WO2008132479A2

WO2008132479A2 - Diving bell assembly

Info

Publication number: WO2008132479A2
Application number: PCT/GB2008/001495
Authority: WO
Inventors: Lukasz Sobckaz
Original assignee: Divex Limited
Priority date: 2007-04-27
Filing date: 2008-04-28
Publication date: 2008-11-06
Also published as: GB0708165D0; WO2008132479A3

Abstract

A diving bell assembly has, in an embodiment, a pressure hull, a frame and two winch lines connected securely to the pressure hull. The winch lines are used to raise and lower the pressure hull and frame, and the assembly has an integral ballast device which is integral with either the frame or bell, for facilitating deployment of the assembly.

Description

Diving Bell Assembly

This invention relates to a diving bell assembly.

Diving bells are well known. Diving bells are typically launched from diving support vessels through a moon pool on the vessel and conventional diving bell assemblies typically comprise a number of distinct parts. The diving bell itself is typically surrounded by a protective cage, and is typically lowered from a winch located above the moon pool that is connected to a single line fixed to the diving bell, which bears the weight of the bell assembly during launch and recovery operations. The path of the bell from the moon pool to the seabed is typically guided by two guide wires that extend between the diving support vessel on the surface and a clump weight that is lowered below the diving bell. The guide wires loosely engage the frame, for example through clamps or runners on the frame, which allow the diving bell and frame to move relative to the guide wires. The clump weight (acting as ballast) suspended below the diving bell by means of the guide wires maintains stability of the diving bell and frame during deployment by keeping the guide wires in tension.

According to the present invention, a diving bell assembly comprises a pressure hull, a frame, at least two winch lines adapted to connect securely to one of the pressure hull and the frame, whereby the pressure hull and frame is raised and lowered by means of the two winch lines, and a ballast device integral with one of the frame and the bell.

The winch lines may be adapted to share the load of the pressure hull and frame during deployment of the assembly. The winch lines may be adapted to connect to one of the pressure hull and the frame at selected connection points for keeping the bell or frame in a level configuration during deployment of the assembly.

The assembly may comprise at least two winches from which the two winch lines extend.

Typically, three winches are provided. Each of the winches may have lines, wires or cables extending from winch drums located on the diving support vessel from which the diving bell assembly is deployed. The winches may be installed on a diving support vessel for lowering the diving bell assembly subsea by means of the winch lines.

The ballast device may be adapted to facilitate lowering of the pressure hull and frame. In particular, the ballast device may be provided in a lower portion of one of the hull and frame for preventing or reducing swinging of the hull and frame during deployment. The ballast device may comprise ballast in the form of one or more weights. The ballast may be arranged equidistantly around the circumference of the frame.

The winch lines are typically adapted to restrain the diving bell assembly against uncontrolled rotation. The pressure hull may define a central axis and winch lines may be attached to one of the pressure hull at attachment locations on opposing sides of and separated radially from the central axis.

The winch lines are typically fixed to the diving bell assembly, for example, to one of the pressure hull and frame. The winch lines may comprise end terminals of the winch lines or cables which are typically securely fastened to padeyes or the like on the pressure hull, so that a permanent connection is made between the diving bell assembly and the end terminal of each line or cable. The end terminals may engage the padeyes for transfer of or according weight of the diving the bell assembly to the winch lines.

In typical embodiments, the pressure hull has a cylindrical or spherical configuration with a central axis, and a first central winch line is provided near to the axis of the pressure hull, and the cable from the central winch is fixed onto the pressure hull. Typically, the assembly may comprise second and third side winches, having lines or cables that extend over sheaves that are optionally radially displaced from the central winch line, and which typically extend to fix onto side lugs on the pressure hull, or on the frame.

The frame typically comprises a base portion extending beneath the pressure hull, so as to space the lower portion of the pressure hull, which typically contains a hatch, from a landing stage for use by divers entering and leaving the hatch.

