GB2272240A - A method of and apparatus for transporting an object to an underwater location - Google Patents

Abstract

A Method of transporting an object (1) to an underwater location includes coupling the object (1) to a submersible structure (5). The submersible structure (5) with the object (1) is propelled to a location on the surface of the water in the vicinity of the underwater location and the submersible structure (5) and object (1) are submersed until the submersible structure (5) or the object (1) touch the seabed. Subsequently, the submersible structure (5) is uncoupled from the object (1). The structure has adjustable buoyancy means in the form of variable ballast tanks (21) and a buoyancy tube (40). Thrusters (20a) are provided to drive the structure (5) when submerged. <IMAGE>

Description

"A Method of and Apparatus for Transporting an Object to an Underwater Location" The present invention relates to transporting means and especially to a method for transporting an object to an underwater location and apparatus for use in the method.

At present subsea structures are installed at offshore locations using heavy lifting barges and this is an expensive operation which is complicated often by the requirement to lift the subsea structure from a transport barge, an operation which requires calm sea conditions.

In accordance with a first aspect of the present invention, a method of transporting an object to an underwater location comprises coupling the object to a floating submersible structure, propelling the submersible structure with the object to a location on the surface of the water in the vicinity of the underwater location, submersing the submersible structure until the submersible structure or the object touches the seabed, and subsequently uncoupling the submersible structure from the object.

In accordance with a second aspect of the present invention, apparatus for transporting an object to an underwater location comprises a floating submersible structure, coupling means mounted on the submersible structure, adjustable buoyancy means mounted on the structure to permit the buoyancy of the structure to be altered, and propelling means mounted on the structure to propel the structure, wherein the coupling means is adapted to couple the object to the structure for transportation to the underwater location and the propelling means and the adjustable buoyancy means are used to locate the structure at the underwater location.

Preferably, the method further includes initially placing the object on the seabed and submersing the submersible structure to couple the object to the submersible structure. Typically, the method also further includes the steps of increasing the buoyancy of the submersible structure to raise the submersible structure and the object coupled to the submersible structure to the surface.

Preferably, the object may be placed on the seabed by the use of a dockside crane or inshore lifting barge.

Typically, the location of the seabed on which the object is placed prior to being coupled to the floating submersible structure is an inshore or coastal location.

Preferably, the step of submersing the submersible structure includes decreasing the buoyancy of the submersible structure and object until the submersible structure and object are substantially neutrally buoyant and thereafter propelling the submersible structure with the object towards the bottom using a propelling means.

Preferably, after the submersible structure has been uncoupled from the object, the submersible structure may have its buoyancy increased to raise the submersible structure to the surface.

Preferably, the propelling means is mounted on the submersible structure and may typically comprise thrusters or propelling units.

Preferably, the apparatus may further comprise ambient pressure monitoring means to monitor the ambient pressure in the vicinity of the submersible structure.

This permits an operator to monitor the depth of the submersible structure. Typically, the pressure monitoring means may comprise pressure sensors, such as bathymetric sensors.

The coupling means for coupling the object to the submersible structure may comprise a releasable latch device mounted on the submersible structure and may typically, also comprise an intermediate coupling device which is fixed to the object and the intermediate coupling device engages with the latch mechanism to couple the object to the floating submersible structure.

Preferably, the adjustable buoyancy means includes a ballast tank which may have ballast added or removed from the tank in order to alter the buoyancy.

Typically, the ballast tank is designed to be used with a liquid, such as water or seawater, as the ballast and the submersible structure includes means for permitting water to be introduced into the ballast tank or removed from the ballast tank.

Preferably, the submersible structure is reusable.

Typically, surveying means is provided to permit the underwater location to be located. Preferably, the surveying means comprises location means positioned on the seabed adjacent to the underwater location to permit the submersible structure to locate the underwater location at which the object is to be placed. Preferably, the location means may comprise transponders.

The submersible structure may be propelled to the location on the surface of the water by being towed by another vessel. Alternatively, the submersible structure may include self propelling means to propel the submersible structure to the location on the surface of the water.

The apparatus may be manned and controlled from a control station on the apparatus. However, preferably, the apparatus is remotely controlled by an operator at a control station remote from the apparatus. The remote control may be carried using an umbilical cable which conveys power and control signals to the apparatus from the remote control station. Typically, the remote control station may be located on another vessel.

