Sail propulsion element comprising a sealed partition separating lower and upper inflatable chambers, and lower and upper air injection devices

Abstract

The inventions relates to a sail propulsion element (6) comprising: - a mast (8); - an inflatable sail (10) internally delimiting an inflatable cavity; - a headboard (12); - a sail receptacle (14); - at least one sealed partition (22) separating, in the inflatable cavity, a lower inflatable chamber (28) and an upper inflatable chamber (24); - at least one upper air injection device (32) capable of injecting air into the upper inflatable chamber (24); and - at least one lower air injection device (30) capable of injecting air into the lower inflatable chamber (28).

Description

[0001] DESCRIPTION

[0002] TITLE: Sail propulsion element comprising a watertight bulkhead separating lower and upper inflatable chambers, and lower and upper air injection devices

[0003] technical field

[0004] The invention relates to a wind-powered vehicle and falls within the field of wind propulsion or hybrid wind propulsion.

[0005] In particular, the invention relates to a sail propulsion element.

[0006] Previous techniques

[0007] A prior art known is a wind propulsion element intended to equip a wind-powered vehicle and described in document WO 2022 / 248812.

[0008] The sail propulsion element described in this document includes a mast, an inflatable sail with a plurality of cells spaced by ribs made of a flexible, air-permeable material, at least one air duct between the inside and outside of the inflatable sail, at least one means of injecting air into the inflatable sail, a headboard and a sail receptacle.

[0009] The lowering (doing so that the sail is lowered) and raising (doing so that the sail is raised) of the sail propulsion element described in document WO 2022 / 248812 have been found to be improvable. In fact, checking the correct positioning of the inflatable sail during these two operations has proven necessary.

[0010] The invention aims at better control of the lowering and raising of an inflatable sail.

[0011] Description of the invention

[0012] The invention relates to a sail propulsion element comprising: a mast; an inflatable sail internally delimiting an inflatable cavity, the sail comprising an upper part, a lower part, a leading edge and a trailing edge, the sail comprising various curves forming bulges, a headboard disposed on the upper part of the sail; a sail receptacle disposed on the lower part of the sail; at least first and second watertight bulkheads separating the inflatable cavity into a lower inflatable chamber, at least one intermediate inflatable chamber and an upper inflatable chamber; at least one upper air injection device capable of injecting air into the upper inflatable chamber; at least one lower air injection device capable of injecting air into the lower inflatable chamber;and at least one intermediate air injection device which is reversible and which is disposed in an opening formed in one of the first and second watertight bulkheads, said intermediate air injection device being capable of circulating air between the inflatable chambers adjacent to said first or second watertight bulkhead through said first or second watertight bulkhead.

[0013] The said lower and upper air injection devices allow air to be injected independently into the upper and lower inflatable chambers and thus allow the upper and lower inflatable chambers to be inflated independently.

[0014] The intermediate air injection device allows air to circulate between the inflatable chambers above and below the first or second watertight bulkhead, that is, between the inflatable chambers adjacent to the first or second watertight bulkhead. The intermediate air injection device thus allows the inflatable chambers adjacent to the first or second watertight bulkhead to be inflated independently.

[0015] Thus, the lower, middle, and upper inflatable chambers can be inflated separately. Raising and lowering the inflatable sail can be carried out sequentially, chamber by chamber, for better control during the process.

[0016] Preferably, the lower and upper air injection devices are separate and capable of operating independently of each other.

[0017] Preferably, said intermediate air injection device is separate from the lower and upper air injection devices and is capable of operating independently of the lower and upper air injection devices.

[0018] The leading edge is the front part of an airfoil. The leading edge contains the stagnation point where the flow of an incident fluid splits in two.

[0019] The trailing edge is the rear part of the airfoil considered in the direction of fluid flow.

[0020] The headboard follows at least part of the upper contour of the sail.

[0021] The sail receptacle is designed to receive the lowered sail. It can integrate other functions such as absorbing tension forces provided by the sail, housing actuators, sensors, or a control unit for the inflatable sail.

[0022] Optionally, at least one of the watertight bulkheads may include a rigid cleat. This rigid cleat allows the watertight bulkhead to be secured within the sail compartment.

[0023] The said watertight bulkhead equipped with the said rigid racket allows reefing by folding the inflatable sail from the bottom up to the said watertight bulkhead.

[0024] Reefing involves reducing the surface area of ​​a sail by partially folding it from the bottom, in order to adapt the sail area to the wind strength.

