System for measuring the flight height of a foiling boat

Abstract

System for measuring the flight height of a boat whose hull is equipped with at least one submerged foil-type lifting surface allowing said hull to fly above the water. The system comprises: - a radar for measuring the flight height of the hull of the boat relative to the water; - an inertial unit comprising at least inertial sensors for linear acceleration and rotation speed on three axes; - a GPS-type geopositioning device; - an inertial navigation unit equipped with a unit for processing electronic signals from the radar, the sensors of the inertial unit and the geopositioning device, comprising means for processing said electronic signals in order to obtain at any time at least one item of information on the height of the hull relative to the water.

Description

Title of the invention: System for measuring the flight height of a foil boat

[0001] The present invention relates to the field of foil boats, or more generally boats whose hull is equipped with a submerged foil-type lifting surface. These are boats which have wing-shaped appendages submerged under the hull of the boat, which generate lift when the boat moves at high speed, in reaction to the circulation of water around them. The invention also applies to surface drones and in particular to unmanned naval surface drones (USV).

[0002] The lift generated by the foil causes the hull to gradually lift out of the water. This lift increases with speed up to a point where the hull is lifted out of the water, correspondingly increasing the efficiency and speed of the boat, because the mere immersion of the foils results in considerably reducing the resistance of the water, which allows the boat to glide over the surface of the water with much less friction. The presence of the foils actually reduces drag to a minimum. Once the boat is sufficiently lifted out of the water, it is in a sense "flying" above the liquid surface. To maintain control, in particular of the trajectory of the vessel, it is then necessary to maintain stability in flight.

[0003] In short, foil boats fly just above the surface of the water, with the hull in the air and the foils in the water. In other words, the physical interface between the medium in which the hull moves and the medium in which the foil(s) move is the surface of the water. However, this is likely to vary quite considerably and very frequently in its shape, in connection with numerous parameters which depend on conditions affecting both environments, for example meteorological factors (notably the wind): thus, when waves appear and the boat flies at a certain speed out of the water, the constantly variable nature of the surface of the water and the height of the hull relative to it is very likely to impact its balance, which can quickly become unstable.

[0004] The flight height of flying boats, the measurement of which is the main object of the invention, in fact obviously depends on the flight conditions of the boat, but also on the state of the sea. The measurement of the flight height is essential to ensure the continuity of the flight and the balance of the boat, by preventing the boat from falling into the water in an uncontrolled and brutal manner. Thus, if the height of the hull relative to the continuously changing surface is poorly evaluated, or estimated too late, the boat may rise too high, with the risk of the foils stalling because they come out of the water, or on the contrary nosing straight towards the sea or into a wave.

[0005] It is therefore very important to be able to correctly measure - that is to say in this case at all times and continuously during the boat's movements - the height of the boat in relation to this irregular and constantly moving surface interface that is the sea surface. In the piloting process, the speed of the boat is also an important parameter. In fact, it is necessary to constantly keep the hull in flight as horizontal - "flat" - as possible above the water, because the very interest of this type of foiling boat lies in the possibility that they can fly flat without being "shaken" by waves or swell.

[0006] Until now, to measure the flight height, so-called "flying" boats have used either mechanical systems (rod and float type) as is the case for example for foiling moths, or electronic altitude sensors using ultrasound to measure the distance between the sensor and the surface of the water. The current choice, in most electronic measurements of the height of foiling boats, of ultrasonic sensors also results from their relative simplicity of implementation and their proven robustness. These sensors make it possible to measure distances compatible with the flight height of the boats, ranging from a few centimeters to a few meters. They are also easy to find, as there are many manufacturers, and relatively affordable.

[0007] As for the sailing racing boats used in competitions, they generally simply use an inertial unit with an altitude sensor to adjust the flight parameters, knowing that in this particular environment, pure speed is paramount and that the regattas in which they participate take place on fairly protected and therefore fairly flat bodies of water. The constraints are therefore more reduced. These boats are also subject to class rules which are sometimes very restrictive as to what the onboard system can or cannot do. In most cases, particularly in the context of the famous America's Cup, the piloting systems cannot be fully automated.

[0008] The mechanical or ultrasonic systems mentioned above are not very precise for measuring the flight height of a boat or a flying machine above the water, particularly in unprotected environments where the water surface is very changeable and sometimes in significant amplitudes. The signal restitution capacity of the control system is affected and is often poor, leading to this mentioned insufficiency in the precision of the measurement obtained. As a result, the piloting of the flight of the hull of the ship on its foil(s) is not very fine, and potentially causes instability.

[0009] The present invention overcomes these deficiencies, and proposes an innovative configuration allowing precise and frequent measurement of the flight height of a boat or a flying machine above the water, with, in addition, a better signal restitution capacity. The precision obtained is notably much higher than that offered by example the mechanical or ultrasonic systems mentioned.

[0010] Thus, according to the invention, the system for measuring the flight height of a boat whose hull is equipped with at least one submerged foil-type bearing surface allowing said hull to fly above the water, is such that it comprises:

[0011] - a radar for measuring the flight height of the boat hull relative to the water;

[0012] - an inertial unit comprising at least inertial acceleration sensors linear and rotational speed on three axes;

[0013] - a GPS-type geopositioning device;

[0014] - an inertial navigation unit equipped with a signal processing unit electronics from the radar, the sensors of the inertial unit and the geopositioning device, comprising means for processing said electronic signals in order to obtain at least one piece of information at any time on the height of the hull relative to the water.

