GB2144680A

GB2144680A - Method and apparatus for vessel repair

Info

Publication number: GB2144680A
Application number: GB08420128A
Authority: GB
Inventors: Hans Adels
Original assignee: Blohm and Voss GmbH
Current assignee: Blohm and Voss GmbH
Priority date: 1983-08-09
Filing date: 1984-08-08
Publication date: 1985-03-13
Also published as: GB8420128D0; SE448715B; SE8404028L; GB2144680B; FI843135A0; NO843144L; JPS6060091A; FR2550510A1; DE3328698C1; DK377584D0; FI843135A; NL8402459A; SE8404028D0; DK377584A

Abstract

A method of repairing underwater parts of a floating marine craft by partial docking is characterised in that, with an offshore platform, for example an offshore platform arranged on two hulls (2) and stabilising columns (3), a floating dock-like trough (5) provided to receive one of the surfaced hulls (2) is floated into place, its ballast tanks are blown until the hull (2) sits on the base (6) of the trough and the edges of the trough (7) surface, and finally that the remainder of the water still located in the trough (5) is pumped into compensation tanks (8) of the trough (5). <IMAGE>

Description

SPECIFICATION A method and apparatus for the repair of underwater parts of a floating or floatable marine structure The invention relates to a method and to an apparatus for the repair of underwater parts of a floating or floatable marine structure by partial docking.

By way of example a method of this kind is known for the repair of the rear part of large merchant or passenger ships, in particular for repair of the propeller bearings (German laying open print 26 12 994).

The present invention is concerned with the repair of marine structures such as offshore platforms and semi-submersible platforms which have multiple hulls. The repair of such structures is particularly difficult because their size would necessitate a very large dock installation, and the need to move the platform to such a dock installation gives rise to high costs and other problems associated with long term lack of utilisation. It is also possible to use two sinkable large pontoons for repairing an offshore platform, however the use of two sinkable large pontoons gives rise to high investment costs.

The invention is based on the problem of providing an apparatus for repairing underwater parts of floating marine structures, and to a method of using this apparatus, which is relative simple, inexpensive and does not give rise to long term lack of utilisation or high investment costs.

In order to solve this problem there is provided, in accordance with the present invention, a method repairing underwater parts of a floating or floatable marine structure by partial docking, characterised in that with an offshore platform, for example an offshore platform arranged on two hulls and stabilising columns, a floating dock-like trough provided to receive one of the surfaced hulls is floated into place, its ballast tanks are blown until the hull sits on the base of the trough and the edges of the trough surface, and finally that the remainder of the water still located in the trough is pumped into compensation tanks of the trough.

Also in accordance with the present invention there is provided an apparatus for repairing underwater parts of a floating or floatable marine structure having a plurality of hulls, in particular for carrying out the method of claim 1, characterised in that the apparatus comprises a trough having the shape of a substantially rectangular box open at its top surface, with the length, width and height dimensions of said box being matched to those of said hulls so that one of said hulls may be accommodated, at least partially, inside said trough; in that said trough is provided with ballast or stabilising tanks for varying the draft of the trough whereby to permit it to be floated into position beneath a said hull and permit its draft to be reduced so that said hull sits on the base of the trough and the edges of the trough surface; and in that means is provided for transferring the water still located in the surfaced trough into tank means of said trough, whereby the hull located inside the trough may be laid dry for repair without changing the buoyancy of the hull and trough arrangement.

In a preferred embodiment said tank means comprises compensation tanks provided in the longitudinal walls of said trough.

The ballast tanks are conveniently provided in the transverse end walls of the trough i.e. at the stem and stern of the trough.

The said tank means may also be defined, at least in part, within the ballast or stabilising tanks.

It is advantageous if the trough base has transverse stiffeners with wooden bearers for adaptation to the base of the hull which is to be laid dry.

This arrangement ensures, amongst other things, good load sharing amongst the transverse stiffeners along the hull and resistance to movement of the hull relative to the semi-floating docking trough.

The invention will now be described in more detail by way of example only and with reference to the accompanying drawings which show: Figures la and lb the trough of the invention shown in perspective and end views alongside a hull which is to be repaired, Figures 2a and 2b the trough of Figures 1a and 1b but in the flooded submerged state in which it is ready to be floated in beneath the hull to be repaired, Figures 3a and 3b the trough of Figures la, Ib and 2a, 2b floated into position beneath the hull to be repaired, Figures 4a and 4b the trough of the preceding figures after water has been displaced from the ballast tanks so that the trough has lifted and the hull is accommodated inside the trough, with the side edges of the trough lying above the waterline, Figures 5a, 5b and 5c the construction of the docking trough as seen in a longitudinal section, in plan view and in a perspective view, and Figures 6a to 6h a schematic representation of the use of a trough similar or identical to that of Figure 1 for the docking of a jack-up rig.

