DESCRIPTION

Application field and description of the prior art

The object of the present invention is a boat appendage which automatically changes, without any intervention from the crew, the external section of its wing profile from symmetrical to asymmetrical, namely with different convexities with respect to the longitudinal axis, obtaining, automatically and immediately, a shape more suitable to oppose the movement of the boat in undesired directions.

As it is known ¹ , the forward movement of sailing boats B (fig. 1) is determined by the development of forces p on the sails V when the latter have a suitable shape and are placed with a suitable incidence with respect to the wind W. The masts and the other riggings transfer these forces to the hull, which, being it floating on water and not constrained, moves with respect of the water itself.

In determined cases, said forces p are generated by the fluid (wind) which flows with a laminar flow on the solid (sail), according to the Bernoulli theorem, and are represented qualitatively in fig. 1 by vector p. In these cases, the forces on the sails are called lift forces. The motion Dp imparted to the hull by said forces will then have, possibly, a different direction from the forward movement along the longitudinal axis x of the boat, such direction will, instead, coincide with the one of said lift force p.

The motion of the boat, determined by the lift forces p on the sails and qualitatively represented by the vector Dp may advantageously be separated, by way of explanation, using the parallelogram law, according to the direction of the forward movement Da and according to its perpendicular Ds; the latter called "leeway".

Being the leeway Ds an undesired component of the motion, since it is directed orthogonally to the forward movement, appendages are commonly fixed to the hull and immersed in water, adapted to oppose the movement in that direction: the lateral surfaces themselves of the hull, centerboards, keels, rudders and others.

Some of the types of these immersed appendages operate merely due to the action and reaction principle: namely they oppose the movement in the direction of the leeway. The most modern and efficient types of appendages, on the contrary, are based on the Bernoulli theorem itself and exploit the flow of the fluid (water) A on the solid body of an appendage S appropriately fixed to the hull, which is determined when the boat starts to move in the direction E.

The direction E results from the interaction of the forces imparted to the sails of the hull and to the opposition to the leeway of the immersed parts.

Appendage S has the aim of generating a lift force P, similarly to the force p generated by the sails, adapted to effectively oppose the leeway, by virtue of the fact that it has a certain component Cp directed in the opposite way to the leeway itself.

As it is also known, the wing sections crossed by a fluid generate lift forces when at least one of the following cases occurs: they are symmetrical wing sections along the longitudinal axis and the fluid crosses them in a different direction from the axis of symmetry itself, namely a certain angle of incidence alpha is present; or they are asymmetrical wing sections, namely they have different convexities on the two sides of the longitudinal axis, thus determining a difference in the speed of the fluid flow that generates, according to the Bernoulli theorem, the lift forces also when there is no incidence.

Appendage S is appropriately fixed to the hull so that its longitudinal axis has the same direction as the longitudinal axis of the hull.

Since the boat, as described above, moves according to a direction E different from its longitudinal axis x, the fluid flows along the wing profile of the immersed appendage S with a given incidence alpha, thus generating the desired lift force P to oppose more effectively the component of the movement Ds in the direction of the leeway.

Almost all the modern sailboats are equipped with such rigid appendages having a symmetric wing profile.

It seems evident that a higher efficiency of the immersed appendages in generating hydrodynamic lift, both in module and in direction, namely in its components opposing the leeway Cp and coinciding with the forward movement, contributes to a higher opposition to the leeway Ds and consequently to determine a direction of the final movement of the boat E nearer to the pure forward movement Da along its longitudinal axis X.

According to the Bernoulli theorem, the lift force that is generated on a wing profile of an appendage S immersed in a moving fluid, depends on the difference of flowing speed of the fluid itself on the two sides of the profile. This difference of speed, and thus the lift force P generated can be increased by increasing, within certain limits, the incidence alpha of the fluid, or by using an asymmetrical wing profile that, being the speed and the incidence of the motion of the fluid A the same, will develop a higher lift force P oriented according to a more suitable direction.

Since the aim of the immersed appendages is to generate lift forces able to oppose the leeway Ds with the highest possible efficiency, thus determining a direction of the forward movement of the boat according to, as much as possible, the direction Da, the research has opted to realize appendages having a wing section as much efficient as possible in generating lift.

There are, indeed, appendages having a symmetrical and rigid wing profile, having different shapes and efficiency characteristics, and there are appendages having a profile that can be modified by suitable mechanisms. Such particular variable profile immersed appendages are described, for example, in the patents US-B-4537143 and US-B- 4280433.