In accordance with a third aspect of the invention there is provided a method for transporting a member constituting a subsea structure or a component part therefore from a dock to an underwater location, comprising lowering said member onto a seabed using a dockside crane or inshore lifting barge, locating over the said member a transporting device, the said transporting device being provided with propelling means to drive it in horizontal and vertical directions and with a bottom platform adapted to engage said member and with variable ballast means to provide operational buoyancy and additional control of descent and ascent of the said transporting device and with releasable connecting means to releasably connect the said transporting device with the said member, lowering the said transporting device whilst adding ballast thereto until the said bottom platform rests on the said member and connecting said bottom platform with said member by connection of the said releasable connection means, then raising said member and the said transporting device as a single connected unit whilst discharging ballast from said transporting device and transporting the said connected unit to an offshore location, thereafter lowering the said connected unit whilst adding ballast from the said transporting device, the descent and positioning of the said connected unit being regulated with input from a transponder array and bathymetric sensors provided via a support vessel until the said connected unit comes to rest on the seabed, disconnecting the said transporting device from the said member on the seabed by actuating release of the said connecting means where upon the said member remains on the seabed and the said transporting device is raised from the seabed whilst discharging ballast from the said transporting device.

Connection and disconnection of the said connection means may be effected by remote control, preferably automatically.

In accordance with a fourth aspect of the invention there is provided a transporting device suitable for use in the method, the device comprising propelling means to drive it in horizontal and vertical directions, a bottom platform adapted to engage the said member, variable ballast means, for instance variable ballast tanks, to provide operational buoyancy and additional control of descent and ascent of the said transporting device and releasable connecting means to releasably connect the said transporting device with the said member.

Two examples of a method of and apparatus for transporting an object to an underwater location in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figs. 1 to 6 show diagrammatically a first example of a transporting device in use; Fig. 7 is a side view of a second example of a transporting device; Fig. 8 is a top view of the transporting device shown in Fig 7; Fig. 9 is an end view of the transporting device shown in Figs. 7 and 8; Fig. 10 is a detailed end view of a part of the transporting device of Fig. 9 showing a latch mechanism in a disengaged position; and Fig. 11 is a detailed end view of a part of the transporting device of Fig. 9 showing a latch mechanism in an engaged position.

Fig. 1 is an end view of a subsea template 1 being lowered onto a seabed 4 by a dockside crane 3.

Fig. 2 shows in end elevation a first example of a transporting device 5 being located over the template 1. The transporting device 5 is provided with thrusters 20a, 20b (see also Fig. 8) to drive the device 5 in horizontal and vertical directions, respectively when submerged. The device 5 is also provided with a bottom platform 6 to engage template 1 and with variable ballast tanks 21 to provide operational buoyancy and additional control of descent and ascent to the transporting device 5. Also provided between the ballast tanks 21 is additional buoyancy in the form of a central buoyancy tube 40.

Fig. 3 in a further stage of the method shows in end elevation the transporting device 5 lowered into a position where the bottom platform 6 of the device 5 rests on the template 1. The platform 6 is connected to the device 5 by connecting means 10-12 (Figs. 9-11).

Fig. 4 in a further stage of the method shows in end elevation the raising from the seabed 4 of the transporting device 5 connected to the template 1 (via the platform 6) as a single connected unit. This is achieved by displacement of water from the ballast tanks 21 to increase the buoyancy of the transporting device 5.

The device 5 can then be towed to the desired offshore location using tow hooks 32 on each ballast tank 21 (see Figs. 5 and 6).

Fig. 5 is a further stage of the method in side elevation the single connected unit of Fig. 4 is transported to an offshore location wherein the seabed 4 is provided with an array of transponders 7. The device 5 also has a transponder (not shown) located on it. A support vessel 9 is linked to the device 5 by an umbilical cable 31 which provides power to and controls the device 50 and also transmits data to the vessel 9 to permit an operator on vessel 9 to monitor the status of the device 5. Bathymetric sensors are mounted on the device 5 and are linked to the umbilical 31 to give an operator on the vessel 9 an indication of the depth of the device 5. The umbilical 31 is coupled to the device 5 via a cable guide 30.

