WO2018002383A1

WO2018002383A1 - Hydrofoil water vessel

Info

Publication number: WO2018002383A1
Application number: PCT/EP2017/066502
Authority: WO
Inventors: John Martin Kleven GODØ; Sverre STEEN
Original assignee: Norwegian University Of Science And Technology (Ntnu)
Priority date: 2016-07-01
Filing date: 2017-07-03
Publication date: 2018-01-04
Also published as: GB201611551D0

Abstract

A water vessel (101, 201) comprises a hydrofoil (111, 112, 211, 212) and an actuator system (150, 160) for driving the hydrofoil (111, 112, 211, 212). The actuator system (150, 160) and the hydrofoil (111, 112, 211, 212) are configured such that the actuator system (150, 160) drives the hydrofoil (111, 112, 211, 212) to provide lift and thrust to the water vessel (101, 201).

Description

HYDROFOIL WATER VESSEL

The present invention relates to a water vessel and a method of providing lift and thrust to a water vessel.

Commercial vessels, particularly fast vessels such as ferries, are currently relatively inefficient. For instance, current passenger ferries approximately use the same or larger amounts of fuel per passenger-kilometre than commercial passenger jet aircraft, despite having a significantly lower speed of travel. The combination of the high fuel consumption and low speeds makes water vessels currently unfavourable in comparison to aircraft.

Indeed current high speed passenger ferries even use several times (around between 2-5 times) more fuel per passenger-kilometre than cars. The reason for the current lack of efficiency is mainly due to large drag factors from the water and inefficient propulsion systems.

It is well known to use static hydrofoils to decrease the wetted area of a water vessel and hence decrease the drag and hence increase the efficiency of a water vessel. The static hydrofoil is fixed to the underside of the vessel such that it passes to through the water. The static hydrofoil acts in much the same way as an aircraft's wing, producing a vertical lift force as it passes through the water. The vertical lift force acts to lift the water vessel at least partially out of the water and so acts to reduce the drag on the water vessel.

In the vast majority of commercial and private water vessels, especially fast vessels, propulsion is provided by propellers or by water jet propulsion. However, such systems are actually quite inefficient for propelling water vessels. Even the best propellers today are only around 50-70% efficient for high speed vessels. One of the reasons for this inefficiency is that the proportion of the maximum possible cross-sectional area of water that they cover is quite small. This can be seen in Figure 1a, which shows a schematic view of a prior art vessel 1 having propellers 2 which cover a small area of water. This effect arises from the fact that the propellers necessarily cover a circular cross-sectional area of water. The diameter of the circular area is limited by the depth of water in which propellers are located and by the maximum propeller blade tip speed, which if too high causes unwanted cavitation. Due to this small cross-sectional area, in order to provide a given thrust to a water vessel, the speed at which a propeller must throw water backwards is higher than if a larger cross-sectional area of water were covered. The inventors have realised that to produce the same thrust it is more efficient, and hence more desirable, for a propulsion mechanism to act on a larger cross-sectional area and throw water backwards at a lower speed. In addition the inventors have realised that it is more efficient to have a propulsion mechanism whose velocity through the water is more even along the propulsion surface, in contrast to propeller blades which have low velocity at central locations and high velocities at outer locations.

There have recently been a small number of suggestions made to provide propulsion to vessels using moving or flapping hydrofoils. For instance, O-foil and Dolprop have developed vessels with such a propulsion system. However, at least due to their infancy, this concept is not yet of practical use for commercial water vessels, especially fast water vessels. Further, these do not provide any lift - they are merely propulsion mechanisms.

There is also a recreational product called the Aquaskipper, which uses a moving hydrofoil to provide propulsion and also to provide some lift to the rest of the product. This is a man-powered recreational device that is of very little relevance to the commercial shipping industry.

The inventors have identified a desire to increase the efficiency of high speed water vessels, such as high speed commercial water vessels, and have devised the present invention with a view of achieving such an improvement.

In one aspect the invention provides a water vessel comprising a hydrofoil and an actuator system for driving the hydrofoil, the actuator system and the hydrofoil being configured such that the actuator system drives the hydrofoil such that the hydrofoil provides lift and thrust to the water vessel.

Thus, as will be understood from the above, the vessel may have a controller for controlling movement of the hydrofoil using the actuator system in order to achieve the required lift and thrust. As used herein, the term "hydrofoil" refers to the foil element and not to the vessel as a whole. The vessel as a whole is referred to as the "vessel" or "water vessel".

The inventors have found that such a vessel is more energy efficient than the typical vessels mentioned above. For instance, the vessel of the first aspect can be up to around 10-80% more efficient than using a static hydrofoil for lift and a propeller for propulsion, with typical examples providing 15-50% increase in total energy efficiency. The increased efficiency is the decreased amount of energy required per distance travelled. This energy efficiency arises due to the same hydrofoil lifting the water vessel out of the water and also providing an efficient hydrofoil-produced thrust. This reduces the total wetted area, and hence increases the efficiency. The efficiency is also increased since a larger cross- sectional area of water is moved at a slower speed by the hydrofoil in comparison to a propeller. The efficiency is also increased since the hydrofoil can move through the water at an even linear speed, in contrast to a propeller whose central parts move at low linear speed and whose outer parts move at high linear speed. The inventors have also found numerous secondary advantages of such a vessel. For instance, the range of the vessel can be increased, the ride can be smoother, and the acoustic signature of the vessel can be reduced when compared to the established state-of-the-art vessels.

Whilst it is known for a vessel to have a propelling hydrofoil (such as the O-foil or Dolprop systems), these hydrofoils do not also provide lift. Whilst it is known for a vessel to have lifting hydrofoils (such as some commercial fast ferries), these hydrofoils do not also provide thrust. The Aquaskipper may use a single hydrofoil to produce lift and thrust, but this is driven directly by the user and not by an actuation system. Thus, in contrast to the proposed vessel, the Aquaskipper hydrofoil is not driven by an actuator system with movement relative to the remainder of the vessel, such as movement relative to a hull of the vessel. The use of a user-driven hydrofoil is clearly very limited and is certainly not of use for large commercial vessels. The proposed water vessel may have a hull that provides buoyancy and the hydrofoil and actuator system advantageously provide lift and thrust for such a hull.

The lift and thrust here may be an average (e.g. mean) lift and thrust taken over time. There may be instants where the hydrofoil is offering more drag than thrust and/or is not providing lift, and may even be providing down force. However, when averaged over time (e.g. over an oscillating cycle, see below) the hydrofoil is configured to provide net thrust and lift.

The thrust may be sufficient to propel the water vessel forward. The lift may be sufficient to at least partially lift the water vessel out of the water.

The actuator system may comprise or consist of a mechanical mechanism for driving the hydrofoil. For instance, the actuator system may comprise a mechanism for changing one form of motion (e.g. rotation) into the desired motion of the hydrofoil. For instance, the actuator system may be driven by or may include a motor or motors, as described below. The actuator system may be powered through a suitable automated arrangement via the controller.

The thrust that propels the vessel may arise purely from the hydrofoil (or hydrofoils, see below), i.e. there may not be any other thrust-producing means. Thus, the vessel may not comprise a propeller, or a water jet, or any other propelling means. However, it may also be possible for the vessel to comprise one or more thrusters (such as propellers or water jet units) for use in slow speed manoeuvring or for augmenting the lift and thrust from the hydrofoil(s). The thrusters may be side thrusters. Whilst such thruster(s) may be present, the thrust that propels the vessel at high speed may purely arise from the hydrofoil (or hydrofoils). In alternative configurations, the vessel may be propelled by a combination of both the hydrofoil(s) and additional thrusters for manoeuvring and/or for increased forward thrust. Preferably, the hydrofoil is configured to provide the lift and/or thrust by oscillating rotationally about a longitudinal axis of the hydrofoil (which will generally correspond to a transverse axis of the vessel) and by oscillating linearly in an at least partially vertical direction. The rotational oscillation about the longitudinal axis may be described as pitching. The oscillation may be provided by the hydrofoil being driven by the actuator system. The actuator system may in turn be powered by a motor under control of a suitable controller. Thus, the motion of the hydrofoil can be controlled in an automated fashion. The rotational oscillation about the longitudinal axis of the hydrofoil, i.e. the pitch motion, may occur via a free movement of the hydrofoil in which the hydrofoil rotates in pitch to 'follow' a linear oscillation. In this case a single oscillating input can be used with a rotatable hydrofoil allowing for passive generation of an oscillating pitch, for example with a spring or similar to return the hydrofoil to an 'at rest' pitch orientation when no force is applied. Alternatively, the pitch motion may be driven by a pitch actuator device, for example an actuator device arranged to generate rotational oscillation of the hydrofoil in co-ordination with and preferably out of phase with the linear vertical oscillation. This adds complication but can allow for a more refined motion of the hydrofoil than free or passive rotation for the pitch motion. One possibility for a pitch actuator device is a second linearly oscillating movement that is out of phase with the actuation of the main vertical oscillation. Another possibility is the use of an actuator coupled to the hydrofoil and arranged to move with the vertical oscillation, such as a dedicated pitch actuator in the form of a motor, solenoid or hydraulic actuator. The actuators that are used may be any type with appropriate mechanisms to obtain the required movement of the hydrofoil. For example, the actuators that could be used include hydraulic actuators, solenoids and any type of motor including linear motors.

The angular amplitude of the rotational oscillation of the hydrofoil may be a function of the combination of forward speed of the vessel, the linear amplitude of the hydrofoil and the oscillation frequency of the hydrofoil. The angular amplitude may be adjusted so as to provide shock-free entry (which is when there is no lift by angle of attack) and/or ideal angle of attack at all times (see more details on this below). For example, the angular amplitude may be 1-40°, preferably 2-20°, further preferably 5-10°.

Unlike the rotational oscillation, the linear oscillation may not be determined in any particular way, but in general the larger the oscillation the better. Of course, it will be possible to have larger linear amplitudes for larger vessels, but the maximum amplitudes will be governed by the maximum draft of the vessel, which may be governed by maximum allowable draft at given quays.

Thus, the linear amplitude may depend on the size of the vessel, and other factors.

However, as an example, the linear amplitude may be 0.1-10m, preferably 0.25-5m. As a specific example, the inventors have found that in a case vessel of a 40m-long fast vessel, the optimum linear amplitude is 0.75m for each of two hydrofoils operated 180° out-of-phase with each other (see more on this below). The linear amplitude may be in the vertical direction, and/or in a partially vertical direction. The linear amplitude may be in the direction of linear motion of the hydrofoil, preferably defined in the vessel reference frame.

The linear amplitude may also depend on the depth of the water and hence the maximum draft of the vessel. It may be possible for the hydrofoil to have a varying linear oscillation amplitude (and possibly also a corresponding varying rotational oscillation amplitude). This may allow the amplitude to be larger when there is no limitation on the draft of the vessel (e.g. in deeper water) and can be reduced when the maximum draft of the vessel is required to be less (e.g. in shallow water). Reducing the amplitude in shallow water is not typically disadvantageous as this is where the vessel will typically be travelling slowly.

Additionally/alternatively, another possible way of reducing the maximum draft of the vessel may be, when two oscillating hydrofoils are present (see below), the lower hydrofoil may be held in its upper position and the thrust may be provided by the upper hydrofoil oscillating (only). Holding the lower hydrofoil stationary in shallow water is not particularly disadvantageous as the vessel will typically be travelling slowly, and so the oscillation of the hull as a reaction to the oscillation of the upper hydrofoil only (which would not be present when the lower hydrofoil oscillates out of phase with the upper hydrofoil) is small. The hydrofoil may also be retractable, as discussed further below. This can allow for the maximum draft of the vessel to be similar to a non-hydrofoil vessel when required.

The oscillations of the hydrofoil may be relative to the static water frame, and/or relative to the frame of the remainder of the water vessel. The longitudinal axis of the hydrofoil may be at least partially horizontal, preferably substantially horizontal, and may be at least partially perpendicular to the longitudinal axis of the vessel, preferably substantially perpendicular to the longitudinal axis of the vessel. The longitudinal axis of the vessel may be generally in the direction of motion of the vessel, e.g. the axis extending from bow to stern of the vessel. Thus, the longitudinal axis of the hydrofoil may be substantially transverse to the direction of movement of the vessel.

Preferably, the hydrofoil is configured to provide the lift and/or thrust by being shaped to cause lift when the vessel moves in a forward direction, preferably when the hydrofoil is at or close to its equilibrium angle.

