Short title: Vessel with movable float

The present invention relates to the unloading of a load from a cargo ship on the open sea.

Description of the state of the art

It is known to transport a load using submersible vessels or ships and to unload said load at a target location by submersing the ship so that the load comes off the ship. The load is in this case usually located on a load deck.

The vessel is provided with one or more ballast tanks, also referred to as reservoirs or compartments, which can be filled completely or partly with water or air as desired. When the ship is submerged, the buoyant force of the water on the load gradually increases and after some time, the load comes off the ship. When the load has come free, the load and the ship move independently of one another.

Unloading the load preferably takes place in a sheltered location, with little wind, current and wave action. This prevents the load and the ship making any movements relative to one another which are excessive and/or sudden, thus greatly reducing the risk of the vessel and the load coming into contact with one another.

However, these days, the loads are often offshore installations intended for operation on the open sea, far from protected locations. Therefore, it is often desirable for the unloading of the load to take place on the open sea nowadays, or at least in less well-protected locations.

This is not readily possible using the current vessels, as with these, there is a considerable risk of the ship and the load colliding with each other. This is caused by the fact that the current ships can only be submerged relatively slowly, so that there

is only a small distance between the load and the ship for a relatively long time. It only takes small movements between the ship and the load to cause a collision, resulting in damage to the load and/or to the ship.

It is an object of the invention to provide a submersible vessel or ship which can be submerged substantially more quickly than the vessels presently known in the field. This results in the relatively quick creation of a separation between the ship and the load.

Summary of the invention

The invention provides a vessel or ship for transporting a load which rests on a support arrangement, in particular formed by a load deck, the vessel being provided with a float which can be moved in a substantially vertical direction relative to the support arrangement for moving the support arrangement in a substantially vertical direction relative to the water surface.

As the float can be moved relative to the load deck, the load deck can move downwards relative to the float. The float is a compartment, reservoir or tank and is usually made of steel. Other suitable construction materials are likewise possible. The float can also be referred to as a ^buoyancy chamber' . The float defines a volume, which is generally filled with air, and has a specific buoyancy. However, it is also possible for the float to be filled with a light material, for example a foam.

The ship drops down on account of its own weight as it were, by increasing the distance between the ship and the float. This movement can be carried out relatively quickly as it is assisted by gravity. The load is usually situated on the load deck and will move downwards together with the load deck at a relatively great speed.

Thus, the buoyancy of the load is increased and as a result the load will at some point in time come off the ship.

The ship then sinks further, so that the distance between load and ship increases relatively quickly.

Generally, the load itself has buoyancy and the load will start to

float as the vessel sinks to a greater depth. However, it is also possible that the load itself has no buoyancy and is positioned on the (sea) bed as a result of the ship being submerged.

The support arrangement may be a load deck or a frame which is designed to carry a load. The support arrangement may also be formed by another suitable element, for example a coupling.

In a preferred embodiment, the float can be moved relative to the vessel by means of a drive, in particular a hydraulic system, a winch or a gear rack system. Systems of this type are reliable and make it possible to control the movement of the float well.

In a preferred embodiment, the float is located near one end, in particular the rear end, of the vessel. Thus, the float can form an integral part of the stern or the bow of the vessel and contribute to the stability of the vessel. In addition, it is thus possible to rotate the vessel about a point near the bow or stern during loading and unloading.

It is also possible for the vessel to comprise a plurality of floats which can be moved in the vertical direction with respect to the load deck. In this case, one or more floats can be located near the bow, so that the vessel can move downwards without having to rotate.

According to one aspect of the invention, the float can be moved along a guide organ. The movement of the float relative to the vessel can thus be controlled easily, and lateral movements of the float with respect to the vessel can be prevented.

The invention likewise relates to a method for unloading a load which is on board a vessel, the vessel being provided with a float which can be moved in a substantially vertical direction relative to a support arrangement, in particular formed by a load deck, the method comprising the step of moving the float upwards relative to the support arrangement in order to move the support arrangement downwards relative to the water surface.

The invention also relates to a method for positioning a load on a

vessel, the vessel being provided with a float which can be moved in a substantially vertical direction relative to a support arrangement, in particular formed by a load deck, the method comprising the steps of: a) positioning the load above the support arrangement; and b) moving the float downwards relative to the support arrangement in such a manner that the support arrangement is moved upwards relative to the water surface.

In this manner, it is possible to place a load on a cargo ship quickly, so that there is only a small risk of collisions between the load and the cargo ship during loading.

The invention also relates to a combination of a vessel according to claim 1 and a load which is on board the vessel, in particular on a load deck of the vessel.

