Sail propulsion element, Sail-powered vehicle

Abstract

The invention relates to a sail propulsion element comprising a mast (3), a sail (1) inflatable or not essentially consisting of two adjacent surfaces (5) substantially sealed and connected to each other on their periphery, thus forming between them at least one closed cavity, said sail comprising an upper part (6), a lower part (7), a leading edge (8) and a trailing edge (9), the sail comprising different curves forming bulges over the entire length, an air duct arranged between the inside and the outside of the cavity of the sail, at least one means for injecting air into said cavity, the sail once inflated having a profile which remains permanently symmetrical, independently of the movement of said propulsion element, the direction or intensity of the wind, a headpiece (10) arranged on the upper part of the sail,and a sail receptacle (11) arranged between the leading edge and the trailing edge on the lower part of the sail. The element according to the invention is characterized in that the mast is arranged in front of the aerodynamic center of thrust of the sail, in that the mast is free or not to rotate 360°, and in that the sail comprises at least one means maintaining a low pressure in the sail. Figure for the abstract: figure 2,

Description

Title of the invention: Sail propulsion element, Sail propulsion vehicle

[0001] The invention relates to an inflatable sail and is situated in the field of sail propulsion or that of hybrid sail propulsion.

[0002] We recall below some definitions used in the following: - Reefing: consists of reducing the surface area of ​​a sail by partially folding it down, in order to adapt the surface area of ​​the sail to the strength of the wind. Reefing can be done manually or automatically. - Reefing bands: horizontal areas with reinforced sections allowing the attachment of reefing lines, for example with eyelets or pulleys. These reefing bands are arranged on the sail at the rib at each height where a reef is planned. There are as many reefing bands as there are possibilities for reducing the surface area of ​​the sail. - Lazy jacks: (in English lazy jack) device allowing the sail to be guided for reefing and lowering maneuvers. - Boom: horizontal spar, articulated near the base of the mast, which allows certain sails to be held and oriented. The boom can also accommodate the sail when it is lowered. - Flaying: A sail that fluffs is one that is insufficiently trimmed and partially deflates. A well-trimmed sail should be at the limit of fluffing. With a fully inflated sail, there is no fluffing, which allows you to stay facing the wind. - Leading edge: front part of a dynamic profile (wing, propeller, etc.) where a fluid will separate in two. - Trailing edge: characteristic part of any profile (wing, keel, rudder, etc.) subject to a flow of a fluid (air, water, etc.) on either side. It designates the part opposite the direction of the steering, or in other words, the rear part considered in the direction of the flow. - Header: upper end of the sail which follows the upper contour of the inflatable sail. Lowering: consists of lowering the sail. - Hoisting: consists of raising the sail. - Rigging: all the fixed and moving parts of a boat, such as a sailboat, allowing its propulsion and maneuvers by the force of the wind. - Sail receptacle: in addition to receiving the lowered sail, it can integrate other functions, such as taking up the tension forces provided by the sail, or housing other actuators, energy storage sensors and control module used to operate the sail. - Hydrodynamic drag: frictional force between the boat and the water. The higher the drag, the more the boat is braked. - Aerodynamic drag: component of the force experienced by a body in motion in a fluid which is exerted in the direction opposite to the direction of movement. According to the invention, the sail generates aerodynamic drag. - Aerodynamic lift: component of the force experienced by a body in motion in a fluid which is exerted perpendicular to the direction of movement. According to the invention, the sail generates aerodynamic lift - Relative wind or apparent wind: vector sum of the wind created by the boat's own speed and the actual wind speed. - Aerodynamic resultant: vector sum of aerodynamic lift and aerodynamic drag. - Sail angle of incidence: angle between the plane of the sail profile and the direction of the relative wind. - Sail angle: angle between the plane of the sail profile and the axis of the boat. Prior art

[0003] Document WO 2017 / 221117A1 already discloses a sail propulsion element comprising an inflatable sail with a symmetrical profile. This propulsion element comprises an inflatable sail consisting essentially of two adjacent surfaces, substantially sealed and connected to each other around their periphery, thus forming at least one closed cavity. The element further comprises a conduit arranged between the inside and the outside of the cavity and means for injecting air into the cavity. This sail, once inflated, has a profile which remains permanently symmetrical, regardless of movement of the element, the direction or intensity of the wind. The sail of this document is constantly inflated during its use in navigation.