Fig. 6 is a final stage of the process shown in side elevation the single connected unit of Fig. 5 which has been lowered to the seabed 4, the descent and positioning of the single connected unit being regulated with by an operator on the vessel 9 in response to signals received from the transponders 7 and the bathymetric sensors 8. Upon actuation of the release of the connecting means 10-12 the template 1 remains on the seabed 4 in its new location and the transporting device 5 is raised from the seabed 4 whilst discharging ballast therefrom.

Fig. 7 is a side elevation and Fig. 8 a plan view, respectively, of a second example of a transporting device 50. The device 50 differs from the device 5 in that additional buoyancy is not provided by a central buoyancy tube 40 but instead is provided by side buoyancy tubes 41.

Fig. 9 is a cross section of the transporting device 5 showing connecting means 10 to connect the device 5 with the platform 6.

Fig. 10 is a detail in section of the connecting means 10 of Fig. 9 in a disconnected state, comprising a projecting cone 11 on the platform 6 and a conical aperture 12.

Fig. 11 is a detail in section of the connecting means 10 in a connected state.

In a preferred mode of operation of the method when the single connected unit is at the offshore location as seen in Fig. 5, the variable buoyancy tanks 21 of the transporting device 5 will be used to make the single connected unit (i.e. device 5, 50, platform 6 and template 1, where appropriate) neutrally buoyant in the water. The buoyancy tanks may be similar to those used in conventional submarines and can be flooded or partially flooded with water or filled or partially filled with air.

The thrusters 20b of the transporting device 5 to drive the devices 5, 50 in a vertical direction may then be employed to push the single connected unit to the seabed 4. As an alternative to, or in addition to, the thrusters 20a, 20b the propelling means may comprise propelling units. The thrusters 20b will generally be the prime means for controlling the descent of the single connected unit once a state of equilibrium in the water using the variable buoyancy tanks has been achieved; minor alterations to the variable buoyancy tanks may be required on descending to compensate for variations in water density.

With the invention it is possible to install heavy subsea structures, such as subsea templates, for instance up to eight hundred tons in water weight, at an offshore location.

Modification and improvements may be incorporated to the invention without departing from the scope of the invention.

Claims (13)

1. A method of transporting an object to an underwater location comprising the steps of coupling the object to a floating submersible structure, propelling the submersible structure with the object to a location on the surface of the water in the vicinity of the underwater location, submersing the submersible structure until the submersible structure or the object touches the seabed, and subsequently uncoupling the submersible structure from the object.

2. A method according to Claim 1, further comprising the steps of initially placing the object on the seabed and submersing the submersible structure to couple the submersible structure to the object on the seabed.

3. A method according to Claim 2, further comprising the step of raising the submersible structure and the object coupled to the submersible structure to the surface before propelling the submersible structure with the object to the location on the surface of the water.

4. A method according to Claim 3, wherein the step of raising the submersible structure comprises increasing the buoyancy of the submersible structure.

5, A method according to any of Claims 2 to 4, wherein the location on the seabed where the object is placed prior to being coupled to the submersible structure is an inshore or coastal location.

6. A method according to any of the preceding Claims, wherein the submersible structure is submersed by decreasing the buoyancy of the submersible structure until it is substantially neutrally buoyant.

7. A method according to any of the preceding Claims, wherein the submersible structure is submersed by using propelling means mounted on the submersible structure.

8. Apparatus for transporting an object to an underwater location, the apparatus comprising a floating submersible structure, coupling means mounted on the submersible structure, adjustable buoyancy means mounted on the structure to permit the buoyancy of the structure to be altered, and propelling means mounted on the structure to propel the structure, wherein the coupling means is adapted to couple the object to the structure for transportation to the underwater location and the propelling means and the adjustable buoyancy means are used to locate the structure at the underwater location.

9. Apparatus according to Claim 8, wherein the coupling means comprises a releasable latch device.

10. Apparatus according to Claim 9, wherein the coupling means also includes an intermediate coupling device which is attached to the object and which engages with the releasable latch device.

11. Apparatus according to any of Claims 8 to 10, wherein the adjustable buoyancy means includes a ballast tank.

12. A method of transporting an object to an underwater location, substantially as hereinbefore described with reference to any of the accompanying drawings.

13. Apparatus for transporting an object to an underwater location, substantially as hereinbefore described with reference to any of the accompanying drawings.