System for vessel control

Description

Field of the Invention

[0001] The present invention relates to a system adapted for control of buoyancy of a vessel, which vessel is a catamaran (CAT), which catamaran is adapted to operate in a first CAT mode, which catamaran is adapted to operate in a second SWATH mode, which catamaran comprises a plurality of ballast tanks, which ballast tanks are mostly empty in the first CAT mode, which ballast tanks are mostly water-filled in the second SWATH mode.Background of the Invention

[0002] US2011203507A discloses an ocean going transport vessel having a pair of parallel spaced apart longitudinal hulls, supporting a first deck portion located above and extending across the hulls and forming a structural link between the hulls, located toward one end of the hulls, and preferably above the normal operating waterline of said vessel. Each hull includes a further deck portion extending at least from the first deck portion to the other end of the hulls. The hulls have ballast tanks to allow adjustment of the draft and trim of the vessel. The hulls and deck portions form a U-shape when viewed from above and below. A void extends between further deck portions and associated hulls for stowage or suspension of a load or a subassembly such as a cradle, a frame, or a deck. The further deck portions extend longitudinally beyond the hulls, supported in cantilever-type fashion as cantilevered deck portions which each include a docking point arranged to support the vessel by the cantilevered deck portions, by the docking point resting on a structural support.

[0003] US 5787828 A discloses the preamble of claim 1.Object of the Invention

[0004] It is the object of the invention to increase the stability of a vessel in both CAT mode and in SWATH mode.Description of the Invention

[0005] The object of the invention can be achieved by a system as disclosed in the opening paragraph and further modified in that the first CAT mode lightship weight is distributed towards midship, and in the second SWATH mode water ballast is distributed towards the ends of vessel which system comprises one or more foils and / or interceptors, which foils and / or interceptors are turned or pitch-controlled by actuators which foils and / or interceptors are controlled by an active ride control system.

[0006] Hereby a vessel designed to operate in two different modes of operation can be achieved where a first CAT mode is preferred for transportation of the vessel which is highly efficient because the vessel is operating at a relatively low draft, and in the CAT mode, the water line follows the two hulls of the vessel. In the light ship CAT mode, most of the mass of the ship is concentrated towards the mid-ship. In this way the moment of inertia is kept relatively small, and the efficiency of the active mode control foils and interceptors is improved. The system can comprise one or more foils and / or interceptors, which foils and / or interceptors are controlled by an active ride control system. In the front end of the vessel, primarily in the two longitudinal hulls, it is possible by using foils or interceptors by changing the pitch of the foils and thereby change the position of the vessel in the water because by means of the foil it is possible to increase or decrease pitch- and roll-inducing forces acting on the hulls. By having the possibility of changing the draft on the front end of the hulls in both sides, it is thereby possible to achieve a fast pitch and roll regulation of the hulls.

[0007] Hereby is achieved that the longitudinal metacentric height in the CAT mode is placed relatively high above the vessel. Therefore the ship has an increased stability, and it is possible by relatively low fuel consumption to operate at a relatively high speed of the vessel because most of the vessel is above water. Only the two hulls have to be driven through the water. In the SWATH mode instead, the vessel is relatively low in water, and the water plane is now distributed on the legs that are connecting the upper part of the vessel to the hulls in water. In that way, the vessel is much heavier because the ballast tanks are now filled with sea water and this leads to a distribution of the mass of the vessel so that heavy weights are formed in both ends of the vessel. In that way it is achieved that the longitudinal metacentre is placed relatively low compared with the place of the longitudinal metacentre in the CAT mode. Hereby is achieved that the vessel now forms a relatively stable working platform which vessel can be moved but at a lower speed than in the CAT mode.

[0008] In a preferred embodiment for the invention, in the first CAT mode the centre of floatation of the vessel can be located well aft of midship. Hereby further hydrodynamic stabilisation of the ship can be achieved. In the CAT mode, the seawater ballast tanks will most often be empty but it is possible to adjust the water level in the ballast tanks.

[0009] In a further preferred embodiment for the invention, in the first CAT mode of operation a quickly acting sea water ballast system can be driven by at least one air compressor. With the ballast system it is possible relatively fast to change the amount of ballast that is effected by the compressors, which in one situation are able to fill the ballast tanks by reducing the pressure above the water level in the tanks, and in the opposite situation, the same compressors can increase the air pressure above the water level and thereby press the water out of the ballast tank. It is possible to let the compressors work in common with more tanks, but it is also possible by a preferred embodiment to have one compressor per tank. When working with one compressor per tank, these compressors can be connected by tubing in a way so that compressors can take over the function of other compressors in situations where malfunction of one of the compressors occurs.