[0004] Unfortunately, such a flexible sail has the drawback of not having an inflation suitable for the different stages of its use, and especially during the lowering and hoisting phases. Indeed, unlike a rigid sail, a flexible sail does not have a well-defined position during these manipulation stages (hoisting and lowering). During these stages, it is important to keep the sail close to the axis of symmetry of the sail profile, so as to prevent the sail from falling into the water or getting caught on an element close to it, or not stacking properly so that it can be stored compactly. Furthermore, it is important to maintain a low pressure inside the sail during the lowering phase or reefing, to prevent it from flapping, which could reduce its lifespan.

[0005] Furthermore, the sail described in this document cannot be properly secured when an electronic or electrical failure occurs in the sail management automation device, namely the controls, sensors, actuators or electrical power supply part.

[0006] Also known from document CN107878720A is a device for hydraulically regulating retractable boat sails. The sail consists of two parts, a lower part and an upper part, which can rotate independently of each other around the mast, depending on the sailing conditions or the wind direction. This device automatically adjusts the angle of attack of each of the two parts of the sail depending on the wind. The retractability of the sails ensures the safety of the boat in the event of poor sailing conditions. However, the retractability of the sail requires the proper functioning of the electronic automation devices. No alternative is proposed in the event of a breakdown. Summary of the invention

[0007] Also there remains the need to have a sail that is continuously inflatable or not, or a non-inflatable sail, or a taut sail, or a rigid sail with an asymmetrical profile, which, in the event of an electronic failure of its automatic management device, can remain in a safe position, both for the sail and for the sailors on board, while minimizing the forces generated by the lift of this inflatable sail. For this, the sail must be able to position itself facing the wind (and / or by a manual mode), so as to very significantly reduce the creation of aerodynamic lift but have only aerodynamic drag. This makes it possible to reduce the forces at the rigging and at the boat level, but also to intervene in complete safety.

[0008] The subject of the invention is a sail propulsion element comprising a mast, an inflatable or non-inflatable sail consisting essentially of two adjacent surfaces which are substantially watertight and connected to each other around their periphery, thereby forming between them at least one closed cavity, said sail comprising an upper part, a lower part, a leading edge and a trailing edge, the sail comprising different curves forming bulges over the entire length, an air duct arranged between the inside and the outside of the cavity of the sail, at least one means for injecting air into said cavity, the sail once inflated having a profile which remains permanently symmetrical, regardless of the movement of said propulsion element, the direction or intensity of the wind, a head arranged on the upper part of the sail, a sail receptacle arranged between the leading edge and the trailing edge on the lower part of the sail.

[0009] The propulsion element according to the invention is characterized in that the mast is arranged in front of the aerodynamic center of thrust of the sail, in that the mast is free or not to rotate 360°, and in that the sail comprises at least one means making it possible to maintain a low pressure in the sail.

[0010] The method according to the invention has the following various advantages. The center of aerodynamic thrust is clearly distinct from the mast, and is sufficiently far away from it towards the rear of the boat. The position of the mast in front of the center of aerodynamic thrust of the sail allows the resultant of the aerodynamic forces on the sail to bring the sail, in all cases, facing the relative wind, except when the relative wind is zero. In addition, maintaining the sail in a sufficiently inflated position thanks to the passive air inlets located, for example, on the leading edge allows its profile to be maintained, and thus prevents it from flapping even without active power. In the situation where the relative wind is zero (thus preventing the sail from being inflated), the sail will not flap. In such a situation of electronic failure, flapping of the sail would cause the sail to flap, and consequently the creation of significant forces risking the destruction of the sail or the mast.Finally, in the event of an electronic failure, the possibility of using the sail very easily and quickly in manual mode reinforces its safety, and consequently that of the boat and its crew.

