DEVICE FOR REDUCING HYDRODYNAMIC FLOW RESISTANCE

Description

Scope of the invention

[0001] The field of the invention relates to the naval field. More specifically, the field of the invention relates to devices for reducing the hydrodynamic drag of ships. The field of the invention therefore relates to increasing the energy efficiency of ships. The field of the invention also relates to ships using fuel cells to provide the electrical power for the vehicle's engines. State of the art

[0002] Drag force is a force opposing the movement of an object immersed in a fluid. This force is applied to the object moving through the fluid by the friction of the fluid on the object.

[0003] Reducing hydrodynamic drag therefore increases a ship's performance by limiting the energy consumed by the vessel. Thus, a hydrodynamic drag reduction device increases the vehicle's efficiency.

[0004] It is known from the state of the art that the use of a static air layer or an airflow in contact with the hull of the ship makes it possible to reduce the friction forces exerted by the water on the hull.

[0005] In the state of the art, some ships incorporate a specially designed cavity in their hull to create an air cushion that covers a portion of the hull surface that would otherwise be in contact with the water. Such a device is described in US patent 2003 / 159637 A1. This device effectively reduces the ship's hydrodynamic drag. However, this type of device is ineffective in heavy swells, as the waves break up the air cushion formed beneath the ship. Furthermore, a compressor is required to provide the pressure necessary to create and maintain the air cushion. Since compressor operation is energy-intensive, the energy efficiency of such a device is insufficient. In addition, the presence of a compressor increases the ship's mass, further reducing its energy efficiency.

[0006] It is also known to use injectors located under the hull to inject air directly onto it. Such a device is described in document KR 2020 0011300 A1, which discloses a hydrodynamic drag reduction device comprising an injector placed under the ship's hull. The injector injects a quantity of air directly into contact with the hull and the water, lubricating the hull and reducing drag. While effective, such a device has the disadvantage of requiring energy to operate a compressor used to inject the air. This energy consumption drastically reduces the efficiency of the system. Furthermore, the presence of a compressor increases the ship's mass, which further reduces its energy efficiency.

[0007] It is also known from the prior art of ships using fuel cells to electrically power their engines. In particular, ships using hydrogen to power fuel cells and provide electrical energy to the engine are known. Typically, a fuel cell uses the chemical reaction between hydrogen supplied from a tank and oxygen from the ambient air to generate electrical energy. During this process, a fuel cell releases a quantity of hot, humid air into the surrounding environment. The fuel cell also releases a quantity of water during the production of electrical energy. Such ships are advantageous because they provide propulsion that limits greenhouse gas emissions. Other relevant prior art documents include US 2005 / 215129 A1, CN 112 238 921 A, JP 2010 264969 A, and CN 105 438 398 A.

[0008] The invention therefore aims to provide a hydrodynamic drag reduction device that overcomes the disadvantages of existing devices. Summary of the invention

[0009] To this end, the invention relates to a hydrodynamic drag reduction device for a ship which comprises: ▪ a hull comprising at least one first means for injecting a fluid; ▪ a fuel cell; and ▪ a means for conveying a first quantity of air rejected by the fuel cell to at least the first injection means, the first injection means being arranged to inject said first quantity of air along a surface of the hull intended to be immersed.

[0010] The hydrodynamic drag reduction device according to the invention advantageously allows for the reduction of greenhouse gas emissions by using a fuel cell. Similarly, through the use of injection means, the device injects a quantity of air under the hull, which reduces the ship's hydrodynamic drag.

[0011] Finally, the device according to the invention allows the air escaping from the fuel cell to be reused and injected under the hull. This arrangement is particularly advantageous because it eliminates the need for a dedicated compressor for injecting air under the hull. Consequently, the device according to the invention significantly increases the energy efficiency of existing drag reduction systems, as it saves the energy used by the compressor. The absence of a dedicated compressor also reduces the ship's mass. Reducing the ship's mass also reduces its energy consumption and therefore increases its energy efficiency.

[0012] In one embodiment, the first injection means includes a sealing element to limit or prevent the upward flow of water into the delivery means. This arrangement prevents water from flowing back into the delivery means and / or the fuel cell.

[0013] In one embodiment, the first quantity of air is injected by the injection means in the form of air bubbles, said air bubbles preferably having a diameter of less than 5 millimeters. Air bubbles represent an effective means of reducing hydrodynamic drag. The 5-millimeter diameter corresponds to the thickness of the boundary layer near the hull; it therefore represents a dimension for which drag reduction is very effective.

