AU2015206001B2

AU2015206001B2 - Marine propulsion multihull ship

Info

Publication number: AU2015206001B2
Application number: AU2015206001A
Authority: AU
Inventors: Gianluca GUELFI; Lionel HUETZ; Matthieu KERHUEL; Hubert Thomas
Original assignee: ADVANCED AERODYNAMIC VESSELS
Current assignee: ADVANCED AERODYNAMIC VESSELS
Priority date: 2014-01-16
Filing date: 2015-01-15
Publication date: 2017-11-23
Anticipated expiration: 2035-01-15
Also published as: HK1225705A1; WO2015107125A1; EP3094549A1; AU2015206001A1; US20160332700A1; FR3016333A1; EP3094549B1; FR3016333B1

Abstract

This ship (10), which has a length-to-width ratio of less than two, comprises a superstructure and at least two hulls, the superstructure forming a wing capable passively of generating aerodynamic lift of between 20 and 90% of the weight of the ship at a cruising speed thereof, the wing comprising curved ends connected to each of the hulls and having an extrados developed surface area substantially equal to the product of the length times the width of the ship. It is characterized in that a point A of application of the aerodynamic lift generated by the superstructure (12) is situated to the rear of the centre of gravity G at which the forces of gravity are applied to the ship, a point H at which the resultant of the hydrodynamic loads generated by the hulls (50, 60) is applied being situated forward of the centre of gravity G.

Description

Marine propulsion multihull ship

The invention relates to the field of marine propulsion multihull ships with passive partial aerodynamic lift.

The invention more particularly relates to ships intended to transport people and/or goods at cruising speeds comprised between 40 and 70 knots.

More specifically, the invention relates to a marine propulsion multihull ship, having a ratio of a length of the ship to a width of the ship smaller than two, and with which an orthogonal frame of reference XYZ is associated, whereof a longitudinal axis Z, oriented from the back to the front of the ship, corresponds to a roll axis of the ship, a transverse axis Y corresponds to a pitch axis of the ship and an axis X corresponds to a yaw axis of the ship, the ship including a superstructure and at least two hulls, the superstructure of the ship forming a wing able to passively generate a significant aerodynamic lift, i.e., comprised between 20 and 90%, preferably between 35 and 90%, of the total weight of the ship at a cruising speed of the ship, said wing including curved ends connected to each of the hulls and having a developed surface of the extrados substantially equal to the product of the length of the ship multiplied by the width of the ship.

Passive partial aerodynamic lift refers to the capacity of the superstructure of the ship to generate an aerodynamic lift by simple difference between the speed of the ship and the speed of the air, as opposed to a hovercraft, for example, which generates an overpressure below the ship via compressors.

Passive partial aerodynamic lift also means that the aerodynamic lift generated by the superstructure is comprised between 20 and 90% of the total weight of the ship at a cruising speed of the ship. This implies that the superstructure has an outer developed surface substantially equal to the product of the length of the ship by the width of the ship, knowing that the length / width ratio of the ship is smaller than two.

Document GB 2,472,797 describes a ship of the aforementioned type.

In general, in the field of naval architecture, it is agreed, as for example illustrated by document US 2,666,406 A1, to place the point A, of application of the aerodynamic lift, in front of the center of gravity G, along the longitudinal axis Z, the point H, of application of the resultant of the hydrodynamic forces being consequently necessarily behind the point G. This configuration is also that of the ship according to document GB 2,472,797.

According to Maurizio Collu, in the article "The longitudinal static stability of an aerodynamically alleviated marine vehicle, a mathematical model", Proc. R. Soc. A 2010, page 466, the traditional analysis of the stability of the ship requires placing the point A in front of the point G, in particular because the hulls have a longitudinal center of hydrodynamic lift H located behind the point G and that moves backward when the ship accelerates under the effect of the speed and the aerodynamic lift.

The inventors of the ship according to the present patent application have identified a fundamental safety problem in this configuration. Indeed, this traditional analysis is based on a linear model valid for a small angles of pitch, around the equilibrium position of the ship. However, for larger angles of pitch, the hypotheses of the linear model used are no longer verified.

