In the known method an increasingly greater trimming force is generated as the sailing speed increases, this force being directed such that the stem of the vessel is pressed toward the water. The possibility of the vessel tipping over backwards is thus prevented. For generating of these increasingly greater trimming forces use is made of trimming surfaces arranged at the rear of the vessel which, as a consequence of the increasing dynamic pres- sure at increasing speed, become increasingly more ac- tive. However, the method is relatively ineffective at less high speeds, so that at such speeds the vessel will generally assume a position wherein the stem is directed upward, which results in considerable wave formation behind the vessel. This wave formation is a nuisance for other vessels on the water and therefore not acceptable in densely navigated areas, while the resistance of the vessel, and thereby the fuel consumption, are hereby sharply increased. In addition, the position with stem raised high above the water results in a decreased direc- tional stability of the vessel, which results in unsteady sailing behaviour.

The invention therefore has for its object to pro- vide a method for trimming the vessel, wherein these drawbacks do not occur. This is achieved according to the invention in that at a first, relatively low sailing speed a first, relatively large trimming force is gener-

ated and at a second, higher sailing speed a second, smaller trimming force is generated. By already generat- ing a large trimming force at a relatively low speed the stem of the vessel is already pressed to the water at such relatively low speeds, whereby the vessel remains level and thus sooner assume a so-called "planing mode".

In such a planing mode the wave formation, and therewith the nuisance for other vessels, and the fuel consumption are low, while the directional stability of the vessel is excellent. In addition, the comfort of those on board a vessel in planing mode is considerably greater than in the situation with the stem raised high above the water, wherein the whole vessel inclines relatively sharply in longitudinal direction.

The invention also relates to a vessel which can be trimmed in the above described manner. Such a vessel, which is provided with at least one hull, means connected to the or each hull for propelling the vessel and con- trollable trimming means connected movably to the or each hull, has the feature according to the invention that the trimming means are adapted to be moved to a very active first position at a first, relatively low sailing speed and to a less active second position at a second, higher sailing speed. The above described advantages are achieved by thus operating the trimming means.

The trimming means preferably comprise at least one floater body arranged behind the centre of gravity of the vessel and movable transversely of the sailing direction, for instance pivotable on a lying axis. Such a floater body is considerably more effective at lower sailing speeds than a trimming surface, since the static and not the dynamic pressure determines the effectiveness of a floater body.

In order to increase the directional stability the vessel preferably has at least two floater bodies ar- ranged on either side of its longitudinal axis. The trimming force is hereby well distributed in transverse

direction of the vessel, while the floater bodies can moreover function as leeboards or keels.

The advantages of the vessel according to the inven- tion come to the fore particularly when the propelling means comprise at least one jet propulsion unit, since precisely at lower sailing speeds such a propulsion unit is not very efficient and the control and directional stability of a vessel equipped therewith could thus leave something to be desired at such speeds.

The invention is now elucidated on the basis of an embodiment, wherein reference is made to the annexed drawing, in which: fig. 1 shows a side view of a vessel according to the invention, fig. 2 is a bottom view of the vessel shown in fig.

1, fig. 3A and 3B are partial rear views of the vessel shown in fig. 1 and 2 with respectively extended and retracted floater body, and fig. 4 is a side view of a floater body of the vessel of fig. 1-3 in extended position.

A vessel 1 (fig. 1) comprises a hull 2 with means 3 arranged therein for propelling the vessel, in the shown embodiment a drive unit such as a diesel engine. The engine can herein drive one or more conventional propel- lers but other forms of propulsion, such as for instance a water jet propulsion, can also be envisaged. Vessel 1 can further be provided with a superstructure 4, such as a pilothouse, arranged on hull 2. Hull 2 has at the front as seen in the sailing direction V a stem 5 and at its rear a stern 6.

The vessel 1 is further provided with controllable trimming means 8 connected movably to hull 2, in the shown embodiment in the form of two floater bodies 9 accommodated in a space 13 in hull 2. Floater bodies 9 can herein be designed as watertight, hollow or foam- filled boxes with great buoyancy. These floater bodies 9, which extend in the shown embodiment over practically a

third of the hull length, are movable transversely of the sailing direction V between a retracted position (fig.

3B), in which they are received wholly in the space 13, and a protruding position (fig. 3A) in which they pro- trude through an opening 12 under the surface 11 of vessel 1. A seal is herein arranged between the walls of space 13 and floater body 9 in order to prevent water being able to enter the space 13 when floater body 9 is extended. Controllable actuating means, for instance hydraulic jacks 16, are present to displace floater bodies 9. Other actuating means can of course also be envisaged instead of hydraulic jacks, such as for in- stance pneumatic jacks or electrically or non-electrical- ly driven mechanical displacement systems on a basis of gear racks or toothed wheels.

