pipe cutting machine or a pipe coupling member of a type which can be fitted to the pipe by means of a submersible or diver.

In an embodiment, for use in conjunction with an underwater structure in the form of a pipe, the device for locating at the anchoring point comprises a base member, a member including a winch and a member including a connector in the form of a docking station, the members being articulated with respect to one another. The base member includes the means of securing the device to the pipe and is in the form of a U-shaped portion having a pair of spaced limbs adapted to lie on either side of the pipe and clamps for gripping the pipe. The clamps are hydraulically activated and are intended to secure the device to a section of pipe from which the concrete coating has been removed. The device can, however, be fitted, in an alternative form, with a further set of hydraulically operated stops which enable the device to accommodate small variations in pipe diameter.Such variations would occur if it is required to mount the device on a pipe which is covered with concrete in parts but has some of the steel pipe exposed elsewhere. The winch including member is in the form of a mounting rotatably secured to a the U-shaped portion. The winch is supported by the mounting and a powered slewing mechanism is provided to rotate the mounting to any position with respect to said portion. The member carrying the docking station is in the form of an arm pivotally secured to the mounting. The arm can be tilted to any azimuth position between vertical and horizontal. The pivot axis for the pivoted arm also preferably carries a guide pulley for the rope which makes one complete turn around the pulley in order to provide continuous guidance of the rope in any azimuth position of the pivoted arm.The pivoted arm is preferably activated by a hydraulic ram, clevis mounted between the arm and the mounting for the winch. At the free end of the arm is mounted the docking station which acts as the final guide for the winch rope. The docking station is the location point for the equipment carrier when it is in the final stage of hauldown and engages with the carrier to retain the carrier at the anchoring position. In order to do this it is preferably equipped with a set of actuators in the form of separate fingers arranged to be moveable between a closed position in which they are able to retain the equipment carrier by gripping a ledge on the nose of the latter and an open position in which they eject the carrier from the docking station prior to the carrier being returned to the water surface.Power for the operation of the device is preferably provided by a power supply system mounted on board the submersible.

In alternative embodiments of the device the base member is not designed for deployment on a pipe but is in the form of an anchor for embedding in the seabed by fluidising the seabed beneath it.

Alternatively, the base member may be fitted with clamps adapted to suit some other existing underwater structure.

The winch may be either a conventional type with the winching power being provided by the drum used to store the rope or, alternatively, a traction winch where the rope is stored on a reeling device. Buoyancy tanks may be mounted on the device. These should be of such a size as to provide sufficient buoyancy to the whole device that, in conjunction with a further detachable buoy, the weight in water of the device is within the carrying capacity of a submersible.

In an embodiment, the carrier of the apparatus comprises a buoyancy mandrel in the form of a hollow boom having a connector at its free end.

The desired equipment is mounted on the boom and is capable of being driven along the boom once the connector of the boom has engaged with the connector of the winching device. The drive which provides the motion of the equipment along the boom is, typically, a chain traverse system powered by a hydraulic motor. The power for the operation of the carrier and equipment is preferably provided by a power supply system mounted on board the submersible.

In operation the apparatus and the device act in a combined manner to give the necessary manoeuvring capability to place the equipment either axially in line with a pipe or astride it or in any prerequisite position.

In use of the aforementioned preferred embodiments, the winching device is lowered to the seabed by a winch working from a suitable surface support vessel. A ballast weight, which is typically a piece of pipe, is carried in the clamps of the base member to ensure an accurate descent path. A submersible is launched and locates the device which carries a homing transponder. On rendezvous, the submersible actuates the clamps of the device and releases the ballast leaving the latter attached to the lowering line. The device, having an effective "weight" of approximately 50 Kg, is then transported by the submersible to its final site. The submersible is guided to the site using an acoustic transponder navigation system (ATNAV) and on locating the pipe whose end has been rough cut in preparation, loads the device onto the pipe and re-energises the clamp to retain it firmly on the pipe.

A buoy, which has been carried in the docking station of the device, is then released to return to the surface. On reaching the surface it is located by the surface support ship which then launches the equipment carrier. The hauldown line, attached to the release buoy, is transferred to the carrier and preparations made for the winch of the device to start hauldown operations.

At this junction it should be noted that a system for flooding the boom of the carrier may be incorporated to increase the angle of descent of the carrier. The carrier descends nose first and its connector mates with the connector of the device so that the carrier is clamped to the device (and hence to the pipe) in its natural descent position. The carrier is then manoeuvred into the desired position by first rotating the winch member with respect to the base member by means of the slewing mechanism to give correct orientation and then moving the pivoted arm with respect to the winch member by means of the ram to align the equipment with the pipe end.