The aforementioned prior art has some important drawbacks.

Appendages having a symmetrical and rigid profile, indeed, reach their maximum efficiency only at determined conditions of speed and direction of the water flow, developing, in any case, a lower lift than desired. They substantially develop the maximum efficiency only in particular conditions of water flow in terms of speed and incidence.

Such drawback is partially solved by said appendages with modifiable wing profile. The latter, however, need an intervention of the crew to modify their profile, making the control of the boat particularly complex, in search of the maximum speed and the best angle of the forward movement with respect to the wind, and continuous adjustments are required following the continuously varying conditions of the water flow.

Furthermore, the data about direction and speed of the water flow on the immersed appendages are difficult to acquire and even more difficult to compare instantly with the most efficient wing section in that given instant, making the data needed to the operator which should modify the section of the appendage actually unavailable.

Furthermore, the mechanisms included in the appendages that necessary to modify the wing profile, make it difficult to realize appendages that can have a load bearing structure having a section and mechanical characteristics sufficient to support the heavy ballasts that are often placed at the lower end of the immersed appendages that are necessary to oppose the heeling of the boat.

Summary of the invention In this given situation, the technical task of the invention is to contrive an immersed appendage able to substantially solve the aforementioned drawbacks.

In the scope of said technical task, an important aim of the invention is to obtain an immersed appendage able to adjust its wing section from symmetric to asymmetric, or vice versa, in a substantially instantaneous and automatic way.

More in particular, the aim of the invention is to provide an immersed appendage which can react in a substantially instantaneous and automatic way to each change of direction and of speed of the water flow which hits it, modifying the shape of its wing section and consequently taking the most efficient wing section to oppose the leeway, when the conditions of the flow, namely the direction of the motion of the boat, vary, without any intervention from operators.

Another important technical task is to obtain an immersed appendage that maintains a resistant section, to be constrained to the hull, sufficient to bear the axial, bending and torsion stresses, induced by the ballast that can be fixed at its lower end, together with the hydrodynamic forces acting on it.

A further aim is to obtain an appendage that can be manufactured and used in an easy and inexpensive way.

The technical task and the aforementioned aims are substantially reached by a boat appendage as claimed in the attached independent claim.

Preferred embodiments are described in the dependant claims.

Description of the drawings

Further characteristics and advantages will become more clear from the detailed description of a preferred, but not exclusive, embodiment of the invention. Such description is provided in the following with reference to the attached figures, given by way of example and thus not limitative, wherein:

figure 1 shows some of the forces involved in a typical sailing situation of a sailing boat viewed from the top and the qualitative directions of the movements;

figure 2 shows schematically a boat associated to an appendage according to the invention;

- figure 3 shows a normal section view of a first embodiment of an appendage according to the invention;

figure 4 shows a normal section view of a second embodiment of an appendage according to the invention; figures 5a, 5b show an appendage, similar to the one shown in figure 3, in two different operating conditions;

figures 6a-6c show schematically a possible engagement mode between elements that are part of the appendage according to the invention;

- figure 7 shows a schematic section view of an appendage according to the invention, wherein geometrical magnitudes are highlighted;

figures 8a-8c show schematic side views of operative configurations of a boat wherein an appendage according to the invention is mounted.

Detailed description

In accordance with the attached figures, the reference 1 indicates a boat appendage according to the present invention.

First of all, it has to be noted that the appendage 1 is adapted to be mounted, directly or indirectly, on the lower part of the hull 1 10 of a boat 100, so that, in operating conditions, the appendage is immersed in sea water (or in lake water) where the boat is navigating.

The appendage I can thus be technically called "immersed appendage".

Preferably, the appendage 1 is used in the field of sailing boats. As schematically shown in figure 2, on the hull 1 10 of the boat 100, opposite to the appendage 1, a sail 120 is mounted.

From the functional point of view, when the appendage 1 is immersed in water it aims to oppose components of the motion of the boat 100 having undesired directions, and in particular having directions different from the forward motion of the boat 100 itself. Similarly, the device can be used successfully in case of boats that use immersed appendages to lift the hull, or the hulls, from water, and thus remarkably reduce the hydrodynamic resistance to the forward movement. Since in this case the force to be opposed is directed vertically (force of gravity) the device will be placed horizontally, or anyway inclined so as to develop a lift force having at least one component according to the vertical direction, and firmly fixed to the hull or to an immersed appendage fixed in its turn to the hull (namely a rudder or leeboard).

