GB2156286A

GB2156286A - Installation and removal vessel

Info

Publication number: GB2156286A
Application number: GB08510822A
Authority: GB
Inventors: Anton Coppens
Original assignee: HEEREMA ENGINEERING
Current assignee: HEEREMA ENGINEERING
Priority date: 1985-04-29
Filing date: 1985-04-29
Publication date: 1985-10-09
Also published as: GB8510822D0

Abstract

A vessel (10) for installing or removing a deck module (16) on or from a platform structure with guides (24) is U-shaped, having an opening (11) within which the platform structure is located, and a bank of cranes (14, 15) on either side (12, 13) of the opening for suspending the deck module (16) over the opening (11). The deck module (16) is raised from or lowered onto the guides (24) of the platform structure whilst the vessel is anchored and the deck module is being suspended. The cranes (14, 15) may merely suspend the module (16) while the module (16) is raised or lowered by ballasting the vessel (10). Rails (18) may be provided to allow the module (16) to be moved to and from a storage position on the vessel deck. <IMAGE>

Description

SPECIFICATION Installation and removal vessel This invention relates to an installation or removal vessel and particularly, though not exclusively, to a vessel for use in installing or removing integrated decks or parts thereof on or from platform structures, or the structures themselves.

According to the present invention there is provided a vessel for use in installing or removing a deck or deck module on or from a platform structure in which there is an opening in the vessel which allows the vessel to be brought up to the platform structure with at least part of the platform structure located within the opening, in which the vessel has means for suspending the deck or deck module over the opening while the deck or deck module is lowered onto or raised from the platform structure.

The invention also provides a method of installing or removing a deck or deck module on or from a platform structure using a vessel as defined above which method comprises the step of bringing the deck or deck module into or out of engagement with the platform structure respectively while the deck or deck module is being suspended from the vessel.

By way of example, some embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a plan view of a vessel according to the invention; Figure 2 is a sectional view through the vessel carrying a deck module; Figure 3 is a plan view of the vessel in more detail, showing module positioning units.

Figure 4 is a side view of the vessel in more detail, showing a module jacking unit; Figure 5 is a sectional view through the vessel showing its use for sub-sea module installation or removal; and Figures, 6, 7 and8 show alternative forms of vessel.

As seen in Figure 1, a module installation or removal vessel 10 is U-shaped, having an opening 11 at one end defined between port and starboard sides 12, 13. The U-shape of the vessel enables it to be brought right up close to the platform structure so that the platform jacket of the structure is located preferably fully within the opening 11.

On each side 12, 13 of the vessel 10 there is provided a bank of cranes 14, 15. Two alternative types of crane are depicted in Figures 1 and 2. The cranes 14, 15 enable a module 16 to be suspended over the opening 11, as shown in Figure 2, so that it hangs above the surface of the water.

Preferably, there is a control means to ensure that the cranes 14, 15 operate in unison so that the module 16 is kept level, which can be fully automatic. In figure 2, the module 16 is an integrated deck structure which is to be fitted to the platform jacket of an offshore structure.

Prior to installation, the module 16 can be carried on the deck 17 of the vessel 10. Rails 18 are provided on top of the vessel 10 to enable the module 16 to be slid, skidded or wheeled along the rails 18 and into position over the opening 11 ready for installation. Blocks 19 are provided for supporting the module 16 over the opening while the cranes 14, 15 are hooked up to the module support frame 20, which in this case is integral with the module 16 itself, so that the module is supported from underneath. Additional girders may be required if the module support frame 20 is not itself strong enough, and the girders themselves may be braced by transverse connecting beams. The rail arrangement on deck avoids the need to equip the vessel 10 with slewing cranes for moving the module into position.

Because the boom tip 21 of the cranes 14, 15 can be quite close to the module support frame 20, only relatively small cranes are needed. The cranes 14, 15 may be equipped with cables or tension rods, and can have winches 22 with their own electrical power generators 23, but this is not essential.

The cranes 14, 15 may also incorporate a heave compensating device to keep steady the vertical position of the module 16 relative to the platform structure.

For installation, the vessel 10 is brought up close to the platform structure so that the platform jacket with its guides 24 is located within the opening 11, as shown in Figure 3. The vessel 10 is held in this position using a number of anchoring lines 25 which are tied to the sea bed, as shown in Figure 1. A nominal clearance is left around the platform jacket in the opening 11 to allow for a limited amount of wave-induced horizontal movement of the vessel 10. The module 16 can now be lowered from its suspended position onto the platform jacket or platform structure via the guides 24. The position of the module 16 relative to the guides 24 may be kept steady despite movement of the vessel 10 by means of hydraulic jacks 26, as shown in Figure 3. Of course, other means such as by hand lines or by cable and winch could equally well be used.The position of the module 16 relative to the guides 24 may be monitored, for example by means of laser, and means such as by computer may be used to operate the module positioning units automatically to keep the module position steady during installation. Naturally, the vessel 10 could equally well be used for the removal of a module 16 from a platform structure in which case, the above described steps are essentially the same but in reverse.