The landing stage may comprise, contain or support the ballast in the form of one or more weights. In certain embodiments of the invention, the ballast can be provided in two or more weights, optionally spaced equidistantly around the circumference of the landing stage. Typically, the side winch lines bear more load than the central winch line, so that the lines or cables extending from the side winches are in greater tension that the line or cable extending from the central winch. Typically, the central winch line is held in relatively constant tension. Typically, all or some of the winches can be synchronised to maintain the bell assembly in a level configuration. The plurality of winches can typically operate independently of one another, and therefore introduce greater redundancy in the system, so that the diving bell assembly can be recovered even in the event of the failure of one winch. In certain embodiments of the invention, a single winch can recover the diving bell to the surface. More specifically, a first winch and associated winch line may be configured to bear sufficient weight to allow the dive bell to be recovered to the surface using the first winch and winch line in the event of failure of another winch and/or associated winch line.

Typically, the assembly may include a heave compensator, and this may be active or passive in its operation in order to dislocate movement between the bell assembly and the vessel after deployment of the bell assembly from the vessel. In certain embodiments of the invention, both active and passive heave compensators are provided for controlling the movement of the bell. In this way, the assembly may include at least one heave compensator which may be operably associated with or operably coupled to the winches.

In a second aspect, the invention provides a method of deploying a diving bell assembly from a vessel, the diving bell assembly comprising a frame, a pressure hull, and a ballast device, and wherein the ballast device is integrated with one of the frame and the bell, the method comprising the steps of

-providing at least two winch lines between the vessel and the diving bell assembly;

-fastening each winch line to the diving bell assembly;

-sharing the load of the bell assembly between the two winch lines during launch or recovery of the bell assembly. Typically more than two winch lines are used, for example three winch lines. Typically each winch line is connected to respective winch. Typically each winch is provided with an independent motor, and advantageously, each winch is provided with more than one (e.g. two) independent motors.

Other method steps may be defined with reference to corresponding technical features of the first aspect of the invention.

In a further aspect, the invention provides a method of deploying a diving bell assembly from a vessel, the diving bell assembly comprising a frame, a pressure hull, and a ballast device, and wherein the ballast device is integrated with one of the frame and the bell, the method comprising the steps of: -providing at least two winch lines between the vessel and the diving bell assembly; and - fastening each winch line to the diving bell assembly.

The method may include the step of sharing the load of the bell assembly between the two winch lines during launch or recovery of the bell assembly.

Other steps may be defined with reference to steps of the second aspect of the invention and/or with reference to corresponding technical features of the first aspect of the invention.

In a yet further aspect, a diving bell assembly comprises a pressure hull, a frame, at least three winch lines adapted to connect securely to one of the pressure hull and the frame, whereby the pressure hull and frame is raised and lowered by means of the winch lines. Other features may be defined with reference to technical features of the first aspect of the invention and/or features corresponding to steps of the second aspect of the invention.

An embodiment of the invention will now be described, by way of example, and with reference to the accompanying drawings, in which

Fig 1 is a perspective view of a dive bell assembly being deployed from a diving support vessel;

Fig 2 is a perspective view of a heave compensation mechanism for the dive bell assembly shown in Fig 1 ; and Figure 3 shows a plan view of a winch deck for a diving bell assembly, showing the floor plan for the winches

Referring now to the drawings, a diving bell assembly 1 comprises a pressure hull 5 of generally cylindrical design, which is similar to conventional designs of pressure hull, and is adapted to withstand and maintain high pressure differentials between the interior and exterior of the pressure hull 5. The pressure hull 5 has an upper surface 5u and a lower surface 5I. The upper surface 5u has a cleat or padeye for attachment of a lifting wire 6 from a central winch 6w on diving support vessel. The lower surface 5I of the pressure hull 5 has a hatch 5h for access to the pressure hull 5.