Simply put, when, under the effect of a relatively significant outside disruption such as a shift of wind or a wave, the ship trims bow up, leaving its equilibrium position, and the angle of attack of the wing increases. This results in an increase in the aerodynamic lift of the wing. The ship then trims bow up even more, entering an unstable dynamic, which may result in the ship tipping over backwards.

Similarly, when the outside disruption causes the ship to dive, the angle of attack of the wing decreases, and the lift consequently decreases. The ship dives even more, entering an unstable dynamic, which may lead to bow diving and the loss of the ship.

Embodiments of the invention therefore aim to resolve the above problems. According to the present invention, there is provided a ship of a marine propulsion multihull type, which has a ratio of a length of the ship to a width of the ship smaller than two, and with which an orthogonal frame of reference XYZ is associated, whereof a longitudinal axis Z, oriented from a back to a front of the ship, corresponds to a roll axis of the ship, a transverse axis Y corresponds to a pitch axis of the ship and an axis X corresponds to a yaw axis of the ship, the ship including a superstructure and at least two hulls, the superstructure of the ship forming a wing which generates an aerodynamic lift, which is comprised between 20 and 90% of the total weight of the ship at a cruising speed of the ship, the wing including curved ends connected to each hull of the at least two hulls and having a developed surface of an extrados of the wing substantially equal to the length of the ship multiplied by the width of the ship, wherein a point A, of application of an aerodynamic lift generated by the superstructure is located, along the longitudinal axis Z, behind a center of gravity G of application of gravitational forces on the ship, a point H of application of the resultant of the hydrodynamic forces generated by the at least two hulls being located, along the longitudinal axis Z, in front of the center of gravity G.

Embodiments of the invention relate to a ship of the aforementioned type, characterized in that a point A, of application of the aerodynamic lift generated by the superstructure, is situated behind a center of gravity G, of application of the gravitational forces on the ship, a point H, of application of the resultant of the hydrodynamic forces generated by the hulls, being situated in front of the center of gravity.

This ship is intrinsically stable, safe and high-performing in terms of speed and fuel consumption owing to the aerodynamic and hydrodynamic concepts implemented around an innovative relative position of the points A, G, H. The increased stability makes it possible to sail the ship faster and thus to benefit from a greater aerodynamic lift, which consequently decreases the resistance to forward movement, and therefore the energy consumption required to propel the ship.

According to specific embodiments, the ship includes one or more of the following features, considered alone or according to all technically possible combinations: - each hull is of the planing hull type, the hulls defining together at least one aerodynamic center of hydrodynamic lift behind the center of gravity and at least one center of hydrodynamic lift in front of the center of gravity; - each hull longitudinally includes, from back to front, at least one rear body having a rear keel line and a front body having a front keel line, the keel lines forming an angle between them between 0 and 6°, in particular 4°, and forming an angle of attack with the horizontal between - 5 and 5° in hydrostatic trim; - each hull includes at least one step between the rear and front bodies; - the front body has a V-shaped cross-section, the half aperture angle of which evolves continuously from a substantially zero angle at the front, to form a bow of the hull, toward a half aperture angle at the step, the front body having a prismatic coefficient measured in hydrostatic trim of less than 0.7; - the rear body includes, below its keel line, an anti-air leak blade; - a leading edge of a central portion of the superstructure is, along the longitudinal axis X, behind a bow of each hull; - a leading edge of an end portion of the superstructure connects a leading edge of a central portion of the superstructure to the bow of a hull following a gradual and curved aerodynamic profile; - a trailing edge of a central portion of the superstructure is, along the longitudinal axis X, behind a transom of each hull; - the ship includes two hulls arranged symmetrically relative to a median plane XZ, the ship being a catamaran; - the ship includes a central hull and two side hulls; the central hull defines a rear hydrodynamic center of lift and the side hulls define front hydrodynamic centers of lift; the ship has a length between 10 and 50 meters, preferably between 18 and 30 meters, in particular 21 meters.

