DESCRIPTION

The present invention relates to an adjustment system for adjusting the draught of at least one hull of a vessel, according to the preamble of claim 1.

The present invention also relates to a vessel comprising said adjustment system as well as to a method for adjusting the draught of at least one hull of a vessel.

In this frame, the present invention finds particular application in the field of SWATH (Small Waterplane Area Twin Hull) multi-hull vessels. However, the present invention is also applicable to mono-hull or single-hull vessels, such as SWASH (Small Waterplane Area Single Hull) vessels.

It is known in the art that a multi-hull vessel is a vessel equipped with more than one hull, and that such vessels offer several advantages over single-hull vessels.

Indeed, due to a longer distance between the centre of gravity and the hulls’ edges, they ensure much better stability; this distinctive feature proves to be advantageous especially on sail-equipped multi-hull vessels, which, due to the greater stability ensured by their hulls, need much less ballast than mono-hull vessels.

Moreover, a multi-hull vessel offers the advantage that it can be designed with narrower hulls, which results in considerably less fluid-dynamic resistance.

The most common types of multi-hull vessels are, essentially, the catamaran, which has two hulls with longitudinal symmetry, and the trimaran, which has a main hull in the centre and two smaller stabilizer hulls arranged symmetrically on both sides of the central hull and joined together by a rigid structure, usually consisting of tubular elements.

In this context, multi-hull vessels are known in the art which are referred to as SWATH (Small Waterplane Area Twin Hull) or SWASH (Small Waterplane Area Single Hull), i.e. vessels wherein at least one hull is positioned under the water surface to minimize the section at the waterline, thus reducing the energy which is lost because of the wave resistance that is typical of dislocating hulls and minimizing the energy absorbed by wave motion, while at the same time improving the vessel’s stability.

Thanks to such hulls positioned under the water surface, the influence of wave motion and the resulting generation of waves are reduced, so that such vessels are particularly interesting for nautical applications of any size.

Nevertheless, such technology suffers from a few criticalities associated with the small variation in submerged volume as the load on the vessel increases or decreases. More specifically, especially as concerns small-to-medium size vessels wherein the unloaded weight is comparable to the load normally added thereto, controlling the depth of the immersed part is a problem that needs to be solved for the system to operate properly, particularly from a hydrodynamic viewpoint. A SWATH hull is, in fact, optimized for working at a specific depth, where resistance to motion, and hence the vessel’s fuel consumption, is lowest.

SWATH hulls are not versatile for applications wherein the vessel’s load varies rapidly in use, e.g. applications for passenger transportation, with frequent passenger boarding and unboarding operations. Due to the small immersed volume variation associated with the structural part above the waterline, a small variation in the load applied to the vessel (e.g. a boarding/unboarding passenger) will cause the vessel to sink or rise by a considerable amount before the water volume necessary for supporting the applied load can be displaced, thus making the boarding or unboarding of other people difficult or even impossible.

With a view to solving the problem of load-dependent variable draught due to the low hydrostatic stiffness of SWATH hulls, several solutions are currently known in the art which employ, in turn, vertical propulsors, mobile arms for immersing sealed floating volumes, mobile mechanical arms for elevating the upper hull above the wave level, adjustable loadbearing surfaces, one or more movable hulls with the possibility of immersing an additional platform, variable buoyancy bags, pneumatic bladders for changing the outer shape of submerged hulls, and so forth.

However, such known solutions require the presence of moving parts in proximity to, or even in contact with, the water; this results in more maintenance required by the associated systems (typically electro-hydraulic ones).

Moreover, the solutions currently known in the art inevitably imply increased complexity and cost of the systems employed in the different solutions.

A further drawback of the solutions currently known in the art is that they cannot ensure an adequate adjustment of the draught of a vessel in real time.

Another drawback of the solutions currently known in the art is that they require a large number of electro-mechanical components and/or the presence of hydraulic components, which inevitably results in higher development and production costs. A further drawback of the solutions currently known in the art is that they are difficult to implement on small hulls unless additional hydrofoil technology is used, which requires high precision and care during production and is therefore disadvantageous from an economical viewpoint. Moreover, hydrofoils are typically made of composite material and are prone to accidental damage in navigation caused by impacts against moorings.