[0014] According to one embodiment, the first quantity of air is injected by the injection means in the form of air bubbles, said air bubbles preferably having a diameter between 0.4 millimeters and 1.3 millimeters. These diameter values ​​allow for an effective reduction of hydrodynamic drag.

[0015] In one embodiment, the hull comprises a water wing intended to be submerged, and said water wing comprises at least one second injection means arranged to inject at least a portion of the first quantity of air. This arrangement reduces hydrodynamic drag on a vessel comprising a water wing.

[0016] In one embodiment, the second water wing injection method is arranged to inject a portion of the first quantity of air along a vertical surface of the water wing. According to this arrangement, injecting air onto the vertical surfaces prevents a reduction in the water wing's lift when the injection is effective.

[0017] In one embodiment, the hull includes an additional portion forming a step upstream of the first injection means, relative to the direction of ship travel. This arrangement creates a low-pressure area downstream of the additional portion. This low pressure draws air through the injection means for injection, thereby reducing drag. This arrangement also creates local turbulent flow, further enhancing the effectiveness of the injected air in reducing hydrodynamic drag.

[0018] In one embodiment, the device includes a control device for the airflow in the conveying means. This arrangement allows control of the injected airflow to optimize the reduction of hydrodynamic drag.

[0019] In one embodiment, the conveying means includes at least one airflow sensor. This arrangement makes it possible to determine the airflow rate in the conveying means. It also allows this flow rate to be adjusted based on its measured value. If the device according to the invention includes a control device, the flow rate information provides the control device with the flow rate information necessary to control said flow rate more effectively.

[0020] In one embodiment, the device includes a means for recovering a second quantity of air from the apparent wind of the vehicle, said recovery means being capable of conveying the second quantity of air to the conveying means. This arrangement makes it possible to supplement the airflow conveyed to the injection means with apparent wind.

[0021] According to one aspect, the invention also relates to a method for reducing the hydrodynamic drag of a ship, which comprises the steps of: conveying a first quantity of air expelled by a fuel cell through a conveying means to an injection means included in a hull; injecting the first quantity of air through the injection means along a surface of the hull intended to be immersed.

[0022] The process according to the invention advantageously allows for the reduction of greenhouse gas emissions by using a fuel cell. Similarly, through the use of injection methods, the quantity of air injected under the hull reduces the ship's hydrodynamic drag.

[0023] Finally, the process according to the invention allows the air escaping from the fuel cell to be reused and injected under the hull. This arrangement is particularly advantageous because it eliminates the need for a dedicated compressor for injecting air under the hull. Consequently, the process according to the invention significantly increases the energy efficiency of existing drag reduction systems, as it saves the energy used by the compressor. The absence of a dedicated compressor also reduces the ship's mass. Reducing the ship's mass also reduces its energy consumption and therefore increases its energy efficiency. Brief description of the figures

[0024] Other features and advantages of the invention will become apparent from the detailed description that follows, with reference to the attached figures, which illustrate: Fig. 1 : a schematic profile view of a ship comprising a drag reduction device according to a first embodiment of the invention. Fig. 2 : a schematic profile view of a ship comprising a drag reduction device according to a second embodiment of the invention. Fig. 3 : a schematic partial cross-sectional view of a ship's hull comprising a drag reduction device according to a third embodiment of the invention. Fig. 4 : a cross-sectional view of a ship's hull according to a fourth embodiment of the invention. Description of the invention

[0025] There figure 1This figure represents a first embodiment of the invention. It is a schematic cross-sectional view of a vessel 10 comprising a hydrodynamic drag reduction device according to the invention. In this application, "vessel 10" refers to any type of floating vehicle. The invention therefore relates to marine vehicles such as boats and barges, for example. Any type of floating craft falls within the scope of the invention. Floating and / or submersible craft also fall within the scope of the invention. Hereafter, the terms "vessel 10" and "boat 10" will be used interchangeably.

[0026] All the characteristics of the hydrodynamic drag reduction device according to the invention can also be applied to the hydrodynamic drag reduction process according to the invention.

[0027] The vessel 10 comprises a hull 20. The hull 20 is the outer shell of the vessel 10 which is in contact with the water on which the vessel 10 floats and / or is submerged.