The invention will be better understood upon reading the following description of particular embodiments, provided solely as an illustration and non-limitingly, the description being done in reference to the appended drawings, in which: - figure 1 is a high angle perspective view of a catamaran, making up a first embodiment of the ship according to the invention; - figure 2 is a low angle perspective view of the catamaran of figure 1; - figures 3 to 5 make up a lines plan of the catamaran of figure 1, figure 3 corresponding to a side half-view; figure 4 to a front half-view and a rear half-view; and figure 5 to a top half-view; - figure 6 is a diagrammatic illustration of the catamaran of figure 1 seen from the side, illustrating the position of the force application points; - figure 7 is a bottom half-view of the catamaran of figure 1, - figure 8 is a wing-shaped profile of the superstructure of the catamaran of figure 1; - figure 9 is a sectional view in a transverse plane XY of the catamaran of figure 1; - figure 10 is a high angle perspective view of a trimaran, making up a second embodiment of the ship according to the invention; - figure 11 is a low angle perspective view of the trimaran of figure 10; - figure 12 is a sectional view along a median plane XZ of a tripod, making up a third embodiment of the ship according to the invention; and - figure 13 is a front view of the tripod of figure 12.

In reference to figures 1 and 9, one particular embodiment of the ship according to the invention will be described.

According to this embodiment, the ship 10 is a catamaran.

It is intended to transport people and/or goods at cruising speeds comprised between 40 and 70 knots, for example 60 knots.

Associated with the ship 10 is a frame of reference XYZ, whereof the longitudinal axis Z, oriented from the back to the front of the ship, corresponds to the roll axis of the ship, the transverse axis Y, oriented from right to left (the terms “right” and “left” used here corresponding to the marine terms “starboard" and "port") corresponds to the pitch axis of the ship, and the axis X, orthogonal to the axes Y and Z, and oriented from bottom to top, corresponds to the yaw axis of the ship. When idle, the plane YZ is horizontal and the axis X is vertical. The frame of reference XYZ is attached to the center of gravity G of the ship 10.

The ship 10 is symmetrical relative to the median plane XZ.

It has a length/width ratio below 2, for example 1.4.

Its length along the axis Z is between 10 and 50 meters, for example between 18 and 30 meters, for example 21 meters. Its width is for example 17 meters.

The ship 10 includes a superstructure 12 and two hulls, right 60 and left 50, respectively.

The superstructure 12 serves to passively generate an aerodynamic lift along the axis X, once the ship 10 has a positive relative speed with respect to the air.

To do this, the superstructure 12 has the shape of a wing, a section of which is shown in figure 6.

The superstructure 12 thus has a leading edge 14 in the front, a trailing edge 15 in the rear, an intrados 16 extending from the leading edge 14 to the trailing edge 15 and constituting a bottom of the superstructure 12, and an extrados 17 extending from the leading edge 14 to the trailing edge 15 and constituting a top surface of the superstructure 12.

The total length I and the thickness d of the wing have a ratio of about 5. For example, the wing is approximately 20 meters long and 4 meters thick.

The superstructure 12 results from the sweep of the profile shown in figure 6, along a contour C, shown in the cross-section of figure 7. The contour C is U-shaped.

Thus, the superstructure includes a central portion 20 and end portions 30 and 40, respectively, curved downward relative to the central portion 20.

The right end portion 40 constitutes a connecting element of the superstructure 12 to the right hull 60, while the left end portion 30 constitutes a connecting element of the superstructure 12 to the left hull 50.

There is therefore aerodynamic continuity between the central portion 20 on the one hand, and the end portions 30 and 40 on the other hand, of the superstructure 12. The end portions 30 and 40 contribute to approximately 20% of the total aerodynamic lift of the superstructure 12 at the cruising speed.

As shown in figures 3 and 4, the intrados 16 of the superstructure 12 forms a tunnel 18 with the surface of the water.

Thus, the superstructure 12 of the ship 10, which is a wing whose ends are curved to be flush with the surface of the water, generates an aerodynamic lift much greater than that of a planar wing, arranged substantially parallel to the surface of the water and open at each of its ends.

The leading edge 14 is, at the central portion 20, approximately 5 meters above the surface of the water, while the trailing edge 15 is, at the central portion 20, approximately 3 meters above the surface of the water.

The superstructure 12 is able to generate a total aerodynamic lift Pa, which applies at a point A. The point A is substantially fixed irrespective of the speed of the ship 10. The point A is located, longitudinally relative to the leading edge 14, substantially at one third of the total length I of the profile of the wing.

The weight Pg of the entire ship 10 is applied on the center of gravity G.

