GB2173453A - A device relating to a semi-submersible craft - Google Patents

Abstract

A device relating to a semi-submersible craft having a deck structure (1) of several decks (9, 10, 11), which over a number of legs, at least one leg (2) in each corner, rests on two longitudinally extended pontoons (3, 4). The craft is particularly designed for diving or rescue operations at sea (DSV), having a work shaft (12) intended for raising or lowering, by means of cranes (13, 15, 16), equipment to be used at a diving operation and running vertically from the main deck down through the decks below, and two diving shafts (17, 19) in the lower deck, intended for launching and taking aboard diving bells (18, 20), at least one of which, the primary shaft (17), continues below the water surface, preferably in the main below the influence of waves, a pressure chamber (21) being devised on the lower deck in connection with the two diving shafts (17, 19). The primary shaft (17) is installed in one leg (2) of the craft and the second diving shaft (19) is installed in such proximity to the primary shaft that the diving bells (18, 20) for the two shafts (17, 19) can be coupled to the same pressure chamber unit (21). The work shaft (12) is installed so close to one of the diving shafts (19) that the diving bell (20) from this shaft can be directly coupled to a work chamber, lowered through the work shaft (12) for dry transfer of divers. In connection with the work shaft (12) on the main deck there is devised a gantry crane or a travelling crane (13) which runs on tracks (14). <IMAGE>

Description

SPECIFICATION A device relating to a semi-submersible craft The present invention relates to a device applicable to a semi-submersible craft having a deck structure of several decks which on top of a number of legs, at r st one leg in each corner, rests on two longitudinally extended pontoons, the craft being particularly designed for diving or rescue operations and having a work shaft, which is designed for raising and lowering, by means of cranes, equipment to be used in diving operations and which runs vertically from the main deck down through the decks below, and two diving shafts, which are designed for launching and taking aboard diving bells through the lower deck, at least one of which, the primary shaft, continues down below the surface of the water, preferably in the main below the influence of waves, pressure chambers being devised on the lower deck in connection with the two diving shafts.

Apart from the type of craft described above, ordinary vessels are also used, generally with a diving shaft or diving shafts devised midships. This is an advantageous placement with regard to the vertical movement of the diving bell in a seaway. However, it is not so advantageous as regards the movement of the diving bell on the horizontal plane, since the diving vessel must be positioned with its bow against wind and sea and a movement on the horizontal plane will then mainly occur as a pendulum movement with the bow as its center. Large horizontal swings of the diving shaft will thus occur. Another disadvantage concerning such vessels is that they, because of their relatively small size and displacement, will have a relatively strong movement in a seaway. On the open sea there will therefore be long periods where diving cannot be undertaken because of a heavy sea.

Diving crafts of the type mentioned by way of introduction have the advantage that they, in a semi-submersible work position, that is, with the pontoons submerged in the main below the influence of waves, show relatively small fluctuations in the vertical direction because of the heaving of the sea.

Previous diving crafts of this type have had their diving shaft or diving shafts devised on one side of the craft. The reason for this is that one thus can place the diving craft close to a structure, for example a fixed structure or a floating rig.

Much of the diving work takes place relatively close to such structures. The disadvantage of this placement, however, is that the movement of the diving shafts on the horizontal plane will be relatively large. The reason for this is that such crafts are usually positioned dynamically, that is, they are kept against the weather by means of propellers. It will be too expensive and too time-consuming to anchor up such platforms. This will then greatly restrict the time during which diving can take place, since for long periods of time there will be too much wind, sea or current for positioning the craft in such a way that there will not be too large horizontal movements of the diving shafts.

It is an object of the invention to provide a device, applicable to a semi-submersible craft, by which diving can be undertaken close to existing structures at the same time as diving can be undertaken for longer periods than before, since the craft is less depend upon wind and weather.

Accordingly, the invention in one aspect provides a device relating to a semi-submersible craft, having a deck structure of several decks which on top of a number of legs, at least one leg being in each corner, rests on two longitudinally extended pontoons, there being a work shaft for raising or lowering, by means of crane means equipment to be used in a diving operation and which runs substantially vertically from the main deck down through the decks below, and two diving shafts in the lower deck, which are designed for launching and taking aboard diving bells, at least one of which, the primary shaft, continues down below the surface of the water, and a pressure chamber unit being arranged on the lower deck in connection with the two diving shafts, the primary shaft being in one leg of the craft and the second shaft being installed in such proximity to the primary shaft that the diving bells for the two shafts can be coupled to the pressure chamber unit, and the work shaft and one of the diving shafts being in such proximity that the diving bell from the one shaft can be coupled directly to a work chamber, lowered through the work shaft for dry transfer of divers.