Known hydrofoils, which are shaped to provide lift, such as those provided on commercial fast vessels, are static. They do not oscillate and do not provide any thrust. Known hydrofoils, which are oscillated to provide thrust, such as those provided on the O-foil or Dolprop, are not shaped to provide lift. The present system can provide lift using an oscillating hydrofoil and can provide thrust using a hydrofoil shaped for providing lift. The hydrofoil may be approximated roughly as a plane, which is orientated in the horizontal direction. This may be its equilibrium position. The hydrofoil may oscillate rotationally and linearly about its equilibrium position.

The hydrofoil may comprise one or more winglets. The, or each, winglet may be located at an end of the hydrofoil. Such an end of a hydrofoil may be distant from the strut(s). The or each winglet may extend from the generally plane of the hydrofoil at least partially vertically upwards or downwards, preferably vertically upwards or downwards. For example, when there are two hydrofoils vertically separated from each other (see below), the or each winglet of the upper hydrofoil may project upwards from the upper hydrofoil and the or each winglet of the lower hydrofoil may project downwards from the lower hydrofoil.

Winglets may be used in order to increase the ratio of lift force to drag force created by the oscillating foils.

When viewed from above, the hydrofoil may be symmetric, it may comprise an axis of mirror symmetry that extends in the direction of motion of the vessel, which may preferably be located toward or at the centre of the vessel. It may additionally or alternatively comprise an axis of mirror symmetry in a horizontal direction perpendicular to the direction of motion of the vessel.

The hydrofoil may preferably be rectangular or trapezoidal in shape in plan view.

However, the hydrofoil may also comprise some curvature in plan view, for example it may be elliptical, or may comprise an elliptical edge. Preferably, the trailing edge is curved. This can provide optimal performance but it is more expensive than straight-edged shapes to manufacture.

The length of the hydrofoil may be as long as possible. The length of the hydrofoil may be substantially equal to, less than or greater than the width of the remainder of the vessel (e.g. the hull). The length of the hydrofoil may extend in a transverse direction of the remainder of the vessel (e.g. the hull). The transverse direction may be horizontal (relative to the vessel) and perpendicular to the longitudinal direction of the vessel (e.g. the direction of motion of the vessel). The width of the hydrofoil may be in the direction perpendicular to the length of the hydrofoil and may be generally horizontal, e.g. the width direction may be generally in the direction of motion.

The hydrofoil may be tapered in shape (when viewed from above). This taper may mean that the width of the hydrofoil may be smaller toward the ends of the length of the hydrofoil and may be greater toward the centre of the length of the hydrofoil.

When it is trapezoidal in shape, the longest edge of the hydrofoil is preferably the leading edge. The trailing edge may be shorter than the leading edge. Alternatively, the longest edge of the hydrofoil may be the trailing edge and the leading edge may be shorter than the trailing edge. The hydrofoil may be an isosceles trapezoid When the hydrofoil comprises curvature (when viewed from above), the curvature may be such that the width of the hydrofoil generally reduces towards the ends of the length of the hydrofoil and is at a maximum generally toward the centre of the length of the hydrofoil.

When the length of the hydrofoil is greater than the width of the remainder of the vessel, the vessel may require some support(s) protruding outside the outer width of the remainder of the vessel. These supports may be arranged to help ensure the vessel keeps sufficient distance to a quay in order to prevent the wide hydrofoils from touching the quay.

When the vessel moves in the forward direction, water passes over the hydrofoil. The shape of the hydrofoil is such that when this occurs a vertically upward lift force is produced, that can be transferred to the rest of the vessel to lift the vessel at least partially out of the water. The shape in question may be the cross-sectional shape when viewed along the longitudinal axis of the hydrofoil, i.e. a transverse cross-section of the hydrofoil. This shape may be referred to as the base geometry of the hydrofoil.

The precise shape will depend on parameters such as speed of vessel motion, size of the hydrofoil, speed of oscillation of the hydrofoil, size of the vessel, etc. However, generally speaking, the hydrofoil may be shaped similarly to an aircraft's wing. For instance, it may comprise a leading edge, a trailing edge, an upper surface extending between the leading edge and the trailing edge and a lower surface extending between the leading edge and the trailing edge. The leading edge may have a leading edge radius of curvature. The upper surface may exhibit some curvature (preferably generally convex with respect to the hydrofoil). The lower surface may exhibit some curvature (which may be concave and/or convex with respect to the hydrofoil), or may be generally planar. The trailing edge may be quite sharp, e.g. its radius of curvature may be (much) smaller than that of the leading edge.

The precise shape of the hydrofoil can be found for each set of parameters to find the optimal lift. It should be understood that it is not only the shape of the hydrofoil that governs how/if it is to provide lift, but also how the shape is used in combination with orientation of the hydrofoil (e.g. angle of attack) and/or in combination with the oscillation(s) of the hydrofoil.

The shape may be such that, at cruising speed of the vessel (and preferably at equilibrium foil and flap angles, see below, e.g. when the foil and the flap are oriented in the same angle, equal to the ideal angle of attack of the foil cross-section, which is close to zero angle, the hydrofoil would provide a lift equal to the (average, mean) lift required to be produced by the hydrofoil.

Preferably, the hydrofoil is configured to oscillate relative to the remainder of the water vessel. The remainder of the vessel may comprise a hull of the vessel and any components (such as cabins, holds, decks, engines, rudders, etc.) housed in or on the hull. The oscillation may be provided by the hydrofoil being driven by the actuator system.

In the vast majority of water vessels it is desirable to have the remainder of the vessel oscillating as little as possible. This ensures a smooth ride for passengers, crew and goods. However, since, in order to provide both thrust and lift, the hydrofoil may be oscillated through the water, it is advantageous to allow the hydrofoil to oscillate relative to the remainder of the water vessel, which generally should not oscillate relative to the water. This is in contrast to the Aquaskipper, where the remainder of the vessel necessarily is oscillated together with the hydrofoil. This is necessary because it is the user's oscillation on the platform and the handle bars that causes the Aquaskipper hydrofoil to oscillate.

Preferably, the hydrofoil is configured to oscillate in a regular pattern. Such a pattern may be generally sinusoidal or triangular. Such a pattern may be periodic. The oscillation may be provided by the hydrofoil being driven by the actuator system. The precise pattern may be determined and selected depending on other parameters, such as the configuration of the hydrofoil, the speed of the vessel, etc. This is in contrast to the Aquaskipper, whose hydrofoil is driven in a relatively uncontrolled way by a user jumping up and down.

The water vessel may comprise a motor or motor(s). The motion of the hydrofoil may be driven by the motor(s). For example, the motor(s) may drive the actuator system that drives the hydrofoil. By "motor" here it is intended to mean any (non-man-powered) machine that converts a form of potential energy (such as chemical or electrical) into mechanical energy. The motor may be an electric motor, or an engine such as an internal combustion engine.

The present water vessel is preferably a boat or ship. For instance, it may be a large vessel for the mass transporting goods and/or people. The boat or ship may comprise one or more hulls. The hull(s) may provide buoyancy such that if/when the boat or ship is stationary (e.g. when the hydrofoil ceases to oscillate) the hull(s) provide sufficient buoyancy to the boat or ship to prevent the boat or ship from sinking under the weight of the boat or ship, and any cargo and/or passengers it might hold.

Preferably, the vessel is a fast vessel. A fast vessel may be a High Speed Craft as defined by SOLAS Chapter X Reg. 1.3, i.e. one that is capable of a maximum speed in m/s equal to or exceeding 3.7 x V¹^, where V is the volume of displacement corresponding to the design waterline (m³). Alternatively but similarly, a fast vessel may be one that has a Froude number of more than 0.4 or 0.5, where the Froude number is given by ^u/ ,— , where u is the vessel speed, g is the gravitational acceleration and L is the overall submerged length when the vessel is resting on the buoyancy of the hull(s) or when running in displacement mode (i.e. when it is not lifted by its hydrofoil(s)). Optionally, the hydrofoil is configured to oscillate (as has been mentioned above) and is also configured to undergo a curvature change during the oscillation to cause at least some of the lift. This curvature change may be thought of as a dynamic curvature change as it occurs as the hydrofoil oscillates. The oscillation and the curvature change may be provided by the hydrofoil being driven by the actuator system. The hydrofoil having a changeable curvature may be described as having variable geometry.

As is known, a hydrofoil can produce lift both due to its shape and due to its angle of attack. However, the inventors have found that it is not desirable to (heavily) rely on the use of angle attack to produce lift using the oscillating hydrofoil. The inventors have realised that attempting to provide lift through angle of attack could lead to an early inception of cavitation, which increases drag, limits lift, and might lead to erosion of the hydrofoil surface and/or other structures nearby. This is of course undesirable. Thus, instead of (heavily) relying on the use of angle of attack, the inventors have devised an alternative method of producing lift, or increasing lift, during oscillation of the hydrofoil. This alternative method is to apply a curvature change to the hydrofoil during oscillation. The curvature change may be such that the amount of lift is increased (at high speed) relative to what is attainable without such a curvature change.

Since over-reliance on angle of attack can be avoided using such an oscillating hydrofoil with a dynamic curvature change, problems such as cavitation, reliance on angle of attack and unpredictable lift and drag properties are reduced or minimised. This may be achieved by ensuring the hydrofoil (e.g. the leading edge) is orientated at the correct angle, which may be achieved by appropriately controlling the oscillation.

Thus, the curvature change may be such that cavitation of water, reliance on angle of attack for lift and/or unpredictable lift and drag properties are/is reduced or minimised.

One possibility for the curvature change is one such that a trailing edge of the hydrofoil is maintained at substantially the same angle throughout the oscillation of the hydrofoil. This same angle may be relative to the global water's frame; however, preferably this angle is relative to the water vessel's frame, since this simplifies the mechanics of the vessel and hydrofoil (e.g. the trailing edge can simply be held against rotational movement relative to the remainder of the vessel). Whilst the trailing edge of the hydrofoil may be maintained at a substantially constant angle, the remainder of the hydrofoil (including the leading edge) oscillates. This oscillation may be such that the hydrofoil (e.g. the leading edge) provides (as closely as possible) substantially shock-free water entry (or equivalently substantially no lift by angle of attack).

The specific angle at which the trailing edge of the hydrofoil may be maintained may depend on the specific situation. However, the specific angle may be selected such that the mean lift from the hydrofoil (averaged over its oscillatory cycles) is equal to the required mean lift from the foil (which, for example, may be ¼ of the vessel weight in cases where there is a pair of oscillating foils in the bow or stern and a static foil in the other end of the vessel).

As mentioned above, the inventors have found that substantially shock-free water entry, or equivalently substantially no lift by angle of attack, is preferable. However, the inventors have also found that maintaining the trailing edge of the hydrofoil at substantially the same angle allows water to always leave the hydrofoil in the correct direction and allows for a simple mechanical actuation system.

The curvature change may be such that it occurs at the same frequency as the oscillation of the hydrofoil. It may be this that allows for the simple mechanical actuation system, since the curvature change can be driven by the same actuation system that drives the overall oscillation of the hydrofoil. The curvature change may therefore occur at a regular (periodic) pattern similar to that of the oscillation of the hydrofoil.

The hydrofoil may comprise a flap. The flap may be used to achieve the curvature change. Thus, the flap may be adjustable in angle relative to the remainder of the hydrofoil about the longitudinal axis of the hydrofoil so as to provide at least some of (and preferably substantially all of) the curvature change. The flap may comprise the trailing edge, and may not comprise the leading edge. Alternatively, the flap may comprise the leading edge, and may not comprise the trailing edge. The flap should be able to change the angle of the leading and trailing edges relative to one another, such that the flap should be able to change the angle of the upstream and downstream parts of the hydrofoil relative to one another. The flap may be hinged to the remainder of the hydrofoil.

The width of the flap may be less than 50%, optionally less than 40%, optionally less than 30%, optionally less than 20%, optionally less than 10% of the width of the hydrofoil. In one example the width of the flap is about 25% of the chord length (the width) of the hydrofoil. The remainder of the width of the hydrofoil may be given by the width of the remainder of the hydrofoil.

The flap may oscillate relative to the remainder of the hydrofoil at the same frequency as the oscillation of the hydrofoil. This may allow for the simple mechanical actuation system, since the flap oscillation can be driven by the same actuation system that drives the overall oscillation of the hydrofoil. The flap oscillation may occur at a regular (periodic) pattern similar to that of the oscillation of the hydrofoil. The flap oscillation may only be linear oscillation. The flap may be held at a constant angle (relative to the remainder of the vessel) throughout its linear oscillation. This is effectively the complete reverse of an aeroplane's aerofoil, where the main body of the wing remains stationary relative to the fuselage and the flap rotates relative to the fuselage. The (constant) flap angle may be selected so that when the hydrofoil is at its mean angular position there is no abrupt change of flow direction when the flow goes from the main body to the flap, i.e. the specific lift component from application of flap angle may be zero.