Lastly, the submerged portions of the hulls 50 and 60 generate hydrodynamic forces, whereof the resultant Ph is applied at a point H.

As illustrated in figure 6, the ship 10 is designed such that the point A is situated, projected along the longitudinal axis Z, behind the center of gravity G.

For equilibrium reasons of the ship 10, the hydrodynamic response is applied at a point H, which must be located, as projected on the longitudinal axis Z, below or in front of the point G.

The fact that, in the ship, the points A, G and H are successively arranged from back to front, along the axis Z, is reflected by a shift toward the rear of the emerging part with respect to the submerged part of the ship 10. More specifically, the ship 10 is designed such that the front end F1 of the flotation plane is situated in front of the leading edge 14 of the superstructure 12. The flotation length L is the distance measured, along the axis Z, between the front F1 and rear F2 ends of the flotation plane. The center of gravity G of the ship is placed at least at 52% of the flotation length L, behind the front end F1 of the flotation plane. Consequently, as shown in figure 6, the leading edge 14 of the superstructure 12 is significantly withdrawn from the bows of the hulls 50, 60, at a first distance d1 therefrom, and the trailing edge 15 is placed withdrawn from the transoms of the hulls 50, 60, at a second distance d2 therefrom.

Advantageously, at each of these end portions, the leading edge 14 is configured so as to connect aerodynamically the leading edge of the main portion 20 of the superstructure and a bow of each hull.

More specifically, as shown diagrammatically in figure 6, as projected on the median plane XZ, the leading edge 14 has, at each end portion 30, 40, a curved profile allowing a connection to the corresponding gradual and very rounded trim, so as to limit the stall of the air flow by crosswind.

Advantageously, the trailing edge 15, at each end portion 30, 40 of the superstructure, makes it possible to connect the trailing edge of a transom of each hull, gradually, so as to maximize the lift of the superstructure.

This particular shape of the end portions 30, 40 of the superstructure makes it possible to generate a very high lift/drag ratio, greater than 20, even by relative crosswind.

The right 50 and left 60 hulls will now be described in detail.

The hull 50, 60, respectively, is of the stepped planing hull type.

The hull 50 successively includes, along the axis Z, a bow 51, a front body 52, a step 53, arranged substantially in a plane parallel to the plane XY, a rear body 54 and a rear transom 55.

The rear end portion of the rear body 54 is able to receive a propulsion system 5, the propeller shaft of which crosses through the rear transom 55 at an angle, such that the propeller(s) are at least semi-submerged at the cruising speed.

Similarly, the left hull 60 includes a bow 61, a front body 62, a step 63, a rear body 64 and a rear transom 65.

The rear end portion 64 receives a propulsion system 6, the propeller shaft of which crosses through the rear transom 65 at an angle, such that the propeller(s) are at least semi-submerged at the cruising speed.

The hull 50, respectively 60, is made up of a front body 52, 62, and a rear body 54, 64, separated from one another by a step 53, 63, forming a discontinuity in alignment, as projected on the plan XZ, between the keel lines 72 and 76, respectively of the front 52, 62, and rear 54, 64, bodies.

The keel lines 72 and 76 are in the extension of one another as projected on a plane YZ (cf. figure 7).

In the plane XZ, as shown in figure 3, at the step 53, respectively 63, the angle a between the keel lines 72 and 76 is between 0 and 6°, in particular equal to 4°.

In the plane XZ, the keel line 76 of the rear body 54, 64, is substantially rectilinear. The keel line 72 of the front body 52, 62, is slightly bowed, such that the bow 51, 61, of the front body 52, 62, leaves the water.

In the plane XZ, the keel lines 72 and 76 form, with the horizontal, an angle of attack β, comprised between - 5 and 5°, based on the speed of the ship 10, and consequently its trim.

The front 52, respectively 62, and rear 54, respectively 64, bodies, respectively make up planing hulls.

The front body 52, 62, thus has two faces, inner 71 and outer 73, respectively, extending laterally from the keel line 72, such that the cross-section of the front body is V-shaped.

The rear body 54, 64, thus has two faces, inner 75 and outer 76, respectively, extending laterally from the keel line 76, such that the cross-section of the rear body is V-shaped.