In this frame, it is the main object of the present invention to provide an adjustment system for adjusting the draught of at least one hull of a vessel, and hence the draught of the whole vessel, which can overcome the drawbacks suffered by the solutions currently known in the art.

In particular, it is one object of the present invention to provide an adjustment system for adjusting the draught of at least one hull of a vessel, wherein said adjustment system is so constructed as to solve the problem of load-dependent variable draught due to the low hydrostatic stiffness of SWATH (or SWASH) hulls, without however employing any moving parts in proximity to, or even in contact with, the water.

It is another object of the present invention to provide an adjustment system for adjusting the draught of at least one hull of a vessel which can also be implemented on small-size hulls without requiring any additional hydrofoil technology; therefore, it is one object of the present invention to provide an adjustment system for adjusting the draught of at least one hull of a vessel, wherein said adjustment system is so constructed as to not require high precision and extreme care during production and is not subject to accidental damage that may occur in navigation, e.g. when components of the vessel hit moorings.

Further objects, features and advantages of the present invention will become apparent in light of the following detailed description and of the annexed drawings, which are provided herein merely by way of non-limiting explanatory example, wherein:

- Figs. 1A and IB show, respectively, a partially sectioned side view and a partially sectioned front view of a rear portion of a vessel comprising a draught adjustment system according to the present invention;

- Figures 2A to 2D show different operative configurations of an adjustment system for adjusting the draught of at least one hull of a vessel, in particular a multi-hull vessel, according to the present invention.

Describing now Figures 1 A and IB, reference numeral 1 designates as a whole a multi-hull vessel according to the present invention. It should however be noted that the present invention is also applicable to a mono-hull or single-hull vessel 1 (not shown in the annexed drawings), such as, for example, a SWASH vessel 1, even though in the following description reference will mostly be made to a SWATH vessel 1.

The vessel 1 comprises a central platform 10 (which may also be defined as the “emerged part” of the vessel 1) connected to at least two hulls 20, in particular each hull 20 being submerged or positioned under the water surface during the navigation of said vessel 1.

Said vessel 1 is, therefore, a SWATH (Small Waterplane Area Twin Hull) vessel, i.e. a vessel

I wherein the hulls 20 are positioned under the water surface on which the vessel 1 is navigating, so as to minimize the section at the waterline and reduce the energy which is lost because of the wave resistance that is typical of dislocating hulls, thereby minimizing the energy absorbed by the wave motion while ensuring stability of the vessel 1.

The central platform 10 is connected to each hull 20 by a junction 11, wherein said junction

I I may be defined as a “vertical element 11”. It should be noted that, in Figures 1 A and IB, the vessel 1 is represented as a type suitable for passenger transportation; it is however clear that the teachings of the present invention are also applicable to a vessel 1 for freight transportation.

The advantage given by the SWATH configuration is better seakeeping in bad weather, particularly compared with a classic catamaran. In fact, since the hulls 20 are deeply submerged and the floating area is reduced, the vessel 1 is much less subject to the destabilizing effects of the waves: its movements are normally reduced by 20% to 50% compared with a mono-hull vessel with equal dislocation.

The deeper positioning of the hulls 20 results in greater draught, and the larger wet area may make the vessel 1 slower.

In accordance with the present invention, at least one hull 20 of the vessel 1 comprises a casing 21 that delimits an inner chamber 22 that houses at least a portion of an adjustment system (designated as a whole by reference numeral 30) for adjusting the draught of said hull 20 (and hence the draught of the whole vessel 1).

Preferably, each hull 20 of the vessel 1 is so constructed as to comprise a respective adjustment system 30; however, the vessel 1 according to the present invention may also be so constructed as to comprise a plurality of hulls 20, wherein at least one hull 20 is so constructed as to not comprise the adjustment system 30 according to the present invention. As can also be seen in Figures 2A to 2D, in accordance with the present invention said adjustment system 30 comprises at least one tank 31 housed in an inner chamber 22 of the hull 20, said at least one tank 31 being provided with: - a first valve 32A permitting a first portion 31 A of the tank 31 to communicate with the atmosphere, so as to allow air to enter and exit said first portion 31 A of the tank 31,

- a second valve 32B permitting a second portion 3 IB of the tank 31 to communicate with the water in which the hull 20 is immersed or submerged, so as to allow water to enter or exit said second portion 3 IB of the tank 31.