[0028] The ship of the figure 1The invention includes a fuel cell 30. The fuel cell 30 uses hydrogen to produce electrical energy. This electrical energy is used to power the vessel. The energy produced by the fuel cell can be used to power an electric motor 30. The electric motor 30 is used to propel the vessel 10. Alternatively or additionally, the fuel cell 30 provides electrical energy to onboard systems such as lighting, heating, or other systems. The invention also relates to fuel cells that do not use hydrogen. A fuel cell operating with reformed methanol or direct methanol is therefore possible. A fuel cell operating with direct boron hydride, formic acid, phosphoric acid, molten carbonate, or protonating ceramic is also possible. All types of fuel cell chemistry can be considered.

[0029] Fuel cell 30 refers to the entire fuel cell system. This includes both the core of the fuel cell, an electrochemical device that produces electricity by converting chemical energy into electrical energy through a redox reaction, in which an electrical voltage is generated by the oxidation of a reducing fuel coupled with the reduction of an oxidant, such as oxygen from the air, at the other electrode, and the auxiliary systems of said fuel cell, namely the fuel cell management electronics and a compressor responsible for supplying the fuel cell core with air to provide it with oxygen.

[0030] Fuel cell 30 uses a chemical reaction between hydrogen and oxygen drawn from ambient air to produce electrical energy. The operation of fuel cell 30 produces air emissions, which are typically released into the environment in hydrogen-powered boats. In the case of a fuel cell not powered by hydrogen, such as the fuel cells described above, the fuel cell also releases air during operation. Therefore, the characteristics described before and after also apply to fuel cells other than hydrogen fuel cells.

[0031] In the context of the invention, the hydrodynamic drag reduction device 40 includes an air conveying means 42. This air conveying means 42 is located at the outlet of the fuel cell 30. This conveying means 42 collects the gases escaping from the fuel cell 30 during its normal operation. The conveying means 42 is directly connected to an exhaust outlet of the fuel cell 30.

[0032] The air delivery means 42 is connected to an injection means 50. The injection means 50 is integrated into the hull 20. The injection means 50 is configured to inject the air delivered by the delivery means 42. To do this, it injects a quantity of air 52 near the hull 20, opposite a surface of the hull 20 that is intended to be submerged when the vessel 10 is underway. The injection means 50 is therefore located below a waterline of the vessel 10. More precisely, the injection means 50 injects the air 52 near a surface 22 of the hull 20 that is intended to be submerged.

[0033] Let us now describe the operation of the hydrodynamic drag reduction system 40.

[0034] When the vessel 10 is in operation, the fuel cell 30 produces electrical energy for it. During this process, the fuel cell releases an initial quantity of air. This initial quantity of air is the exhaust from the fuel cell 30. The initial quantity of air is collected by the conveying means 42. The conveying means 42 conveys this initial quantity of air to the injection means 50. This injection means is located under the hull 20 of the vessel 10. The injection means 50 injects this initial quantity of air 52 opposite the surface 22 of the hull 20 that is intended to be submerged. As a reminder, the surface 22 of the hull 20 intended to be submerged refers to a surface 22 of the hull 20 located below the waterline of the vessel 10.

[0035] The hydrodynamic drag reduction device therefore includes the fuel cell 30, the conveying means 42, the hull 20 and the injection means 50.

[0036] The hydrodynamic drag reduction device according to the invention thus makes it possible to reuse the air emanating from the fuel cell when it is producing electrical energy. Air emanating from the fuel cell refers to the air produced during the chemical reaction taking place within it.

[0037] Reusing the initial quantity of air, which is routed to the injection means 50, allows for the injection of said quantity of air near the hull 20. This air injection provides "lubrication" to the hull 20, reducing the hydrodynamic drag force that the water exerts on the hull 20. The device 40 according to the invention thus enables a reduction in hydrodynamic drag, which in turn reduces the energy consumption of the vessel 10. Furthermore, since the air comes directly from the fuel cell, the device 40 does not require an external means of pressurizing the air for injection. Therefore, the device 20 according to the invention significantly increases the efficiency available with prior art devices, as it does not consume energy to inject the air, which is a by-product of the electrical energy production of the fuel cell 30.Furthermore, the drag reduction device according to the invention reduces the mass of the vessel 10 because a compressor is a heavy component. This mass reduction also increases the energy efficiency of the vessel 10. Alternatively, the drag reduction device 40 may include an additional compressor. The additional compressor supplements the airflow in the conveying means 42. In this way, if the airflow and / or pressure supplied by the fuel cell 30 are insufficient, the additional compressor provides the necessary flow and / or pressure. Despite the presence of the additional compressor, the drag reduction device 40 still improves energy efficiency compared to a conventional drag reduction device because the necessary additional compressor has lower power and mass than the compressor used in prior art devices.