The variation of the incidence angle will be, in this example, determined by the inclination of the hull or hulls along the longitudinal axis. Thus the changes to the geometry of the wing profile it determines will contribute to adjust automatically the direction and the intensity of the lift force developed, keeping the hull or hulls nearer to the desired horizontality, without any adjustment of the incidence by the crew. By ensuring the desired support to the hulls, the self-adjustment of the device contributes to limit the pitching (oscillation of the longitudinal axis) and the consequent risk of heeling (sinking of the forward part) that is typical in this type of boat.

The qualitative functioning of the appendage 1 in this second application is shown schematically in the figures 8a-8c, wherein the appendage 1 is schematically mounted at the lower end of a rudder T: the boat 100 may comprise a plurality of hulls 110 (only one of them is visible in the figures); the arrow FF represents qualitatively the resultant of the forces (or at least a significant component of such resultant) developed by the appendage 1 as a function of the conditions of the boat 100. In particular, in the situation shown in figure 8a, wherein the bow is at a higher level than the stern, the appendage significantly increases the lift directed upwards; in the situation shown in figure 8b, wherein bow and stern are substantially at the same level, the appendage 1 still develops a reaction directed upwards, but less intense; in the situation shown in figure 8c, wherein the stern is at a higher level than the bow, the appendage develops a significant reaction directed downwards.

More in particular, the appendage 1 comprises first of all a hydrodynamic load bearing body 10, adapted to be fixed to the boat 100 or to an element (rudder, leeboard) extending from the hull of the boat.

The load bearing body 10 comprises a substantially rigid structural core 10a. By way of example, the structural core 10a can be made of metallic material, such as for example, steel, high-resistance aluminum, carbon, titanium, cast iron or other alloys. Combinations of two or more metallic materials can also be used, for example selected among the aforementioned ones. High-resistance fiber composite materials can also be used.

The material which the load bearing body 10, and in particular the structural core 10a, is made of has to resist to external mechanical stresses so that it does not prejudice the correct movement and the correct functioning of the main baffle 20, and possibly of the auxiliary baffle 40, that will be described in the following.

Preferably the structural core 10a has mechanical and geometrical properties adapted to bear the stresses induced by the ballasts, if any, and by the hydrodynamic forces generated by the appendage 1 as a whole. The load bearing body 10, and in particular the structural core 10a, furthermore, has a section adapted to be fixed integrally to the hull 1 10 of the boat 100 and to the ballast itself.

The load bearing body 10 can substantially have a prismatic shape, whose generating lines are arranged according to a main direction DD.

In an embodiment wherein the appendage 1 extends directly from the hull of the boat 100, the main direction DD in use is substantially vertical, namely it coincides with the direction according to which the appendage extends from the boat 100, when it is mounted on the latter. In this embodiment, the appendage 1 is mounted to the hull 110 in a substantially direct way.

In a different embodiment, wherein the appendage 1 is mounted at the lower end of an element such as a rudder or a leeboard, the main direction DD in use is substantially horizontal, namely substantially orthogonal to the planar extension of the rudder or leeboard of the boat 100. In this embodiment, the appendage 1 is preferably mounted at the lower end of the rudder or leeboard.

Preferably the load bearing body 10 has, in a section according to a plane substantially orthogonal to the main direction DD, a shape of the type schematically shown in the figures 3, 4.

The load bearing body 10 is laterally delimited by a perimetral surface 11.

Preferably, the load bearing body 10 comprises a covering 10b, associated to the load bearing core 10a, for example in correspondence of a front end of the latter.

The covering 10b can be made, for example, of plastic material, preferably of the self- lubricating type.

Advantageously, the material which the covering is made of 10b has biocidal characteristics, so as to prevent the development of vegetal/animal organisms on the load bearing body 10. Such formations may, indeed, obstruct the movement of the baffles 20, 40 (described in the following) and thus prevent a correct functioning of the appendage 1.

By way of example, the covering 10b can be made of plastic material currently marketed with the commercial name "Teflon"®. Advantageously, the material which the covering 10b is made of is a material substantially resistant to compression, and able to allow the reciprocal movement of the baffles 20, 40, even in case of particularly intense axial and transverse stresses.