[0015] In short, the measuring system of the invention behaves like a sensor specifically dedicated to flying boats, namely craft navigating on a fluid surface in more or less erratic motion because randomly affected by chop, waves, swell, wakes, etc., themselves having a speed of several km / h to several tens of km / h. The movements of said surface obviously take place in particular but not only in a vertical direction which is of interest for measuring the height of the hull above the water.The inertial navigation unit uses data from the sensors of the inertial navigation unit, which has no data processing capacity, as well as data emitted by the radar and the GPS, using algorithms which integrate in particular the data from the inertial sensors and result in data which can be used for controlling the boat, primarily and within the framework set by the invention, data on the height of the hull relative to the fluid and perpetually moving surface of the water.

[0016] Preferably, according to the invention, the radar is a pulsed Doppler radar, more particularly efficient for measuring the relative speed of moving objects with respect to the radar itself, and which is therefore well suited to the changing environment provided by the surface of moving water. The pulsed Doppler radar emits pulses, generally radiofrequency waves, which propagate to the target, i.e. a portion of the moving surface of the water, where they are reflected. When the radar signals are reflected by the moving water, the frequency of the reflected signals is modified in particular as a function of the relative speed of said portion of the target surface with respect to the radar.The radar detects the change in frequency of the reflected signals and measures the speed of the said targeted portion in the radial (the speed component in the direction of the radar) and tangent (the speed component in a direction normal to that of the radar) directions. This . allows the system to have instantaneous information on the moving profile of the water surface at a frequency that will be imposed high (see below). In fact, the system allows not only the measurement of the height of the hull above the water by the radar sensor, but also to process data relating to the liquid surface independently of the attitude of the boat.

[0017] The speed of height measurement is much faster with the radar system of the invention than with an ultrasonic sensor, said system also making it possible to obtain a signal of better quality and more robust, then sent to a computer of the measurement system or for real-time display. The measurement speed and sensitivity are essential for operation on agitated surfaces, knowing that this type of signal has only been used until now for water level measurements in reservoirs and canals where the surface is little disturbed, unlike the context of the invention where it is necessary to measure a surface in rapid perpetual motion from a mobile device itself in motion (horizontal and vertical) evolving on this surface.With the radar, the GPS and the inertial unit, the measurement system of the invention actually integrates all the sensors necessary to be autonomous, so that the measurement carried out is independent of the physical model of the ship and does not require calibration or parameterization specifically dedicated to this ship.

[0018] In practice, according to the invention, the radar is capable of measuring a height between the hull and the water of between 0.2 and 2 m. It should also be noted that the measurement system of the invention may comprise a printed circuit comprising the radar, a 6-axis inertial unit, a 3-axis magnetometer, a microcontroller and communication interfaces, said printed circuit being housed in a waterproof housing incorporating a radome.

[0019] The magnetometer is used for orientation detection (like a kind of electronic compass) by measuring in particular the magnetic component of the Earth's field. The radome can in particular protect the radar antenna.

[0020] The invention also relates to a boat whose hull is provided with at least one submerged foil-type bearing surface allowing said hull to fly above the water, and which comprises at least one measuring system according to the characteristics stated above.

[0021] Several measuring systems can also be positioned in different places on the boat, allowing a certain redundancy of measurements to be obtained, which provides a much higher level of security in the event of failure of one of the systems.

[0022] By using mainly the inertial component of the inertial navigation unit, the measurement system of the invention makes it possible to isolate the movement of the measurement reference frame (the boat) to obtain a filtered measurement corresponding to the water surface motion independent of the attitude of the vessel. The inertial component refers to the measurement of the acceleration and rotation of the measured object (the vessel's hull), using accelerometers and gyroscopes, in order to determine the position, orientation and velocity of this object as a function of time.

[0023] By using primarily the navigation component of the inertial navigation unit, the measurement system of the invention makes it possible to isolate the components (period, height and direction) of the wave system, independently of the heading and speed of the moving vessel. The navigation component is in practice obtained via the data provided by the inertial component (i.e. the acceleration and rotation measurements) to determine the position, orientation and speed of the moving vessel relative to a reference starting point.

[0024] The examples mentioned are obviously not exhaustive of the invention, which encompasses differences in structure / geometry, dimensions etc. which may affect the measuring system or the vessel.

Claims

Claims

1. System for measuring the flight height of a boat whose hull is provided with at least one submerged foil-type bearing surface allowing said hull to fly above the water, characterized in that it comprises: - a radar for measuring the flight height of the hull of the boat relative to the water; - an inertial unit comprising at least inertial sensors for linear acceleration and rotation speed on three axes; - a GPS-type geopositioning device; - an inertial navigation unit provided with a unit for processing electronic signals from the radar, the sensors of the inertial unit and the geopositioning device, comprising means for processing said electronic signals in order to obtain at each instant at least one item of information on the height of the hull relative to the water.

2. System for measuring the flight height of a boat according to the preceding claim, characterized in that the radar is a pulsed Doppler radar.

3. System for measuring the flight height of a boat according to one of the preceding claims, characterized in that the radar is capable of measuring a height between the hull and the water of between 0.2 and 2m.

4. System for measuring the flight height of a boat according to one of the preceding claims, characterized in that it comprises a printed circuit comprising the radar, a 6-axis inertial unit, a 3-axis magnetometer, a microcontroller and communication interfaces, said printed circuit being housed in a waterproof case incorporating a radome.

5. Boat whose hull is provided with at least one submerged foil-type bearing surface allowing said hull to fly above the water, comprising at least one measuring system according to one of the preceding claims.

6. Boat according to the preceding claim, characterized in that several measuring systems are positioned in different places on the boat.