[0025] The mast can be telescopic or non-extendable.

[0026] When a mast is telescopic, it consists of different elements that slide successively relative to each other to extend or retract. In a telescopic mast, the masthead is fixed to the upper element of the telescopic mast and is able to maintain a degree of rotational freedom around a longitudinal axis of the mast, either the upper element of the mast being able to rotate around the longitudinal axis or the masthead being able to rotate around the mast.

[0027] When the mast is inextensible, the head is movable along the mast.

[0028] The telescopic or non-extendable mast may be free to rotate relative to the hull. Alternatively, the mast may be fixed, at least in rotation, relative to the hull.

[0029] The inflatable sail is attached to the headrest so that it goes up or down at the same time as the headrest.

[0030] The headboard has sufficient rigidity to transmit various physical forces from the inflatable sail to the mast and to support the weight of the inflatable sail.

[0031] The sail rotation control unit can be configured to control the angle of the sail relative to the wind.

[0032] The control unit may also be capable of controlling the raising and lowering of the inflatable sail.

[0033] The inflatable sail can consist of two canvases connected to each other around their perimeter and forming the inflatable cavity.

[0034] Each piece of fabric in the inflatable sail can have a weight between 50 and 300 g.m' 2 .

[0035] Advantageously, the sail propulsion element includes at least one additional intermediate air injection device disposed in an opening formed in the other of said first and second watertight bulkheads, said additional intermediate air injection device being capable of circulating air between the inflatable chambers adjacent to said other watertight bulkhead through said other watertight bulkhead.

[0036] Optionally, at least one of the lower, upper, and intermediate air injection devices is equipped with a valve to prevent air from flowing through said air injection device. Optionally, the additional intermediate air injection device is equipped with a valve to prevent air from flowing through said air injection device.

[0037] Optionally, at least one of said lower and upper air injection devices is reversible.

[0038] Optionally, the additional intermediate air injection device is reversible.

[0039] Advantageously, the sail propulsion element includes at least one pressure-sensing means arranged in one of said inflatable chambers.

[0040] The control unit may be capable of controlling the operation of the air injection devices based on signals from said pressure-sensing means.

[0041] The control unit may also be capable of controlling the raising and lowering of the inflatable sail based on signals from said pressure-detecting means.

[0042] The present invention also relates to a wind-powered or hybrid-powered vehicle comprising at least one hull, at least one wind propulsion element as defined above, the mast of said wind propulsion element being fixed to said hull, the inflatable sail of said wind propulsion element being free to rotate.

[0043] The present invention also relates to a method for hoisting an inflatable sail of a sail propulsion element as defined above, comprising at least: the injection of air into the upper inflatable chamber by means of the upper air injection device; the hoisting of a part of the inflatable sail; the injection of air into the lower inflatable chamber by means of the lower air injection device; and the complete hoisting of the inflatable sail.

[0044] In an embodiment in which the sail propulsion element includes at least one intermediate air injection device disposed in an opening formed in the watertight bulkhead adjacent to the upper inflatable chamber, the method may include injecting air into the upper inflatable chamber by means of said upper and intermediate air injection devices.

[0045] Optionally, said intermediate air injection device allows air to flow through said airtight bulkhead when the inflation sail is fully hoisted.

[0046] Thus, the pressure is uniform between the inflatable chamber below said watertight bulkhead and the inflatable chamber above said watertight bulkhead.

[0047] Optionally, the process includes injecting air into the upper inflatable chamber by means of the upper air injection device and / or injecting air into the lower inflatable chamber by means of the lower air injection device when the inflatable sail is fully hoisted.

[0048] The present invention also relates to a method for lowering an inflatable sail of a sail propulsion element as defined above, comprising at least: the extraction of air from the lower inflatable chamber by means of the lower air injection device; the lowering of a part of the inflatable sail; the extraction of air from the upper inflatable chamber by means of the upper air injection device; and the complete lowering of the inflatable sail.

[0049] In an embodiment in which the sail propulsion element includes at least one intermediate air injection device disposed in an opening formed in the watertight bulkhead adjacent to the lower inflatable chamber, the method may include the extraction of air from the lower inflatable chamber by means of said lower and intermediate air injection devices.