Control is then transferred from the device to the carrier so as to cause the equipment supported by its buoyancy systems, to run along the boom to the position where it is to carry out the operation on the pipe. It is possible to move the equipment in stages along the boom and it is also possible to clamp the equipment to the pipe and then release the clamps of the device thereby enabling the latter to be moved further along the pipe. These operations can be repeated at will to enable progress to be made along the pipe.

The above operations relate specifically to loading machinery onto the axis of the pipe but it should be noted that the system can be readily used to place other items astride the pipe or on the seabed.

Recovery of the apparatus is broadly, a reverse of the hauldown operation above described after the boom, if flooded, has been emptied of water by means of a supply of compressed air carried on the equipment carrier.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings, in which: Figure 1 is a schematic view of a device and an apparatus of the present invention at a first stage during the effecting of a working operation on an underwater pipe by the method of the present invention; Figure 2 is a perspective schematic view of the device and apparatus of Figure 1 at a later stage in effecting the method; Figure 3 is a schematic view similar to that of Figure 1 showing the device and apparatus at a further stage in effecting the method; Figure 4 is an end view of the device shown in Figures 1,2and3; Figure 5 is a schematic view of the device of Figures 1 to 4 in combination with an alternative form of apparatus in accordance with the invention;; Figure 6 is a schematic view of another device and apparatus in accordance with the invention; Figure 7 is a schematic view of a further device and a further apparatus of the present invention at a first stage during the effecting of a working operation on an underwater pipe by the method of the present invention; Figure 8 is a schematic view similar to that of Figure 7 showing the device and apparatus at a further stage in effecting the method; and Figure 9 is a schematic view similar to that of Figure 8 showing the device and apparatus at a stiil further stage in effecting the method.

Referring first to Figure 4 there is shown a winching device suitable for use in juxtaposing the underwater pipe and an apparatus initially located at the water surface. The device comprises a first member generally denoted by referenc numeral 1 which includes a means of securing the device to the pipe, a second member 12 including a connector for engagement with the carrier, and a third member 8 carrying a winch and articulated between the first and second members.

The first member 1 includes an inverted Ushaped base portion comprising spaced limbs 3 and 4 and a saddle-like bridging member 2.

Located at the periphery of each limb 3 and 4 is a pipe clamp member 5 pivotally mounted on the limb and linked to the limb by an hydraulic cylinder 6. The cylinders 6 are arranged to move their respective clamp members 5 between pipe clamping positions (as shown in Figure 1) and open positions in which they do not co-operate with the pipe. Rotatably mounted on the bridging member 2 is a turntable 7 supporting the third member 8.'The U-shaped base portion includes a hydraulic drive motor 9 to rotate the third member 8 with respect to the base-portion.

Rollers 10 (shown in dotted lines only) are provided on the bridging member 2. Buoyancy tanks 40 (not shown in Figures 1, 3 and 4) are secured to the third member 8.

The third member 8 is in the form of a fabricated box which carries a hydraulically driven winch denoted generally by reference numeral 11 and which serves as a mounting for the second member 1 2 which is in the form of a pivotable arm. A hydraulic cylinder 41 (see Figures 1 and 3) is operably connected between the second and third members so as to pivot the arm about axis 1 3 with respect to the third member 8. The arm 1 2 includes a connector at its free end in the form of a conical female docking guide 14 and the axis 13 carries a guide pulley 1 3a for the hauldown line 15.

Referring now to Figures 1, 2 and 3 there is shown the device of Figure 4 in combination with a buoyant apparatus in accordance with the present invention. The apparatus is generally denoted by reference numeral 20 and incorporates a buoyant carrier in the form of a hollow boom 21 upon which is mounted equipment in the form of a frame 22 carrying a pipe cutting machine 23. The machine 23 is an orbital cutting machine including a cutting tool mounted for rotation within the frame 22. The frame 22 also carries buoyancy tanks 24 and is moveable along the longitudinal axis of the boom 21 via a chain winch mechanism. The chain winch mechanism comprises a chain 25 having its ends secured to the boom 21 at positions longitudinally displaced along the boom. A sprocket wheel (not shown) is mounted on the frame 22 so that it is in engagement with the chain.A hydraulic motor (not shown) is provided for rotating the sprocket wheel thereby to cause the equipment to be displaced along the boom 21. A connector in the form of a male docking member 27 is provided at the free end of the boom 21 (see Figures 1 and 3).