Relative to the vessel, the flap may oscillate with heave only and the remainder of the hydrofoil may oscillate with heave and rotation.

Thus, the hydrofoil devised by the inventors may be such that the angle of attack of the hydrofoil is not the primary mechanism for causing the lift. In some examples the angle of attack lift mechanism is minimal or non-existent (or as close to non-existent as possible). With the proposed vessel the hydrofoil(s) are used to provide both vessel lift and vessel thrust. These hydrofoils can effectively be considered with reference to both mean lift, averaged over time, and oscillating lift, which has a mean of zero. The thrust produced by the hydrofoils arises from the oscillating lift. This may increase and decrease the total lift of the hydrofoil in phase with the direction of the lift being altered as a result of the local inflow angle varying in phase with the vertical oscillation velocity. The mean lift will preferably be provided by the shape of the oscillating hydrofoil, for example from the foil cross-section, while the oscillating lift may either be provided by angle of attack during the oscillation cycles, or optionally by a dynamically changing curvature during the oscillation cycles. The total lift from the hydrofoil may be provided primarily via the shape of the foil and the mean lift induced during forward motion, in which case the angle of attack is not the primary mechanism for producing such lift. It will however be appreciated that the angle of attack and variations in the angle of attack can generate some lift as well as generating thrust, which then creates lift, and therefore the angle of attack may provide a contribution to the mean lift as well as in some cases being the primary source of oscillating lift.

The hydrofoil may be located toward the front (bow) of the vessel, but is located toward the rear (stern) of the vessel in some examples. Alternatively, there may be multiple hydrofoils, or multiple sets of hydrofoils, such as a hydrofoil (or set of hydrofoils) at the bow and a hydrofoil (or set of hydrofoils) at the stern as discussed below.

The hydrofoil may be held at a depth below the remainder of the vessel (such as a hull) by at least one strut, preferably by two or more struts, preferably located at, or close to, opposite ends of the hydrofoil, in the longitudinal direction of the hydrofoil.

The strut(s) may also support a stabilising static hydrofoil. Such a stabilising hydrofoil may include a flap that can be rotated by an actuator system or with possibilities of rotating the whole static hydrofoil by an actuator system in order to provide control forces, but in general the hydrofoil is static in relation to vertical movement relative to the remainder of the vessel, i.e. it may not oscillate relative to a hull of the vessel.. This hydrofoil may extend transversely from the strut and also may extend upwardly in the vertical direction. It may provide lift only (i.e. not thrust) and its upward slope may provide stability to the vessel against rolling and pivoting. It may be a surface-piercing hydrofoil.

Any suitable actuation system may be used that is capable of producing the desired oscillation of the hydrofoil. In one example, the strut(s) may (each) comprise an actuator for oscillating the hydrofoil (both rotationally and linearly). The actuator system may be driven by the motor mentioned above, preferably housed in or on the hull of the vessel. The distance between the hydrofoil and the remainder of the vessel (e.g. the hull) may vary as the hydrofoil oscillates. In another example, the hydrofoil is driven by the actuator system to oscillate linearly and it is allowed to rotate freely about a desired axis of rotation in order to allow for pitch rotation to be generated passively in reaction to the linear movement. This rotation may allow for a passive variation of pitch driven by forces on the hydrofoil. There may be a mechanism for elastically resisting pitch rotation and for urging the hydrofoil toward a resting position. This mechanism may include spring elements or similar resilient devices. Thus, the hydrofoil may oscillate in pitch motion against an elastic force with passive movement paired to the active (drive) vertical oscillation.

The actuator system may comprise at least two actuators, for example for driving both linear and rotational oscillation of the hydrofoil. One or more linear actuator(s) may be used for providing linear inputs to the actuator system. This can be for linear or rotational movement, depending on the mechanism used to attach the linear actuator(s) to the hydrofoil. One or more rotational actuator(s) may be used for providing rotational inputs to the actuator system. Again, this can be for linear or rotational movement, depending on the mechanism used to attach the rotational actuator(s) to the hydrofoil.

The two actuators may be two actuators for providing linear movement, where the two actuators are spaced apart in a direction perpendicular to the longitudinal direction of the hydrofoil, i.e. across the width of the hydrofoil. The two actuators may be spaced apart at least partially horizontally (preferably horizontally) when the vessel is at rest and/or when the vessel is in motion. The two actuators may be arranged and connected to the hydrofoil such that they can cause the linear and rotational oscillation of the hydrofoil. For instance, they may turn linear (e.g. linear movement in the direction defined by the strut or actuator) oscillation of the actuator into linear (e.g. linear movement in the direction defined by the strut or actuator) and rotational oscillation of the hydrofoil. The two actuators may also be used to cause the curvature of the hydrofoil to change as mentioned above. A second actuator may be attached to, or proximate to, the trailing edge (e.g. the flap). A first actuator may be attached to the remainder of the hydrofoil, e.g. at, toward, or proximate to the leading edge. The remainder of the hydrofoil may be a main body of the hydrofoil.

The hydrofoil may be connected to the actuator(s) at a pivot point, such that the hydrofoil can pivot relative to the actuator(s). Preferably, only the main body of the hydrofoil can pivot about the pivot point(s) and the flap does not pivot, so that the main body can oscillate linearly and rotationally but the flap can only oscillate linearly (relative to the remainder of the vessel).

The actuator(s) may (each) comprise a hydrofoil-connecting portion to which the hydrofoil is attached. This portion may be configured to move generally linearly, preferably parallel to the longitudinal direction of the strut(s), which may be generally vertical or swept back rearwards or swept forwards (at an angle between the vertical and the longitudinal direction of the vessel). This portion may comprise the pivot point. This portion may (also) comprise an actuation member. The actuation member may extend parallel to the longitudinal direction of the strut(s), which may be generally vertical or swept back rearwards or swept forwards (at an angle between the vertical and the longitudinal direction of the vessel). The actuation member may be substantially linear, and may be a linear member. This portion may be housed in a recess in the strut. The recess may extend in said linear direction, e.g. in the direction of the actuator and/or the strut, which may be vertically or swept backwards or swept forwards. The recess allows the actuator to not protrude out of the strut, and so reduces drag from the water, cavitation risk and wear of the actuator.

The actuator(s) may be held in position on the strut, but allowed to move relative to the strut, by rail(s) and/or wheel(s) or the like, which may cooperate with the recess(es).

The strut(s) may (each) be generally planar, the plane being perpendicular to the longitudinal direction of the hydrofoil and extending at least partially vertically, preferably vertically. Thus, the normal of the plane may have a component parallel to the longitudinal direction of the hydrofoil, preferably the normal of the plane is parallel to the longitudinal direction of the hydrofoil. The length of the strut(s) may define a longitudinal direction, which may extend from the hull downward vertically or may extend at an angle in between the vertical direction and the longitudinal direction of the vessel (e.g. the struts may be swept rearwards or forwards).

The actuation system may be driven by a mechanism using one or more eccentric wheels, which may convert rotational kinetic energy (e.g. from the motor) into linear oscillating movement (e.g. of the actuator(s)), and hence into linear and rotational oscillating movement of the hydrofoil.

With regard to the two actuators, there may be a forward actuator and a rearward actuator. The forward actuator may be attached to the main body at or proximate to the leading edge of the hydrofoil. The rear actuator may be attached to the main body toward the trailing edge, and/or to the flap, and/or at the pivot/hinge between the flap and the main body. The flap may not be allowed to pivot relative to the rear actuator, but the main body may be allowed to pivot relative to the rear actuator. This may allow for the main body to oscillate rotationally, but may not allow the flap to oscillate rotationally. Since the actuators may be fixed to the hydrofoil, and since the hydrofoil undergoes a rotational (pitching) oscillation, the horizontal distance (relative to the remainder of the vessel) separating the pivot points for the respective actuators may alter during the oscillation. In order to allow for this, at least one of the actuators may be allowed to move not only with a component of motion parallel with the motion of the other actuator, but may also be allowed to oscillate with a second component of motion. This second component may be, for example, perpendicular to the longitudinal direction of the strut; perpendicular to the general linear oscillation direction of the actuators; and/or in the longitudinal direction of the vessel. Both actuators may be allowed to oscillate with an oscillation having said second component. However, preferably only one of the actuators is allowed to oscillate in such a way. The other actuator may be held relative to the strut to prevent any such second component in its oscillation.

Stated another way, a first of the actuators may preferably oscillate linearly (only) and a second of the actuators may preferably oscillate linearly and rotationally. The frequencies of the linear and rotational oscillations are preferably the same. The frequency of the rotational oscillation might in some cases be twice the frequency of the linear oscillation.

Other arrangements may be used in place of the two linearly operating actuators described above. For example the actuator system may include: a first actuator for relative movement between the hydrofoil and the vessel in order to provide the vertical oscillation of the hydrofoil; and a second actuator mounted to the hydrofoil for rotational movement of the hydrofoil to provide the required rotating oscillation. The first actuator may be an actuator for linear movement of the hydrofoil as discussed above and the second actuator may be an actuator for controlling the rotational angle of the hydrofoil, such as a rotating actuator or a piston type actuator coupled to the hydrofoil spaced apart from an axis of rotation of the hydrofoil in order to pivot the hydrofoil during the linear vertical oscillation. For example, a solenoid or a hydraulic actuator may be used.

One possible way of driving linearly operating actuator(s), where present, comprises driving the actuator(s) by means of a wheel. Each actuator may be driven by a respective wheel, or may be driven by the same wheel. The rotation of the wheel(s) is converted into generally linear oscillatory motion of the hydrofoil by means of (respective) crank(s). The crank(s) may connect between the wheel(s) and the actuation member(s). The wheels can be driven by the same motor or by different motors. The wheel(s) can be controlled so as to control the oscillation of the hydrofoil. For instance, the speed and direction of rotation of the wheel(s) can be controlled. The wheel(s) can be referred to as eccentric wheels. The axis of rotation of the wheel(s) may be parallel to the longitudinal direction of the hydrofoil, e.g. horizontal (with respect to the vessel) and perpendicular to the longitudinal direction of the vessel. In order to steady the actuation member(s) into generally linear motion a guide may be provided for the actuation member or each respective actuation member.

If an actuator is desired to undergo only linear oscillation parallel to the longitudinal direction of the strut, then its guide may be configured to constrain the motion of the actuation member to be only linear motion in said direction. This may be achieved by having two or more guides (such as rollers) supporting two sides of the actuation member, the two sides being separated in the radial direction of the wheel. At least two of the guides may be separated from each other in said linear direction, thus preventing any pivoting the actuation member out of the desired linear direction. The guide thus may prevent the actuation member from pivoting, and hence may prevent any said second component being present in the oscillation of the actuation member.

In one example, there may be three (such as only three) guides present. Two of the guides may be placed on a first side of the actuation member and one guide may be placed on the other side of the actuation member. The guide placed on the other side is located between the two guides placed on the first side of the actuation member, with respect to the direction of the length of the actuation member.

If an actuator is desired to undergo oscillation including the second component, then its guide may be configured to constrain the motion of the actuation member to allow some pivoting of the actuation member. This may be achieved by having two guides (such as single rollers). These guides may be separated in the desired linear direction, and one may be on a first side of the actuation member and one on a second side of the actuation member (the first and second sides may be separated in the radial direction of the wheel). The guides may therefore allow for some pivoting of the actuation member out of the purely linear direction. The guide may allow the actuation member to pivot.

As an alternative mechanism for allowing the horizontal distance between the pivot points to change during oscillation of the hydrofoil, the oscillation of the actuator (or one of the actuators or both of the actuators) may include a component in the second direction. This two-direction oscillation may be generated by having a guide that guides the motion of the actuation member (driven by the wheel) into a generally linear direction, but also acts as a pivot about which the actuation member can pivot. The actuator may also comprise a pivot bar attached between a point on the hull about which the pivot bar can pivot and a pivot point located on the actuation member between the guide and the hydrofoil about which the pivot bar can pivot. The pivot bar may extend in a direction in the same plane as the radial direction of the wheel. The guide and the pivot bar are arranged such that, when the actuation member is driven by the wheel, the guide guides the actuation member into generally linear motion but also acts as a pivot about which the actuation member can oscillate with an oscillation including the second component to the oscillation, the second component being caused and controlled by the pivot bar.