As shown in figure 9, the half aperture angle γ of the V-shaped section of the rear body is substantially constant, and equal to approximately 75°.

However, the half aperture angle γ of the V-shaped section of the front body decreases as one moves longitudinally from the step 53, 63, toward the bow 51,61. For example, this half angle is equal to approximately 75° near the step and is substantially zero near the bow. More specifically, the front body is characterized by a prismatic coefficient measured in hydrostatic trim of less than 0.7.

The front body 52, respectively 62, thus has a spatulate shape. In case of excessive modification of the angle of attack of the ship 10 with the nose down, the section of the front body that enters the water provides a significant hydrodynamic force, able to reestablish the angle of attack of the ship. The risks of nose diving are thus reduced.

The geometry of the hulls 50 and 60 is such that the resultant of the hydrodynamic forces Ph at the point H is split between a front contribution Ph 1, generated by a submerged portion of the front body of each hull and which is applied at the point H1, and a rear contribution Ph2, generated by a submerged portion of the rear body of each hull and which is applied at the point H2. Thus, the hulls define front centers of lift and rear centers of lift for the ship 10.

The behavior of the ship 10 according to the described example embodiment is as follows.

Stopped, when the aerodynamic lift Pa is null, the point H is aligned with the point G: these two points are combined in projection along the axis Z. The front and rear centers of hydrodynamic lift provide stability of the ship 10.

At low speeds, i.e., below 20 knots, the ship 10 behaves like a ship with a semidisplacement hull. It has a limited resistance to forward movement owing to a relatively low wetted surface/displacement ratio.

At average speeds, between 20 knots and a critical speed Vc, which represents the maximum resistance to forward movement and which is between 30 knots and 40 knots, the front body generates a depression in the surface of the water, in its wake. The rear body of the hull then being less supported by hydrodynamic forces, the ship tilts backward. However, in motion, the aerodynamic lift Pa that applies to the point A, behind the point G, generates a movement around the transverse axis Y that tends to modify the trim of the ship 10, such that the rear transoms 55 and 65 of the hull rise.

Thus, the backward tilting caused by a loss of hydrodynamic bearing at the rear of the ship is limited by the aerodynamic lift generated by the superstructure, which is able to compensate the decrease in hydrodynamic forces on the rear of the ship.

The hydrodynamic forces applied to the center of lift H2 decreasing with the speed, the point H moves gradually forward, toward the center of lift H1. This forward movement of the point H makes it possible to counterbalance the increase of the moment of the lift. The forward movement of the point H is allowed owing to the particular shape of the hulls.

At high speeds, i.e. above the critical speed Vc, in particular at the cruising speed, the ship 10 is such that the wetted surface has an optimized angle of attack, corresponding to the angle β defined above, allowing a maximal lift/resistance to forward movement ratio.

At these speeds, the aerodynamic lift Pa generated by the superstructure 12 is significant relative to the total weight Pg of the ship 10. Through the aerodynamic lift effect of the superstructure 12, the ship 10 accelerates, such that the weight perceived by the hulls (primarily the front body of each hull) is greatly reduced. Consequently, the resistance to forward movement of the ship is extremely reduced.

Furthermore, this causes not only a damping of the oscillating rotational movements around the axis Y, but above all a significant decrease in the heaving movements along the axis X.

If the aerodynamic lift increases sharply due to an outside disruption caused by a wind shift, the corresponding moment lifts the ship 10 from behind. This results in automatically decreasing the angle of attack of the aerodynamic profile of the superstructure of the ship, and therefore the intensity of the generated aerodynamic lift. Consequently, the ship returns to its equilibrium position by tilting backward. The equilibrium position of the ship 10 is consequently a stable equilibrium position. The ship 10 is thus stable in terms of pitch. In one extreme case, the lifting of the rear of the ship 10 would cause the propellers of the propulsion means to leave the water, which would result in canceling out the propulsion force and therefore reducing the relative speed of the ship. The aerodynamic lift would then decrease and the ship would return, by tilting backward around the axis Y, to its equilibrium position.

Thus, the geometry of the ship 10 makes it possible to guarantee that it is safe to use.