[0038] The vessel 10 may include a hydrogen tank 32. In the example shown in figure 1 The vessel 10 has three hydrogen tanks 32. These tanks 32 are located on the roof of the vessel 10. The hydrogen tanks 32 are an efficient way to store dihydrogen, in gaseous and / or liquid form, which will be used by the fuel cell 30 for its operation. In the case of a fuel cell operating with a gas other than hydrogen, the tank 32 can be used to store a gas other than dihydrogen.

[0039] The vessel 10 may advantageously be a catamaran. A catamaran is defined as a vessel comprising two hulls or floats. This is notably the case for the vessels 10 shown in the figures of this application, where the portion of the hull 20 shown is one of the two floats comprising said hull 20. However, the invention also relates to monohull vessels or multihull vessels. Thus, all the features of the drag reduction device 40 according to the invention presented in this application apply equally to monohull vessels, catamarans, multihulls, or any other type of vessel.

[0040] The vessel 10 may include an exhaust stack 37. The exhaust stack allows for the evacuation of excess gas that may have formed in the fuel cell 30. This stack 37 is connected to the fuel cell and is used in the event of overpressure in the fuel cell 30. The exhaust stack 37 is also used in the event of overpressure in the auxiliary systems of the fuel cell 30, such as the distribution systems or the tanks for example.

[0041] According to one aspect, the fuel cell 30 electrically powers an electric motor 35. This electric motor 35 enables the propulsion of the ship 10.

[0042] In one aspect, the fuel cell 30 electrically powers one or more electric batteries, which it then charges. In this aspect, it is the electric batteries that electrically power the electric motor 35.

[0043] In one respect, vessel 10 is a passenger transport vessel. According to this characteristic, passengers are transported in a cabin 12 of vessel 10. Alternatively or additionally, vessel 10 is a vessel dedicated to another use, for example, cargo transport, fishing, recreational boating, or military applications. This list of uses for vessel 10 is not exhaustive. Delivery of the first quantity of air

[0044] In one respect, the means for conveying the air expelled by the fuel cell 30 is a duct. A duct is understood to mean any type of means such as a pipe or a set of pipes connected together. Alternatively or additionally, the conveying means 42 is a tube, preferably a flexible tube. The conveying means 42 can also be a set of tubes connected together. For example, a conveying means comprising a rigid tube and a flexible tube placed in series can be provided.

[0045] According to one aspect, the conveying means 42 includes a heat exchanger 44 along its path. The heat exchanger 44 recovers heat from the first quantity of air expelled by the fuel cell 30. It should be noted that the air expelled by the fuel cell 30 is hot. Advantageously, the heat recovered by the heat exchanger 30 is used to heat the cabin 12 of the ship 10.

[0046] In one aspect, the hydrodynamic drag reduction device includes a control device for the airflow conveyed by the conveying means 42. According to this aspect, the control device allows for the control of the flow rate passing through the conveying means 42. This arrangement allows for the control of the airflow exiting the fuel cell 30. This arrangement also allows for the control of the airflow injected by the injection means 50. Thus, the injected airflow can be controlled to optimize the lubrication of the hull 20 by air. In one aspect, the conveying means 42 includes an exhaust (not shown in the figures) that allows for the release of excess airflow.In this way, if the air flow exiting the fuel cell 30 is greater than that desired for lubrication, it is possible to release part of this flow into the surrounding air or water to adapt the flow released by the injection means 50.

[0047] In one respect, the control system also controls the operation of the fuel cell 30. For example, it can control the power output of the fuel cell 30, as well as its supply of reactants such as hydrogen. The control system can also be used to control other components of the vessel 10 in addition to the drag reduction device 10.