[0011] Preferably, the aerodynamic center of thrust of the sail is distant from the mast by a length ranging from 0 to 10m.

[0012] Preferably, the pressure maintaining means is an air intake opening arranged facing the relative wind. This air intake makes it possible to maintain an internal pressure in the sail maintained by the relative wind.

[0013] Preferably, during said rotation of the mast the transmission of energy and controls is carried out with a device which does not hinder said rotation.

[0014] Preferably, the device which does not hinder rotation is chosen from the rotating joint or the cable chain if it is accepted that there is not infinite freedom of rotation but rather limited to a few turns.

[0015] Preferably, the air intake opening comprises a movable closing valve.

[0016] Preferably, at least one guide line consisting of one or more parts is arranged in the closed cavity of said sail, for the hoisting and lowering maneuvers of the sail, said guide line extending from the leading edge to the trailing edge of said sail, passing through the head and the sail receptacle.

[0017] Preferably, when a guide line is present, it is made in one part, and is fixedly attached to the sail receptacle on the trailing edge and movable by furling on the leading edge, or, movable by furling to the sail receptacle on the trailing edge and fixed on the leading edge and in that the guide line is arranged along the headboard in a movable manner on at least one pulley between the trailing edge and leading edge.

[0018] Preferably, when a guide line is present, it is made up of two parts, the first part on the trailing edge side is fixed or movable with a pulley on the head and movable by a winder on the receptacle, the second part on the leading edge side is fixed or movable with a pulley on the head and movable by a winder on the receptacle.

[0019] Another object of the present invention is a sail-powered or hybrid vehicle comprising at least one sail-powered element as mentioned above, a hull and a mast secured to said hull, but still free to rotate. This vehicle is characterized in that the mast is arranged inside the inflatable sail cavity mentioned above.

[0020] By vehicle is meant any machine comprising wheels or not, moving on land, water, ice, snow, mud.

[0021] Preferably, the sail is oriented according to the direction of the wind, and the direction of travel of the vehicle manually or automatically, making it possible to optimize the thrust in the axis of the boat or to achieve the desired thrust, while limiting the forces, pressures and heeling to acceptable values.

[0022] When the mast is not free to rotate infinitely, it can simply, for example, make two turns on itself, in one direction, without blocking with a cable chain. In such a case, it will then have to turn in the opposite direction to put it back in a correct sailing position.

[0023] By hybrid propulsion vehicle according to the invention, we mean sail propulsion coupled to another propulsion source such as for example propulsion by a propeller, driven by an electric or combustion engine, with energy storage of batteries, hydrogen (with a fuel cell), natural gas or fuel. Description of the drawings

[0024] The invention will be described with the aid of the following figures, schematic and not necessarily to scale, and in which: - [Fig.l] represents a reminder of the different physical forces which are applied to a ship, for example of the sailboat type with an engine, and in particular the projection of the resulting aerodynamic force; - [Fig.2] represents a schematic sectional view of the sail propulsion element according to the invention, arranged on a boat hull; - Figures 3A, 3B and 3C each represent a schematic top view of the position of the propulsion element according to the invention, as a function of different relative wind angles.

[0025] Before explaining in more detail the sail propulsion element, object of the present invention, with the aid of the figures cited, a reminder of some definitions of hydrodynamics and aerodynamics is set out below.

[0026] A sail-powered vehicle, hereinafter referred to as a sailboat or ship, is in contact with the air and with the water. From a physical point of view, the predominant factors are the hydrodynamic and aerodynamic forces which are exerted on the hull, the sails and the appendages (daggerboards, keel, rudder), propeller.

[0027] As shown in [Fig.l], the aerodynamic force (or sail thrust) results from the deflection of the air by at least one sail. The aerodynamic force is relative to the sail and to the position and strength of the relative wind. The drag force is in the direction of the relative wind, the lift force is in the perpendicular direction of the relative wind, it is not always perpendicular to the sail. For example, at 0°, a symmetrical profile has no lift due to the fact that the air travels strictly the same distance on the extrados and the intrados. At this moment, it only generates drag.