In particular, the adjustment system 30 comprises a first duct 33A that makes it possible to obtain the communication of said first portion 31 A and first valve 32A with the atmosphere. Preferably, said at least one tank 31 is provided with at least one anti-sloshing plate or cap, in particular to prevent water agitation in the second portion 3 IB of the tank 31.

The adjustment system 30 also comprises at least one compressor 34 connected to the first portion 31 A of the tank 31 for delivering compressed air into said first portion 31 A.

In particular, the connection between the compressor 34 and the first portion 31 A of the tank 31 is obtained by means of a second duct 33B. Preferably, also the compressor 34 is in communication with the atmosphere, in particular through a third duct 33C that connects said compressor 34 to the first duct 33 A; in this regard, however, it must be pointed out that the third duct 33C may also be designed to provide a direct connection between the compressor 34 and the atmosphere (e.g. via a further duct, not shown in the annexed figures). As shown in Fig. 1 A, the adjustment system 30 preferably comprises a plurality of tanks 31 positioned in a hull 20, wherein each tank 31 is so constructed as to comprise a first portion 31A equipped with a first valve 32A for air inflow/outflow, and a second portion 3 IB equipped with a second valve 32B for water inflow/outflow. Moreover, Fig. 1 A shows only one compressor 34 connected to each tank 31 of said plurality of tanks 31, but it is clear that the adjustment system 30 according to the present invention may also be constructed in such a way as to comprise a plurality of compressors 34, e.g. a number of compressors 34 substantially matching the number of tanks 31.

The adjustment system 30 according to the present invention further comprises a control unit (not shown in the annexed figures) connected to the first valve 32 A, to the second valve 32B and to the compressor 34 so as to control their operation as a function of a measurement of the draught of the hull 20 (corresponding to the draught - or vertical elevation - of the vessel 1) taken by a detection system (not shown in the annexed figures, which may comprise, for example, at least one capacitive or resistive immersion sensor) associated with said hull 20 and connected to said control unit, wherein the control unit controls said valves 32A, 32B and the compressor 34 in such a way as to keep said draught of the hull 20 substantially constant also as the load applied to said hull 20 varies (i.e. with variations in the load transported by the vessel 1). It should be noted that the connection between the control unit and said elements of the adjustment system 30 and of the detection system may, without distinction, be either a wired or a wireless one.

The adjustment system 30 according to the present invention comprises also a power supply system (designated as a whole by reference numeral 35) for supplying electrical power to the components of said adjustment system 30, in particular the first valve 32A, the second valve 32B and the compressor 34 (and also, optionally, the control unit). In the embodiment shown in the annexed figures, said power supply system 35 is shown to include a plurality of batteries adapted to supply power to the vessel 1 when the latter is equipped with electrical propulsion; it is however clear that said power supply system 35 may also be conceived otherwise, since it may consist of, for example, an auxiliary power supply system installed aboard the vessel 1, in particular when the latter is equipped with at least one thermal engine, in particular supplied with fossil fuels.

Preferably, the adjustment system 30 according to the present invention comprises a bulkhead 36 movably positioned inside said at least one tank 31 and adapted to variably divide the first portion 31 A and the second portion 3 IB of the tank 31 (and also the respective fluids, i.e. compressed air and water, contained within said first portion 31A and second portion 3 IB).