[0048] In one aspect, the hydrodynamic drag reduction device 10 includes at least one flow sensor 46. The flow sensor 46 measures the air flow rate. The flow sensor 46 can be located at the outlet of the fuel cell 30. The flow sensor can, for example, be integrated into the air delivery means 42. It can, for example, be positioned to measure the air flow rate in the delivery means 42 at the outlet of the fuel cell 30. A flow sensor 46 can also be provided at the outlet of the delivery means 42, before the injection means 50. In one aspect, the device 10 includes several flow sensors 46. These sensors can, for example, be located at the inlet and outlet of the delivery means 42.

[0049] In one aspect, the hydrodynamic drag reduction device 10 includes at least one pressure sensor 48. The pressure sensor 48 measures the air pressure. The pressure sensor 48 can be located at the outlet of the fuel cell 30. The pressure sensor 48 can, for example, be integrated into the air delivery means 42. It can, for example, be positioned to measure the air pressure in the delivery means 42 at the outlet of the fuel cell 30. A pressure sensor 48 can also be provided at the outlet of the delivery means 42, before the injection means 50. In one aspect, the device 10 includes several pressure sensors 48. These pressure sensors 48 can, for example, be located at the inlet and outlet of the delivery means 42.

[0050] According to one aspect, the conveying means 42 comprises at least one pressure sensor 48 and at least one flow sensor 46. According to the embodiment shown in figure 1The conveying means 42 includes a flow sensor 46 and a pressure sensor 48 at the outlet of the fuel cell 30. According to this embodiment, the conveying means 42 also includes a flow sensor 46 and a pressure sensor 48 at the outlet of the conveying means 42, upstream of the injection means 50.

[0051] According to one aspect of the invention, the hydrodynamic drag reduction device 40 includes an airflow control system. In this aspect, the device 40 includes at least one pressure sensor 48 and one flow sensor 46. In this aspect, the device 40 also includes at least one exhaust as described above. According to this aspect, the control system can open the exhaust based on pressure and / or flow information transmitted by the sensors 46 and 48. This arrangement allows for automatic opening of the circuit in the event of overpressure, for example.

[0052] According to one aspect, the drag reduction device 40 includes a control unit. The control unit is configured to control the exhaust opening based on pressure data from the pressure sensor(s) 48. The control unit can also control the exhaust opening based on flow data from the flow sensors 46. Apparent wind capture

[0053] According to an embodiment presented to the figure 3 The drag reduction device 40 includes a means 43 for recovering air from the apparent wind of the ship 10. Apparent wind is understood to be the wind felt on board the ship 10 when it is moving. Apparent wind is the combination of the true wind and the relative wind created by the movement of the ship 10.

[0054] The apparent wind recovery means 43 is located on the vessel 10 at a level which is above the waterline of said vessel 10. Thus, the recovery means 43 recovers the apparent wind and not water.

[0055] The recovery means 43 conveys a second quantity of air to the conveying means 42. In this way, the second quantity of air is added to the first quantity of air from the fuel cell 30. Thus, the flow rate of air conveyed to the injection means 50 can be increased. Similarly, if the fuel cell 30 does not provide enough air to ensure a sufficient reduction in drag, the second quantity of air can be added to inject enough air.

[0056] According to one aspect, the recovery means 43 includes an opening 45 through which the apparent wind is collected. This opening 45 may be a vent leading to the outside air.

[0057] In one aspect, the recovery means 43 includes a tube or pipe. This tube or pipe may be rigid or flexible. It connects the opening 45 or the inlet of the recovery means 43 to the conveying means 42.

[0058] According to one aspect, the recovery means 43 is linked to the conveying means 42 at a junction 47.

[0059] In one aspect, the recovery means 43 includes a cross-sectional reducer 49. According to this arrangement, the tube or pipe of the recovery means 43 has a normal cross-section. This normal cross-section is substantially constant along the length of the tube or pipe. At the cross-sectional reducer 49, the cross-section narrows. This arrangement allows, through the Venturi effect, for the airflow in the recovery means 43 to be accelerated.

[0060] According to one aspect, the junction 47 between the conveying means 42 and the recovery means 43 is located at the section reduction 49 of the recovery means 43. This arrangement is visible in figure 3 This arrangement allows for an acceleration of the flow of the first quantity of air from the conveying means 42, by venturi effect.

[0061] According to one aspect, the junction 47 is located at the section reduction 41 of the conveying means. This arrangement allows for an acceleration of the flow of the second quantity of air from the recovery means 43, by venturi effect.

[0062] According to one embodiment, the recovery means 43 includes at least one pressure sensor (not shown). The pressure sensor allows the air pressure in the recovery means 43 to be measured.