The diving bell assembly has a frame 10 that is generally cylindrical in outline, and which generally surrounds the pressure hull 5. The frame 10 includes a fixed stage that provides a platform beneath the lower surface 5I of the pressure hull 5, facilitating access to the pressure hull 5 through the hatch 5h. The stage 10s of the frame 10 is weighted by ballast 15. The ballast 15 is typically arranged in a number of different weights, which are advantageously arranged equidistantly around the circumference of the stage 10s of frame 10. The ballast 15 is typically welded, bolted, integrated or otherwise immovably attached to the frame 10, or to the bell 5, typically at the lowest point on the frame and/or stage, so that the effective centre of gravity of the diving bell assembly 1 will be as low as possible. Thus, the ballast 15 is deployed subsea along with the bell 5 and frame 10. The weight distribution provided by the integration of the ballast helps to prevent swinging and provides lateral and rotational stability of the assembly at all deployment depths. The stage 10s or ballast 15 can optionally be separable from the rest of the assembly. For example, if a single bell installation is used it is common practice to allow the bell to become buoyant to allow emergency ascent. In this case, the stage 10s or ballast 15 could be ditchable by the divers from inside, optionally along with all the other connections such as the lift wires and umbilical. Also, if two bells are used then the stage 10s would not necessarily be ditchable, but could still be removable for transport and maintenance purposes, for example, by the surface crew.

Between the upper and lower surfaces of the pressure hull 5u/5l, there is a generally cylindrical side wall. It will be understood that in other embodiments the pressure hull takes a spherical form and has side walls curved accordingly. Attached to the side walls of the pressure hull on the outer surface thereof, there is provided a pair of padeyes, cleats or other connecting members welded, bolted or otherwise immovably secured to the cylindrical side wall of the pressure hull 5. Typically, the padeyes etc are spaced at diametrically opposed positions on the cylindrical wall of the bell, so that the padeyes on the cylindrical side wall and the cleat or pad eye on the upper surface 5u lie on the same diameter of the pressure hull 5. The padeyes on the cylindrical side walls provide permanent connection points for second and third lift wires 7 and 8 respectively. The lift wires 6, 7 and 8 are typically connected to their respective padeyes by means of shackles, bolts, or other typical permanent connection members, so that the lifting wire 6, 7, 8 are all immovably attached to the bell 5. It is possible for the lifting wires to be attached to the frame 10 instead of to the pressure hull 5, and such embodiments are within the scope of the present invention.

In certain embodiments, ends of the lift wires 6, 7 engage with the padeyes or other connecting member in use, e.g. during recovery or deployment of the bell, such that the weight of the assembly is felt by and is transmitted to the lift wires 6,7 through the engaging components. In one specific embodiment, the ends of the lift wires are provided with end terminals, for example a reinforced loop, which is designed to co-operate and engage with the padeye connecting member of the hull or frame. By virtue of the weight exerted on the end terminal, relative movement of the end terminal and lift wire with respect to the padeyes is avoided.

The lifting wires 6, 7 and 8 pass over sheaves located above the moon pool (not shown) in the diving support vessel, before being wound onto the respective winches. Typically, each winch is separately controlled, and has an individual drive motor, and typically each winch can have two independent drive motors, typically arranged as master and slave, optionally with full load sharing, and sized so that any single winch can safely recover the bell within safe distance of the vessel, for example a single winch and single motor is typically able to recover the bell to just below the vessel, within the range of the standby diver. In certain embodiments, the winches and motors can be sized so that any two winches can safely recover the bell assembly completely free from the moon pool to enable connection of the bell to the decompression chambers. In certain configurations of the present invention, each winch can have a separate motor supplied from different power sources, for example from different drive rooms, in order to increase the redundancy in the system and reduce the risk of single point failures leading to an inability to recover the diving bell assembly.

Provision of lifting wires attached as described above allows therefore the weight of the assembly to be shared between wires. Independently operable winches can also tension the wires to share loads accordingly.

The diving bell assembly can be supplied with an umbilical to supply power etc to the bell.