[0028] The aerodynamic force generated by the sail can also be broken down in the frame of reference of the boat, and not in that of the sail, to be composed of the sail propulsive force (which is in the axis of travel of the boat) and a drift force (perpendicular to the axis of the boat) which can induce heeling (transverse inclination of a boat caused by an external phenomenon such as the wind).

[0029] The hydrodynamic force results from the friction of the water on the hull and the drift or keel and the various submerged appendages. Its direction depends on the aerodynamic force to which it opposes, the propulsive force in hybrid mode, the state of the sea and the marine currents. The longitudinal component is called hydrodynamic drag, and the transverse component is called drift lift or anti-drift force or hydrodynamic lift. The direction and intensity of the hydrodynamic force does not depend only on the aerodynamic force. For a building (boat) operating in hybrid mode (wind and other energy), the hydrodynamic force will depend strongly on the speed of the building generated by thermal or electric propulsion for example, the state of the sea and the marine currents.

[0030] When the sail force is greater than the hydrodynamic force, the boat accelerates. When the sail force is less than the hydrodynamic force, the boat slows down. Furthermore, if the aerodynamic force is greater but directed towards the rear of the boat, the latter will slow down. If the hydrodynamic force is in the direction of travel of the boat (because there is a strong current), the boat (sailboat) will accelerate.

[0031] It is by optimizing the adjustment of the sail that the boat (sailboat) will achieve its maximum performance in terms of sail thrust in the direction of travel. Indeed, it is the optimization of the angle of the sail in relation to the relative wind, to the direction of the boat and the adjustment of the surface of the sail which will allow the boat to achieve the maximum of its sail propulsion in the axis of the boat. There can be an additional adjustment by playing on the internal pressure of the sail. This thus makes it possible to increase the speed of the boat or on the contrary to maintain the same speed while reducing the consumption of other energies, thanks to the sail propulsion.

[0032] [Fig.l] takes up each of the preceding names with a reference specific to it listed below: a: Lift force b: Drag force c: Aerodynamic resultant force d: Aerodynamic thrust force (along the ship's axis) e: Aerodynamic drift force f: Relative wind g: Relative wing angle - boat axis (e.g.: 15°) h: Relative wind angle and boat axis (e.g.: 30°) i: Propeller propulsive force j: Hull k: Sail 1: Mast m: Center of aerodynamic thrust n: Propeller o: sensor on fixed part (hull reference) p: sensor on moving part (sail reference) The information given by [Fig.l] allows switching from data sensors coming from the hull reference to data sensors coming from the sail reference, and vice versa.

[0033] [Fig.2] represents the sail propulsion element according to the invention, mounted on a boat, sailboat type, in operating position. This element comprises a general reference sail 1 mounted on the hull 2 ​​of a boat. The element comprises a mast 3 whose base 4 is fixed to the hull 2, while allowing the rotational movement of the mast 3. The mast 3 is self-supporting. The connection of the mast 3 with the hull 2 ​​is carried out using a support (not shown) intended to recover the physical force forces and leave the degree of freedom in rotation. The forces are measured at the level of the support(s). The sail 1 comprises two adjacent surfaces 5 (only one is shown in the figure) connected together so as to form a closed cavity. The material used for the two adjacent surfaces 5 must limit permeation so as to reduce air consumption, and thus allow the recovery and transmission of the various forces present.In some cases it may be necessary to add different treatments to the material in order to ensure, for example, a certain re- . resistance to fire, UV, or to apply an antistatic treatment.

[0034] The sail 1 comprises several curves (not shown) regularly distributed over the height (the curves are larger in the lower part of the sail, and smaller in the upper part). The height of the curve is often linked to the length of the profile chord.