[0063] According to one embodiment, the recovery means 43 includes at least one flow sensor (not shown). The flow sensor allows the air flow rate in the recovery means 43 to be measured.

[0064] Depending on one aspect, the flow sensor of the recovery means 43 and / or the pressure sensor of the recovery means 43 are connected to the control system. This system can control the opening or closing of the recovery means 43 to control the airflow arriving from it into the conveying means 42.

[0065] All the provisions described here concerning the apparent wind recovery means 43 are compatible with the characteristics described in the other embodiments. Air injection

[0066] As previously stated, the drag reduction device 40 includes at least one means for injecting air 50.

[0067] Injection means 50 means, for example, an injector 50. The injection means can also be an opening in the conveying means 42 at the hull 20 of the ship 10.

[0068] According to one provision, the hull 20 comprises a plurality of injection means 50, in addition to the injection means 50 shown on the figure 1For example, the hull 50 may have two injection means 50, one located slightly to port, relative to a longitudinal axis of the hull of the ship 10, and another to starboard. In this way, the submerged parts of the hull 50 are lubricated by air injected across the entire width of the hull 50. Alternatively, several injection means 50 may be provided along an axis running from the bow to the stern of the ship 10. In one aspect, the plurality of injection means 50 covers a large portion of the surface 22 of the hull 20 intended to be submerged. When the drag reduction system 40 has several injection means 50, the conveying means 42 has several branches to supply air to all the injection means 50.

[0069] A plurality of injection means 50 can also be provided along the surface 22 of the hull 20 intended to be submerged. For example, a plurality of injection means 50 can be aligned along two lines forming a "V" under the hull 20. The point of the "V" can point either towards the bow of the vessel 10 or towards its stern. Several injection means 50 can also be arranged along a line of the hull 20 perpendicular to the longitudinal axis of the vessel 10. Several lines of injection means 50 can also be provided along the hull 20. For example, two parallel lines can be provided, each containing a plurality of injection means 50, the two lines being perpendicular to the longitudinal axis of the vessel 10. The number of injection means 50 along each line can vary from one line to another. For example, there can be ten injection means 50 per line.We can also have one line with ten 50 injection means, and another line with five 50 injection means.

[0070] The number and distribution of the injection means 50 remains at the discretion of the person skilled in the art, in order to maximize the effectiveness of the reduction of hydrodynamic drag.

[0071] In one embodiment, the submerged surface 22 of the hull 20 has a substantially flat bottom. According to this arrangement, the flat bottom keeps the injected airflow under the hull. In this way, the air does not rise to the water's surface through the sides of the hull 20. Thus, the injected airflow covers a larger area instead of escaping around the edges. Consequently, a larger portion of the submerged surface 22 is covered by the airflow. The lubrication of the hull 20 is therefore more effective.

[0072] According to one aspect, the injection means 50 includes a non-return means. The non-return means is a device preventing water from flowing back up from outside the vessel 10 through the conveying means 42. This arrangement prevents water from flowing back into the vessel, and in particular towards the fuel cell 30.

[0073] In one respect, the non-return device is a check valve. Alternatively, the non-return device is a valve, preferably a solenoid valve controlled by the control system.

[0074] In one aspect, the injection means 50 does not include a non-return means. According to this variant, external water can enter the conveying means 42. When air is not injected, water therefore rises in the conveying means 42 up to the waterline of the vessel 10. When the drag reduction device 40 is activated, the injected air forces the water out of the conveying means 42.

[0075] In one aspect, the air injected by the injection means 50 is injected in the form of air bubbles. These air bubbles are a very effective means of air lubrication for the hull 20.

[0076] Depending on one aspect, the injected air bubbles have a diameter between 0.1 millimeters and 100 millimeters. Depending on another aspect, the injected air bubbles have a diameter between 0.2 millimeters and 20 millimeters.

[0077] According to one aspect, the air bubbles have a diameter of less than 5 millimeters. According to this arrangement, the air bubbles therefore have a diameter that is less than 5 millimeters, a distance corresponding to the thickness of the fluid flow boundary layer near the hull 20.

[0078] According to one aspect, the injected air bubbles have an average diameter between 0.4 millimeters and 1.3 millimeters. Bubbles in this diameter range are highly effective at reducing hydrodynamic drag.