Each winch can be controlled electronically, and the system can be integrated, possibly using PLCs, to allow automation of certain functions. Embodiments of the invention could equally use hydraulically powered or hydraulically actuated winches.

Each winch can be provided with two independent braking systems, for example electro-hydraulic disc braking systems. Typically one brake can be controlled by the winch motor drive unit, and can act as a parking brake applied after an inverter drive has brought the winch to a stop. The brake can be failsafe so that in the event of power loss it is activated automatically. The second brake can be disabled by hydraulic pressure provided by an accumulator, but can be applied by manual release of the pressure, and is typically adapted to function as an emergency brake, which releases the pressure to apply the brake in the event of loss of power or manual selection. Typically, each winch has two braking systems, which in combination hold the bell load although the brake systems can be configured so that any single braking system (or pair of braking systems) can safely support the bell in the event of failure of one of the brakes.

Provision of the multiple winches and integral ballast in the dive bell assembly of the invention enables launching and recovery in higher sea states than was previously possible. In addition, the rotational stability of the dive bell assembly is improved, and the high weight reduces lateral drift due to mid-water currents. Additional advantages arise from the elimination of any impacts between the bell assembly frame and the traditional clump weight, since they are now integral parts. Furthermore, since the lifting wires are secured to the pressure hull or to the frame, this reduces the f rictional wear on wires that would otherwise need to move relative to the frame or the bell assembly. The elimination of moving parts between the lines and the bell assembly reduces the risks of wear on a power umbilical that is paid out separately. It enables the moon pool to be closed after the diving bell assembly has been recovered from the moon pool, as the whole assembly is typically recovered from the water, and avoids the need to disconnect the guide wires from the bell assembly during recovery. Typically the winches can share a common design, and dependencies on different spares can be reduced. More than three winch lines can be used, and additional winch lines can be added, optionally using additional winches, which could be identical to the winches described, in order to support the additional loads of heavier bell assemblies. For example, four, five or six or more winch lines can be provided, each typically extending from a separate winch. Modifications and improvements can be incorporated without departing from the scope of the invention.

Claims

1. A diving bell assembly comprises a pressure hull, a frame, at least two winch lines adapted to connect securely to one of the pressure hull and the frame, whereby the pressure hull and frame is raised and lowered by means of the two winch lines, and a ballast device integral with one of the frame and the bell.

2. A diving bell assembly as claimed in Claim 1 , wherein the winch lines are adapted to share the load of the assembly during deployment of the assembly.

3. A diving bell assembly as claimed in Claim 1 or Claim 2, wherein the winch lines are adapted to connect to one of the pressure hull and the frame at selected connection points for keeping the bell or frame in a level configuration during deployment of the assembly.

4. A diving bell assembly as claimed in any one of Claims 1 to 3, wherein the assembly comprises at least two winches from which the two winch lines extend.

5. A diving bell assembly as claimed Claim 4, wherein the assembly comprises three winches, the winches having respective winch lines extending from winch drums located on a diving support vessel from which the diving bell assembly is deployed.

6. A diving bell assembly as claimed in Claim 4 or Claim 5, wherein the winches are adapted to be installed on a diving support vessel for lowering the diving bell assembly subsea by means of the winch lines.

7. A diving bell assembly as claimed in any one of Claims 4 to 6, wherein two or more of the winches are synchronised to maintain the bell assembly in a level configuration.

8. A diving bell assembly as claimed in Claims 4 to 7, wherein the winches are configured to operate independently of one another.

9. A diving bell assembly as claimed in any one of Claims 4 to 8, wherein a first winch and associated winch line is configured to bear sufficient weight to allow the dive bell to be recovered to the surface using the first winch and winch line in the event of failure of another winch and/or associated winch line.

10. A diving bell assembly as claimed in any one of the preceding claims, wherein the ballast device is adapted to facilitate lowering of the pressure hull and frame.