Either or both of the actuation members can be allowed to, or forced to, oscillate using any of the above systems. Either of the actuation members may be held against horizontal oscillation using any suitable means.

When two actuators are present in one strut, one may be allowed to oscillate with the second component in the oscillation (e.g. it may be allowed to pivot) and one may not be allowed to oscillate with the second component in the oscillation (e.g. it may not be allowed to pivot). Alternatively, both may be allowed to oscillate with an oscillation including the second component. Alternatively, neither may be allowed to oscillate with an oscillation including the second component. In this case, some alternative adjustment may be necessary to allow the horizontal distance between the pivot points to change during the oscillation of the hydrofoil.

The hydrofoil may be a first hydrofoil and, preferably, the water vessel comprises a second hydrofoil, the second hydrofoil being configured to provide lift. The second hydrofoil may be located toward the stern, but is preferably located toward the front (bow) of the vessel. The second hydrofoil may also provide thrust, but preferably it does not provide thrust, i.e. it only provides lift (and a small, but inevitable, amount of drag). Thus, the second hydrofoil may be described as a static hydrofoil. The second hydrofoil may provide lift when it is pushed through the water by the vessel travelling in the forward direction.

The second hydrofoil may be configured to stabilise the water vessel. This can be done actively or passively, and may be to prevent/control rolling (rotation about a longitudinal axis of the vessel) or pitching (rotation about a transverse axis of the vessel). The stabilisation could be supplied when the second hydrofoil is a hydrofoil configured to produce thrust and lift (indeed the first hydrofoil could also be configured to provide stabilisation by any of the means discussed herein), but preferably the stabilisation is supplied (only) by a static second hydrofoil.

To actively prevent/control rolling and/or pitching, the second hydrofoil may comprise at least one control surface. The control surface may comprise an elevator flap and/or an aileron flap.

To actively prevent/control pitching, the second hydrofoil may comprise at least one actuatable elevator flap. The flap may be located at the trailing edge of the second hydrofoil. If excess pitching is detected (either by an automatic system or by a user) the flap may be actuated to compensate for the pitching. When a hydrofoil is configured to produce thrust and lift, the elevator flap may be the same flap as that discussed above. This is analogous to the function of an elevator flap on an aircraft. For instance, when the second hydrofoil is located toward the front of the vessel, if there is excess pitching such that the front of the vessel is pitching downward, the elevator flap located at the rear of the second hydrofoil may be actuated such that it rotates downward with respect to the remainder of the second hydrofoil thus forcing the front of the vessel upward; and if there is excess pitching such that the front of the vessel is pitching upward, the elevator flap located at the rear of the second hydrofoil may be actuated such that it rotates upward with respect to the remainder of the second hydrofoil thus forcing the front of the vessel downward.

Alternatively, when the second hydrofoil is located toward the rear of the vessel, if there is excess pitching such that the front of the vessel is pitching downward, the elevator flap located at the rear of the second hydrofoil may be actuated such that it rotates upward with respect to the remainder of the second hydrofoil thus forcing the front of the vessel upward; and if there is excess pitching such that the front of the vessel is pitching upward, the elevator flap located at the rear of the second hydrofoil may be actuated such that it rotates downward with respect to the remainder of the second hydrofoil thus forcing the front of the vessel downward.

To actively prevent/control rolling, the second hydrofoil may comprise at least two actuatable aileron flaps, each being at least partially horizontally spaced in opposite directions from the central longitudinal axis about which the vessel is rolling. Thus, there may be a right (starboard) and left (port) aileron flap. The aileron flaps may be located at the trailing edge of the second hydrofoil. If excess rolling is detected (either by an automatic system or by a user) the aileron flaps may be actuated to compensate for the rolling. When a hydrofoil is configured to produce thrust and lift, the flap mentioned above concerning changing hydrofoil curvature, may be (at least partially) formed by the aileron flaps. The elevator flap may comprise the aileron flaps. Thus, the aileron flaps may be used as the elevator flap and/or the curvature-changing flap.

The function of the aileron flaps is analogous to the function of the aileron flaps on an aircraft. For instance, if there is excess rolling such that the right (starboard) of the vessel is rolling downward, the right aileron flap located at the rear of the second hydrofoil may be actuated such that it rotates downward with respect to the remainder of the second hydrofoil and the left aileron flap located at the rear of the second hydrofoil may be actuated such that it rotates upward with respect to the remainder of the second hydrofoil. This forces the right of the vessel upward and the left of the vessel downward.

Alternatively, if there is excess rolling such that the left (port) of the vessel is rolling downward, the left aileron flap located at the rear of the second hydrofoil may be actuated such that it rotates downward with respect to the remainder of the second hydrofoil and the right aileron flap located at the rear of the second hydrofoil may be actuated such that it rotates upward with respect to the remainder of the second hydrofoil. This forces the left of the vessel upward and the right of the vessel downward.

To passively control and/or prevent pitching, the second hydrofoil may be shaped such that it provides more lift the deeper it is submerged into the water. For instance, the second hydrofoil may comprise at least one lift-producing hydrofoil portion that extends in a direction intermediate the horizontal and vertical directions, preferably from a lower central location beneath the vessel upwards and outwards. Preferably there are two such portions that are arranged symmetrically about a central longitudinal axis of the vessel. As the depth of the second hydrofoil increases, the amount of the second hydrofoil under water increases and hence the lift produced increases. As the depth of the second hydrofoil decreases, the amount of the second hydrofoil under water decreases and hence the lift produced decreases. In this way, the pitching of the vessel can be passively controlled.

To passively control and/or prevent rolling, the second hydrofoil may be shaped such that it provides more lift on the side that is rolled downwards and less lift on the side that is rolled upwards. For instance, the second hydrofoil may comprise two lift-producing hydrofoil portions that extend in a direction intermediate the horizontal and vertical directions, preferably from a lower central location beneath the vessel upwards and outwards.

Preferably there are two such portions that are arranged symmetrically about a central longitudinal axis of the vessel.

As the vessel rolls to the right, the depth of the second hydrofoil increases on the right hand side and decreases on the left hand side, the amount of the second hydrofoil under water on the right hand side increases and the amount of second hydrofoil under water on the left and side decreases, and hence the lift produced increases on the right hand side and decreases on the left hand side. Further, the average location of the hydrofoil underwater on the right hand side moves further out from the centre of the vessel, which can increase the lifting torque. The second hydrofoil may have a width greater than that of the vessel such that a portion of the hydrofoil extends outward beyond the right-hand extremity of the vessel. Thus, when the vessel rolls to the right, there may be lifting from laterally outward of the vessel on the right-hand side, which further increases the lifting torque. Thus, the roll may be corrected.

As the vessel rolls to the left, the depth of the second hydrofoil increases on the left hand side and decreases on the right hand side, the amount of the second hydrofoil under water on the left hand side increases and the amount of second hydrofoil under water on the right hand side decreases. Further, the average location of the hydrofoil underwater on the right hand side moves further out from the centre of the vessel, which can increase the lifting torque. Hence the lift produced increases on the left hand side and decreases on the right hand side. Further, the average location of the hydrofoil underwater on the left hand side moves further out from the centre of the vessel, which can increase the lifting torque. The second hydrofoil may have a width greater than that of the vessel such that a portion of the hydrofoil extends outward beyond the left-hand extremity of the vessel. Thus, when the vessel rolls to the left, there may be lifting from laterally outward of the vessel on the left- hand side, which further increases the lifting torque. Thus, the roll may be corrected.

Any combination of active and/or passive pitching and/or rolling prevention can be used on any of the hydrofoils present. However, preferably the pitching and/or rolling prevention means is provided only on a static hydrofoil, i.e. the thrust and lift-providing hydrofoil does not comprise any such means. This is preferable as it greatly simplifies the control of the thrust and lift-providing hydrofoil. There is no need for it to be concerned with maintaining the stability of the vessel, rather this can be done through an active or passive static hydrofoil.

In addition to, or as an alternative to, the above, the thrust-producing hydrofoil may also be used for pitch-correction of the vessel. When the vessel pitches, the mean pitch of the oscillating hydrofoil may also pitch. This may lead to an automatic correction of the vessel pitch. For instance, when the hydrofoil is located at the rear of the vessel and the vessel pitches upward, the mean pitch of the hydrofoil also pitches upward. This provides additional lift to the rear of the vessel (e.g. to an increased angle of attack), and hence corrects the pitching of the vessel. When the vessel pitches downward, the mean pitch of the rear hydrofoil also pitches downward. This provides reduced lift to the rear of the vessel, and hence corrects the pitching of the vessel.

The hydrofoil(s) may be configured such that, when the vessel is in motion (such as at high speed), the ride height of the vessel may be so as the whole vessel/hull is lifted out of the water. However, the clearance between the vessel/hull and the water may be small, such as less than around 5m, optionally less than around 2m, optionally less than around

1 m, optionally less than around 0.5m. The hull may be shaped or configured so that it works well (hydrodynamically) even if it was not lifted out of the water. This way any potentially dangerous situations where one hits an object and in the worst case destroys the second hydrofoil would be resolved by the hull simply falling through a short drop back on to the water surface. In typical hydrofoil vessels it is preferable to have the hull lifted by more than 0.5m out of the water.

When the hull is in the water in such a way (e.g. after falling into the water), the ride of the vessel will be more affected by waves. However, the oscillating hydrofoil(s) can provide large damping forces and so the ride would be improved in comparison to conventional propulsion means.

Preferably, the water vessel comprises a third hydrofoil, such as a further actuated hydrofoil that is configured to provide lift and thrust to the water vessel. Thus, there may be multiple actuated hydrofoils such as a pair of actuated hydrofoils. Here the term "third" is simply an arbitrary label. It does not necessarily mean the second (e.g. static) hydrofoil is also present, although of course it may be. The third hydrofoil may comprise any of the above-discussed features mentioned as being relevant to the first thrust and lift-producing hydrofoil.

The further actuated hydrofoil may be driven by the actuator system or by a different actuator system. The actuator system or the different actuator system that drives the further actuated hydrofoil may comprise any of the features discussed herein with relation to the actuator system that drives the first hydrofoil.

When multiple actuated hydrofoils are used then two actuated hydrofoils may be configured to oscillate out of phase with respect to one another. Thus, the vessel may comprise a controller for controlling a pair of hydrofoils to move in oscillating fashion as described above whilst their oscillations are out of phase with one another. The pair of actuated hydrofoils may be configured to oscillate at least 150°, further preferably at least 170°, further preferably 180° out of phase. The inventors have found that using only one oscillating hydrofoil may cause the remainder of the vessel to oscillate, which is undesirable in some applications. In order to reduce this oscillation, two actuated hydrofoils can be provided, and operated out of phase with each other. This might to a large extent cancel the oscillatory forces produced by each of the hydrofoils and so produces a particularly smooth ride for the vessel. The oscillation of each of the hydrofoils may be substantially identical (both in rotational oscillation and linear oscillation characteristics) other than being out of phase. The oscillation of the multiple actuated hydrofoils may be controllable independently of each other (e.g. when a different actuator is used). The control of the oscillation of the further actuated hydrofoil may be dependent on the control of the first actuated hydrofoil (e.g. when the same actuator system is used).

The multiple actuated hydrofoils may be thought of as a pair. There may be only two such hydrofoils per pair. There may be one pair, or a plurality of pairs.

The multiple actuated hydrofoils may be arranged such that they are separated at least partially vertically, preferably substantially vertically. Here, at least partially vertically means that the upper hydrofoil overlaps the lower hydrofoil when viewed from vertically above, and substantially vertically means that the upper hydrofoil substantially completely aligns with the lower hydrofoil to overlap the lower hydrofoil when viewed from vertically above. The multiple actuated hydrofoils may be supported by the same strut(s), e.g. the strut(s) discussed above. The shape and dimensions of the multiple actuated hydrofoils may be similar or identical. The multiple actuated hydrofoils may be driven by the same or different motor(s) and actuator(s). The distance between the multiple actuated hydrofoils in the linear direction of their oscillation when they are at their equilibrium positions may depend on the oscillation amplitude. This distance may be set so that the hydrofoils still have some clearance when the lower foil is in its top position and the upper foil is in its bottom position. With a 180° phase offset in heave oscillation this will happen simultaneously. As mentioned below, some hydrodynamic interaction may be present between the foils in this position, and additional clearance might be necessary in order to make sure that peak forces here are not extremely high as compared to forces at other time instants, leading to structural strength issues or cavitation problems due to low pressures caused by interaction effects. With this in mind, the inventors have found that the distance between the equilibrium positions of the foils may be at least twice the linear amplitude, optionally plus at least around a quarter or a half of the chord length (i.e. a quarter or a half of the length from trailing edge to leading edge of the hydrofoil).