[0079] In one embodiment, the injected bubbles form an air pocket beneath the ship's hull. In another embodiment, the air bubbles are injected at a sufficient flow rate to merge after exiting the injection means. This arrangement creates an air pocket beneath the hull, which significantly reduces friction on the hull. Consequently, hydrodynamic drag is greatly reduced.

[0080] In one embodiment, the air bubbles form a mixed layer beneath the hull. A mixed layer is defined as a layer comprising parts where the air is in sheet form and parts where it is in bubble form. This arrangement reduces friction on the ship's hull while requiring a lower injected air flow rate than in the case of a sheet.

[0081] In one aspect, the injection device 50 includes an adaptable nozzle. According to this aspect, the nozzle has an adaptable shape to adjust the air injection. In another aspect, the nozzle diameter is adaptable. According to this aspect, the nozzle diameter is adjusted to control the size of the injected air bubbles. In another aspect, the nozzle adaptation is controlled by the control device. In this way, the control device can control the air injection. Preferably, the control device controls the nozzle diameter. Thus, the diameter of the air bubbles is directly controlled by the control device. Water Wings

[0082] In one embodiment, the hull 20 comprises at least one water wing 60. The hull may additionally comprise one, two, three, four, or more additional water wings 60. A water wing 60 is a component of the hull 20 with a hydrodynamic profile that raises the vessel 10 when it is in motion. This type of device is also often called a "hydrofoil" or "foil".

[0083] Raising the vessel 10 during its movement reduces the surface area and volume of the vessel in the water. This type of device thus reduces the forces opposing the movement of the vessel 10 from the surrounding water.

[0084] There figure 2 illustrates the case of a hull 20 with two water wings 60. The figure 2also represents a waterline 70 of the ship. This waterline 70 is located lower on the hull 30 than the waterline of the ship 10 at rest, under the effect of the water wing 60. Thus, when the boat 10 is in motion and its waterline is at the level of the waterline in Archimedean mode 70, the water forces opposing its motion are weaker than without a water wing 60.

[0085] According to one aspect, the water wing 60 includes at least one means 50 for injecting air supplied by the conveying means 42. The injection means 50 of the water wing 60 lubricates the surface of the water wing 60. This arrangement increases the effectiveness of the drag reduction device 40 by reducing the hydrodynamic drag experienced by the water wing 60. When the hull 20 has several water wings 60, each of them may include at least one injection means 50.

[0086] In one aspect, the injection means 50 for the water wing(s) 60 are located solely on the vertical parts of the water wing. According to this arrangement, the air injected near the water wing 60 does not affect the area surrounding its horizontal parts. The horizontal parts of the water wing are responsible for the lift of said water wing 60. In other words, it is the horizontal parts of the water wing 60 that allow the vessel 10 to rise when it is in motion. Not lubricating these parts with injected air prevents a reduction in the lift provided by said water wings 60. Thus, the lifting effect of the water wings 60 is not limited.

[0087] According to one aspect, the control system allows the air injection to be stopped at the level of one or more injection means 50.

[0088] According to one aspect, the control system can control the closing of valves of the conveying means 42. Thus, the control system can stop the injection of air into the desired injection means 50. Hull fitting

[0089] According to one aspect of the invention, the hull 20 has a step 24. This step 24 is visible on the figure 3 The step 24 is a step in the hull 24 having a surface that is vertical when the vessel 10 is in the water. The vertical surface of the step 24 is oriented on a free side towards the stern of the vessel 10.

[0090] In one aspect, the injection means 50 are positioned on the vertical surface of the step 24. In this way, the injection means 50 inject air into the water in a direction from the front to the rear of the boat 10. The step 24 advantageously creates a low-pressure area behind the step when the boat 10 is moving. This low pressure draws air from the conveying means 42 through the injection means 50. This arrangement thus facilitates air injection. Furthermore, the step 24 makes the water flow in the vicinity of the step 24 turbulent. Creating a turbulent flow near and behind the step 24 allows the injected air bubbles to oscillate along the hull 30. The oscillation of the injected air bubbles increases the efficiency of the lubrication and therefore the efficiency of the drag reduction device 40.

[0091] According to one aspect, the hull 20 has a recess 26. The recess 26 is a portion of the hull 20 that is pushed inward. Advantageously, the recess 26 includes the notch 24. It is also formed by at least two other lateral notches. The recess 26 forms a cavity in the surface 22 of the hull 20 that retains the injected air in contact with the hull 20, preventing it from flowing back up the sides of the hull 20. In this way, the injected air follows the hull along its entire length. Thus, the rear of the hull 20 is well lubricated by the injected air. The recess 26 therefore forms a channel for the injected air.