The hull 20 may also be so constructed as to comprise at least one wing 37 (which may also be defined as “damping wing”) for damping the dynamic oscillations in the pitch, roll and heave degrees of freedom in the presence of external dynamic stresses that might destabilize the static behaviour of the vessel 1 in navigation. Preferably, said wing 37 is associated with the respective hull 20 in such a way as to extend horizontally from said hull 20 (towards an internal or central portion of the vessel 1, as clearly shown in Fig. IB). It must be pointed out that said at least one wing 37 may also provide lift to help lift the vessel 1 in some specific cases or speed ranges, thus providing a hybrid mode of operation between SWATH and foil. In a preferred embodiment, the casing 21 of the hull 20 is provided with at least one sealed hatch 38 allowing access to the components of the adjustment system 30 housed in the inner chamber 22, in particular for the purpose of carrying out maintenance operations on said components of the adjustment system 30. It must be pointed out that such maintenance operations are carried out after draining the water from the second portion 3 IB of the tank 31, so as to cause the hull 20 to emerge at least partially; thus, through said hatch 38 it is possible to gain access to the components of the adjustment system 30 housed in the inner chamber 22 of the hull 20 without having to haul the vessel 1, thereby considerably reducing the downtime of said vessel 1.

Preferably, the adjustment system 30 according to the present invention comprises an air lubrication system (designated as a whole by reference numeral 40 in Fig. 1 A) for lubricating said at least one hull 20, wherein said air lubrication system 40 is obtained by tapping a part of the air flow emitted by the compressor 34.

In particular, said air lubrication system 40 comprises a piping 41 adapted to connect the compressor 34 to the casing 21 of the hull 20, and a grid 42, in particular a microperforated one, obtained or formed on the casing 21 to create an air cushion on a bottom of the hull 21 by means of said tapping of a part of the air flow emitted by the compressor 34, said air cushion being adapted to drastically reduce the viscous friction when the vessel 1 is navigating.

As clearly shown in Fig. 1 A, said air lubrication system 40 preferably comprises a concavity 43 formed on a bottom of the hull 20 and extending longitudinally in said hull 20, said concavity 43 being adapted to avoid losing the air tapped from the compressor 34 and to maximize the effect of the air cushion.

Essentially, the air lubrication system 40 permits lubricating the hull 20 by using three different technologies: two of such technologies do not require the presence of the concavity 43, i.e. microbubble lubrication (“Bubble Drag Reduction”, or BDR) and lubrication with a uniform and homogeneous air layer (“Air Layer Drag Reduction”), while a third technology provides lubrication with an air cushion contained in the concavity 43 (“Partial Cavity Drag Reduction”, or PCDR).

The peculiar provisions of the adjustment system 30 according to the present invention (i.e. a technology that may also be defined as “WISE”, or “Water-air Injectable Swath Elevator”) permit the introduction of a degree of adjustment of the draught of each hull 20 (and hence of the draught of the whole vessel 1), which is given by the water/air contents of at least one tank 31 housed in the submerged hulls 20 of the SWATH system, thus ensuring real-time control of their hydrostatic thrust.

In fact, as previously explained herein and as will be further illustrated below, the adjustment system 30 exploits at least one tank 31 pressurized by at least one compressor 34, and a system of active valves 32A, 32B that permit draining/filling said at least tank 31 at will by using the surrounding water in which the SWATH hull 20 is immersed. Basically, the draught of each hull 20 is adjusted by modifying the hydrostatic thrust of the SWATH hull 20, and more specifically by:

- filling with water at least one tank 31 positioned in the inner chamber 22 of the hull 20 when the load applied to the hull 20 is low (that is, in a situation in which the load carried by the vessel 1 is light, i.e. when the vessel 1 is completely or substantially unladen), or

- draining the water from said at least one tank 31, in particular by pressurizing the first portion 31 A of the tank 31 by means of the compressor 43 and opening the second valve 32B to expel the water accumulated in the second portion 32B of the tank 31, when the load applied to the hull 20 is high (that is, when the load carried by the vessel 1 increases, i.e. when the vessel 1 is being loaded or is fully laden).

Thus, the draught of the SWATH hull 20 will remain constant with any load applied to the vessel 1, staying at the level for which its hydrodynamic behaviour was optimized at the design stage.

It is therefore apparent that the vessel 1 according to the present invention is constructed in such a way as to solve the problem of the load-dependent variable draught due to the low hydrostatic stiffness of the hulls 20, in particular of the SWATH type, without however requiring the use of any moving parts in proximity to, or even in contact with, the water. Therefore, the adjustment system 30 for adjusting the draught of a hull 20 according to the present invention has been conceived to avoid the necessity of servicing its components, while at the same time being quite simple and not requiring a large number of components (e.g. electro-mechanical ones); consequently, the provision of the draught adjustment system 30 according to the present invention implies lower development and production costs.