The appendage 1 comprises also a main baffle 20, substantially rigid and movable with respect to the load bearing body 10. The main baffle 20 can be made, for example, of metallic material (e.g. steel, titanium, aluminum).

Preferably, the material which the main baffle 20 is made of has an elastic module which is less flexible than the material used for the load bearing body 10, and in particular for the structural core 10a.

The main baffle 20 is thus able to follow possible transverse deformations of the load bearing body 10 and, thus, to work correctly, even when such deformations are present. Otherwise, when such deformations are present, the main baffle 20 can get stuck or be damaged, and anyway it would not be able to move in a suitable way.

Advantageously, the material which the baffle 20 is made of allows to vulcanize elastomeric materials (rubber) on it.

The fact that the main baffle 20 is made of rigid material allows the main baffle 20 itself to resist to the front stresses (whose intensity is often considerable) which it undergoes during the navigation, and to support the external element 30 (which will be described more fully in the following) in its resistance to such stresses.

Preferably, the main baffle 20 is associated to the load bearing body 10 so as to modify its own position with respect to the load bearing body 10 itself only according to vectors lying on a plane substantially orthogonal to the main direction DD.

In other words, by imagining that the main direction DD is directed vertically, namely substantially orthogonal to the water surface when the boat 100 is in operating conditions, the main baffle 20 is constrained to the load bearing body 10 so that it can move only according to vectors arranged horizontally.

In a different embodiment, wherein the appendage 1 is, for example, mounted at the lower end of a rudder or of a leeboard of the boat 100, the main direction DD can be horizontal. In this case, the vectors describing the motion of the main baffle 40 lie on a vertical plane, namely orthogonal to the main direction DD.

More in particular, the main baffle 20 is constrained in a way that the only movement allowed with respect to the load bearing body 10 is a rotation according to pairs of vectors lying on a plane orthogonal to the main direction DD.

The axis of rotation YY, in such movement, will thus be substantially parallel to the main direction DD.

Advantageously, the axis of rotation YY is geometrically placed within the load bearing body 10. The angle of rotation of the main baffle 20 can be comprised, for example, between 3° and about 5°, and it can be substantially equal to 4°.

From a geometrical point of view, by considering a plane with a section orthogonal to the main direction DD (figure 7), the distance 200 between the point representative of the axis of rotation YY and the front end (namely towards the bow) of the appendage 1 is higher than the distance 300 between such front end and the vector R resulting from the forces developed the by profile of the appendage 1 itself. The front end of the appendage 1 can be defined, in this case, as the point of incidence of the flow F hitting the appendage 1 itself.

For this reason, such forces determine a rotation arm, which it its turn determines the rotation movement (represented by the arrow J) of the main baffle in the desired direction.

It should be noted that such distances are preferably measured in the direction of the flow.

It should also be noted that the observations stated above are valid either when the appendage has a symmetrical profile, or when the appendage has an asymmetrical profile.

Figure 7 also shows schematically the diagram of the forces developed by the profile of the appendage 1 , which determine the aforementioned resultant R.

When the boat starts to sag to leeward, the flow F hitting the appendage 1 is no longer oriented according to the longitudinal axis XX and, since an angle different to zero is determined, the pressures on the two sides of the wing profile are no longer equal. The mechanism is build so that the resultant R of this difference of pressure does not cross the center of rotation YY of the baffle, thus determining an arm that makes the mechanism rotate in the desired direction, as indicated by the arrow J.

The main baffle 20 has an internal surface 21 and an external surface 22.

The internal surface 21 faces the perimetral surface 1 1 of the load bearing body 10. Advantageously, the main baffle 20 comprises a pair of striker arms 23, 24 that, by abutting on the load bearing body 10, limit the angular range of the main baffle 20 itself.

The striker arms 23, 24 have also the aim of provoking a deformation of the external element 30 from the opposite side with respect to the one in correspondence of which a transverse stress is received. Preferably the striker arms 23, 24 can be slightly elastic/modifiable, in order to reduce the stress exerted on the internal surface of the external element 30.

In an embodiment (figure 3), the main baffle 20 is, in a section according to a plane substantially orthogonal to the main direction DD, substantially Y-shaped.

In a different embodiment (figure 4), the main baffle 20 is, in a section according to a plane substantially orthogonal to the main direction DD, substantially "M"-shaped. In general, the main baffle has a shape adapted to serve as a lever operated by the hydrodynamic forces transferred to it by the external element 30.