Further, multiple actuated hydrofoils may be spaced in the vertical direction such that when they oscillate (180°) out of phase with each other they do not touch at their closest distance (i.e. when the upper hydrofoil is at its lowest position and the lower hydrofoil is at its highest position).

The distance between the multiple actuated hydrofoils in the linear direction of their oscillation when they are at their closest distance (e.g. when the lower foil is at its uppermost position, the upper foil is at its lowermost position, and the two foils are 180° out of phase) is optionally less than or equal to 5 chord lengths, 2 chord lengths, 1.5 chord lengths, 1 chord length, or 0.5 chord lengths. The distance between the multiple actuated hydrofoils in the linear direction of their oscillation when they are at their closest distance may for example be in the range of 0.25-1.0 chord lengths.

It may be advantageous to have the two hydrofoils brought close enough together at their closest positions during the out of phase oscillation such that water pressure is increased between the two hydrofoils as they are brought together (i.e. the water is squeezed between the two hydrofoils) and water pressure is correspondingly reduced as they move away from each other. If this occurs, and the orientation and/or oscillation of the hydrofoils are appropriately controlled, then there can be increased acceleration of water toward the rear of the vessel caused by these two effects (the increasing and decreasing pressure). This increased acceleration of water produces an increased thrust of the vessel. As has been mentioned above, there may be disadvantages associated with doing this however (e.g. due to very high or very low pressures being generated), and whether or not this step is carried out will depend on the specific situation. There may be an approximate 10% increase of lift forces if a pair of foils are lifting in opposite directions and put at around one chord length distance between each other. At 0.5 chord length distance, there may be an approximate 20% increase in forces.

Additionally/alternatively there may be multiple actuated hydrofoils that are offset, or even separated, in a horizontal direction, preferably in the longitudinal direction of the vessel. If the leading edges are offset by a distance greater than the width of the hydrofoils then the hydrofoils will be separated. In order to reduce oscillation of the remainder of the vessel, the multiple actuated hydrofoils may be oscillated out of phase with respect to one another in such a way so as to minimise the oscillation of the remainder of the vessel, that is to say, to minimise the oscillatory part of the net forces from the overall hydrofoil system or minimise the accelerations of the remainder of the vessel. In this case, the multiple actuated hydrofoils may or may not also be separated vertically.

The offset may be selected such that the leading edges (and/or trailing edges) are offset relative to each other by an amount such that energy can be recovered from vortices in the water, i.e. the offset is selected so that the rear hydrofoil partly or completely cancels out the vortices from the forward hydrofoil. The precise offset will therefore depend on the oscillation, the form of the hydrofoils, the speed of the vessel, etc. For example, if there are only two foils oscillating 180° out of phase, then the offset between them will have to be determined as a function of expected travel speed, so that the rear one cancels vortices from the front one.

There may be more than two hydrofoils configured to provide both lift and thrust. These may be horizontally and/or vertically spaced from each other, and may be arranged in any desired orientation. For example, there may be (only) two, three or four hydrofoils. The additional hydrofoil(s) may comprise any of the above-discussed features mentioned as being relevant to the first thrust- and lift-producing hydrofoil. They may be supported on the same strut(s) as each other, or may be split into pairs with hydrofoils in each pair being supported by respective strut(s), or may be split into single hydrofoils each single hydrofoil being supported by respective strut(s). Pairs of hydrofoils may be supported by the same strut(s) or may be supported by separate struts. The strut(s) may be the strut(s) discussed above. The shape and dimensions of the hydrofoils may be similar or identical to each other, or may be different to each other. The hydrofoils may be driven by the same or different motor(s) and actuator(s), which may comprise any of the features of the actuators discussed herein. When split into pairs then the respective pairs may be driven by the same or different motor(s) and actuator(s), which may comprise any of the features of the actuators discussed herein. The hydrofoils on the same strut(s) may be driven by the same or different motor(s) and actuator(s), which may comprise any of the features of the actuators discussed herein. In one example, there may be a pair of the hydrofoils toward the rear (stern) of the vessel. Additionally/alternatively, there may be a pair of the hydrofoils toward the front (bow) of the vessel. There may optionally be multiple sets of hydrofoils, such as multiple vertically spaced pairs, with the pairs spaced apart along the length of the vessel, such as having one set of hydrofoils at the bow of the vessel and one set of hydrofoils at the stern of the vessel.

As used herein, horizontal and vertical directions may be defined relative to the vessel.

In order to reduce oscillation of the remainder of the vessel, the respective phases of the oscillating hydrofoils may be selected and/or controlled so as to reduce the oscillation of the remainder of the vessel, or the oscillatory part of the net forces applied from the hydrofoil system on the vessel. This may be done by user input, or automatically.

The hydrofoil(s) may be substantially symmetrical, preferably mirror symmetrical about a vertical plane running in the longitudinal direction of the vessel at a midpoint of the vessel between the right (starboard) and left (port) sides of the vessel.

The hydrofoil(s) may be controlled so as to produce as smooth a ride as possible.

This may be achieved by selecting the number of hydrofoils, the location of the hydrofoil(s), the shape of the hydrofoil(s), the presence of static hydrofoil(s), the form of the static hydrofoil(s) and/or the location of the static hydrofoil(s). This may also be achieved by controlling the oscillation of the hydrofoil(s) (e.g. the pattern, the frequency, the amplitude, the phase) and/or the actuation of the flap(s)/aileron(s)/elevator(s)/control surface(s).

The inventors have identified another secondary advantage of having controllable oscillating hydrofoil(s) attached to a vessel. Not only can the oscillation of the hydrofoil(s) be controlled when travelling (at high speeds) to provide a smooth ride as possible, they can be controlled to stabilise the vessel when stationary or traveling at low speeds. At slow or zero vessel speeds, the hydrofoil(s) can be used to reduce the motion (e.g. heave, rolling, pitching) of the vessel. The stabilisation can be achieved using the motion of the hydrofoil as a whole, but is preferably achieved using the motion of the flap relative to the remainder of the hydrofoil (only), for example when the vessel is moving at high speeds. The stabilisation can be achieved using the motion of the flap relative to the remainder of the hydrofoil (only), but is preferably achieved using the motion of the hydrofoil as a whole when the vessel is moving at low or zero speeds. This stabilisation is of great benefit when, for example, docking the vessel.

Such stabilisation control for reduction of motion in waves is preferably done with the control surface(s) mentioned above. These are preferably placed on the static parts of the foil system, but additionally/alternatively may be placed on the oscillating parts of the system. The control surface(s) may comprise the flap(s) discussed above in connection with thrust production. The motion of the remainder of the oscillating hydrofoil(s) (e.g. the non- flap part) may additionally/alternatively be controlled to provide control forces that counteract the changes in forces due to incoming waves. In this case, the control surface(s) may comprise the remainder of the hydrofoi!(s).

The oscillating hydrofoil(s) may be part of an oscillating hydrofoil assembly. This assembly may comprise the one or more struts supporting the oscillating hydrofoil(s), the actuator(s), the static stabilising hydrofoil(s), etc.

The oscillating hydrofoil assembly may comprise a motor housing in which a motor is housed. This motor may drive the actuator(s) and the hydrofoil(s).

The oscillating hydrofoil assembly may be a single unit that can be mounted onto a vessel. For example, it may be configured to be mounted to the rear of the vessel, such as onto a strengthened backboard or bracket or transom. Such a backboard, bracket or transom may be capable of and designed for supporting a conventional outboard motor. The oscillating hydrofoil assembly may comprise an attachment bracket, which may be of the type conventionally used for outboard motors, to attach it to the backboard, bracket or transom.

Thus, the oscillating hydrofoil assembly may be removable from and attachable to the vessel. Thus existing vessels may be retrofitted with the oscillating hydrofoil(s) of the present invention.

The oscillating hydrofoil assembly may be moveable (e.g. translatable and/or rotatable about a vertical axis and/or a horizontal axis) relative to the remainder of the vessel. This relative motion may be such that it allows the vessel to be steered or manoeuvred, e.g. when about a vertical axis. This relative motion may be such that it allows the pitch of the hydrofoil(s) to be altered, e.g. when about a horizontal axis, and so allows the lift to be controlled. A vertically extending translating motion and/or a rotation may allow for retraction of the hydrofoils, for example to decrease the draft of the vessel as noted above.

In another aspect, the invention provides a propulsion unit for a water vessel, the propulsion unit comprising a hydrofoil and an actuator for driving the hydrofoil, the actuator and the hydrofoil being configured such that the actuator drives the hydrofoil such that the hydrofoil may provide lift and thrust to the water vessel when the unit is attached to the vessel, wherein the unit is configured to be attachable to the vessel.

The propulsion unit may be the oscillating hydrofoil assembly discussed above. Thus, the propulsion unit may be configured to be releasably attachable to the vessel.

In another aspect, the invention provides a water vessel comprising the propulsion unit discussed above. The propulsion unit may be moveable relative to a hull of the vessel when the propulsion unit is attached to the vessel, said relative motion being such that the vessel may be manoeuvred by said relative motion. This water vessel may comprise any of the features discussed herein.

The second (static, stabilising) hydrofoil may be part of a second hydrofoil assembly. The second hydrofoil assembly may also comprise one or more struts that support the second hydrofoil relative to the vessel.

The second hydrofoil assembly may be attachable to and/or removable from the remainder of the vessel hull. Thus existing vessels may be retrofitted with the static hydrofoil(s) of the present invention.

The second hydrofoil (or the second hydrofoil assembly) may be connected to the hull via one or more pads. The pad(s) may act to spread the force transmitted from the second hydrofoil to the hull, to prevent the hull from being damaged.

The propulsion unit and the second hydrofoil assembly may be part of the same unit. In this way, a single unit can be attached to hull to retrofit the hull.

In another aspect, the invention provides a method of providing lift and thrust to a water vessel, wherein the water vessel comprises a hydrofoil and an actuator for driving the hydrofoil, the method comprising driving the hydrofoil using the actuator so as to provide the lift and the thrust to the water vessel. This method may include using a vessel as described above, for example, a vessel with any of the features of the hydrofoil or actuator system described above.

The method may comprise providing the lift and/or thrust by oscillating the hydrofoil rotationally about a longitudinal axis of the hydrofoil and by oscillating the hydrofoil linearly in an at least partially vertical direction.

As discussed above, the hydrofoil may be configured to provide the lift and thrust by being shaped to cause lift when the vessel moves in a forward direction.

The method may comprise oscillating the hydrofoil relative to the remainder of the water vessel, preferably by using and/or controlling the actuator accordingly.

The method may comprise oscillating the hydrofoil in a regular pattern, preferably by using and/or controlling the actuator accordingly. The method may use a controller for controlling the actuator.

The method may comprise driving the hydrofoil using a motor. Preferably, the motor drives the actuator or is part of the actuator.

The water vessel is preferably a boat or ship.

The method may comprise oscillating the hydrofoil and changing a curvature of the hydrofoil during the oscillation to cause at least some of the lift, preferably by using and/or controlling the actuator accordingly. Preferably, the method may comprise reducing or minimising cavitation of water and/or reliance on angle of attack for lift by changing the curvature of the hydrofoil. Preferably, the method may comprise maintaining a trailing edge of the hydrofoil at substantially the same angle relative to the water vessel throughout the oscillation of the hydrofoil by changing the curvature of the hydrofoil. Preferably, the method may comprise changing the curvature at a frequency equal to the frequency of oscillation of the hydrofoil. Changing the curvature of the hydrofoil may comprise adjusting an angle of a flap relative to the remainder of the hydrofoil about a longitudinal axis of the hydrofoil.

The angle of attack of the hydrofoil may not be the primary mechanism for causing the lift, for example the mean lift as discussed above.

The hydrofoil may be a first hydrofoil and the water vessel may comprise a second hydrofoil. The second hydrofoil may be configured to provide lift, preferably only lift (i.e. and not also thrust). The method may comprise providing lift using the second hydrofoil. The method may comprise stabilising the water vessel using the second hydrofoil.

The hydrofoil may be a first hydrofoil and the water vessel may comprise a further actuated hydrofoil. The further actuated hydrofoil may be configured to provide lift and thrust to the water vessel. The method may comprise driving the further actuated hydrofoil so as to provide the lift and the thrust to the water vessel. Preferably, the method comprises oscillating the multiple actuated hydrofoils out of phase with respect to one another, preferably 180° out of phase. Additionally, the hydrofoils may be arranged such that they are separated at least partially vertically. The further hydrofoil may be driven by the actuator system or by a different actuator system.

