The invention is related to a ship comprising a hull having a front section which comprises a bow, an aft section which comprises a stern, side walls which extend between the bow and the stern, a bottom joining the lower edge of the side walls and a deck joining the upper edge of the side walls, wherein the front section of said hull defines a main draft which is generally constant over at least part of the front section.

In particular, the invention is related to a ship or vessel which may be used as a platform for carrying out offshore operations, such as drilling or mining operations and the like. In this connection, it is desirable for such ship or mining vessel to have an operation window which is as long as possible so as to reduce downtime. This has a favorable influence on the operation costs of the ship and of the associated installations on board the ship.

The operation window is to a large extent determined by the ship's behavior under wave and wind conditions. A stable behavior with respect to harsh conditions results in a large operation window and reduced operation costs. In particular, the ship's response to waves and wind in the form heave and roll motions etc. is of importance. Prior art ships however have an operation window which is too small.

The object of the invention is therefore to provide a ship the hull of which provides a relatively long operation window. This object is achieved in that the waterline of the front section at least partly has a triangular shape, the top of which triangular shape is located at or near the bow and in that the aft section of the hull comprises a reduced draft.

The side walls are arranged according to the triangular shape. As a result of the triangular shape of the hull, first of all a small waterline surface is obtained at the front section of the ship, resulting in a relatively low buoyancy at that location. Thereby, the pitch motions of the ship are mitigated. Furthermore, the centre of gravity of the triangular shaped hull is located relatively close to the stern. Thus, a stable platform is obtained and, in particular at the relatively wide aft section a large surface for carrying out operations is provided. The arm of this wide aft section with respect to the centre of gravity is relatively small, which also is favorable for creating stable working conditions. This advantage can be used for instance for locating a moon pool in that area for drilling purposes. Preferably, such moon pool is arranged in the vicinity of the centre of gravity. It is pointed out that, although the front section of the hull has a relatively small waterline surface, and thus the capacity for carrying cargo at said front section per se is limited, this is compensated by the reduced draft at the aft section. In this way, imbalance is avoided.

A further advantage of the hull shape is that it allows a relatively high speed of the ship. In comparison to prior art ships, such as mining vessels, the hull has a relatively low resistance. In combination with the sharp, rectangular bow, which cuts through the waves, this makes it possible to travel faster.

According to a first embodiment, the stern may coincide with the base of the triangular shape. However, it is not always necessary to have the triangular shape of the front section extend up to the stern. According to a second, alternative embodiment, the hull may comprise a mid section which is located between the front section and the aft section, which mid section has a waterline has a shape which is different from the triangular shape of the front section.

The mid section may have a reduced draft which merges into the reduced draft of the aft section. The mid section may have a reduced draft over the part thereof adjoining the aft section and the same draft as the front section over the part of the mid section which adjoins the front section. Alternatively, the mid section may have a reduced draft over its full length.

The waterline of the front section may be defined by a triangle shape the top of which is smaller than the top of the triangular shape of the front section. Also, the waterline of the mid section may be parallel, i.e. the side walls at the location of the mid section may be parallel in longitudinal direction.

The large area available at the aft section provides ample space for the installations which are used in carrying out the operation, such as mining equipment and installations for handling the materials obtained by the mining operation.

Alternatively or additionally, a drill rig and the like may be located at the aft section. The triangular shape of the hull with its relatively wide aft section also provides the ship with favorable properties in relation to wheathervaning and head winds. The ship in question may have a considerable size; as an example, it may have a length of around 250 m, a largest width of 60 m and a draft of 10 m.

The ship can be carried out in several ways. For instance, the section of the hull having a reduced draft may extend between generally the centre of gravity of the hull and the stern. Preferably, the front section, when seen in longitudinal direction, has a constant main draft. Furthermore, the draft of the hull near or at the stern amounts to about 0 - 0,5 times the main draft. Preferably, the draft is reduced monotonously.

However, in order to prevent slamming of the stern it extends to below the waterline. The top angle of the triangular shape may be in the range between 0° and 60°.

Preferably, the side walls are generally perpendicular with respect to the deck and/or the bottom.