Preferably, the main baffle 20 has a substantially constant section along the main direction DD.

In an embodiment, the main baffle 20 can be supported by a support base, being part of the load bearing body 10 and arranged at a distal end of the latter.

In order to allow the movement of the main baffle 20 with respect to such support base, round pawls and/or ball bearings can, for example, be used.

Figures 6a-6c schematically show a mode of engagement between the main baffle 20 and the load bearing body 10.

Such example refers in particular to the case wherein the direction DD is substantially vertical.

Figure 6a shows in particular a schematic lateral view of the appendage 1 , wherein some parts were removed to show others more clearly.

The dashed line H shows that not the whole extension of the appendage 1 according to the main direction DD is illustrated.

Figures 6b, 6c, on the contrary, show top schematic views of details of figure 6a. Such details are shown, respectively, by the dashed circles 6b, 6c.

In figure 6b it is possible to notice that the lower end of the main baffle 20 is provided with an expansion 26, having, for example, a substantially cylindrical shape; such expansion is adapted to move, integrally with the main baffle 20, in the guide 27 made in the support plate 12 radially extending from the lower end of the load bearing body 10.

In figure 6c it is possible to notice that the upper end of the main baffle 20 is integral with a connection element 25, the latter being hinged to the load bearing body 10.

As mentioned above, the appendage 1 comprises also an external element 30, at least partially deformable. The external element 30 can be made, for example, of fabric reinforced rubber.

The external element 30 has an internal surface 31 , at least partially facing and constrained to, at least in one point, the external surface 22 of the main baffle 20 and of the arms.

By way of example, the external element 30 can be fixed to the external surface 22 of the main baffle 20 by vulcanization.

Advantageously, when the main baffle 20 moves with respect to the load bearing body 10, it provokes corresponding deformations of the external element 30.

More in particular, each change of the position of the main baffle 20 provokes a corresponding deformation of the external element 30.

Preferably, the external element 30 is shaped automatically by means of the deformations imposed by the movement of the main baffle 20, between a first condition and a second condition.

In the first condition, the external element 30 defines a wing profile substantially symmetrical with respect to a longitudinal axis XX of the appendage 1 (figures 3, 4, 5a).

The longitudinal axis XX defines, in practice, the forward direction of the boat 100.

In the second condition, the external element 30 defines a wing profile substantially asymmetrical with respect to a longitudinal axis XX. See, in this regard, figure 5b, wherein the axis XX and XX' illustrate the rotation performed by the main baffle 20. The internal surface 31 of the external element 30 is at least partially fixed to a corresponding portion of the external surface 22 of the main baffle 20.

Preferably, the external element 30 covers the main baffle 20, and possibly part of the main body 10, along their whole length according to the main direction DD.

Preferably, the external element 30 is constrained in a removable way to the load bearing body 10. This allows an easy removal of the external body 30 when the latter has to be repaired or replaced.

The Applicant, indeed, believes that the external element 30 can be more subjected to wear than the load bearing body 10 and the main baffle 20; the external element 30 will need more maintenance and replacement operations than the other components of the appendage 1.

Preferably, the external element 30 keeps the main baffle 20, and the auxiliary baffle 40, if any, constrained to the load bearing body 10 in horizontal direction, namely according to directions lying on a plane orthogonal to the main direction DD. In other words, the external element 30 prevents the main baffle 20, and the auxiliary baffle 40, if any, from moving away from the load bearing body 10 according to directions orthogonal to the main direction DD. By virtue of the deformability of the external element 30, the main baffle 20, and the possible auxiliary baffle 40, however, can rotate with respect to the load bearing body 10, as described above.

In an embodiment (figure 3), the external element 30 has a portion 30a fixed to the load bearing body 10.

Preferably, the portion 30a of the external element 30 is associated to a pair of wings 32, 33 housed in respective seats 34, 35 made in the perimetral surface 1 1 of the load bearing body 10.

The wings 32, 33 are fixed to the portion 30a of the external element 30 by vulcanization.

The wings 32, 33 have the aim of keeping the external element 30 appropriately constrained to the load bearing body 10, and, in particular, of preventing the external element from losing the contact and the adhesion with the load bearing body 10 itself, during the maneuvering in reverse.

Preferably, the wings 32, 33 are slidingly associated to the respective seats 34, 35 so as to allow the external element 30 to be slipped off when, for example, it has to be repaired or replaced.