In use of the apparatus and the winching device of the present invention in carrying out a working operation on an underwater pipe in accordance with the instant invention, the winching device is launched from a suitable vessel and is manoeuvred by, for example, a submersible so that it is seated on the pipe (denoted by reference numeral 30) at a desired position adjacent to the end of the pipe. The device is supported from a buoy (not shown) via a haul down line passing through the female docking guide 14 and is carried in a claw of the submersible from its drop point to its final location. The attitude of the device when suspended from the buoy is such that the open end of the device (as defined by the limbs 3 and 4) is directed downwardly.In this way, the device can be lowered onto the pipe so that it straddles the same with the limbs 3 and 4 passing on opposite sides of the pipe and the rollers 10 in contact with the top of the pipe. Alternatively, the same result can be achieved by sliding the device on to the end of the pipe. The rollers 1 0 enable the device to be moved along the pipe to a desired position. Preferably, a sonic locating device (a so called pinger) is provided on the device to enable the submersible to find the same at the drop point and similarly it is preferred to provide a pinger on the pipe itself to aid the navigation of the submersible to the pipe end.

The relative dimensions of the limbs 3 and 4 and the pipe 30 should be such that the clamp members 5 are over-centre locking clamps. Thus, once the device is straddling the pipe in the desired position the submersible or diver actuates the hydraulic cylinders 6 so that the clamp members 5 move to their clamping positions in which they engage with the underside of the pipe and hold the device securely to the pipe so that the device constitutes a firm anchoring point. The arrangement is such that the submersible or the diver is then able to affectively release the winch and thereby ailow the buoy to carry the haul down line to the surface for connection to the apparatus 20 which, at this stage, is floating at the surface with the axis of the boom 21 in a generally horizontal plane.The line is connected to the body via the male docking member 27 and this connection can be effected by a surface swimmer or by the crewman of a small boat.

Once the line has been connected to the apparatus 20, the operation of the winch is commenced by the submersible or the diver, so that the line is gradually drawn in. The resultant pull of the line on the apparatus turns it so that the boom 21 is in a generally vertical plane.

Whilst current drag on the apparatus will affect the direction of haul-down in an unpredictable manner, generally the axis of the boom 21 will lie on a continuation of the haul down line. The length of the line is reduced by the winch until the male docking member 27 is engaged in the female docking guide 14. The member 27 and guide 14 are then locked together by means of a hydraulic locking system (not shown). The attitude of the apparatus 20 when first engaged with the device is shown in Figure 1. Figure 2 also shows the apparatus 20 in this attitude as denoted by reference A. Further tension in the haul down line and operation of the hydraulic cylinder 41 then causes the arm 12 to pivot about the axis 13 so that the boom 21 is in a general horizontal plane. Thus, the carrier and the machine 23 carried thereby are moved with respect to the anchoring point.The attitude of the apparatus at this stage is denoted by reference B in Figure 2 and is shown in Figure 3. The relative dimensions of the winching device 1 and of the apparatue 20 are such that when the boom 21 is in a generally horizontal plane the frame 22 is, or can be upon appropriate rotation of the member 8 on turn-table 7, coaxial with and spaced from the end of the pipe 30.

In order to complete the relocation of the machine 23 with respect to the anchoring point, the machine 23 is then moved onto the pipe by operating the chain winch mechanism, the actuation of the same being effected by the submersible or diver. Thus the frame 22 and the machine 23 are driven forwardly with respect to the boom 21 and onto the end of the pipe. Once in the desired position, as shown by reference 29 in Figure 3, the frame 22 is clamped onto the pipe by hydraulic locking rams (not shown). The machine 23 is then actuated by the submersible or diver so that its cutting tool rotates with respect to the frame 22 and about the circumference of the pipe 30 so that it severs the pipe at the desired position. After the pipe has been cut the apparatus 20 and the device 1 can be removed from the pipe by a reversal of the above procedure.

It can be seen from the foregoing that, although the apparatus 20 follows an unknown path down to the pipe, the path does terminate at a fixed position and that once the apparatus is at this fixed position, it is then manoeuvred with respect to the structure so that its equipment is located in a desired position.

A particularly preferred feature of the present invention is that the apparatus is buoyant. Thus, if it should be that the haul down line should break, the apparatus will rise to the surface and will not be lost as would be the case if it were more dense than water. A similar situation would occur in the event of winch failure.

Referring now to Figure 5, parts corresponding to parts of Figures 1 to 4 are denoted by like reference numerals.