According to another of its aspects the invention provides a device relating to a semisubmersible craft having a deck structure of several decks which on top of a number of legs, at least one leg in each corner, rests on two longitudinally extended pontoons, the craft having a work shaft for raising or lowering, by means of cranes equipment to be used in a diving operation and which runs substantially vertically from the main deck dowh through the decks below, there being two diving shafts in the lower deck, which are designed for launching and taking aboard diving bells, one of which at least, the primary shaft, continues down below the surface of the water, and there being a pressure chamber on the lower deck in connection with the two diving shafts, the primary shaft being installed in a leg of the craft, the other diving shaft being installed in proximity to the primary shaft, the diving bells from the two shafts being adapted to be coupled to the same pressure chamber unit, the work shaft being installed so close to one of the diving shafts that the diving bell from the one shaft can be coupled directly to a welding chamber (habitat) or the like, lowered through the work shaft for dry transfer of divers, the legs of the craft having a longitudinally extended cross section with their longitudinal axis pointing in the direction of the craft's headway, and all bracing of the legs being above the waterline.

When the primary shaft is installed in one leg of the craft, one will position the craft with this leg, that is, one corner of the craft, against wind and sea, and a possible pendulum movement will occur with this leg or this corner as its center. One thus achieves minimal horizontal movement. By the very fact that the second diving shaft is installed so close to the first one that they can be served by then same pressure chamber unit, the horizontal movement of this diving shaft will also be relatively small. Apart from this advantage and the one mentioned above, viz. that the two diving shafts can be served by the same pressure chamber unit, one also obtains the further advantage that, when the bells from both shafts are used, the crew can cooperate on a common task without having to move particularly far on the horizontal plane.

The characteristic that the work shaft is installed so close to one diving shaft means, as previously stated, that one can make a socalled dry transfer of a crew from a diving bell to, for example, a welding chamber. This offers the same advantage as the one mentioned above, viz. it saves the divers from covering the distance between the diving bell and the welding chamber. Any movement is very exhausting for a diver, especially at a great depth, and will reduce a work capacity which is small enough from before. In addition to the movement between the diving bell and the work chamber, it also saves the divers the opening of doors in and out of sluices.

Another characteristic of the invention consists in installing, in connection with the work shaft, a gantry crane or a traveling crane on the main deck. By means of such a crane the equipment, for example a welding chamber, can be moved far more accurately and carefully than by the jib cranes normally used, which are installed on the main deck and mainly used for handling of goods to and from the craft.

In addition to the gantry crane or traveling crane, one or more jib cranes may be installed.

A further object of the invention is to give directions for a device relating to a craft of the type mentioned by way of introduction, by means of which one in addition to the above advantages achieves great speed and mobility with the craft in its transport position.

Crafts of this type will often have long periods without assignments. A demand for the assistance of such a craft can suddenly arise, if an accident or a mishap has occurred. The craft which then can move fastest will obviously have a great advantage as far as assignments are concerned. Crafts of the above type can usually only move at a very low speed, for example 3-4 knots. Situations will thus easily arise where current and wind in fact move at a greater speed, so that one in reality will have a negative velocity for the craft. Such crafts are therefore as a rule dependent upon the assistance of tugboats, which is very costly.This disadvantage is eliminated by means of a device relating to a craft of the type mentioned by way of introduction, which is characterized by a combination of features, viz. that the primary shaft is installed in one leg of the craft, that the other diving shaft is installed in such proximity to the primary shaft that the diving bells for the two shafts can be coupled to the same pressure chamber unit, that the work shaft is installed so close to one diving shaft that the diving bell from this shaft can be coupled directly to a welding chamber or the like, lowered through the work shaft, for dry transfer of divers, that a cross section of the legs has an elongated shape, oval, streamlined or the like, pointed in a forward direction, and that all bracing of the legs is provided above the waterline.

By means of such an embodiment, the craft will be capable of relatively high speed, for example 10-12 knots by its own motors, and this relatively high speed combined with the possibilty of longer diving periods than nor mal, makes the craft more competitive and thereby more profitable.

The invention is hereinafter described, by way of example, with reference to the accompanying drawings.

Figure 1 shows a craft according to the invention seen from astern; Figure 2 shows the craft of Fig. 1 seen from the starboard side; Figure 3 shows the main deck of the craft of Fig. 1 seen directly from above; and Figure 4 shows the lower deck of the craft of Fig. 1 from above.

The semi-submersible craft according to the invention consists of, in the main, a deck section 1 which on four legs 2, one in each corner, rests on two longitudinal pontoons 3, 4. During transport the craft is lowered down to the waterline 5 and during work to the waterline 6. Each pontoon is equipped with several propellers 7, 8, for example of the type Thruster. In the shown embodiment there are three decks in the deck section, a main deck 9, an intermediate deck 10 and a lower deck 11.

On the main deck 9 there is installed a work shaft 12 which runs vertically down through all three decks. In connection with the work shaft there is installed a gantry crane or a traveling crane 13, which can run on tracks 14 and which has a crab, not shown, for crosswise movements on the crane. In addition to the gantry crane 13 there are installed two jib cranes 15, 16 which also can service the work shaft. These cranes can, for example, transfer equipment of different kinds, to be used in connection with the work shaft, from a delivery boat to the craft and vice versa.