[0050] Brief description of the drawings

[0051] The present invention will be better understood by studying the detailed description of embodiments, taken by way of non-limiting examples and illustrated by the attached drawings in which: [Fig 1] is a front view of a wind-powered vehicle according to a first example of an embodiment of the invention;

[0052] [Fig 2] is a side view of the inflatable sail of the wind-powered vehicle in Figure 1;

[0053] [Fig 3] is a schematic representation of a hoisting method according to the invention; and

[0054] [Fig 4] is a schematic representation of a lowering method according to the invention.

[0055] Detailed description

[0056] Figure 1 illustrates a sail-powered vehicle 2, for example a sailboat or ship, comprising a hull 4 and a sail propulsion element 6. Alternatively, the sail-powered vehicle 2 could comprise more than one hull 4, for example when the sail-powered vehicle 2 is a catamaran or trimaran.

[0057] The sail propulsion element 6 includes a self-supporting mast 8 made attached to the hull 4 by a support (not shown), an inflatable sail 10, a head 12 and a sail receptacle 14.

[0058] The inflatable sail 10 internally delimits an inflatable cavity. The inflatable sail 10 here comprises two fabrics 16 connected to each other around their perimeter so that the mast 8 extends longitudinally between the two fabrics 16. The inflatable sail 10 comprises an upper part, a lower part, a leading edge and a trailing edge.

[0059] The head 12 is positioned on the upper part of the inflatable sail 10, the sail receptacle 14 being positioned on the lower part of the inflatable sail 10. The head 12 is supported by the mast 8. The head 12 is here fixed to the upper end of the mast 8. The sail receptacle 14 is fixed to the support.

[0060] The sail receptacle 14 is fixed to the support. As will be described in more detail later, the head 12 is movable relative to the sail receptacle 14, which is fixed. The sail receptacle 14 extends from the leading edge to the trailing edge. The sail receptacle 14 is designed to receive all or part of the inflatable sail 10 when it is deflated.

[0061] The inflatable sail 10 is made free to rotate relative to the hull 4 of the wind-powered vehicle 2 by any suitable means. In particular, the wind propulsion element 6 includes a control unit 17 (shown schematically) for the inflatable sail 10, capable of modifying the orientation of the inflatable sail 10 relative to the hull 4 of the wind-powered vehicle 2 in order to optimize or regulate the aerodynamic thrust generated by the inflatable sail 10.

[0062] Each of the two canvases 16 is, for example, made of a coated material, in particular textile, which allows it to meet conditions of mechanical resistance, waterproofing, and protection against fire and UV radiation.

[0063] The two interconnected fabrics 16 form a closed inflatable cavity. The inflatable sail 10 comprises a plurality of partitions 18 made of a flexible material, each extending within the inflatable cavity from the leading edge to the trailing edge. The partitions 18 delimit a plurality of cells 20 within the inflatable cavity, along the span of the inflatable sail 10. The partitions 18 are attached to the inflatable sail 10, for example by sewing, welding, or gluing, and give the inflatable sail 10 different curves, forming bulges. At least the first and second partitions 18, and here the first, second, and third partitions 18, are made of a watertight material so as to form watertight first, second, and third partitions 22.The waterproof material of the watertight partitions 22 is, for example, a coated material, particularly a textile, that meets requirements for mechanical resistance, watertightness, and fire protection. The other partitions 18 are made of a permeable material to allow air to circulate through them.

[0064] Optionally, at least one or each watertight bulkhead 22 may include a rigid rack, in order to press the watertight bulkhead 22 concerned into the sail receptacle 14 and to allow reefing.

[0065] The inflatable sail 10 exhibits a profile that remains constantly symmetrical when inflated, regardless of the movement of the wind-powered vehicle 2, the orientation of the inflatable sail 10, or the direction and intensity of the wind. Alternatively, an asymmetrical profile could be provided for the inflatable sail 10 when inflated.

[0066] As illustrated more visibly in Figure 2, the first, second and third watertight bulkheads 22 separate the cavity into an upper inflatable chamber 24, two intermediate inflatable chambers 26, and a lower inflatable chamber 28.

[0067] The sail propulsion element 6 includes a lower air injection device 30, in particular reversible, for example a fan, in particular reversible, mounted on the sail receptacle 14 and in fluidic communication with the lower inflatable chamber 28. The lower air injection device 30 is capable of injecting air into the lower inflatable chamber 28. When the lower air injection device 30 is reversible, it is capable of extracting air from the lower inflatable chamber 28.