In this embodiment, the equipment mounted on the hollow boom 21 comprises frame 22 and a pipe coupling member 40 carried by the frame. ln use, the apparatus comprising the boom 21 and the equipment is puiled down to the winching device and secured thereto in the manner previously described. Thereafter the device is articulated so that the coupling member 40 is coaxial with the pipe, the end of which has previously been prepared so as to remove the concrete and protective coatings therefrom. The coupling member 40 is then moved along the boom 21 by means of the chain winch mechanism so that it is in the desired position with its end fitted over the end of the pipe.The pipe may then be secured to the coupling member 40 by for example, explosive welding and the other end of the coupling member may be joined to some other pipe in a suitable manner so that a connection is provided between the two pipes.

Referring now to Figure 6, parts corresponding to parts of Figures 1 to 4 are denoted by like reference numerals.

In this embodiment, the base portion of the winching device is in the form of a framework upon which the turntable 7 is mounted and including a supporting platform 50 carrying a plurality of depending legs 51.The legs 51 are hollow and are provided with a plurality of apertures (not shown). A means (not shown) is provided to pump water through the legs 51 and out through the apertures. In this embodiment, the frame 22 of the boom 21 carries a component 52 for location at a desired position underwater.

In use, the winching device is placed on the seabed as close to the desired position as possible and water is pumped through the legs 51 and out through the apertures to fluidise the seabed in the vicinity of the legs 51. Thus the legs 51 sink into the seabed. The water flow is then stopped to allow sand and silt to settle around the legs and secure the framework to the seabed. The apparatus comprising the boom 21 and component 52 is then hauled down to the winching device as previously described and the component 52 is then manoeuvred into the desired position by appropriately articulating the device and appropriately actuating the chain winch mechanism of the boom 21.

Referring now to Figures 7, 8 and 9, parts corresponding to parts of Figures 1 to 4 are denoted by like reference numerals. In this embodiment, the equipment mounted on the boom 21 is in the form of a means of moving the pipe laterally across the ocean floor. This means is in the form of a beam 60 mounted on frame 22 which, as before, is longitudinally moveable along the boom 21 by means of a chain winch mechanism (not shown). The beam 60 is itself mounted so that it may be moved with respect to the frame 22 in a direction generally normal to the longitudinal axis of the boom 21. A second chain winch mechanism of which only the chain 63 is shown, similar to the first, is provided to move the beam 60 in said direction. Mounted on the beam 60 is a pair of legs 61 which can be raised or lowered by means of a hydraulic ram (not shown).A buoyancy tank 62 is provided at each end of the beam 60.

In use, the apparatus comprising the boom 21 and the pipe moving equipment is pulled down to and engaged with the winching device secured to the pipe 30 in the manner previously described.

Thereafter the winching device is articulated so that the frame 22 is aligned with the pipe 30 and the frame 22 is then moved along the boom 21 by means of the chain winch mechanism until it is astride the pipe 30 in the desired position (see Figure 7). It is then clamped to the pipe by hydraulic locking rams (not shown). In order to move the pipe laterally, the legs 61 are extended downwards so as to lift the pipe 30 and the frame 22 away from the ocean floor (see Figure 8).

Then, the second chain winch mechanism is actuated so as to move the frame 22 and pipe 30 laterally along the beam 60 (see Figure 9). After lifting the legs 61 so that the pipe 30 and frame 22 rest on the floor once more, the beam 60 can then be moved with respect to the frame 22 and pipe 30 so that the above cycle can be repeated until the desired amount of lateral movement has been achieved.

Although the present invention is primarily concerned with placing equipment on the seabed for the repair of pipelines in deep water, it is not exclusively limited to either pipelines or deepwater: On the contrary, it is capable of operation by divers using supplies from, say, a diving bell. Neither is it exclusive to the repair of pipelines. The invention can be carried out using more than one haul down device attached to the ends or corners of a large object yet is also suitable for accurate location of small objects.

Typically it may also be used to place long lengths of pipe in the form of spool pieces, drilling templates and transponders.

Claims

1. A method of placing an object in a desired position underwater which method comprises (i) securing one end of a line to the object and the other end of the line to an underwater anchoring point in the vicinity of said desired position, (ii) reducing the length of the line until the object is drawn to the anchoring point, and (iii) moving the object from the anchoring point to the desired position.

2. An apparatus for placing an object in a desired position underwater, which apparatus comprises in combination.

(a) a carrier, (b) the object mounted on the carrier, (c) a device having means for securing it to an underwater anchoring point in the vicinity of said desired position, (d) a line linking the device and the carrier, (e) a means of reducing the length of the line so as to draw the carrier to the device at the anchoring point, (f) a means of connecting the carrier and the device together at the anchoring point, and (g) a means of moving the object with respect to the anchoring point to place the object at the desired position.