[0092] According to one arrangement, the hull 20 includes at least one strip arranged on its surface 22. A strip is defined as a projecting, sausage-like shape extending from the hull 20. The projection is preferably of low height, thus creating turbulent water flow downstream of the strip. In other words, the strip has a sausage or half-sausage shape arranged on the hull 20. Alternatively, one or more strips may be provided in a half-cylinder shape. The strip preferably has a streamlined shape. A streamlined shape is defined as a shape that offers little resistance to the flow of a fluid in the vicinity of the shape. Preferably, this strip is located directly upstream of one or more injection means 50. This strip can also be located directly downstream of the injection means 50. The strip advantageously makes the water flow turbulent as it passes over said strip.This arrangement therefore makes lubrication by injected air more efficient. Additionally, the hull 20 can include a plurality of strips located upstream and downstream of each injection means 50. Strips can also be provided downstream of the injection means 50, but located further away from them. These strips can prevent the flow in contact with the hull from becoming laminar, in order to maintain turbulent flow in contact with the hull throughout the passage of the injected air. Nomenclature :

[0093] 10: Ship 12: Cabin 20: Hull 22: Hull surface intended to be submerged 24: Hull step 26: Hull recess 30: Fuel cell 32: Hydrogen tank 35: Engine 37: Exhaust stack 40: Hydrodynamic drag reduction device 42: Means of conveying air rejected by the fuel cell 43: Means of recovering apparent wind 44: Heat exchanger 45: Opening of the means of recovering apparent wind 46: Air flow sensor 47: Junction 48: Pressure sensor 49: Reduction of the cross-section of the means of recovering apparent wind 50: Means of injecting the first quantity of air 52: Air injected by the injection means 60: Water wing 70: Waterline

Claims

1. A device for reducing hydrodynamic drag (40) of a vessel (10) including: ▪ a hull (20) comprising at least one first means of injection (50) of a fluid; ▪ a fuel cell (30) capable of generating an electrical voltage through the oxidation of a reducing fuel coupled to the reduction on the other electrode of an oxidant and ▪ a means of conveyance (42) of a first amount of air discharged by the fuel cell (30) to at least the first means of injection (50), the said amount of air discharged resulting from the oxidation reaction of the said reducing fuel, the first means of injection (50) being arranged to inject said first amount of air along a surface (22) of the hull (20) intended to be immersed.

2. The device (40) according to the preceding claim characterized in that the first means of injection (50) comprises a sealing element to limit or prevent the rise of an amount of water to the means of conveyance (42).

3. The device (40) according to any one of the preceding claims characterized in that the first amount of air is injected by the means of injection (50) in the form of air bubbles, said air bubbles preferably having a diameter of less than 5 millimeters.

4. The device (40) according to any one of the preceding claims characterized in that the hull (20) comprises a water wing (60) intended to be immersed and in that said water wing (60) comprises at least one second means of injection (50) arranged to inject at least a portion of the first amount of air.

5. The device (40) according to the preceding claim characterized in that the second means of injection (50) of the water wing (60) is arranged to inject the portion of the first amount of air along a vertical surface of the water wing (60).

6. The device (40) according to any one of the preceding claims characterized in that the hull (20) comprises an additional portion forming a setback upstream of the first means of injection (50), relative to the direction of movement of the vessel (10).

7. The device (40) according to any one of the preceding claims characterized in that it comprises a command-control device for the air flow in the means of conveyance (42).

8. The device (40) according to any one of the preceding claims characterized in that the means of conveyance (42) comprises at least one air flow sensor (46).

9. The device (40) according to any one of the preceding claims characterized in that it comprises a means of recovery (43) of a second amount of air from the apparent wind of the vessel (10), said means of recovery (43) being capable of conveying the second amount of air to the means of conveyance (42).

10. A method for reducing the hydrodynamic drag of a vessel (10) including the steps of: ▪ Conveying a first amount of air discharged by a fuel cell (30) by a means of conveyance (42) to a means of injection (50) comprised by a hull (20); ▪ Injecting the first amount of air by the means of injection (50) along a surface (22) of the hull (20) intended to be immersed.