The method may comprise selecting the configuration of and/or controlling the hydrofoil(s) so as to stabilise the vessel when moving and high speed, when moving at low speeds and/or when stationary. Preferably, the method comprises using the hydrofoil(s) to reduce and/or minimise unwanted motion of the vessel (such as heaving, rolling and/or pitching).

In another aspect, the invention provides a method of retrofitting a vessel with a propulsion unit, the propulsion unit comprising a hydrofoil and an actuator system for driving the hydrofoil, the actuator system and the hydrofoil being configured such that the actuator system drives the hydrofoil such that the hydrofoil may provide lift and thrust to the water vessel when the unit is attached to the vessel, wherein the unit is configured to be attachable to the vessel, the method comprising: attaching the unit to the vessel. The method, the vessel and/or the propulsion unit may comprise any of the features discussed above. The propulsion unit may be attached to (or proximate to) the rear of the vessel. The method may also comprise attaching a static hydrofoil unit to the vessel (which may comprise the second hydrofoil). This may be attached to the vessel at a location distant from the rear of the vessel, e.g. toward the front of the vessel. The propulsion unit and the static hydrofoil unit may be part of one single unit. Certain preferred embodiments will now be described by way of example only and with reference to the accompanying drawings, in which

Figures 1a and 1 b show a schematic comparison between the two different propulsion methods;

Figure 2 shows an exemplary embodiment of a water vessel according to the present invention;

Figures 3a and 3b show a schematic comparison between two different hydrofoil shapes;

Figure 4 shows a schematic view of an exemplary hydrofoil for use with a water vessel according to the present invention;

Figures 5a to 7 show schematic views of exemplary actuating mechanisms for driving the hydrofoil of the present invention;

Figures 8 and 9 show exemplary stability-controlling systems for the water vessel of the present invention;

Figure 10 shows a side view an exemplary embodiment of another water vessel according to the present invention;

Figure 11 a rear view of the vessel of Figure 10;

Figure 12 shows a front view of the underside of the vessel of Figure 10; and

Figure 13 shows an enlarged view of a hydrofoil assembly of the vessel of Figure 10. With regard to Figure 1a, as is mentioned above in the introduction section, this shows a schematic view of a prior art vessel 1 having propellers 2 which cover a small area of water. The reason these propellers cover only a relatively small area of water is that the propellers 2 necessarily cover a circular area, and the diameter of the circular area is limited by the depth of water in which propellers are located and by the maximum propeller blade tip speed, which if too high causes unwanted cavitation. Due to this small area, in order to drive a water vessel at a given speed, the speed at which a propeller 2 must throw water backwards is higher than if a larger area of water were covered. The inventors have realised that to produce the same thrust it is more efficient, and hence more desirable, to cover a larger area and throw water backwards at a lower speed.

With regard to Figure 1b, this shows a schematic view of a prior art vessel 11 , such as the O-foil mentioned above, having a driven hydrofoil 12 for providing thrust to the vessel. The hydrofoil 12 covers a larger area of water than the propellers 2 do. The reason the hydrofoil 12 can cover a larger area is that it can be rectangular in shape and the increased size does not increase the risk of cavitation (unlike propellers 2). Due to this large area, in order to drive a water vessel at a given speed, the speed at which the hydrofoil 12 must throw water backwards is lower than if a smaller area of water were covered (such as by propellers 2). This arises due to thrust being proportional to the difference between outflow velocity from the propulsion mechanism and inflow velocity to the propulsion mechanism, while input energy is proportional to the difference between outflow velocity squared and inflow velocity squared. This leads to hydrofoil thrust being more efficient than propeller thrust.

With regard to Figure 2, this shows a perspective view of an exemplary water vessel

101 according to an embodiment of the present invention. The vessel 101 is a boat or ship, such as a commercial transportation fast ship, that comprises a hull 102 which comprises cabins, decks, engines, motors, etc. In the present embodiment, the vessel 101 is a catamaran, which is a particularly efficient hull 102 design for fast commercial vessels, but could have any other known shape, such as a monohull, a trimaran, or a smaller private leisure boat.

Attached to the hull 102 and vertically offset in the downward direction from the hull

102 is a rear hydrofoil assembly 110 and a forward hydrofoil assembly 120.

The rear hydrofoil assembly 110 comprises a pair of hydrofoils 111 , 112 that are configured to produce thrust and lift when driven. The pair of hydrofoils 111 , 112 are attached to the hull 102 by two struts 113 located at opposite ends of the hydrofoils 111 , 112, in the longitudinal direction of the hydrofoils 111 , 112. The hydrofoils 1 11 , 112 are shaped so that they provide lift, even if held statically relative to the hull 102 (i.e. even if they do not oscillate), when the vessel 101 moves in a forward direction.

Each hydrofoil 111 , 112 can be approximated as a plane, which is orientated substantially in the horizontal direction, although as is described below each hydrofoil 111 , 112 oscillated about this generally horizontal orientation. When viewed from above, each hydrofoil 111 , 112 is rectangular in shape, the length of the rectangle being substantially equal to the width of the hull 101 and each hydrofoil 111 , 112 being arranged such that the length of the rectangle extends across the hull 102 in the transverse direction of the hull 102. The length of the hydrofoils 111 , 112 is in a longitudinal direction of the hydrofoils 111 , 12.

When the vessel 101 moves in the forward direction, water passes over the hydrofoils 11 1 , 112. The shape of the hydrofoils 111 , 112 is such that when this occurs a vertically upward lift force is produced. This lift force is transferred to the hull 102 via the struts 113 (and/or possibly through the hydrofoil actuator(s) 150, 160, see below), thus lifting the vessel 101 at least partially out of the water.

The cross-section shape of the hydrofoils 1 11 , 112 (when viewed along the longitudinal direction of the hydrofoils) is such that, at cruising speed of the vessel and preferably at equilibrium hydrofoil and flap angles (see below), e.g. when the hydrofoil and the flap are orientated horizontally, the hydrofoils 11 1 , 1 12 provides a lift equal to the lift required by the vessel 101. The precise shape depends on parameters such as speed of vessel motion, size of the hydrofoils 1 11 , 112, speed of oscillation of the hydrofoils 1 11 , 112, size of the vessel 101 , etc. However, generally speaking, the hydrofoils 11 1 , 112 are shaped similarly to an aircraft's wing.

In one example (see Figure 3b) the hydrofoils 1 11 , 112 comprise a leading edge 131 , a trailing edge 132, an upper surface 133 extending between the leading edge 131 and the trailing edge 132 and a lower surface 134 extending between the leading edge 131 and the trailing edge 142. The leading edge 131 has a greater radius of curvature than the trailing edge 132. The upper surface 133 exhibits some convex curvature and the lower surface 134 is slightly concave.

In another example (see Figure 4) the hydrofoils 111 , 112 comprise a leading edge 141 , a trailing edge 142, an upper surface 143 extending between the leading edge 141 and the trailing edge 142 and a lower surface 144 extending between the leading edge 141 and the trailing edge 142. The leading edge 141 has a greater radius of curvature than the trailing edge 144. The upper surface 143 exhibits some convex curvature and the lower surface 144 is also convex.

Returning to Figure 2, the hydrofoils 111 , 112 are driven by an actuation mechanism (not shown) such that the hydrofoils produce thrust and lift by oscillating rotationally about the longitudinal axis of the hydrofoils 111 , 112 and by oscillating linearly in an at least partially vertical direction. The rotational and at least partially vertical oscillations are oscillations relative to the remainder of the vessel 101 , e.g. the hull 102 and the struts 113.

The pair of hydrofoils 111 , 112 comprises an upper hydrofoil 111 and a lower hydrofoil 112. The struts 113 extend from the hull 102 downward in the vertical direction and rearward. The hydrofoils 111 , 112 are arranged such that they are separated partially vertically such that the upper hydrofoil 11 1 partially overlaps the lower hydrofoil 112. The shape and dimensions of the two hydrofoils 111 , 112 are substantially identical to each other. In the embodiment of Figure 1 , the hydrofoils 111 , 1 12 are also partially offset in the longitudinal direction of the vessel 101

The hydrofoils 111 , 112 are driven so as to oscillate 180° out of phase with respect to one another. The oscillation of the two hydrofoils 111 , 112 is such that the oscillation of the remainder of the vessel 101 (such as the hull 102) that may be caused by the oscillating hydrofoils 111 , 112 is minimised.

The hydrofoils 111 , 112 are spaced in the vertical direction such that when they oscillate 180° out of phase with each other they do not touch at their closest distance (i.e. when the upper hydrofoil 111 is at its lowest position and the lower hydrofoil is at its highest position 112). When at their closest distance, the two hydrofoils 111 , 112 are spaced apart such that water pressure between the two hydrofoils 1 11 , 112 is increased as they are brought together (i.e. the water is squeezed) and water pressure is reduced (i.e. it is "pulled apart") as they move away from each other. When this occurs, and the orientation and oscillation of the hydrofoils is appropriately controlled, then there is an increased acceleration of water toward the rear of the vessel 101 caused by these two effects (the increasing and

decreasing pressure). This increased acceleration of water produces an increase thrust of the vessel 101.

With regard to Figure 3, this shows a comparison between the shape of the hydrofoils 111 , 112 configured to produce lift and thrust discussed above and the shape of known hydrofoils that provide thrust only, such as those oscillating hydrofoils used for propulsion in existing technologies.

Figure 3a shows a schematic view of an oscillating hydrofoil 211 shown at different stages of its oscillating path. In Figure 3a the hydrofoil 211 is travelling through the water from right to left (or water is passing over they hydrofoil 211 from left to right). This hydrofoil 211 produces thrust only.

Figure 3b shows a schematic view of the hydrofoil 111 , 1112 shown at different stages of its oscillating path. In Figure 3b the hydrofoil 111 , 112 is travelling through the water from right to left (or water is passing over they hydrofoil 111 , 112 from left to right). This hydrofoil 1 11 , 112 produces lift as well as thrust. The lift and thrust are produced by a combination of the hydrofoil's 111 , 112 shape and oscillation. The cross-section shape of the hydrofoil 111 , 112 is discussed above. Whilst only one hydrofoil 111 , 112 is shown, as discussed above there are preferably a pair of such hydrofoils 111 , 112.

Figure 4 shows an alternative hydrofoil 1 11 , 112 shown at different stages of its oscillating path. In Figure 4 the hydrofoil 111 , 112 is travelling through the water from left to right (or water is passing over they hydrofoil 111 , 112 from right to left). This hydrofoil 111 , 112 produces lift as well as thrust. The lift and thrust are produced by a combination of the hydrofoil's 1 11 , 112 shape and oscillation. The cross-section shape of the hydrofoil 111 , 112 is discussed above. Whilst only one hydrofoil 111 , 112 is shown, as discussed above there are preferably a pair of such hydrofoils 111 , 1 12.

This hydrofoil 111 , 112 of Figure 4 is configured to undergo a curvature change during the oscillation. This curvature change feature could be applied to any suitable hydrofoil 111 , 112, such as that of Figure 3b. The curvature change causes at least some of the lift produced by the hydrofoil 111 , 112. The curvature change is such that the amount of lift is increased relative to what is attainable by the hydrofoil 111 , 112 without such a curvature change. As can be appreciated from Figure 4, the curvature change is such that as the pitch of the leading edge 141 oscillates due to rotational oscillation of the hydrofoil 111 , 112, the pitch of the trailing edge 142 does not change. Thus, despite the oscillation of the hydrofoil 1 11 , 112, the trailing edge 142 is maintained at substantially the same angle relative to the remainder of the vessel 101 and/or the water frame. Whilst the trailing edge 142 of the hydrofoil is maintained at a substantially constant angle, the remainder of the hydrofoil 111 , 112 (including the leading edge 141 ) oscillates rotationally.

This allows the oscillation of the hydrofoil 111 , 1 12 (e.g. the leading edge 141 ) to give substantially shock-free water entry and substantially no lift by angle of attack, whilst ensuring water leaves the hydrofoil 111 , 112 at the trailing edge 142 in the correct direction.

Changing the curvature of the hydrofoil 111 , 112 in this way means that over-reliance on angle of attack can be avoided. This might reduce the risk of cavitation, as one can provide dynamically varying lift without large deviations from ideal angle of attack.

Essentially, the curvature change is such that the leading edge 141 has an optimum angle (driven by the desire to avoid lift by angle-of-attack) whilst the trailing edge 142 also has an optimum angle (driven by the desire to have water leave they trailing edge 142 at the optimum angle).