The spatulate shape of the front body of the hulls makes it possible to retain good performance levels despite the forward movement of the point H with the speed of the ship. Indeed, it makes it possible to preserve good pitch stability at high speeds: although the surface of the flotation plane quickly becomes smaller with the speed, the longitudinal inertia of the flotation plane decreases little, the length of the flotation plane remaining significant, still larger than the distance between the step and the transom.

In the described example embodiment, each rear body is equipped with a blade 80, for example shown in figures 2 and 3. This makes it possible to prevent the air circulating in the tunnel 18, defined by the intrados 16 of the superstructure, from laterally escaping between the surface of the water and the keel line 76 of the rear body 54, 64 of each hull 50, 60 at high speeds, when the rear body leaves the water. This blade 80 is arranged substantially in a plane parallel to the plane XZ and extends, along the axis X, from the keel line 76 of the rear body away from the latter, and along the axis Z, from the step 53, 63 toward the transom 55, 65. This anti-air leak blade 80 makes it possible to form a partition between the keel line 76 of the rear body and the surface of the water. Consequently, the confinement effect of the air in the tunnel 18 is maintained even for high speeds.

Many alternatives of the catamaran described above can be considered.

Thus, the rear end of the rear body can include a lowered rear portion, i.e., protruding toward the negative Xs relative to the keel line of the rear body, so as to guarantee that the propeller remains at least semi-submerged at all speeds.

Alternatively, the hulls do not include steps, the keel lines of the front and rear bodies then being in the continuation of one another in a plane parallel to the plane XZ, while retaining an angle between them, at their connection point.

Alternatively, each hull includes a plurality of through steps, and intermediate bodies between the front and rear bodies.

Instead of a catamaran architecture, other embodiments of the multihull ship according to the invention can be considered.

In particular, as shown in figures 10 and 11, in one embodiment, the ship 110 is of the trimaran type.

In these figures, the elements identical to the elements of the catamaran of figures 1 to 9 are identified using the same reference numbers increased by one hundred.

The trimaran 110 is symmetrical relative to the median plane XZ.

It includes a superstructure 112 able to generate an aerodynamic lift at a point A situated, as projected on the axis Z, behind the center of gravity G.

It includes a central hull 190 and left 150 and right 160 side hulls. Each of these hulls is similar to one of the hulls of the catamaran described above in detail. In particular, each hull is configured such that the resultant of the hydrodynamic forces H is situated, as projected along the axis Z, below or in front of the center of gravity, and in that this point H moves forward with the speed.

The superstructure 112 has a wing-shaped straight portion, the ends of which are continuously downwardly deformed so as to connect, on the one hand, to the right side hull 150 and, on the other hand, to the central hull 190, and a left wing-shaped portion, the ends of which are continuously downwardly deformed so as to connect on the one hand to the left side hull 160 and the other hand the central hull 190. The intrados 114 of each wing-shaped portion defines a tunnel 118 with the surface of the water. The two tunnels 118 are able to generate a duct effect increasing the lift generated by the superstructure 112.

Like the left 160 and right 150 hulls, the central hull 190 is a step planing hull that includes a bow 191, a front body 192, a step 193, a rear body 194 and a transom 195.

Projected in a plane YZ, the keel lines 172 and 176 of each hull of the trimaran 110 are in the extension of one another. In the plane XZ, the keel lines 172 and 176 form an angle between 0 and 6°, in particular equal to 4°. In the plane XZ, the keel line 176 is substantially rectilinear. The keel line 172 is slightly bowed, such that the bow 191 leaves the water. The keel lines 172 and 176 form, with the horizontal, an angle of attack β, comprised between - 5 and 5°, based on the speed of the ship 110.

For the rear body 194, the faces extending from the keel line give the rear body a V-shaped cross-section, largely open. For the front body 192, the faces extending from the keel line give the front body a V-shaped cross-section, open near the step and closing toward the bow 191. A third embodiment, called tripod, that constitutes an alternative of the second embodiment, trimaran, is shown in figures 12 and 13. In these figures, the elements identical to the elements of the trimaran of figures 10 to 11 are identified using the same reference numbers increased by one hundred.

In the tripod 210, the central hull 290 is essentially reduced to a rear body 294, able to define a rear hydrodynamic center of lift of the ship. The left 250 and right 260 side walls of the tripod 210 include a front body and a rear body, but the front body makes up the majority of the length of the side hull, such that the latter essentially defines a front hydrodynamic center of lift of the ship, the rear body essentially being limited to an anti-leak blade.