Preferably, the triangular shape is isosceles. According to a specific

embodiment, the opposite ends of the stern may comprise cutoffs forming stern planes which are angled with respect to each other. The bottom may have at least a

reinforcement structure, such as a bent, curved or folded bottom portion for the purpose of increasing the resistance of the bottom against buckling.

The invention is furthermore related to a hull for a ship described before, said hull having a front section which comprises a bow, an aft section which comprises a stern, side walls which extend between the bow and the stern, a bottom j oining the lower edge of the side walls and a deck joining the upper edge of the side walls, wherein the front section of said hull defines a main draft which is generally constant over at least part of longitudinal direction the front section. This hull is characterized in that the waterline of the front section at least partly has a triangular shape, that the top of the triangular shape is located at or near the bow and in that the aft section of the hull comprises a reduced draft.

Reference is made to the hull design as disclosed in WO- A-01/79054. The hull thereof has a draft which is reduced all the way from the bow to the stern. The purpose of this design is to allow transonic speeds. Such design is not fit for serving as a stable work platform aimed at carrying out offshore operations.

The Ramform Sovereign (as disclosed in the article "Brief History of the Ramform, Why Build a Third Generation Ramform?") and the ships disclosed in WO00/07873 and US23,626 each show a ship with a triangular-shaped hull. However, each of these are also designed for specific purposes and are not suitable for serving as a stable work platform for offshore operations. The Ramform Sovereign and the ship disclosed in WO00/07873 are designed for seismic surveying, and are designed to have a wide stern to able to hold many streamers and collect seismic data with as little noise as possible from the vessel. US23,626 is a vessel with a triangular construction so that it is capable of great carrying capacity and of traveling at a high speed.

The hull design according to EP-A-678445 has a reduced draft at the aft section. The waterline shape is not triangular but sinusoidal. The purpose of this design is to provide a homogeneous flow of water under the stern.

The invention will now be described further with respect to the embodiments shown in the drawings.

Figure 1 shows a side view of a first embodiment of the ship.

Figure 2 shows a top view of the ship of figure 1.

Figure 3 shows a side view of a second embodiment of the ship.

Figure 4 shows a top view of the ship of figure 3.

Figure 5 shows a view in perspective of the second embodiment of the ship.

The ship shown in figures 1 and 2 consists of a hull 1 having side walls 2, 3, a bottom 4 and a deck 5. The side walls 2, 3 extend generally according to the legs of an isosceles triangle the imaginary top of which is indicated at 10. The base of the triangular shape coincides with the stern 7 of the hull 1. The bow 6 has a somewhat rounded shape.

The hull 1 has a front section 8 and an aft section 9. At the location of the front section 8, the hull 1 has a constant main draft, as indicated by the flat bottom part 11. The draft at the location of the aft section 9 is reduced towards the stern 7, as indicated by the sloping bottom part 12. The centre of gravity is shown at 13. As a result of the hull's shape, the location of this centre of gravity 13 is relatively close to the stern. Around this area, a moon pool 15 is located in the embodiment shown. The deck house 14 is located on the aft section 9.

According to a slightly different embodiment, the stern 7 may have cutoffs 16 at the corners of the hull 1 as shown by the dotted lines in figure 2. Such layout may be useful for launching and recovering ROV's, deep sea mining equipment and the like.

Although the ship as described before and as shown in the drawings is fit for carrying out different operations, it is pointed out that it can in particular be used as a mining vessel for carrying out mining operations on the sea bottom.

The embodiment of the ship as shown in the figures 3-5 has a hull 1 which comprises a mid section 17 as well. This mid section adjoins the front section 8 and the aft section 9. The side walls 18 of the mid section 17 may have a waterline which coincides with a triangle the top of which has an angle which is smaller than the top angle of the front section 8.

List of reference numerals

1. Hull

2., 3. Side wall

4. Bottom

5. Deck

6. Bow

7. Stern

8. Front section

9. Aft section

10. Imaginary top

1 1. Flat bottom part

12. Sloping bottom part

13. Centre of gravity

14. Deck house

15. Moon pool

17. Mid section

18. Side wall mid section