The hydrofoil 111 , 112 is arranged and driven such that the curvature change occurs at the same frequency as the oscillation of the hydrofoil, and follows the same regular periodic pattern to that of the oscillation of the hydrofoil.

The hydrofoil 111 , 112 comprises a main body 145 and a flap 146. The flap 146 is configured to change angle relative to the main body 145, e.g. via a pivot or hinge. The flap 146 comprises the trailing edge 142 and the main body comprises the leading edge 141. Thus, the desired curvature change discussed above can be achieved by alternating the angle of the flap 146 relative to the main body 145. The flap 146 is adjustable in angle relative to the main body 145 about the longitudinal axis of the hydrofoil 111 , 112.

The flap 146 rotationally oscillates relative to the main body 145 at the same frequency as the oscillation of the hydrofoil 111 , 112 as a whole. In this way, the flap 146 stays at a constant angle relative to the vessel and oscillates purely linearly relative to the vessel 101 , whilst the main body 145 rotates both linearly and rotationally relative to the vessel 101.

With regard to Figures 5a, 5b, 6 and 7, these show some possible mechanical actuation solutions for driving the oscillation of the hydrofoils 111 , 112 and the flap 146.

Figure 5a shows a schematic view of a hydrofoil 111 , 112 and one of the struts 113 viewed along the longitudinal axis of the hydrofoil 111 , 112. Figure 5b shows a perspective view of the same. The strut 113 comprises two actuators 150, 160 for oscillating the hydrofoil 111 , 1 12 both rotationally and linearly. The actuators 150, 160 are driven by a motor (not shown), preferably housed in or on the hull 102 of the vessel 101 or in the strut 113.

There is a forward actuator 150 and a rearward actuator 160. The two actuators 150, 160 are spaced in a direction perpendicular to the longitudinal direction of the hydrofoil 11 1 , 112, and horizontally (i.e. they are spaced in the longitudinal direction of the vessel 101 ). The two actuators 150, 160 are arranged and connected to the hydrofoil such that they cause the linear and rotational oscillation of the hydrofoil 111 , 112 when driven. The actuators 150, 160 turn generally linear oscillation of the actuators 150, 160 into linear and rotational oscillation of the hydrofoil 111 , 112. The two actuators 150, 160 are also used to cause the curvature of the hydrofoil 111 , 112 to change.

The forward actuator 150 is attached to the main body 145 proximate the leading edge 141. The rear actuator 160 is attached to the main body 145 toward the trailing edge 142, or to the flap 146, or at the pivot/hinge.

The hydrofoil 111 , 112 is connected to each of the actuators 150, 160 at respective pivot points 151 , 161 in a pivoting manner, such that the hydrofoil 111 , 112 can pivot relative to the actuators. The main body 151 is attached to actuator 150 via a pivot point 151 and to actuator 160 via a pivot point 161. The main body 151 can pivot relative to the actuators 150, 160 and to the remainder of the vessel 101 around pivot points 151 , 161. The flap is connected to actuator 160 via pivot point 161. However, unlike the main body 145, the flap 146 cannot pivot relative to the actuator 160 or relative to the remainder of the vessel 101 since the flap is arranged such that it cannot pivot about pivot point 161 (e.g. it is held relative to pivot point 161 ).

The actuators 150, 160 each comprise a hydrofoil-connecting portion 152, 162 to which the hydrofoil 111 , 112 is attached. This portion 152, 162 is configured to oscillate generally linearly. In the embodiment of Figure 5, this generally linear movement is in the generally vertical direction, since the struts 113 extend generally vertically in Figure 5.

However, when the struts 113 are swept backwards as shown in Figure 1 , the movement may be parallel to the direction in which the struts extend (e.g. the longitudinal direction of the struts).

The portions 152, 162 comprise the pivot points 151 , 161. The portions 152, 162 also comprise respective actuation members 153, 163, which extend parallel to the longitudinal direction of the struts 113 (vertically in Figure 5 and swept rearwards in Figure

1 )- The portions 152, 162 are housed in respective recesses 154, 164 in the strut 113.

The recesses 154, 164 extend in a linear direction parallel to the longitudinal direction of the strut 113. The recesses 154, 164 and the actuator portions 152, 162 are configured such that the actuator portions 152, 162 do not protrude out of the strut 113.

The actuators 150, 160 are held in position in the recesses 154, 164 of the strut 113, but are allowed to move relative to the strut 1 13. This is achieved, for example, by using wheel(s) 165 in the recess(es) 150, 160. The wheels 165 shown in Figure 5a can also be used to support a carriage 172 in the recess 164, which can be used to prevent rotation of the flap 146.

Since the actuators 150, 160 are fixed to the hydrofoil 1 11 , 112, and since the hydrofoil 111 , 112 undergoes a rotational (pitching) oscillation, the horizontal distance (relative to the remainder of the vessel 101 ) separating pivot points 151 , 161 will alter during the oscillation.

In order to allow for this, at least one of the actuators 150, 160 is allowed to oscillate not only parallel with the other actuator (e.g. parallel to the longitudinal direction of the strut 113), but also may be allowed to oscillate with a second component in the oscillation motion (e.g. perpendicular to the longitudinal direction of the strut 113; perpendicular to the general linear oscillation direction of the actuators 150, 160; and/or in the longitudinal direction of the vessel 101 ). Whilst both actuators may be allowed to oscillate with said second component, in Figure 5 only the forward actuator 150 is allowed to oscillate in such a way. The rear actuator 160 is held relative to the strut 113 by wheels 165 in the recess 164 to prevent any such second component oscillation. Stated differently, the forward actuator 150 oscillates rotationally and linearly and the rear actuator 160 oscillates linearly (only), where both oscillations are at the same frequency. Of course, it may be possible for the forward actuator 150 to oscillate linearly (only) and the rear actuator 160 to oscillate rotationally and linearly instead.

Figure 5a shows the hydrofoil 111 , 112 in its mean angular position. In this mean angular position, the flap 146 is at an angle such that there is no abrupt change of angle of the upper or lower surfaces of the hydrofoil 111 , 112 between the main body 145 and the flap 146 (e.g. the curvature of the hydrofoil 111 , 112 is substantially constant, even at the pivot 161 , when the hydrofoil 111 , 112 is at its average angular position). It is this angle that the flap 146 is maintained at (relative to the remainder of the vessel 101 ) as the hydrofoil

111 , 112 main body 145 oscillates rotationally. Thus, the curvature of the hydrofoil 111 , 112 and the flap 146 angle are selected so that when the hydrofoil 111 , 112 is at its mean angular position (Figure 5a) there is no abrupt change of flow direction when the flow goes from the main body 145 to the flap 146, i.e. the specific lift component from application of flap angle may be zero.

Figure 6 shows a schematic view of an exemplary system for driving the actuators 150, 160. Each actuator 150, 160 is driven by a respective drive wheel 156, 166. The rotation of each wheel 156, 166 is converted into linear oscillatory motion of respective actuation members 153, 163 by means of respective cranks 157, 167 that connect between the wheels 156, 166 and the actuation members 153, 163.

In order to steady the actuation members 153, 163 into generally linear motion, respective guides 158, 168 are provided.

If an actuator is desired to undergo only linear oscillation parallel to the longitudinal direction of the strut 113 (the rearward actuator 160 in the present embodiment), then its guide 168 is configured to constrain the motion of the actuation member 163 to be only linear motion. In the present embodiment, this is achieved by having two pairs of roller guides separated in the desired linear direction, thus preventing any pivoting the actuation member 163 out of the desired linear direction. The guide 168 prevents the actuation member 163 pivoting, and hence prevents any said second component to the oscillation.

If an actuator is desired to undergo oscillation including the second component (the forward actuator 150 in the present embodiment) then its guide 58 is configured to constrain the motion of the actuation member 153 to allow some pivoting of the actuation member 153. In the present embodiment, this is achieved by having two single roller guides separated in the desired linear direction, which allow for some pivoting of the actuation member 153 out of the purely linear direction. The guide 158 allows the actuation member 153 to pivot. Although not shown in Figure 6, the rollers of guide 158 might not be spaced in the direction of linear motion. This would allow pivoting without losing the contact between one roller and the actuation member 153.

An alternative mechanism is shown in Figure 7. In this alternative, the oscillation of the rearward actuator 160 includes a component in the second direction. This two-direction oscillation is generated by having a guide 168 that guides the motion of the actuation member 163, but also acts as a pivot about which the actuation member 163 can pivot. The actuator 169 also comprises a pivot bar attached between a fixed pivot point 170 on the hull 102 about which the pivot bar 169 can pivot and a fixed pivot point 171 located on the actuation member 163 between the guide 168 and the hydrofoil 111 , 112 about which the pivot bar 169 can pivot. As can be appreciated from Figure 7, when the actuation member 163 is driven up and down vertically by the wheel 166, the end of the actuation member 163 attached to the hydrofoil 111 , 112 will also oscillate horizontally.

The struts 113 are each generally planar, the plane being perpendicular to the longitudinal direction of the hydrofoil 111 , 112 and extend partially vertically (see Figure 1 ) or vertically (see Figure 5). Thus, the normal of the plane is parallel to the longitudinal direction of the hydrofoil 11 1 , 112.

Returning to Figure 2, as mentioned above, the vessel 101 comprises a forward hydrofoil assembly 120. Whilst this forward hydrofoil assembly 120 could comprise any of the features discussed above in relation to the rearward hydrofoil assembly 110, preferably the forward hydrofoil assembly 120 does not produce any thrust and purely provides lift to the vessel 101.

Thus, the forward hydrofoil assembly 120 comprises one (see Figure 8) or two (see Figure 1 ) static (i.e. non-oscillating) hydrofoils that are shaped to provide lift when the vessel 101 is propelled through the water. Like the rearward hydrofoil assembly 110, the forward hydrofoil assembly 120 comprises two struts 123 that hold the hydrofoil(s) 121 , 122 relative to the remainder of the vessel 101. The struts 123 are orientated and arranged in much the same manner as the struts 113.

Figure 8 shows a schematic view of the vessel 101 that comprises an active stabilisation system. The active stabilisation system takes the form of an actuatable control surface 124 on the trailing edge of the hydrofoil(s) 121 , 122. The control surface 124 comprises at least one flap 124 that is controllably pivotable relative to the remainder of the hydrofoil(s) 121 , 122. The control surface 124 comprises two aileron flaps, each being partially horizontally spaced in opposite directions from the central longitudinal axis about which the vessel 101 can roll.

Thus, there is right (starboard) and left (port) aileron flap. If excess rolling is detected (either by an automatic system or by a user) the aileron flaps are actuated to compensate for the rolling. The function of the aileron flaps is analogous to the function of the aileron flaps on an aircraft.

For instance, if there is excess rolling such that the right (starboard) of the vessel is rolling downward, the right aileron flap located at the rear of the second hydrofoil is actuated such that it rotates downward with respect to the remainder of the second hydrofoil and the left aileron flap located at the rear of the second hydrofoil is actuated such that it rotates upward with respect to the remainder of the second hydrofoil. This forces the right of the vessel upward.

Alternatively, if there is excess rolling such that the left (port) of the vessel is rolling downward, the left aileron flap located at the rear of the second hydrofoil is actuated such that it rotates downward with respect to the remainder of the second hydrofoil and the right aileron flap located at the rear of the second hydrofoil may be actuated such that it rotates upward with respect to the remainder of the second hydrofoil. This forces the left of the vessel upward.

The control surface 124 comprises an elevator flap. In this embodiment, aileron flaps together make the elevator flap.

If excess pitching is detected (either by an automatic system or by a user) the elevator flap is actuated to compensate for the pitching. This is analogous to the function of an elevator flap on an aircraft. For instance, with regard to Figure 8c, if there is excess pitching such that the front of the vessel is pitching downward, the elevator flap is actuated such that it rotates downward with respect to the remainder of the second hydrofoil thus forcing the front of the vessel upward; and with regard to Figure 8b, if there is excess pitching such that the front of the vessel is pitching upward, the elevator flap is actuated such that it rotates upward with respect to the remainder of the second hydrofoil thus forcing the front of the vessel downward.

An additional pitch-compensating mechanism is also shown in Figure 8. As can be seen in Figure 8b, when the vessel 101 pitches upward, the mean pitch of the rear hydrofoil assembly 110 also pitches upward. This provides additional lift to the rear of the vessel 101 , and hence corrects the pitching of the vessel 101. As can be seen in Figure 8c, when the vessel 101 pitches downward, the mean pitch of the rear hydrofoil assembly 110 also pitches downward. This provides reduces lift to the rear of the vessel 101 , and hence corrects the pitching of the vessel 101.