In a different embodiment (figure 4), the appendage 1 comprises an auxiliary baffle 40 associated to the load bearing body 10 opposite to the main baffle 20.

In other words, the main baffle 20 is associated to the front part (directed towards the bow) of the load bearing body 10, while the auxiliary baffle 40, when present, is associated to the rear part (directed towards the stern) of the load bearing body 10. The auxiliary baffle 40 has functional characteristics similar to the ones of the main baffle 20. In particular the auxiliary baffle 40 aims to contribute to the variation of the shape of the profile by increasing the convexity on the desired side.

Preferably the auxiliary baffle 40 is associated to the load bearing body 10 so that, when the auxiliary baffle 40 moves with respect to the load bearing body 10, it provokes corresponding deformations of the external element 30.

From a structural point of view, the auxiliary baffle 40 has an internal surface 41 and an external surface 42.

The internal surface 41 faces the perimetral surface 1 1 of the load bearing body 10. The external surface 42 faces and is constrained to a respective portion of the internal surface 31 of the external element 30.

Preferably, the auxiliary baffle 40 comprises a pair of striker arms 43, 44 that, by abutting on the load bearing body 10, limit the angular range of the auxiliary baffle 40 itself.

In this embodiment a blocking structure is provided (not shown) that can be selectively operated between a first condition and a second condition: in the first condition, the blocking structure is active on the auxiliary baffle 40 in order to prevent a substantial movement with respect to the load bearing body 10, and to keep it in a position wherein it defines a symmetrical wing profile with respect to the longitudinal axis XX; in the second condition , the blocking structure does not prevent the auxiliary baffle 40 from moving with respect to the load bearing body 10.

The blocking structure can be operated manually by the crew of the boat 100, between the first and the second condition.

The blocking structure is particularly useful when the boat 100 has to be maneuvered in reverse, and it is thus necessary that the auxiliary baffle 40 keeps a symmetrical wing profile in order to avoid interfering negatively with the movement of the boat 100 itself.

In addition, or alternatively, the auxiliary baffle 40 can be configured to block automatically, without the need for any intervention by the crew, when a it is maneuvered in reverse.

From an operating point of view what follows has to be noticed.

When the water starts to flow on the appendage 1 due to the movement of the boat 100, if the direction of the water flow is not oriented along the longitudinal axis of the appendage 1, namely if a sag to leeward occurs, the hydrodynamic forces, generated by the flow of the fluid and applied on both sides of the appendage 1, are different from each other, being a certain incidence present. In particular, on the side where a pressure is determined, the deformation of external element 30, being it partially deformable, transfers such pressure to the main baffle 20 and to the auxiliary baffle 40 (if present). The main baffle 20, and the auxiliary baffle 40 - if present, react to this force applied to them and, since they are not fully constrained to the load bearing body 10, they make a rotatory motion, wherein the center of rotation depends on their geometry. In particular, the main baffle 20 and the auxiliary baffle 40 - if present, modify their position with respect to the load bearing body 10, defining an asymmetrical wing profile. Such movement is transferred to the external element 30 on the opposite side with respect to the one which received the stress, so that the external element 30 is deformed, and in this specific case it increases its convexity.

Thus the appendage 1 as a whole is allowed to take its desired asymmetrical wing profile, in an automatic and instant way, in normal section, adapted each time to the different and variable conditions of direction and speed of the water flow to develop the highest possible lift force.

Reciprocally, on the side of appendage 1 on which the hydrodynamic forces determine, on the contrary, a respective depression, the latter will induce the same motion to the mechanism and it will generate the same desired deformation to the external element 30 of the appendage 1 as a whole.

The hydrodynamic forces that made the mechanism work are variable in direction and intensity, since they are generated by the instant characteristics of the flow of the fluid flowing on the appendage 1. Such flow, in its turn, is dependent on the speed and direction of the boat 100 to which the appendage is integrally fixed. This continuous variation, directly related to the motion of the boat, thus determines continuous differences in the rotation of the main baffle 20 and, possibly, of the auxiliary baffle 40, with a consequent deformation of the external element 30, so that the appendage 1 takes the desired and most efficient wing section, in an instantaneous and automatic way, without any intervention from the operators, to oppose the leeway, and the hydrodynamic forces generated by the same variation of shape can be effectively transferred to the hull, determining an improved direction and speed, by means of the baffle that, although it can rotate, is contrived to transfer loads to the bar keel, fixed, in its turn, to the hull.