[0068] The sail propulsion element 6 includes an upper air injection device 32, in particular reversible, for example a fan, in particular reversible, mounted on the sail receptacle 14 and in fluidic communication with the upper inflatable chamber 24. The upper air injection device 32 is capable of injecting air into the upper inflatable chamber 24. When the upper air injection device 32 is reversible, it is capable of extracting air from the upper inflatable chamber 24.

[0069] Each watertight bulkhead 22 is provided with an opening in which an intermediate air injection device 34 is located, which may be reversible, for example, a reversible fan. The intermediate air injection device 34 is mounted in a watertight manner through the opening. The intermediate air injection device 34 of each watertight bulkhead 22 is capable of circulating air through the opening of the watertight bulkhead 22 between the inflatable chamber 26, 28 located below the watertight bulkhead 22 and the inflatable chamber 24, 26 located above the watertight bulkhead 22.

[0070] The sail propulsion element 6 comprises a plurality of pressure-sensing means (not shown) each disposed in an inflatable chamber 24, 26, 28 of the inflatable sail 10 and capable of measuring the air pressure in the inflatable chamber 24, 26, 28 concerned.

[0071] The control unit 17 is capable of controlling the operation of the lower air injection device 34, the upper air injection device 32, and each intermediate air injection device 34 based on signals from the pressure-sensing means. The control unit 17 is also capable of controlling the raising and lowering of the inflatable sail 10 based on signals from the pressure-sensing means.

[0072] Each of the lower air injection devices 30, upper air injection devices 32, and intermediate air injection devices 34 is equipped with a valve 36 capable of preventing the circulation of air through the air injection device 30, 32, 34 considered.

[0073] The control unit 17 is capable of controlling each valve 36 according to signals from the pressure-sensing means.

[0074] In the example shown, the inflatable sail 10 includes first, second, and third watertight bulkheads 22. Alternatively, the inflatable sail 10 could include only first and second watertight bulkheads 22 separating, within the inflatable cavity, an upper inflatable chamber 24, an intermediate inflatable chamber 26, and a lower inflatable chamber 28. One of the first and second watertight bulkheads 22 includes an opening for an intermediate air injection device 34. The other of the first and second watertight bulkheads 22 may include an opening for an air injection device or may not have an opening for an air injection device. Alternatively, the inflatable sail 10 could include a different number of watertight bulkheads 22, for example, four watertight bulkheads 22, or five or more. In the example shown, each watertight bulkhead 22 has an opening for an air injection device.Alternatively, some watertight bulkheads 22 could include two openings each fitted with a check valve, the two check valves allowing air to flow in opposite directions in order to regulate the pressure in the inflatable cavity.

[0075] Figure 3 schematically illustrates a method of hoisting the inflatable sail 10 of the sail propulsion element 6.

[0076] We begin, in step 38, by injecting air into the upper inflatable chamber 24. During step 38, the upper air injection device 32 performs an injection of air into the upper inflatable chamber 24.

[0077] Optionally, during step 38, the intermediate air injection device 34 of the reefing bulkhead 22 separating the upper inflatable chamber 24 from the adjacent intermediate inflatable chamber 26 also injects air into the upper inflatable chamber. Thus, the intermediate and lower inflatable chambers 26, 28 remain pressed against the sail receptacle 14.

[0078] In step 38, a portion of the inflatable sail 10 is hoisted by continuing to inject air into the upper inflatable chamber 24 so that the air pressure in the upper inflatable chamber 24 is sufficient to maintain its shape without risk of collapse. The hoisting of the inflatable sail 10 is controlled by the control unit 17 and is achieved by deploying the mast 8, which in the illustrated embodiment is telescopic. During the hoisting of the inflatable sail 10, the head 12 is movable relative to the fixed sail receptacle 14.

[0079] In step 40, air is then injected into the intermediate inflatable chamber 26, which is adjacent to the upper inflatable chamber 24. For example, each intermediate air injection device 34 injects air into the intermediate inflatable chamber 26, which is adjacent to the upper inflatable chamber 24. In step 40, the partial hoisting of the inflatable sail 10 is also continued, and air is injected into the upper inflatable chamber 24 by means of the upper air injection device 32 in order to maintain constant pressure in the upper inflatable chamber 24.

[0080] In the same way as in step 40, the intermediate inflatable chamber 26, which is adjacent to the lower inflatable chamber 28, is then inflated.