Moreover, the draught adjustment system 30 according to the present invention can also be implemented on small-size hulls 20 without having to resort to additional technology; as a consequence, the provisions of the present invention make it possible to realize a multi-hull vessel 1 which does not require extreme precision and care during the production of the draught adjustment system 30, and which is not subject to accidental damage that may occur in navigation, e.g. caused by components of the vessel 1 hitting moorings.

The provision of the air lubrication system 40 then permits creating an air cushion on a bottom of the hull 20 by tapping a part of the air flow emitted by the compressor 34, said air cushion being adapted to drastically reduce the viscous friction when the vessel 1 is navigating.

In particular, the lubrication system 40 according to the present invention makes it possible to achieve two goals with a single pneumatic system; in fact, said at least one compressor 34 supplies compressed air for both adjusting the draught of the vessel 20 and injecting air or microbubbles underneath said hull 20. In this regard, it must be pointed out that one of the limitations of the air lubrication provided by the systems currently known in the art lies in the addition, aboard a vessel, of a system of compressors and a system for supplying power thereto, and that the compressors and the associated power supply systems are specifically used for providing air lubrication only. In this context, the added cost and weight of the compressors to be used for said air lubrication is not always justified by a correspondingly great increase in performance or reduction in friction. According to the provisions of the present invention, instead, a single pneumatic system is employed which provides both functions of draught adjustment and air lubrication, so that costs are reduced through the use of a single system which proves very efficient for both functions. Furthermore, on SWATH vessels, wherein the friction part due to wave generation is virtually cancelled, and wherein there is only wall skin friction, air lubrication turns out to be particularly efficient in abating a significant share of the total friction.

With particular reference to Figures 2A to 2D, the following will describe a method for adjusting the draught of at least one hull 20 of a vessel 1, said at least one hull 20 being submerged or positioned under the water surface (i.e. said vessel 1 is of the SWATH, “Small- Waterplane-Area Twin Hull”, or SWASH, “Small Waterplane Area Single Hull”, type, wherein said at least one hull 20 is positioned under the water surface on which the vessel 1 is navigating).

The method according to the present invention comprises an activation of an adjustment system 30 for adjusting the draught of said at least one hull 20 of said vessel 1 in order to execute either a phase of filling with water, or (alternatively) a phase of draining water from, a second portion 3 IB of a tank 31 positioned in an inner chamber 22 of said at least one hull 20, wherein said filling and draining phases are managed by a control unit of said adjustment system 30 as a function of a measurement of the draught of the hull 20 (i.e. the draught or vertical elevation of the vessel 1) taken by a detection system (which may comprise, for example, at least one capacitive or resistive immersion sensor) associated with the hull 20 and connected to said control unit, wherein said filling phase and said draining phase are managed by the control unit in such a way as to keep said draught of the hull 20 substantially constant also as the load applied to said hull 20 varies (i.e. with different loads carried by the vessel 1). In particular, said phase of filling the second portion 3 IB of the tank 31 is shown in Fig. 2C and is carried out by means of the following steps (which may occur substantially simultaneously):

- opening a first valve 32A to allow a first portion 31 A of the tank 31 to communicate with the atmosphere;

- opening a second valve 32B to allow said second portion 3 IB of the tank 31 to communicate with the water in which the hull 20 is immersed, the opening of said second valve 32B allowing water to enter the second portion 3 IB;

- closing said first valve 32A and second valve 32B when the draught of the vessel 1 measured by the detection system matches a predefined draught.

It should be noted that the phase of filling the second portion 3 IB of the tank 31 makes it possible to obtain a phase of dynamic fall (“Dynamic fall regulation”) of the vessel 1, said phase of dynamic fall being useful whenever it is necessary to lower the navigation height of the vessel 1, e.g. when there are only a few people aboard, or when docking to allow the passengers to easily and stably get on/off In this frame, the filling of the second portion 3 IB of the tank 31 with water is obtained by opening the first valve 32A and the second valve 32B, thereby expelling into the atmosphere the air contained in the first portion 31 A of the tank 31 and facilitating the entry of water into the second portion 3 IB of the tank 31. In this condition, the first portion 31 A of the tank 31 occupies a small volume within the tank 31, and the vessel 1 has accumulated sufficient weight (due to the water contained in the second portion 3 IB of the tank 31) to sink to the desired depth.