[0035] The curves give it the external appearance of a bellows. The sail 1 comprises an upper part 6, a lower part 7, a leading edge 8 and a trailing edge 9. At least one air inlet 18 is arranged, for example, at the lower part 7 of the sail 1. Other air inlets 30 may also be arranged on the surface of the leading edge 8. At least one active means for injecting air 7a into the cavity of the sail is arranged in the extension of the air duct so as to be able to inject air into the cavity of the sail. The sail further comprises a head 10 arranged on its upper part 6, and a sail receptacle 11 arranged on its lower part 7 between the leading edge 8 and the trailing edge 9. This receptacle 11 is intended to receive all or part of the sail when it is lowered.This receptacle 11 may include different actuators and sensors facilitating manual or automatic maneuvering when hoisting or lowering the sail 1.

[0036] The sail propulsion element according to the invention comprises a guide line 12 arranged in the cavity of the sail 1. This guide line is intended for hoisting and lowering maneuvers and for reefing the sail 1. This line 12 extends substantially around the perimeter of the sail 1. The guide line 12 is fixed in a removable or non-removable, but non-movable manner, to an end 13 located close to the intersection of the trailing edge 9 and the sail receptacle 11. It then extends towards the upper part 6 of the sail 1, to run along the headboard 10 between the trailing edge 9 and the leading edge 8. The guide line 12 is movable along the headboard 10 using at least two pulleys or other possible return systems (not shown) each arranged on either side of the mast 3.This guide line 12 is adjacent to the leading edge 8, towards the sail receptacle 11, to then be fixed using a winder 19 on the sail receptacle 11 substantially at the level of the leading edge 8. The guide line 12 can be mounted towards a locking cleat if it is operated manually. On the other hand, it is wound onto an automatic winder for the automated version.

[0037] The guide line 12 has a length of approximately 50 meters for a sail having a total surface area of ​​approximately 100m2, and a tension of between approximately 50 and 250N depending on the uses made of it during the various lowering or hoisting maneuvers.

[0038] The mast 3 can be telescopic or fixed. When the mast 3 is telescopic, the head 10 is integral with the last element of the telescopic mast 3, being able to retain a degree of freedom in rotation, either relative to the mast, or with the last element of the mast which rotates. When the mast 3 is telescopic, it is made up of different elements which slide successively on each other to deploy or retract. If there is no reefing (case of transport ships) it is possible to deploy one element after the other constituting the telescopic mast, or all the elements at the same time.

[0039] When the mast 3 is fixed, only the head 10 is movable along the mast 3. The sail 1, being fixed to the head 10, descends or rises with the latter. The head can be freely rotating, locked in rotation or locked in rotation up to a certain force value. It is also possible to have a servo-control of the angular position of the head so as to control the twisting of the sail. Indeed, since the wind speed is not the same at all altitudes, it may be interesting to adapt the angle of incidence of the sail to the different altitudes to adapt to the different variations in relative wind.

[0040] It is also possible to combine a telescopic mast 3 and a headrest 10 which slides along the mast 3.

[0041] The head 10 comprises sufficient rigidity to communicate the physical forces existing between the different ropes and the mast 3, but also to support the weight of the sail when it is not inflated. According to the different embodiments according to the invention, the head 10 can be, as desired, freely rotating around the mast 3, locked in rotation around the mast 3, locked in rotation around the mast 3 up to a torque limit value to limit the forces to an acceptable value (the maximum acceptable value will depend on the construction of the system and the parts that one wishes to protect with this safety system) or even controlled so as to control the twisting of the sail.

[0042] The mast 3 is connected, fixed to the hull 2 ​​using a mast support 14 whose role is to take up the different physical forces existing between the sail and the boat while leaving the mast a degree of freedom in rotation so as to be able to position itself at the right angle in relation to the relative wind.

[0043] At the base of the mast 3, at the level of the hull 2, there is a system 15 for adjusting the angle of incidence which makes it possible to control the rotation of the sail 1 by rotating the mast 3 and all the operating parts fixed to said mast 3. This system 15 can consist, among other things, of a motor. This system 15 allows the sail 1 to be able to rotate around the axis of rotation of the mast 3, and consequently to control the desired angle of incidence of the sail 1. This system for adjusting the angle of incidence can also be mounted integrally with the mast 3, for example on the Nest with a motor driving via a pinion a crown integral with the hull.