[0081] Then, in step 42, air is injected into the lower inflatable chamber 28. In step 42, the lower air injection device 30 injects air into the lower inflatable chamber 28.

[0082] Optionally, during step 42, the intermediate air injection device 34 of the reefing bulkhead 22 separating the lower inflatable chamber 28 from the adjacent intermediate inflatable chamber 26 also injects air into the lower inflatable chamber 28, while the upper air injection device 30 injects air into the upper inflatable chamber 24 to maintain constant pressure in the upper inflatable chamber 24. Alternatively, the valve 36 of the intermediate air injection device 34 of the bulkhead 22 separating the lower inflatable chamber 28 from the adjacent intermediate inflatable chamber 26 is closed during step 42.

[0083] During step 42, the lifting of the inflatable sail 10 continues until the inflatable sail 10 is fully lifted.

[0084] When the inflatable sail 10 is fully hoisted, air is injected into the upper inflatable chamber 24 by means of the upper air injection device 32, and air is injected into the lower inflatable chamber 28 by means of the lower air injection device 34, in order to maintain the air in each inflatable chamber 24, 26, 28 at a nominal pressure. This nominal pressure corresponds to the pressure expected in the inflatable cavity when the inflatable sail 10 is fully hoisted and inflated. This compensates for any potential air leakage from the inflatable cavity. Alternatively, the valves 36 of the lower and upper air injection devices 30, 32 are closed when the inflatable sail 10 is fully hoisted and inflated to the nominal air pressure.Alternatively, the injection of air into the upper inflatable chamber 24 is continued by means of the upper air injection device 32 when the inflatable sail 10 is fully hoisted and inflated, the valve 36 of the lower air injection device 34 being closed, or the injection of air into the lower inflatable chamber 28 is continued by means of the lower air injection device 34 when the inflatable sail 10 is fully hoisted and inflated, the valve 36 of the upper air injection device 32 being closed.

[0085] When the inflatable sail 10 is fully hoisted, the valve 36 of each intermediate air injection device 34 is opened to allow air to flow through the intermediate air injection device 34 in question. This maintains a constant air pressure in the inflatable cavity.

[0086] Figure 4 schematically illustrates a method for lowering the inflatable sail 10 of the sail propulsion element 6.

[0087] We begin, in step 44, by extracting air from the lower inflatable chamber 28. During step 44, the lower air injection device 30 performs an extraction of air from the lower inflatable chamber 28.

[0088] Optionally, during step 44, the intermediate air injection device 34 of the reefing bulkhead 22 separating the lower inflatable chamber 28 from the adjacent intermediate inflatable chamber 26 also extracts air from the lower inflatable chamber. Alternatively, the valve 36 of the intermediate air injection device 34 of the reefing bulkhead 22 separating the lower inflatable chamber 28 from the adjacent intermediate inflatable chamber 26 is closed during step 44.

[0089] In step 44, a portion of the inflatable sail 10 is lowered by continuing the extraction of air from the lower inflatable chamber 28. The lowering of the inflatable sail 10 is controlled by the control unit 17 and is achieved by retracting the mast 8. During the lowering of the inflatable sail 10, the head 12 is movable relative to the fixed sail receptacle 14. Then, in step 46, air is extracted from the intermediate inflatable chamber 26, which is adjacent to the lower inflatable chamber 28. For example, each intermediate air injection device 34 extracts air from the intermediate inflatable chamber 26, which is adjacent to the lower inflatable chamber 28.During step 46, the partial lowering of the inflatable sail 10 is also continued and the extraction of air from the lower inflatable chamber 28 is continued by means of the lower air injection device 30 in order to keep the lower inflatable chamber 28 pressed against the sail receptacle 14.

[0090] In the same way as in step 46, the intermediate inflatable chamber 26, which is adjacent to the upper inflatable chamber 24, is then deflated.

[0091] Then, in step 48, air is extracted from the upper inflatable chamber 24. In step 48, the upper air injection device 32 performs an air extraction from the upper inflatable chamber 24.

[0092] During step 48, the lowering of the inflatable sail 10 continues until the inflatable sail 10 is completely lowered.

[0093] In the embodiments just described, the mast 8 is telescopic and made up of different elements that slide successively to extend or retract. The head 12 is fixed to the last element of the mast 8. Alternatively, the mast 8 could be fixed, with the head 12 then moving along the mast 8. Another alternative would be to combine a telescopic mast 8 with a head 12 that slides along this telescopic mast 8.