Although the geometry of the side hulls is similar to that of the hulls of the other embodiments, in the tripod 210, the keel line 274 of the central hull 290 has a large angle of attack relative to the horizontal. Thus, the center of lift defined by this central hull is located very backward along the axis Z when stopped and moves toward the rear with the increase in speed of the ship, before disappearing when the aerodynamic lift is sufficient to take the central hull out of the water.

In another alternative embodiment of the trimaran, the right and left side hulls do not make a significant hydrodynamic contribution, aside from assistance with the stability when stopped. At high speeds, they essentially constitute an anti-leak blade over the entire length. These side hulls conversely participate in the total aerodynamic lift by being flush with the surface of the water so as to form, with the intrados of the right and left superstructures, a tunnel able to generate a duct effect.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. - A ship of a marine propulsion multihull type, which has a ratio of a length of the ship to a width of the ship smaller than two, and with which an orthogonal frame of reference XYZ is associated, whereof a longitudinal axis Z, oriented from a back to a front of the ship, corresponds to a roll axis of the ship, a transverse axis Y corresponds to a pitch axis of the ship and an axis X corresponds to a yaw axis of the ship, the ship including a superstructure and at least two hulls, the superstructure of the ship forming a wing which generates an aerodynamic lift, which is comprised between 20 and 90% of the total weight of the ship at a cruising speed of the ship, the wing including curved ends connected to each hull of the at least two hulls and having a developed surface of an extrados of the wing substantially equal to the length of the ship multiplied by the width of the ship, wherein a point A, of application of an aerodynamic lift generated by the superstructure is located, along the longitudinal axis Z, behind a center of gravity G of application of gravitational forces on the ship, a point H of application of the resultant of the hydrodynamic forces generated by the at least two hulls being located, along the longitudinal axis Z, in front of the center of gravity G.
2. - The ship according to claim 1, wherein each hull of the at least two hulls is of the planing hull type, the at least two hulls defining together at least a first hydrodynamic center of lift, which is located along the longitudinal axis Z behind the center of gravity G, and at least a second hydrodynamic center of lift, which is located along the longitudinal axis Z in front of the center of gravity G.
3. - The ship according to claim 2, wherein each hull of the at least two hulls includes, from back to front along the longitudinal axis Z, at least a rear body, which has a rear keel line, and at least a front body, which has a front keel line, the rear and front keel lines forming between them an angle between 0 and 6° and forming with an horizontal line an attack angle between - 5 and 5° in hydrostatic trim.
4. - The ship according to claim 3, wherein each hull of the at least two hulls includes at least one step between the rear body and front body.
5. - The ship according to claim 4, wherein the front body has a V-shaped cross-section, the half aperture angle of which evolves continuously along the longitudinal axis Z from a substantially zero angle at the front, to form a bow of the hull, toward a half aperture angle at the step, the front body having a prismatic coefficient measured in hydrostatic trim of less than 0.7.
6. - The ship according to claim 4, wherein the rear body includes, below the rear keel line thereof, an anti-air leak blade.
7. - The ship according to any one of claims 1 to 6, wherein a leading edge of a central portion of the superstructure is, along the longitudinal axis Z, behind a bow of each hull of the at least two hulls.
8. - The ship according to claim 7, wherein a leading edge of an end portion of the superstructure connects a leading edge of a central portion of the superstructure to a bow of one hull of the at least two hulls, following a gradual and curved aerodynamic profile.
9. - The ship according to any one of claims 1 to 8, wherein a trailing edge of a central portion of the superstructure is, along the longitudinal axis Z, behind a transom of each hull of the at least two hulls.
10. - The ship according to any one of claims 1 to 9, including two hulls arranged symmetrically relative to a median plane XZ, the ship being a catamaran.
11. - The ship according to claim 1, including a central hull and two side hulls.
12. - The ship according to claim 11, wherein the central hull defines a rear hydrodynamic center of lift and the two side hulls define two front hydrodynamic centers of lift.
13. - The ship according to claim 1, having a length between 10 and 50 meters, preferably between 18 and 30 meters, in particular 21 meters.