[0044] It is recalled that the measurement of the angle of incidence makes it possible to know the angular positioning of the sail 1 relative to the axis of the boat. Such a device allows sail 1, hull 2 ​​and the relative wind to be placed in the same reference frame, regardless of where the wind measurement is taken on sail 1 or hull 2. Such an on-board system simplifies navigation, in automatic mode.

[0045] The sail propulsion element according to the invention arranged on the hull of a boat can furthermore be combined with a torque limiter, arranged at the base of the mast 3, and known to limit the maximum torque transmissible by the sail 1 to the hull 2.

[0046] The propulsion element according to the invention arranged on the hull of a boat may further comprise an electronic control system 16 arranged in the sail receptacle 11. An electrical rotating joint 17 may be added in the hull at the lower base of the mast 3. This joint 17 makes it possible to transmit the electrical power and the electrical controls between the hull 2 ​​and the lower part 7 of the sail 1, without limiting the number of rotations around the mast 3 achievable with the sail. The joint 17 may also be replaced by a suitable conventional cable chain. When the energy used to actuate the element according to the invention is, for example, hydraulic or pneumatic, a hydraulic or pneumatic rotating joint may be used.

[0047] Among the various measuring sensors, one can find the sensors for measuring the force transmitted from the sail 1 to the hull 2, the sensors for measuring the force in the transverse axis of the hull 2, the sensors for measuring the force in the longitudinal axis of the hull 2, the pressure sensor in the internal cavity of the sail 1, and the sensor for measuring the speed and angle of the relative wind. This last measurement can be carried out on both the sail 1 and the hull 2. In the case where the sensors are arranged on the part secured to the mast 3, they measure the forces in the longitudinal axis and the transverse axis of the sail 1.

[0048] The sail 1 may further comprise a sail neutralizer (not shown) which would be stored in the sail receptacle 11 or in the head 10. Such a neutralizer would make it possible, when deployed from the bottom to the top of the sail, or from the top to the bottom of the sail, to encapsulate the sail, thus reducing its volume by removing the internal air, and therefore preventing it from flapping, and reducing its wind resistance.

[0049] Figures 3A, B and C are distinguished from each other by a different angle of incidence of the sail.

[0050] In [Fig.3A], the relative wind is in the axis of the sail. In [Fig.3B], the axis of the sail has an angle substantially equal to 15° relative to the direction of the relative wind, and in [Fig.3C], the axis of the sail has an angle symmetrical and equal to that shown in [Fig.3B] relative to the direction of the relative wind.

[0051] In Figures 3A, 3B and 3C, the sail 1 has a substantially symmetrical profile. The mast 3 is symbolized by a circle. The relative wind is symbolized by the arrow 23.

[0052] [Fig.3A] represents a sail 1 in a stabilized state, facing the wind 23. The different efforts are balanced. The aerodynamic lift is zero (because it is identical on both sides of the sail due to its symmetrical profile), only drag 24 exists and maintains sail 1 along an axis parallel to the axis of the relative wind.

[0053] [Fig.3B] shows a sail 1 whose axis has an angle of about 15° with respect to the direction of the relative wind. The axis of rotation of the mast 3 is offset towards the front of the profile with respect to the center of thrust 25 of the aerodynamic forces along the axis of symmetry of the profile. [Fig.3B] shows that the torque generated by the aerodynamic force at a certain distance from the center of rotation of the mast 3 tends to bring the sail back to its position facing the relative wind, where it can remain stable thanks to the symmetrical profile of the sail.