3. An apparatus as claimed in Claim 2 wherein said means of reducing the length of the line is a winch mounted on said device.

4. An apparatus as claimed in Claim 2 or 3 wherein said device includes (a) a first member provided with the means for securing the device to the anchoring point, (b) a second member articulated to the first member and provided with a means of forming a connection with the carrier, and (c) a means to articulate the members with respect to one another so as to move the carrier, and the object carried thereby, with respect to the anchoring point when the carrier and the device are connected together at the anchoring point.

5. An apparatus as claimed in Claim 4 when appendant to Claim 3 wherein said device includes a third member carrying said winch and connected between the first and second members.

6. An apparatus as claimed in Claim 2, 3, 4 or 5 wherein the object mounted on the carrier is moveable with respect to the carrier.

7. An apparatus as claimed in any one of Claims 2 to 6 wherein the object is equipment for carrying out an underwater operation at said desired position.

8. An apparatus as claimed in Claim 7 wherein the equipment is a machine for cutting or turning a pipe located at the said desired position.

9. A method in accordance with Claim 1 substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.

10. An apparatus as claimed in Claim 2 substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 4 of the accompanying drawings.

11. A device for use in accordance with the method of Claim 1 for juxtaposing an underwater structure and an apparatus located at the water surface and comprising a carrier and equipment for effecting an operation on the structure, which device comprises (a) a means of securing the device to the structure, (b) a winch for hauling the apparatus down from the surface into juxtaposition with the structure, and (c) a connector for engagement with the carrier so as to form a connection between the device and the carrier when the apparatus is in juxtaposition with the structure.

12. A device as claimed in Claim 11, which comprises (a) a first member incorporating the means of securing the device to the structure, (b) a second member incorporating said connector, and (c) a third member incorporating the winch, the first and second members being articulated to the third member.

13. A device as claimed in Claim 11 or 12 and for use in juxtaposing the apparatus with an underwater structure in the form of a pipe, wherein said means of securing the device to the structure includes a U-shaped portion comprising (a) a pair of spaced limbs arranged to pass on either side of the pipe, and (b) a bridging member linking the limbs, said portion including moveable clamps for engagement with the pipe.

14. A device as claimed in Claim 13 wherein the winch is supported on a mounting which is rotatable with respect to the U-shaped portion and a means is provided to rotate the mounting.

1 5. A device as claimed in Claim 14 wherein an arm is pivotally secured to the mounting, said device additionally including a means of pivoting the arm with respect to the mounting and said arm carrying said connector at its free end.

16. A device as claimed in any one of Claims 11 to 1 5 and additionally including a buoyancy tank.

17. A device as claimed in Claim 11 substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 4 of the accompanying drawings.

1 8. An apparatus for carrying out an operation at a desired position on an underwater structure and for use in conjunction with the device of Claim 11, which apparatus comprises (a) equipment for carrying out the operation, (b) a carrier for supporting the equipment and for hauling down from the water surface to the vicinity of the underwater structure, and (c) a means of connecting the carrier to the structure when in said vicinity, the equipment being moveably mounted with respect to the carrier so that it may be moved to said desired position when the carrier is connected to said structure.

19. An apparatus as claimed in Claim 18 wherein the carrier is in the form of a boom and the equipment is mounted for axial movement along the boom.

20. An apparatus as claimed in Claim 19 wherein the connecting means is in the form of a connector located at a free end of the boom.

21. An apparatus as claimed in Claim 18, 19 or 20 wherein the underwater structure is in the form of a pipe and the equipment is a pipe cutting or pipe turning machine.

22. An apparatus as claimed in Claim 18 substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 3 of the accompanying drawings.

23. In combination, a device as claimed in any one of Claims 11 to 1 7 and an apparatus as claimed in any one of Claims 18 to 22.

24. A method in accordance with Claim 1 substantially as hereinbefore described with reference to Figure 5 or Figure 6 or Figures 7 to 9 of the accompanying drawings.

25. An apparatus as claimed in Claim 2 substantially as hereinbefore described with reference to Figure 5 or 6 or Figures 7 to 9 of the accompanying drawings.

26. A device as claimed in Claim 11 substantially as hereinbefore described with reference to and as illustrated in Figure 6 of the accompanying drawings.

27. An apparatus as claimed in Claim 1 8 substantially as hereinbefore described with reference to and as illustrated in Figure 5 or 6 or Figures 7 to 9 of the accompanying drawings.