[0010] In a further preferred embodiment for the invention, in the second SWATH mode the water plane area can be distributed on three or more legs. Hereby is achieved that in the SWATH mode the water plane is very limited because the water plane is only around the relatively small-area legs that are connecting the upper part of the vessel with the two longitudinal hulls. In that way the influence of the waves rolling along the ship is very limited because the volume for drift that is being changed to be below or above water level is very limited.

[0011] In a further preferred embodiment for the invention, in the second SWATH mode the main part of the water plane area can be concentrated towards mid ship. Hereby it can be achieved that the longitudinal metacentre is placed relatively low.

[0012] In a further preferred embodiment for the invention, in the second SWATH mode a quickly acting sea water ballast system can be driven by air compressors used for trim of the vessel. By means of the air compressors it is possible to change the pressure in the seawater ballast tanks, as the ballast tanks can be filled with seawater by reducing the air pressure above the water level, and the ballast tanks can be emptied by increasing the air pressure above the water level.

[0013] In a further preferred embodiment for the invention, vertical accelerations of the vessel can be reduced by increasing the moment of inertia of the vessel by increasing the mass of the vessel, and by maximizing the distance between the water ballast and the vessel centre of gravity.

[0014] Large vertical accelerations on a vessel have several negative effects on the operability of the vessel and its crew. The vertical accelerations are directly connected to the metacentric height, which is a measurement of the initial static stability of a floating body.

[0015] In this case the floating body is a catamaran vessel with the ability to increase the draft into the second SWATH mode (Small Waterplane Area Twin Hull) by means of a quickly acting sea water ballast system. A large metacentric height generally results in large accelerations. A too small metacentric height endangers the stability of the vessel.

[0016] The metacentric height is calculated as the distance between the centre of gravity of a ship (G) and its metacentre (M). The metacentre is determined by the ratio between the inertia resistance of the boat and the volume of the boat. The inertia resistance is a quantified description of how the water plane area at the waterline is distributed in order to resist overturning. On vessels one usually talks about the longitudinal (M L ) and the transverse (M T ) metacentric height which refers to the initial static stability of the vessel in pitch and roll respectively. To achieve a large longitudinal metacentric height one would prefer a large water plane area which distribution is concentrated towards the ends of the vessel.

[0017] Further, the accelerations can be reduced by increasing the moment of inertia of the vessel. In practice this can be effected by increasing the mass of the vessel and by maximizing the distance between the weight and the vessel centre of gravity. A lightweight vessel generally experiences larger accelerations than does a heavier vessel.

[0018] Unfortunately the hull design characteristics that favour high speed result in a water plane area that is concentrated towards the aft end of the vessel, and thereby increases the metacentric height. Light weight is also preferred to achieve a high cruising speed at low fuel consumption. Again, this results in large accelerations on board.

[0019] The reason for changing into SWATH mode is to cancel the poor acceleration characteristics of a high-speed catamaran hull by making use of the above-mentioned principles. The waterplane area is minimized and concentrated towards midship. The mass is increased as the ballast tanks are filled with sea water, and the location of the tanks further increases the moment of inertia. The result is a vessel with both the characteristics of a high-speed catamaran, as well as the benefits of a very stable working platform of a SWATH vessel. It is all made possible by a quickly acting sea water ballast system driven by air compressors.

[0020] CAT mode Centre of floatation is located well aft of midship Lightship weight is distributed towards midship Quickly acting sea water ballast system is driven by air compressors Active ride control system is operating via multiple foils and / or interceptors

[0021] SWATH mode Waterplane area is distributed on three or more legs Main part of waterplane area is concentrated towards midship Water ballast is distributed towards ends of vessel Quickly acting sea water ballast system is driven by air compressors Description of the Drawing

[0022] Figure 1 shows a sectional view of a vessel. Figure 2 shows a further sectional view of the invention. Detailed Description of the Invention

[0023] Figure 1 shows a sectional view of a vessel 4 which vessel comprises a deck or upper section and underwater hulls 6,8 which underwater hulls 6,8 comprise front ballast tanks 10,2 and aft ballast tanks 14,16. Further there are indicated engine rooms 18,20 and on the deck there are indicated front compressors 22,24 and aft compressors 26,28.