[0054] The existing offset between the rotation point of the mast 3 and the center of thrust 25 allows the propulsion element of the invention to ensure that the sail 1 is maintained both in situations of large angular deviation from the wind direction and those of small deviation. Such an offset between this rotation point of the mast 3 and the center 25 allows the sail 1 to be recalled towards the neutral position of the sail, that is to say facing the wind when it deviates therefrom. Such an offset enhances the safety of navigation since the sail returns on its own to a position adapted and optimal relative to the direction of the relative wind, which minimizes the efforts and keeps the sail in a position facing the wind. However, this distance must be minimized so as not to overly increase the efforts required for the rotation of the sail.

[0055] [Fig.3C] is the symmetrical figure to that of [Fig.3B] with respect to the relative wind axis. The same remarks as those of [Fig.3B] apply.

[0056] Example The following example is given for illustration purposes only and is in no way limiting. The following table lists different possible situations. Cargo Sailboat Boat length (meter) 2 100 Number of sails 1 4 Inner layer of sail polyester (g / m2) 220 240 Outer layer of sail coated polyester (g / m2) 110 160 Sail height (meter) 17 40 Longest sail length (meter) 8 17 Longest sail width (meter) 1.8 3.5 Sail area (m2) 100 500 Number of partitions 30 35

[0057] The outer layer of the sail, also called bodywork, is made of a fabric comprising an outer part in contact with the outside air, and an inner part. This fabric can be made of a polyester woven fabric coated with polyurethane. The weight of this fabric can be 110g / m2 for a sail area of ​​approximately 100m2.

[0058] The upper part of the sail can be attached using Velcro-type self-gripping strips. The connections between the outer parts of the sail and the ribs (internal connections) as well as the connections between the components of the outer part can be made by welding or gluing or any other means of connection (zipper for example) making it possible to guarantee both a sufficiently low level of permeation compatible with the existing inflation system and also to guarantee the passage of forces.

Claims

1.

2.

3.

4. Claims Sail propulsion element comprising: a. a mast (3), b. an inflatable sail (1) consisting essentially of two adjacent surfaces (5) substantially sealed and connected to each other around their periphery, thus forming between them at least one closed cavity, said sail comprising an upper part (6), a lower part (7), a leading edge (8) and a trailing edge (9), the sail comprising different curves forming bulges over the entire length, said sail having an aerodynamic center of thrust, c. an air duct arranged between the inside and outside of the sail cavity, d. at least one means for injecting air into said cavity, the sail once inflated having a profile which remains permanently symmetrical, regardless of the movement of said propulsion element, the direction or intensity of the wind, e. a headpiece (10) arranged on the upper part (6) of the sail (D, f. a sail receptacle (11) arranged between the leading edge (8) and the trailing edge (9) on the lower part (7) of the sail, characterized in that the mast is arranged in front of the aerodynamic center of thrust of the sail, in that the mast is free or not to rotate 360°, in that it comprises a system (15) for adjusting the angle of incidence which makes it possible to control the rotation of the sail 1 by rotating the mast (3) and in that the sail comprises at least one means maintaining a low pressure in the sail. Element according to claim 1, in which the aerodynamic center of thrust of the sail (1) is distant from the mast (3) by a length ranging from 0 to 10 m. Element according to claim 1, wherein the pressure maintaining means is an air intake opening arranged facing the relative wind. Element according to claim 1, wherein during said rotation of the mast a transmission of energy and controls is carried out with a device which does not hinder said rotation.

5. An element according to claim 4, wherein the device which does not hinder rotation is chosen from the rotating joint or the cable chain.

6. Element according to one of claims 3, in which the air intake opening comprises a movable closing valve.

7. Element according to one of the preceding claims, in which at least one guide line consisting of one or more parts is arranged in the closed cavity of said sail, for the hoisting and lowering maneuvers of the sail, said guide line extending from the leading edge to the trailing edge of said sail, passing through the head and the sail receptacle.

8. Sail or hybrid propulsion vehicle comprising at least one element according to one of the preceding claims, a hull and a mast (3) made integral with said hull but still free to rotate, characterized in that the mast (3) is arranged inside the cavity of said inflatable sail.

9. A vehicle according to claim 7, wherein the sail is oriented according to the direction of the wind, and the direction of travel of the vehicle manually or automatically.