As regards the phase of draining the second portion 3 IB of the tank 31, it is carried out by means of the following steps (which may occur substantially simultaneously):

- keeping the first valve 32A and the second valve 32B in the closed condition (see Fig. 2A), so as to prevent the first portion 31A of the tank 31 from communicating with the atmosphere and to prevent water from entering the second portion 3 IB of the tank 31;

- activating a compressor 34 in order to deliver compressed air into said first portion 31 A of the tank 31 (again, see Fig. 2A);

- opening the second valve 32B in order to allow at least a part of the water contained in the second portion 3 IB of the tank 31 to flow out, in particular while keeping the first valve 32A in the closed condition (see Fig. 2B);

- closing said second valve 32B when the draught of the vessel 1 measured by the detection system matches a predefined draught. In substance, the draining phase comprises a phase of delivering compressed air into the first portion 31 A of the tank 31 (Fig. 2A), wherein said compressed air can be used for causing the water contained in the second portion 3 IB of the tank 31 to flow out (Fig. 2B). Said compressed-air supply step may occur at any time in navigation, whenever a certain amount of air may need to be compressed in order to obtain a quick discharge of the accumulated water for any purpose (e.g. quick draught adjustment to avoid an obstacle, a sudden wave, stability problems, etc.). It should be noted that the compressor 34 always keeps the air in the first portion 31A of the tank 31 under pressure, so that it is ready for use, already compressed, for the filling phase or the draining phase, and also for air lubrication. Thus, with compressed air always available, there is no limitation caused by a fixed power level of the compressor 34, and the compressor 34 can always be made to operate within its most efficient range, without being necessarily bound to a power level necessary for executing the draining phase within a given short time. The compressor 34 according to the present invention can therefore compress the air also in navigation and leave it compressed inside the first portion 31 A of the tank 31, so that it will not necessarily have to provide air compression during the filling and/or draining phases; it is thus also possible to reduce the noise associated with the compressor 34, which can also be made to operate at lower rpm.

It must be pointed out that the phase of draining the second portion 3 IB of the tank 31 provides a phase of dynamic rise (“Dynamic rise regulation”) of the vessel 1. Once the vessel 1 has been loaded (with passengers and/or cargo), the navigation phase begins. The “WISE” adjustment system 30 comes in operation by opening the second valve 32B that prevents the water from flowing out, and the pressure of the air accumulated in the first portion 31A of the tank 31 ensures a quick discharge of the amount of water contained in the second portion 3 IB of the tank 31 to obtain the desired rise. Once the optimal navigation height has been reached, the first valve 32A is closed and the vessel can navigate under ideal conditions. At the same time, the compressor 34 can slowly recharge the first portion 31A of the tank 31 with compressed air in view of a later discharge that may be required for dynamic control in case of emergency (e.g. unbalanced vessel 1). When the vessel 1 is carrying a heavy load (passengers and/or cargo), during the navigation the second portion 3 IB of the tank 31 is normally half-empty. Conversely, when the vessel 1 is not carrying a heavy load (passengers and/or cargo), the opposite condition may occur, in which case it will be necessary to increase the amount of water in the second portion 3 IB of the tank 31 to prevent the hull 20 from getting too close to the water surface, which would result in poor hydrodynamic performance.

Assuming that the flow ports of the first valve 32A and second valve 32B are designed accurately, thus ensuring that the proper amount of water can be removed from or delivered into the tank 31, the dynamics of the filling and draining phases can be very fast; this will ensure fast control dynamics to overcome sudden stability problems caused by adverse navigation conditions.

The method according to the present invention may also comprise a maintenance phase (schematically shown in Fig. 2D), which comprises the following steps:

- keeping the first valve 32A in the closed position;

- opening the second valve 32B in order to allow substantially all the water contained in the second portion 3 IB of the tank 31 to flow out, so as to cause the hull 20 to emerge;

- closing said second valve 32B when the hull 20 has risen enough to allow access to a hatch 38 of said hull 20;

- opening said hatch 38 to gain access to the components of the adjustment system 30 positioned in an inner chamber 22 of the hull 20.