11. A diving bell assembly as claimed in any one of the preceding claims, wherein the ballast device is provided in a lower portion of one of the hull and frame for preventing swinging of the hull and frame during deployment.

12. A diving bell assembly as claimed in any one of the preceding claims, wherein the ballast device comprises ballast in the form of one or more weights.

13. A diving bell assembly as claimed in any one of the preceding claims, wherein the winch lines are adapted to restrain the diving bell assembly against uncontrolled rotation.

14. A diving bell assembly as claimed in any one of the preceding claims, wherein the pressure hull defines a central axis and winch lines are attached to one of the pressure hull at attachment locations on opposing sides of and separated radially from the central axis.

15. A diving bell assembly as claimed in any one of the preceding claims wherein the winch lines are fixed to one of the pressure hull and frame.

16. A diving bell assembly as claimed in any one of the preceding claims, wherein the winch lines comprise end terminals securely fastened to padeyes on the pressure hull, so that a permanent connection is made between the diving bell assembly and the end terminal of each line or cable.

17. A diving bell assembly as claimed in Claim 16, wherein the end terminals engage the padeyes for transfer of weight of the diving the bell assembly to the winch lines.

18. A diving bell assembly as claimed in any one of the preceding claims, wherein the pressure hull has a cylindrical configuration with a central axis, and a first central winch line is provided near to the axis of the pressure hull, and the central winch line is fixed onto the pressure hull.

19. A diving bell assembly as claimed in Claim 18, wherein the assembly comprises second and third side winch lines that are radially displaced from the central winch line, and which extend to fix onto side lugs on the pressure hull, or on the frame.

20. A diving bell assembly as claimed in Claim 19, wherein the assembly comprises second and third side winches respectively comprising the first and second side lines which extend over sheaves radially displaced from the central winch line.

21. A diving bell assembly as claimed in any one of Claims 18 to 20, wherein the side winch lines bear more load than the central winch line.

22. A diving bell assembly as claimed in any one of Claims 18 to 21 , wherein the central winch line is held in relatively constant tension.

23. A diving bell assembly as claimed in any preceding claim, wherein the frame is stiffened to control rotational movement of the bell around its axis.

24. A diving bell assembly as claimed in any preceding claim, wherein the frame comprises a base portion extending beneath the pressure hull, so as to space a lower portion of the pressure hull, which contains a hatch, from a landing stage for use by divers entering and leaving the hatch.

25. A diving bell assembly as claimed in Claim 24, wherein the landing stage comprises ballast in the form of one or more weights.

26. A diving bell assembly as claimed in Claim 25, wherein the ballast is provided in two or more weights spaced equidistantly around the circumference of the landing stage.

27. A diving bell assembly as claimed in any one of Claims 4 to 9, or in any one of Claims 10 to 26 when dependent on any one of Claims 4 to 9, wherein the assembly includes a heave compensator operably coupled to the winches, the heave compensator being active or passive in its operation in order to dislocate movement between the bell assembly and the vessel after deployment of the bell assembly from the vessel.

28. A diving bell assembly as claimed in Claims 4 to 9, or in any one of Claims 8 to 27 when dependent on any one of Claims 4 to 9, wherein the assembly comprises both active and passive heave compensators for controlling the movement of the winches.

29. A method of deploying a diving bell assembly from a vessel, the diving bell assembly comprising a frame, a pressure hull, and a ballast device, and wherein the ballast device is integrated with one of the frame and the bell, the method comprising the steps of: providing at least two winch lines between the vessel and the diving bell assembly; and - fastening each winch line to the diving bell assembly.

30. A method as claimed in Claim 29, wherein the method comprises the step of sharing the load of the bell assembly between the two winch lines during launch or recovery of the bell assembly.

31. A method as claimed in Claim 29 or Claim 30, wherein the method comprises the step of using more three or more winch lines, each winch line connected to respective winches.

32. A method as claimed in Claim 31 , wherein the method comprises the further step of using the winches to control the load borne by the winch lines during deployment.