[0024] In CAT mode the vessel 2 will operate with ballast tanks 10,12 and 14,16 being mostly empty. Therefore a relatively heavy mass of the vessel is concentrated in the engine rooms 18,20. Therefore most of the weight of the ship is concentrated near the centre. In the CAT mode where the mass is concentrated midship whereby a relatively high placement of the longitudinal metacentre is achieved. In the opposite position when the ballast tanks 10,12 and 14,16 are mostly water-filled, the vessel is operating in SWATH mode. The heavy weight of the ballast water is now placed in the front and in the aft of the hulls. This will give a mostly lower placement of the longitudinal metacentric height. Hereby a relatively stabilised working condition is achieved when the ship has to be operating for example near an open-sea windmill farm. The SWATH mode is highly efficient for keeping the vessel very stable, but is not efficient for sailing over long distances.

[0025] Figure 2 shows a further sectional view of the invention, but now in the horizontal plane, and relatively below water level. The figure 2 indicates the two underwater hulls 6,8 comprising ballast tanks 10,12,14 and 16. Further there are indicated engine rooms 18 and 20 placed in the hulls 6,8. Front thrusters are indicated in cavities 30 and 32 in the hulls 6,8. The front thrusters of course comprise one or more propels which can be operated in the channels 30,32. Further there are indicated foils 34 and 36 which foils are operated by actuators 38 and 40. Additional foils and / or interceptors may be located near the stern. Aft of the hulls 6,8 there are indicated screw shafts 42 and 44 and screws 46 and 48. The screws may also be located below the hulls.

[0026] In operation the ballast tanks 10,12,14,16 can more or less be filled with seawater by means of compressors as indicated in fig. 1. The foils 34,36 can be turned or pitch-controlled by the actuators 38,40. Because the change of the foils can be performed rather rapidly it is a highly efficient way of achieving further stability of the vessel 4. If the vessel has some speed ahead it is possible to change the pitch and roll by turning the foils 34,36 and in that way stabilise the vessel.Reference numbers used in drawings

[0027] 2 System 4 vessel 6 hull 8 hull 10 Ballast tank 12 Ballast tank 14 Ballast tank 16 Ballast tank 18 engine room 20 engine room 22 compressor 24 compressor 26 compressor 28 compressor 30 thruster cavity 32 thruster cavity 34 foil 36 foil 38 foil controller 40 foil controller 42 shaft 44 shaft 46 screw 48 screw

Claims

1. System (2) adapted for control of buoyancy of a vessel (4), which vessel (4) is a catamaran (CAT), which catamaran is adapted to operate in a first CAT mode, which catamaran is adapted to operate in a second SWATH mode, which catamaran comprises a plurality of ballast tanks (10,12,14,16), which ballast tanks (10,12,14,16) are mostly empty in the first CAT mode, which ballast tanks (10,12,14,16) are mostly water-filled in the second SWATH mode, wherein the first CAT mode lightship weight is distributed towards midship, and in the second SWATH mode water ballast is distributed towards the ends of the vessel, characterized in that the system comprises two or more foils and / or interceptors (34,36) to be arranged in the front end of the vessel, which foils and / or interceptors (34,36) are controlled by an active ride control system.

2. System according to claim 1, characterized in that in the first CAT mode the centre of floatation of the vessel is located well aft of midship.

3. System according to claim 1 or 2, characterized in that in the first CAT mode of operation a quickly acting sea water ballast system is driven by at least one air compressor (22,24,26,28).

4. System according to one of the claims 1-3, characterized in that in the second SWATH mode the waterplane area is distributed on three or more legs.

5. System according to one of the claims 1-4, characterized in that in the second SWATH mode the main part of the waterplane area is concentrated towards midship6. System according to one of the claims 1-5, characterized in that in the second SWATH mode the quickly acting sea water ballast system is driven by the air compressors (22,24,26,28) in use for trim of the vessel.

7. System according to one of the claims 1-6, characterized in that vertical accelerations of the vessel are reduced by increasing the moment of inertia of the vessel by increasing the mass of the vessel, and by maximizing the distance between the water ballast tanks (10,12,14,16) and the vessel centre of gravity.