Said maintenance phase provides access to the components of the adjustment system 30 located in the inner chamber 22 of the hull 20 without the necessity of hauling the whole vessel 1, thus reducing the downtime of said vessel 1.

The features of the vessel 1 and of the associated adjustment system 30 according to the present invention, as well as the advantages thereof, are apparent from the above description. In fact, the adjustment system 30 according to the present invention substantially consists of a pneumatic system whose reliability and maturity has been known for decades, and which has proven to be more efficient than the electro-hydraulic or electro-mechanical systems used in the prior art. In addition, the absence of any parts directly in contact with, and moving relative to, the water makes it possible to obtain a reliable and durable system with low maintenance costs. Moreover, the possibility of modulating the system by dividing one hydro-pneumatic chamber into multiple independent chambers associated with the same pneumatic compressor 34 (or with several independent compressors 34) improves the adjustability and dynamic response of the system for small load variations.

Another advantage of the adjustment system 30 (also referred to as “WISE” system in the present description) according to the present invention lies in the fact that it permits the implementation of SWATH technology also on small-size hulls which would otherwise suffer from the lack of draught adjustability so that, notwithstanding the clear hydrodynamic advantages, they could not use such technology unless in combination with additional hydrofoil technology. Thanks to the teachings of the present invention, a hull 20 of the SWATH type can be entirely optimized for the speed ranges at which it will have to operate, in particular without the use of any additional subsystems (such as hydrofoils) that would impair its hydrodynamic performance at low speeds. Furthermore, the real-time adjustment of the opening of the first valve 32A and second valve 32B, which control the flow of air and water, respectively, into/from the tank 31 of the submerged hull 20 requires less energy than a draught adjustment achieved by means of electro-mechanical and electro-hydraulic systems, which are affected by low efficiency.

Lastly, the friction undergone in motion by the hull 20 (and hence by the vessel 1) is reduced in comparison with prior-art systems, due to the air lubrication system 40 that creates an air cushion which lubricates the bottom of the hull 20 when the vessel 1 is moving forwards or navigating. In particular, the lubrication system 40 according to the present invention permits reaching two goals by means of a single pneumatic system; in fact, said at least one compressor 34 supplies compressed air for both adjusting the draught of the hull 20 and injecting air or microbubbles underneath said hull 20; in this regard, by providing both functions of draught adjustment and air lubrication through a single system, costs are reduced, and the single system employed proves to be very effective in performing both functions. Moreover, on SWATH vessels, wherein the friction part due to wave generation is virtually cancelled, and wherein there is only wall skin friction, air lubrication is especially efficient and can abate a significant share of the total friction.

The small number of electro-mechanical components and the absence of any hydraulic components in the “WISE” adjustment system 30 result in lower development and production costs compared with prior-art systems. Furthermore, an economical advantage is achieved over the hydrofoil system, since the latter requires such high precision and care during production that inevitably result in a great increase in the cost of the whole SWATH system and a greater number of structural and functional parts.

Furthermore, the hydrofoil systems currently known in the art are typically made of composite material and are subject to accidental damage that may occur in navigation, e.g. caused by impacts against moorings. The only subsystems employed in the “WISE” adjustment system 30 are valves and at least one compressor, i.e. components which are known to be cheap and highly reliable due to their technological maturity. Lastly, the easy maintenance of the “WISE” adjustment system 30 makes it competitive in terms of operating costs, because it is not necessary to haul the hull 20 in order to be able to inspect the components housed therein.

The vessel 1 and the associated adjustment system 30 described herein by way of example may be subject to many possible variations without departing from the novelty spirit of the inventive idea; it is also clear that in the practical implementation of the invention the illustrated details may have different shapes or be replaced with other technically equivalent elements.

It can therefore be easily understood that the present invention is not limited to the abovedescribed vessel 1 and associated adjustment system 30, but may be subject to many modifications, improvements or replacements of equivalent parts and elements without departing from the inventive idea, as clearly specified in the following claims.