In Figure 1 the trough 5 is brought alongside the hull 2 which is connected with the platform 1 by stabilising columns 3. The trough 5 is held in this position by tugs (not shown). All tanks and the trough are empty. The transverse floor stiffners 12 are locally provided with wooden bearers.

In Figure 2 the tank 5 is flooded and the position and draft is controlled with the aid of the stabilising ballast tanks 9. Mooring lines are brought to the hull 2 and tugs assist the floating-in manoeuvre (not illustrated in detail). The trough 5 can also be displaced under the hull 2 from the inside, particularly if outwardly extending anchor cables are deployed.

Figure 3 shows that the trough 5 is brought into the correct position relative to the hull 2 by means of lines and tugs. The stabilisation tank and the compensation tank 8 are emptied. The edge 12 of the trough then emerges out of the water in a short time. The trough 5 is blown (emptied) until the hull 2 has emerged by several centimeters. As can be seen from Figure 4 the hull 2 is raised by several centimeters. The remaining water in the trough 5 is pumped into the compensation tanks 8 and into the stabilisation tanks 9. In this way the trough 5 is dry, the floating position of the semisubmersible platform does not however change.

The construction of the trough 5 can be seen from Figures 5a to Sc with reference to the reference numerals. The offshore platforms can be constructed both as semi-submersible platforms and also as jack-up rigs.

Figures 6a to 6h show the manner in which the trough can be used to repair a jack-up rig.

Figure 6a shows the jack-up rig in its normal operating state in which the operating platform 14 is supported above the surface of the sea on legs which engage the bed of the sea. In Figure 6b the platform 14 has been lowered so that it is floating on the surface. The trough is shown in the normal floating state alongside the platform. In Figure 6c one leg of the platform 14 has been raised and the trough has been partially submerged so that it may be floated in beneath the raised leg of the platform. Figure 6d shows the position after the trough has been manoeuvred into place beneath the jacked-up leg of the platform. In Figure 6e the tanks 8 and/or the tanks 9 have been partially blown or emptied so that the buoyancy of the trough has increased and the side edges of the trough support the platform adjacent the raised leg.In Figure 6f the leg has been lowered somewhat so that it sits on the base 6 of the trough.

The platform 14 is now jacked-up above the surface of the sea as shown in Figure 6g and this calls for increasing buoyancy at the right hand hull section of the platform in order to prevent bending loads on the leg contacting the bed of the sea. This increase in buoyancy is achieved by displacing further water out of the stabilisation and/or compensation tanks 8 and 9 as shown in Figure 6g. The uppermost side edges of the trough remain in contact with the underside of the associated hull section of the offshore platform as shown in Figure 6g, however the trough itself is full of water. As shown in Figure 6h the water inside the trough is then pumped into the compensation tanks 8 and/or into the stabilisation tanks 9 so that the interior of the trough is dry permitting repair work to be carried out on the platform but without changing the overall buoyancy of the trough.

Claims

1. A method of repairing underwater parts of a floating or floatable marine structure by partial docking, characterised in that with an offshore platform (1), for example an offshore platform arranged on two hulls (2) and stabilising columns (3), a floating dock-like trough (5) provided to receive one of the surfaced hulls (2) is floated into place, its ballast tanks are blown until the hull (2) sits on the base (6) of the trough and the edges of the trough (7) surface, and finally that the remainder of the water still located in the trough (5) is pumped into compensation tanks (8) of the trough (5).

2. Apparatus for repairing underwater parts of a floating or floatable marine structure having a plurality of hulls, in particular for carrying out the method of claim 1, characterised in that the apparatus comprises a trough having the shape of a substantially rectangular box open at its top surface, with the length, width and height dimensions of said box being matched to those of said hulls so that one of said hulls may be accommodated, at least partially, inside said trough; in that said trough is provided with ballast or stabilising tanks for varying the draft of the trough whereby to permit it to be floated into position beneath a said hull and to permit its draft to be reduced so that said hull sits on the base of the trough and the edges of the trough surface; and in that means is provided for transferring the water still located in the surfaced trough into tank means of said trough, whereby the hull located inside the trough may be laid dry for repair without changing the buoyancy of the hull and trough arrangement.

3. Apparatus in accordance with claim 2, characterised in that said tank means comprises compensation tanks provided in the longitudinal walls of said trough.

4. Apparatus in accordance with either of claims 2 or 3 and characterised in that said ballast tanks are provided in the transverse end walls of said trough.

5. Apparatus in accordance with either of claims 2 or 4, characterised in that at least part of said tank means is defined within said stabilising tanks.

6. Apparatus in accordance with any one of the preceding claims 2 to 5, characterised in that the trough base has transverse stiffeners with wooden bearers for adaptation to the base of the hull which is to be laid dry.

7. A method substantially as herein described with reference to and as shown in the accompanying drawings.

8. Apparatus substantially as herein described with reference to and as illustrated in the accompanying drawings.