On the lower deck, Fig. 4, there is installed a diving shaft 17, which runs down through one leg 2 to an area in the main below the influence of waves. Through this shaft a diving bell 18 can be lowered by conventional hoisting equipment, not shown. Approximately diagonally beyond the diving shaft 17 there is installed a second diving shaft 19 with a separate diving bell 20. This shaft runs only through the deck section, and the diving bell is moved in the open down from the deck section to the surface of the sea 6. In connection with the two diving shafts there is devised a pressure chamber unit 21, which is divided into three chambers 22, 23 and 24 with different pressures. The chamber 22 is connected to a lifeboat with a pressure chamber.This means that a crew staying in the pressure chamber unit 21 during an accident when the craft must be abandoned, can go aboard the lifeboat and be saved, since they will be maintained at the same pressure in the lifeboat as in the pressure chamber unit. The pressure chamber unit is devised in such a way that both shafts 17 and 19 with diving bells 18 and 20 can be serviced. In connection with the peessure chamber 22 there is devised a rescue pressure chamber 26, alternatively a lifeboat with a pressure chamber.

At the same time as the two diving shafts 1 7 and 19 are in such proximity to each other that they can be serviced by the same pressure chamber, they are also so close to each other that divers from the diving bells 18 and 20, at a certain depth, will be so close to each other that the divers from the two bells at any moment can work together without having to cover any significant horizontal distance. The work shaft is so close to the diving shaft 19 that the diving bell 20 can be coupled to, for example, a welding chamber (habitat) which is lowered through the work shaft.

As one will see from Fig. 4, the main diving shaft is placed in one corner of the deck. The craft is positioned with this corner against wind and weather so that the pendulum movement or swaying which takes place will occur with this corner as its center. The horizontal movement of the diving shaft 17 will thus be quite minimal. Owing to the fact that the craft is submerged with the pontoons in the main below the influence of waves, the vertical movement will also be minimal. It will thus be possible to work from the main diving shaft even in a heavy sea. Owing to the fact that the diving shaft 19 and the work shaft 12 are placed at a relatively short distance from the main shaft, all shafts being placed in the same quadrant of the craft, the pendulum movement for shafts 12 and 19 will also be relatively small. All shafts particularly shaft 17 can be brought very close to a structure if the diving work is to take place at this structure.

As is apparent from Figs. 1 and 2, there is no bracing of the legs below or close to the waterline. In the shown embodiment the bracing is placed in the deck structure.

Claims (7)

1. A device relating to a semi-submersible craft, having a deck structure of several decks which on top of a number of legs, at least one leg being in each corner, rests on two longitudinally extended pontoons, there being a work shaft for raising or lowering, by means of crane means equipment to be used in a diving operation and which run substantially vertically from the main deck down through the decks below, and two diving shafts in the lower deck, which are designed for launching and taking aboard diving bells, at least one of which, the primary shaft, continues down below the surface of the water, and a pressure chamber unit being arranged on the lower deck in connection with the two diving shafts, the primary shaft being in one leg of the craft and the second shaft being installed in such proximity to the primary shaft that the diving bells for the two shafts can be coupled to the pressure chamber unit, and the work shaft and one of the diving shafts being in such proximity that the diving bell from the one shaft can be coupled directly to a work chamber, lowered through the work shaft for dry transfer of divers.

2. A device according to claim 1, in which a gantry crane or a travelling crane running on tracks is installed on the main deck.

3. A device according to claim 1, in which the gantry crane or travelling crane is for use in the work shaft.

4. A device according to claim 2 or claim 3, in which one or more jib cranes is or are installed in addition to the gantry crane or travelling crane.

5. A device according to any preceding claim, in which the three shafts are installed in the same quadrant of the deck section, and in which they are generally arranged on a diagonal through the deck section running through the centre of the deck and one leg.

6. A device relating to a semi-submersible craft having a deck structure of several decks which on top of a number of legs, at least one leg in each corner, rests on two longitudinally extended pontoons, the craft having a work shaft for raising or lowering, by means of cranes equipment to be used in a diving operation and which runs substantially vertically from the main deck down through the decks below, there being two diving shafts in the lower deck, which are designed for launching and taking aboard diving bells, one of which at least, the primary shaft, continues down below the surface of the water, and there being a pressure chamber on the lower deck in connection with the two diving shafts, the primary shaft being installed in a leg of the craft, the other diving shaft being installed in proximity to the primary shaft, the diving bells from the two shafts being adapted to be coupled to the same pressure chamber unit, the work shaft being installed so close to one of the diving shafts that the diving bell from the one shaft can be coupled directly to a welding chamber (habitat) or the like, lowered through the work shaft for dry transfer of divers, the legs of the craft having a longitudinally extended cross section with their longitudinal axis pointing in the direction of the craft's headway, and all bracing of the legs being above the waterline.

7. A device relating to a semi-submersible craft, substantially as hereinbefore described with reference to the accompanying drawings.