The invention will be explained hereinbelow in more detail with reference to the following, non-limiting figures, in which:

Figs. Ia, Ib, Ic show three steps during unloading of a load from a cargo ship according to the prior art;

Figs. 2a and 3b show a diagrammatic rear view of the cargo ship according to the invention; Figs. 3a and 3b show a diagrammatic side view of the ship according to the invention during unloading of the load; and

Fig. 4 shows a detail of the vessel according to the invention in side view.

Fig. Ia shows a ship 1 according to the state of the art with a load 2, which is located on a load deck 4. The ship 1 has a bow 14 and a stern 16, between which the load deck 4 is situated. The ship 1 has ballast tanks 3 which can be filled completely or partly with water or air as desired, for varying the buoyancy of the ship 1. The ship in this case has a fixed float 5 near the stern 16, which provides the ship 1 with buoyancy and stability.

In Fig. Ia, the ship 1 is in a ^λ high' position, i.e. a position in which the ballast tanks 3 are substantially filled with air, so that

the draught 18 of the ship 1 is light. The buoyancy of the ship 1 is high, and the load deck 4, which has the load 2 on it, is above the water surface 12.

In Fig. Ib, in a subsequent step, the ballast tanks 3 are partially filled with water so that the water displacement of the ship 1 is increased and the draught 18 increased. In the meantime, the load deck 4 has moved below the waterline 12 and the load 2 is subject to a certain buoyant force of the water, the buoyant force being not yet sufficient to cause the load 2 to come off the load deck 4.

In Fig. Ic, the load deck 4 of the ship 1 is so far below the waterline 12, that the load 2 has come off the ship 1 on account of the buoyant force and floats independently. A free space is created between the ship 1 and the load, the distance 20 between the ship 1 and the load 2 gradually increasing. As a result of the beating of the waves, wind and currents, the load 2 may move relative to the ship 1 and consequently collide with the ship 1, for example at point 6.

Fig. 2a shows a ship 1 according to the invention, provided with a float 7 which can be moved in the vertical direction with respect to the ship 1. The float 7 forms an additional float, in addition to one or more fixed floats or buoyancy chambers 5 in the stern. However, it is also possible that no fixed buoyancy chambers 5 are provided but only a movable float 7. The float 7 will generally be filled with air.

The float 7 can be moved from a first, ^λ low' position 30 to a second, ^λ high' position 32, with the vertical distance 21 between the float 7 and the load deck 4 being greater in the second position than in the first position 30. In Fig. 2a, the float is in the low position 30. The direction of movement of the float 7 relative to the ship 1 does not have to be exactly vertical, but may also have a horizontal component. The vessel 1 usually has its own drive mechanism, but it may also be a non-driven vessel. The vessel 1 is usually a seaworthy ship.

By moving the float 7 upwards relative to the load deck 4, the ship

1 sinks lower into the water, and the load deck 4 moves downwards, further away from the water surface 12, in particular from the second position 36 to a third position 38.

In Fig. 2b, the state of the ship 1 is shown after the float 7 is moved upwards into the second position. The distance 20 between the load deck 4 and the load 2 has increased considerably within a relatively short time, so that a substantial freedom of movement is created between the load 2 and the ship 1. The risk of collisions is thus considerably reduced.

The load 2 is now able to move in a direction 8 relative to the ship 1 in order to be moved away from the ship.

The float 7 may be connected to the hull of the ship 1 by means of a releasable coupling. In this manner, the float 7 can be fixedly coupled to the ship in the first position and thus form an integral part of the ship 1.

It will be clear to those skilled in the art that the procedure is reversed for loading the ship.

Furthermore, it is possible for the vessel 1 not to have ballast tanks, and for the submersing and lifting of the vessel to take place only by means of the float (s) 7.

Fig. 3 shows the alongship behaviour while the ship is being submersed. The float 7 is located at the rear of the ship 1. By moving the float 7 upwards relative to the ship 1, the ship sinks down and rotates about point 9. The point 9 is in this case the centre of gravity of plan at waterline of the bow 14.

Fig. 4 shows the stern 16 of the ship 1 according to the invention, guide rails 22 being provided for guiding the float 7 in the vertical direction. A drive 24 is provided in the shape of a winch which moves the float 7 relative to the vessel 1 by means of a cable 26.

It is also possible for the float 7 to be eccentrically pivotable

about a substantially horizontal axis, so that when the float 7 is pivoted, the centre of gravity of the water-displacement volume which is defined by the float 7 is moved in the vertical direction with respect to the load deck 4.

A person skilled in the art will understand that many other drive mechanisms are possible, such as a hydraulic, pneumatic or electrical drive.

It is also possible for the float 7 to be able to move along a gear rack relative to the ship 1.

The scope of the present invention is not limited to the embodiments described above, but rather various changes and modifications thereof are possible without departing from the protective scope of the invention as defined in the attached claims.