As an alternative to the active stabilisation system, the vessel 101 may comprise a passive stabilisation system. The forward hydrofoil assembly 120 shown in Figures 2 and 8 can be replaced with a surface piercing hydrofoil assembly, for instance the hydrofoil assembly 180 shown in Figure 9. This assembly comprises a main horizontal hydrofoil 181 with a longitudinal direction perpendicular to the longitudinal direction of the vessel. The assembly 180 also comprises two angled side hydrofoils 182 that are also orientated perpendicular to the longitudinal direction of the vessel 101 , but are at an angle intermediate the horizontal and the vertical, such that they extend upwards from the main hydrofoil 181 at greater distances from the midpoint of vessel 101. The additional hydrofoils 182 are configured such that when the vessel is not pitching or rolling, the upper portions of the additional hydrofoils 182 extend out above the water. The hydrofoils 181 and 182 are connected to the hull 102 by struts 183. There are additional struts 184 supporting the side hydrofoils 182 relative to the struts 183. The struts 183 are vertical and are connected to opposite ends of the main hydrofoil 181 , and inner ends of the respective side hydrofoils. The additional struts 184 are at least partly horizontal and connect between the respective struts 183 and side hydrofoils 182. The hydrofoils 181 and 184 produce lift when propelled through water, the lift is transferred to the remainder of the vessel 101 via the struts 183. The additional struts 184 can also provide lift, particularly when the vessel 101 is travelling at low speeds. At higher speeds, the additional struts 184 may be lifted out of the water to reduce drag and the main hydrofoil 181 provides sufficient lift to do so. This hydrofoil assembly 180 does not provide thrust.

This assembly 180 passively controls and prevents pitching, since it is shaped such that it provides more lift the deeper it is submerged into the water. As the depth of the assembly 180 increases, the amount of the additional hydrofoil 182 under water increases and hence the lift produced increases. As the depth of the assembly 180 decreases, the amount of the additional hydrofoils 182 under water decreases and hence the lift produced decreases. In this way, the pitching of the vessel can be passively controlled.

This assembly 180 also passively controls and prevents rolling, since it is shaped such that it provides more lift on the side that is rolled downwards and less lift on the side that is rolled upwards. As the vessel 101 rolls to the right, the depth of the right hand additional hydrofoil 182 increases and the depth of the left hand additional hydrofoil 182 decreases. Thus, the amount of the additional hydrofoil 182 under water on the right hand side increases and the amount of additional hydrofoil 182 under water on the left and side decreases, and hence the lift produced increases on the right hand side and decreases on the left hand side. Further, the average location of the hydrofoil 180 underwater on the right hand side moves further out from the centre of the vessel 101 , which increases the lifting torque. In this way the roll is corrected. As the vessel rolls to the left, the depth of the additional hydrofoil 182 increases on the left hand side and the depth of the additional hydrofoil 182 decreases on the right hand side. Thus, the amount of the additional hydrofoil under water on the left hand side increases and the amount of additional hydrofoil under water on the right hand side decreases, and hence the lift produced increases on the left hand side and decreases on the right hand side. Further, the average location of the hydrofoil 180 underwater on the left hand side moves further out from the centre of the vessel 101 , which increases the lifting torque. In this way the roll is corrected.

With regard to Figure 10 to 13, shown is another embodiment of a water vessel 201 according to the present invention. The vessel comprises a hull 202, which in this specific example is a monohull 202. The vessel 201 comprises a rear hydrofoil assembly 210 and a forward hydrofoil assembly 220. Except where discussed below, the vessel 201 is substantially similar to or identical to the vessel 101 discussed above.

Thus, the rear hydrofoil assembly 210 comprises a pair of hydrofoils 211 , 212 that are configured to produce thrust and lift when driven. The pair of hydrofoils 211 , 212 are attached to the hull 102 by a single strut 213 located centrally with respect to the width of the vessel 201. The single strut 213 (and/or the actuators associated with the strut 213) transfers the lifting force from the hydrofoils 211 , 212 to the vessel 201. The strut 213 extends from the hull 202 downward in the vertical direction. The hydrofoils 211 , 212 extend out from the strut 213 in a horizontal transverse direction by substantially the same amount for both hydrofoils 211 , 212 and in both directions. Each hydrofoil 211 , 212 may be one piece that extends through the strut 213, or may comprise two symmetric pieces that each terminate at the strut 213 and extend out from the strut 213 in different transverse directions. At either end of each hydrofoil 21 1 , 212 (i.e. the ends distal from the central strut 213), each hydrofoil 211 , 212 comprises two winglets 214, one at each end. The winglets 214 of the upper hydrofoil 211 project upwards from the hydrofoil 211 , and the winglets 214 of the lower hydrofoil 212 projects downwards from the hydrofoil 212.

Located above the hydrofoils 211 , 212 is a stabilising hydrofoil 215. Hydrofoil 215 extends transversely from the strut 213 and also extends upwardly in the vertical direction. Hydrofoil 215 is a stationary hydrofoil that provides lift only and its upward slope provides stability to the vessel 201 similarly to hydrofoil 182, i.e. it is a surface-piercing hydrofoil.

The rear hydrofoil assembly 210 comprises a motor housing 216, in which a motor is housed to drive the actuators that drive the hydrofoils 211 , 212.

The rear hydrofoil assembly 210 is a single unit that can be mounted onto a vessel 201 , for example to a strengthened backboard or bracket or transom 203 that is capable of and designed for supporting a conventional outboard motor. The rear hydrofoil assembly 210 comprises an attachment bracket (not shown), which may be of the type conventionally used for outboard motors, to attach it 210 to the transom 203.

The rear hydrofoil assembly 210 is removable from the vessel 201. The rear hydrofoil assembly 210 is moveable (e.g. rotatable about a vertical axis) relative to the hull 202 such relative motion of the rear hydrofoil assembly 210 and the hull 202 allows the vessel to be steered.

The forward hydrofoil assembly 220 does not produce any thrust and purely provides lift to the vessel 201. The forward hydrofoil assembly 220 comprises one static (i.e. non- oscillating) hydrofoil 221 that is shaped to provide lift when the vessel 201 is propelled through the water. The forward hydrofoil assembly 220 comprises two struts 223 that hold the hydrofoil 221 relative to the remainder of the vessel 201. The struts 223 are orientated vertically.

The hydrofoil 221 may or may not comprise the active stabilisation system of Figure 9. The hydrofoil 221 extends from the struts 223 transversely toward the centre of the vessel 201 and downwardly. It is V-shaped. The downward sloping portions allow for (at least partial) passive rolling and pitching stabilisation of the vessel 201. The hydrofoil 215 is a surface-piercing hydrofoil, when the vessel 201 is in motion at high speed.

The forward hydrofoil assembly 220 is attached to the hull 202 via pads (not shown) that act to spread the force transmitted from the forward hydrofoil assembly 220 to the hull, to prevent the hull from being damaged. The forward hydrofoil assembly 220 may be attached to the hull 202 releasably.

The forward and rear hydrofoil assemblies 210, 220 may be thought of as units that are attachable to a hull 202 to turn an existing hull 202 into a vessel 201 powered by oscillating hydrofoils 211 , 212, i.e. they may be used to retrofit an existing hull. As will be apparent to the skilled person, the present invention is not limited to the combination of features set out in relation to the Figures. For example, the skilled person would recognise that it may be possible to combine certain features discussed in relation to one embodiment with certain features of another embodiment. Variations may also be made, with alternative or additional features. For example, the actuators may be substituted for actuators of other types, including hydraulic actuators, solenoids and any type of motor including linear motors. As well as this, the principle of operation may be varied such as by using a solid hydrofoil and omitting the flap 146; replacing the actuator rod 160, 163 used for rotating the hydrofoil of Figures 5a-7 with a piston type actuator fitted to the hydrofoil for pivoting it relative to the actuator rod 150, 153; and/or adding a retraction system for retracting the hydrofoil to decrease the draft of the vessel.

Claims

CLAIMS:

1. A water vessel comprising a hydrofoil and an actuator system for driving the

hydrofoil, the actuator system and the hydrofoil being configured such that the actuator system drives the hydrofoil such that the hydrofoil provides lift and thrust to the water vessel.

2. A water vessel as claimed in claim 1 , wherein the actuator system is configured to drive the hydrofoil such that the hydrofoil provides at least some of the lift and thrust by oscillating rotationally about a longitudinal axis of the hydrofoil and by oscillating linearly in an at least partially vertical direction.

3. A water vessel as claimed in claim 1 or 2, wherein the hydrofoil provides at least some of the lift and thrust by being shaped to cause lift when the vessel moves in a forward direction.

4. A water vessel as claimed in claim 1 , 2 or 3, wherein the hydrofoil, when driven by the actuator system, is configured to oscillate with movement relative to the remainder of the water vessel.

5. A water vessel as claimed in any preceding claim, comprising a controller

configured to control the actuator system to provide the required movement of the hydrofoil.

6. A water vessel as claimed in any preceding claim, wherein the actuator system comprises or is driven by a motor.

7. A water vessel as claimed in any preceding claim, wherein the hydrofoil is

configured to oscillate and is configured to undergo a curvature change during the oscillation to cause at least some of the lift.

8. A water vessel as claimed in claim 7, wherein the curvature change is such that cavitation of water and/or reliance on angle of attack for lift are/is reduced or minimised.

9. A water vessel as claimed in claim 7 or 8, wherein the curvature change is such that a trailing edge of the hydrofoil is maintained at substantially the same angle throughout the oscillation of the hydrofoil.

10. A water vessel as claimed in claim 7, 8 or 9, wherein the hydrofoil comprises a flap being adjustable in angle relative to the remainder of the hydrofoil about a longitudinal axis of the hydrofoil so as to provide at least some of the curvature change.

11. A water vessel as claimed in any preceding claim, wherein the actuator system drives the hydrofoil and the hydrofoil is arranged such that the angle of attack of the hydrofoil is not the primary mechanism for causing the lift.

12. A water vessel as claimed in any preceding claim, wherein the hydrofoil is a first hydrofoil and the water vessel comprises a second, static, hydrofoil, the static hydrofoil being configured to provide lift and/or to stabilise the water vessel.

13. A water vessel as claimed in any preceding claim, wherein the hydrofoil is a first actuated hydrofoil and the water vessel comprises a further actuated hydrofoil, the further actuated hydrofoil and the actuator system, or another actuator system, being configured such that the further actuated hydrofoil is driven to provide lift and thrust to the water vessel.

14. A water vessel as claimed in claim 13, wherein the multiple actuated hydrofoils oscillate out of phase with respect to one another, preferably substantially 180° out of phase.

15. A water vessel as claimed in claim 13 or 14, wherein the multiple actuated

hydrofoils are arranged such that they are separated at least partially vertically.

16. A propulsion unit for a water vessel, the propulsion unit comprising a hydrofoil and an actuator system for driving the hydrofoil, the actuator system and the hydrofoil being configured such that the actuator system drives the hydrofoil such that the hydrofoil may provide lift and thrust to the water vessel when the unit is attached to the vessel, wherein the unit is configured to be attachable to the vessel.

17. A propulsion unit as claimed in claim 20, wherein the propulsion unit is configured to be releasably attachable to the vessel.

18. A method of providing lift and thrust to a water vessel as claimed in any of claims 1 to 15, the method comprising driving the hydrofoil using the actuator system so as to provide the lift and the thrust to the water vessel.

19. A method as claimed in claim 18, comprising providing the lift and thrust by

oscillating the hydrofoil rotationally about a longitudinal axis of the hydrofoil and by oscillating the hydrofoil linearly in an at least partially vertical direction.

20. A method as claimed in claim 18 or 19, wherein the hydrofoil is a first actuated hydrofoil and the water vessel comprises a further actuated hydrofoil configured to provide lift and thrust to the water vessel, the method comprising driving the further actuated hydrofoil so as to provide the lift and the thrust to the water vessel.

21. A method as claimed in claim 20, comprising oscillating the multiple actuated hydrofoils out of phase with respect to one another, for example substantially 180° out of phase.

22. A method of retrofitting a water vessel with a propulsion unit, the propulsion unit comprising a hydrofoil and an actuator for driving the hydrofoil, the actuator and the hydrofoil being configured such that the actuator drives the hydrofoil such that the hydrofoil may provide lift and thrust to the water vessel when the unit is attached to the vessel, wherein the unit is configured to be attachable to the vessel, the method comprising: attaching the propulsion unit to the vessel.