When floater bodies 9 are extended, the buoyancy L of hull 2 of vessel 1 is thereby increased locally.

Because this increase in buoyancy occurs behind the centre of gravity CG of vessel 1, a moment M will thereby be generated, whereby the stem 5 of the vessel is pressed toward the water 7. The natural tendency of the stem 5 to rise upward as speed increases is hereby compensated, whereby vessel 1 is held level. In this manner a planing mode can be reached relatively quickly. Operation of the floater bodies 9 is herein adapted such that they are fully extended at a relatively low speed to press the stem 5 downward and thereby urge vessel 1 into planing mode, and are fully or partially retracted again at a higher speed when the vessel reaches a natural and stable planing mode. The trimming action of the extended floater bodies 9 is further reinforced by their smooth design, whereby they also operate in the manner of conventional trimming surfaces.

This contributes toward enabling the floater bodies 9 to be further retracted at higher speeds, since at a constant extension the trimming surface action would then increase as a result of the increasing dynamic pressure.

The smooth design further contributes toward a possible

increase of the hull resistance, as a result of the extending of floater bodies 9, being limited as far as possible.

Although the extension of floater bodies 9 can be controlled manually by the pilot of the vessel 1, it is obvious to apply an automatic control system for this purpose. Such a control system could for instance com- prise a computer which is programmed to compute an ideal extension of floater bodies 9 for any situation on the basis of a number of measured parameters and to ensure that floater bodies 9 also actually obtain and maintain this extension. The parameters which could be considered in the program are the hull speed of the vessel, the trim mode thereof, the engine rotation speed, the fuel con- sumption and the spectrum of the swell.

Thus, when for instance the rotation speed of the engine is increased, the hull speed will increase and the trim angle to the rear will also become larger. This can then be corrected by extending floater bodies 9, for instance until the trim angle of the vessel is brought back to a value lying between 0 and 10 and preferably between 3 and 70. When vessel 1 then eventually reaches a speed wherein it arrives in natural manner in a planing mode, the trim mode herein changes in that the stem of vessel 1 will drop closer to the water surface. This can be corrected by once again retracting the floater bodies 9, whereby the set trim angle is preserved.

The optimum value of the trim angle can herein be chosen subject to for instance the anticipated swell or the desired fuel consumption. The computer will be fur- ther adapted to modify the program when the trim mode of vessel 1 is changed as a result of a change in its load situation, for instance due to the decreasing fuel weight or the displacement of load.

By extending floater bodies 9, which will of course always have to be operated collectively, the directional stability of vessel 1 is further increased. This is linked to the fact that the two floater bodies 9, which

in the shown embodiment have an inner wall 14 which is bent in longitudinal direction, in fact function as leeboards or keels, whereby lateral displacements of hull 2 are prevented. In the extended situation the two float- er bodies 9 moreover bound a tunnel 15 inside which the propulsion means 3 can be situated. The propulsion effi- ciency is hereby increased at the same time.

It is possible, as stated, to choose as propulsion a water jet propulsion. With such a propulsion, which has relatively little effectiveness at lower speeds but which does on the other hand produce a high efficiency at very high sailing speeds, the trimming system according to the present invention provides great advantages, since the resistance at lower speeds is thereby reduced in that the vessel is urged into planing mode and the directional stability is moreover improved at such low speeds. In order to improve the propulsion efficiency even further, use can otherwise be made of a number of jet propulsion units of differing power which can be switched on jointly or separately. At lower sailing speeds use can thereby be made of jet propulsion units of relatively low power which are then used at full load and therefore display a high efficiency. At higher sailing speeds a plurality of units can additionally be switched on, or the smaller units switched off and the larger units switched on.

The method and trimming system according to the invention result in a vessel which already reaches plan- ing mode at relatively low speeds and thereby has a lesser wave formation and a lower fuel consumption than existing vessels, while the comfort of those on board and the directional stability are improved at the same time.

Although the invention is described above with reference to a single-hull vessel, it will be apparent that it can also be applied advantageously in multi-hull vessels. In addition, the invention is not limited to the application in motorized vessels, but could also be used in fast sailing vessels. Nor is it limited to pivotable floater bodies. All that is important is that the floater body is displaceable in vertical direction in order to vary the buoyancy. A floater body placed in front of the centre of gravity would also provide the same effect if it were retracted and extended in opposite manner. The scope of the invention is therefore defined solely by the annexed claims.