Claims

DEMANDS 1. Sail propulsion element (6) comprising: a mast (8); an inflatable sail (10) internally delimiting an inflatable cavity, the sail (10) comprising an upper part, a lower part, a leading edge and a trailing edge, the sail (10) comprising various curves forming bulges, a head (12) disposed on the upper part of the sail (10); a sail receptacle (14) disposed on the lower part of the sail (10); characterized in that it comprises: at least first and second watertight bulkheads (22) separating the inflatable cavity into a lower inflatable chamber (28), at least one intermediate inflatable chamber (26) and an upper inflatable chamber (24); at least one upper air injection device (32) capable of injecting air into the upper inflatable chamber (24); at least one lower air injection device (30) capable of injecting air into the lower inflatable chamber (28); and - at least one intermediate air injection device (34) which is reversible and which is disposed in an opening formed in one of the first and second watertight bulkheads (22), said intermediate air injection device (34) being capable of circulating air between the inflatable chambers adjacent (24, 26, 28) to said first or second watertight bulkhead (22) through said first or second watertight bulkhead (22).

2. Sail propulsion element (6) according to claim 1, comprising at least one additional intermediate air injection device (34) disposed in an opening formed in the other of said first and second watertight bulkheads (22), said additional intermediate air injection device (34) being capable of circulating the air between the inflatable chambers adjacent (24, 26, 28) to said other watertight bulkhead (22) through said other watertight bulkhead (22).

3. Sail propulsion element (6) according to claim 1 or 2, wherein at least one of said air injection devices (30, 32, 34) is provided with a valve (36) capable of preventing the circulation of air through said air injection device (30, 32, 34).

4. Sail propulsion element (6) according to any one of claims 1 to 3, wherein at least one of said lower and upper air injection devices (30, 32) is reversible.

5. Sail propulsion element (6) according to any one of claims 1 to 4, comprising at least one pressure sensing means arranged in one of said inflatable chambers (24, 26, 28).

6. Sail propulsion element (6) according to claim 5, further comprising a control unit (17) capable of controlling the operation of the air injection devices (30, 32, 34) as a function of signals from said pressure-sensing means.

7. Vehicle (2) with sail propulsion or hybrid propulsion comprising at least one hull (4), at least one sail propulsion element (6) according to any one of claims 1 to 6, the mast (8) of said sail propulsion element (6) being integral with said hull (4), the inflatable sail (10) of said sail propulsion element (6) being free in rotation.

8. Method of hoisting an inflatable sail (10) of a sail propulsion element (6) according to any one of claims 1 to 7, comprising at least: the injection of air (38) into the upper inflatable chamber (24) by means of the upper air injection device (32); the hoisting (38) of a part of the inflatable sail (10); the injection of air (40) into the lower inflatable chamber (28) by means of the lower air injection device (30); and the complete hoisting (42) of the inflatable sail (10).

9. A method according to claim 8, wherein the sail propulsion element (6) comprises at least one intermediate air injection device (34) disposed in an opening formed in the bulkhead sealed (22) adjacent to the upper inflatable chamber (24), the method comprising injecting air into the upper inflatable chamber (24) by means of said upper and intermediate air injection devices (32, 34).

10. Method according to claim 8 or 9, wherein said intermediate air injection device (34) allows air to flow through said airtight partition (22) when the inflation sail (10) is fully hoisted. 1 1. Method according to any one of claims 8 to 10, comprising injecting air into the upper inflatable chamber (24) by means of the upper air injection device (32) and / or injecting air into the lower inflatable chamber (28) by means of the lower air injection device (30) when the inflatable sail (10) is fully hoisted.

12. Method for lowering an inflatable sail (10) of a sail propulsion element (6) according to any one of claims 1 to 7, comprising at least: the extraction of air (44) from the lower inflatable chamber (28) by means of the lower air injection device (30); the lowering (44) of a part of the inflatable sail (10); the extraction of air (48) from the upper inflatable chamber (24) by means of the upper air injection device (32); and the complete lowering (48) of the inflatable sail (10).

13. Method according to claim 12, wherein the sail propulsion element (6) comprises at least one intermediate air injection device (34) disposed in an opening formed in the watertight bulkhead (22) adjacent to the lower inflatable chamber (28), the method comprising the extraction of air from the lower inflatable chamber (28) by means of said lower and intermediate air injection devices (30, 34).

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