In Figure 4 it will be seen that the cranes 14, 15 themselves do not have to have a lifting capability: the module 16 can be lifted initially by means of hydraulic jacks 27, supported on blocks 18 and hooked up to the crane cables 29. The cranes 14, 15 may simply be required to suspend the module 16, in which case the module could be lowered into position on the platform jacket by ballasting the vessel 10.

Figure 5 shows how the vessel 10 can equally well be used for installing or removing sub-sea modules 16, such as well-heads, templates, foundations or complete structures. Here, the module 16' is lowered through the opening 11 in the vessel 10. Of course, it is necessary in this case for there to be additional girders spanning the opening 1 in order to support the module 16' while it is being hooked up to the cranes 14, 15. These additional girders can be moved on rails 18, or alternatively, revolving cranes may be used or the girdes can be retracted from the sides 12, 13 of the vessel 10.

In an alternative embodiment shown in Figure 6, the vessel 10 is provided with one or more heavy shear legs 30 for lifting and suspending the module 16. Of course, many different types of crane and combinations of types could be used, and the location of the cranes around the opening 11 in the vessel 10 could also be varied. The module 16 may incorporate lifting eyes 31 for hooking up to the cranes 14, 15. Instead of the opening being defined by a U-shaped vessel, the vessel 10 could of course be some other suitable shape, such as Tshape or possibly W-shape, and it may have more than a single opening 11.

In another alternative embodiment shown in Figure 7, the vessel 10 is a semi-submersible vessel and there may be cross-bracings 32 which link together two or more of the cranes 14, 15. This makes controlling the cranes 14, 15 in unison easier.

In a furhter alternative embodiment shown in Figure 8, the vessel 10 is a conventional floating barge or ship.

Claims

1. A vessel for use in installing or removing a deck or deck module on or from a platform structure in which there is an opening in the vessel which allows the vessel to be brought up to the platform structure with at least part of the platform structure located within the opening, in which the vessel has means for suspending the deck or deck module over the opening while the deck or deck module is being lowered onto or raised from the platform structure.

2. A vessel as claimed in Claim 1 wherein the opening is at the bow or stern of the vessel.

3. A vessel as claimed in Claim 1 or Claim 2 wherein the opening is defined by the vessel being U-shaped at least in part.

4. A vessel as claimed in Claim 1, Claim 2 or Claim 3 wherein the means for suspending the deck or deck module hangs by a tether, such as a cable, or tethers.

5. A vessel as claimed in Claim 4, wherein the vessel comprises means for lifting and lowering the deck or deck module onto and off the suspending means.

6. A vessel as claimed in Claim 4 or Claim 5 wherein the at least one boom is part of crane means and the crane means has power to lift and lower the deck or deck module.

7. A vessel as claimed in Claim 6 wherein there are a plurality of cranes and there is means for controlling operation of the cranes in unison so that the deck or deck module remains level.

8. A vessel as claimed in Claim 6 or Claim 7 wherein there are a plurality of cranes and there is means for controlling operation of the cranes to compensate for heave.

9. A vessel as claimed in any preceding claim comprising means for moving the deck or deck module to and from a storage position on the deck of the vessel from and to a position over the opening.

10. A vessel as claimed in Claim 9 wherein said moving means includes a pair of rails extending over the deck of the vessel and on two sides of the opening, along which rails the deck or deck module can be moved.

11. A vessel as claimed in any preceding claim further comprising means for adjusting the horizontal position relative to the vessel of the deck or deck module while it is being suspended over the opening.

12. A vessel as claimed in any preceding claim further comprising means for monitoring the horizontal position relative to the platform structure of the deck or deck module while it is being suspended over the opening.

13. A vessel as claimed in Claim 12 comprising means for operating said adjusting means automatically in response to said monitoring means.

14. A vessel as claimed in any preceding claim and further comprising means to span the opening and carry a module thereon, which means is removable from the opening.

15. A vessel as claimed in Claim 14 wherein the module is a sub-sea module, a platform structure or part of a platform structure which is lifted and lowered through the opening in the vessel.

16. A vessel substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

17. A method of installing or removing a deck or deck module on or from a platform structure using a vessel as claimed in any preceding claim which method comprises the step of bringing the deck or deck module into or out of engagement with the platform structure respectively while the deck or deck module is being suspended from the vessel.

18. A method as claimed in Claim 17 including the step of anchoring the vessel when the platform structure is at least partly located within the opening.

19. A method as claimed in Claim 18 wherein the deck or deck module is brought into or out of engagement with the platform structure by lowering or lifting the deck or deck module respectively onto or off the platform structure.

20. A method as claimed in any of Claims 17 to 19 including moving the deck or deck module from a storage position on the deck of the vessel to a position over the opening for installation of the deck or deck module, and vice versa for removal.

21. A method as claimed in any of Claims 17 to 20 wherein the module is a sub-sea module, a platform structure or part of a platform structure, and the method includes lifting or lowering the module through the opening in the vessel.

22. A method substantially as hereinbefore de scribed with reference to the accompanying drawings.