A hinged raft wave energy conversion apparatus and method of use

Abstract

The present disclosure provides a hinged raft wave energy conversion apparatus comprising: a first buoyant body (102); a second buoyant body (104); and a linkage mechanism (101), wherein the linkage mechanism comprises a hinge (106) and wherein the first buoyant body is hingedly connected to the second buoyant body via the hinge, such that the first and second buoyant bodies can rotate relative to each other around a first axis of rotation through a working angular range, the first axis of rotation being arranged parallel to the horizontal and transverse to the direction of wave propagation, in use, and wherein the first and second bodies extend away from the hinge in opposite directions, the linkage mechanism further comprising: a first linkage member (118) and a second linkage member (122), the first linkage member pivotably connected to the first buoyant body such that the first buoyant body and the first linkage member can rotate relative to each other around a second axis of rotation, the first linkage member further pivotably connected to the second linkage member, the second linkage member pivotably connected to the second buoyant body, wherein a rotation of the buoyant bodies relative to each other about the first axis of rotation through a first angle within the working angular range causes a rotation of the first linkage member relative to the first buoyant body around the second axis of rotation through a second angle, and wherein the magnitude of the second angle and the magnitude of the first angle are different.

Description

[0001] A HINGED RAFT WAVE ENERGY CONVERSION APPARATUS AND METHOD OF USE

[0002] Field of the invention

[0003] The present invention relates to hinged raft wave energy conversion devices for use in marine environments.

[0004] Background to the invention

[0005] It is known to provide hinge raft wave energy convertors which absorb wave energy and convert this into useful power. However, waves typically have high forces and low velocities, while generators are typically most efficient in low-torque, high-velocity regimes. Typically, this has been addressed using, e.g. gearboxes or hydraulic or pneumatic gearing systems. However, these systems are known to have reliability and efficiency issues and require frequent maintenance.

[0006] It is in this context that the present inventions have been devised.

[0007] Summary of the invention

[0008] In accordance with an aspect of the present invention, there is provided a hinged raft wave energy conversion apparatus comprising: a first buoyant body; a second buoyant body; and a linkage mechanism, wherein the linkage mechanism comprises a hinge and wherein the first buoyant body is hingedly connected to the second buoyant body via the hinge, such that the first and second buoyant bodies can rotate relative to each other around a first axis of rotation through a working angular range, wherein, when the apparatus is in a neutral position, the first and second bodies extend away from the hinge in opposite directions, the linkage mechanism further comprising: a first linkage member and a second linkage member, the first linkage member pivotably connected to the first buoyant body such that the first buoyant body and the first linkage member can rotate relative to each other around a second axis of rotation, the first linkage member further pivotably connected to the second linkage member, the second linkage member pivotably connected to the second buoyant body, wherein a rotation of the buoyant bodies relative to each other about the first axis of rotation through a first angle within the working angular range causes a rotation of the first linkage member relative to the first buoyant body around the second axis of rotation through a second angle, wherein the magnitude of the second angle and the magnitude of the first angle are different. For example, it may be that the rotation of the buoyant bodies relative to each other about the first axis of rotation is a rotation wherein the buoyant bodies pass through the neutral position and that the magnitude the second angle is different to (e.g. greater) than the magnitude of the first angle.

[0009] Thus, when the apparatus is provided in a body of water such that the largest dimension of the apparatus extends in a direction aligned with the direction of propagation of the waves of the body of water, each body may encounter the wave independently such that the motion of the first buoyant body is out of phase with the motion of the second buoyant body. This difference in phase of the motion of the bodies upon interaction with a wave induces a rotation of the buoyant bodies relative to one another about the hinge joint.

[0010] Advantageously, by providing a linkage mechanism as described herein, a gearing is created between the rotation of the buoyant bodies and the rotation of the first linkage member such that the rotational velocity of the buoyant bodies causes a rotation of the first linkage member with a rotational velocity different to that of the buoyant bodies. Furthermore, the gearing can be achieved without need for complex gearing systems, such as gearboxes and hydraulic systems. Thus, less maintenance is required, and the reliability and efficiency issues of typical gearing systems are avoided.

[0011] It may be that the first axis of rotation is arranged parallel to the horizontal, e.g. in use. It may be that the first axis of rotation is arranged transverse to the direction of wave propagation, e.g. in use. It may be that the first axis of rotation is arranged to extend in a direction having a component parallel to the horizontal (e.g. forming an angle to the horizontal of less than 60°, e.g. less than 45°, e.g. less than 10°, optionally more than 0.5°). It may be that the first axis of rotation is arranged to extend in a direction having a component transverse to the direction of wave propagation (e.g. forming an angle to the direction of wave propagation of less than 60°, e.g. less than 45°, e.g. less than 10°, optionally more than 0.5°).

[0012] It will be understood that the neutral position (of the apparatus) is a position (e.g. configuration) wherein the first and second buoyant bodies and the linkage mechanism are at rest, e.g. floating on still water. The neutral position may be characterised by the first and second buoyant bodies extending away from the hinge in opposite directions (e.g. in a horizontal direction, optionally in a direction having a major component in parallel to the horizontal).

[0013] It may be that across certain ranges of rotation of the buoyant bodies relative to each other about the first axis of rotation, the magnitude of the second angle is the same as or smaller than the magnitude of the first angle. For example, for rotations of the buoyant bodies wherein the buoyant bodies do not pass through the neutral position, the magnitude of the second angle may be the same as or smaller than the magnitude of the first angle for at least part of the rotation. For rotations of the buoyant bodies wherein the buoyant bodies from more than 40° to greater angles, optionally from more than 60° to greater angles, optionally more than 80° to greater angles above or below the neutral position, or from angles above or below the neutral position by more than 80° to smaller angles (but not reaching the neutral position), the magnitude of the second angle may be the same as or smaller than the magnitude of the first angle for at least part of the rotation.

[0014] It may be that the magnitude of the second angle is greater than the magnitude of the first angle. Thus, a rotation of the buoyant bodies around the hinge, as a result of wave action, may drive a rotation of the first linkage member at a higher rotational velocity than that of the buoyant bodies.

[0015] It may be that the magnitude of the second angle is less than the magnitude of the first angle. It may be that the ratio of the first angle to the second angle is variable throughout the working angular range. It may be that the magnitude of the second angle is less than the magnitude of the first angle when the magnitude of the angle between the first and second bodies falls below a predetermined angular limit, where it will be understood that the angle between the first and second bodies in a still water rest position is 180 degrees. Thus, at extreme angles (e.g. in extreme weather or in extreme sea conditions) the rotational velocity of the first linkage member is reduced, avoiding high inertial forces and protecting the apparatus.

[0016] The first and second buoyant bodies may be elongate buoyant bodies (e.g. in that they are longer than they are wide or deep). The first and second buoyant bodies may (e.g. each) have a largest dimension extending (e.g. in a horizontal direction, optionally in a direction having a major component in parallel to the horizontal) from the hinge by a distance of at least one meter, e.g. at least five meters, e.g. at least ten meters, optionally at least 20 meters, typically less than 350 meters, e.g. less than 200 meters, e.g. less than 100 meters.

[0017] Advantageously, hinged raft wave energy convertors (WECs) with buoyant bodies of this size are large enough to absorb wave energy from large waves in open ocean conditions, without being so large that the force of the waves acting on the buoyant bodies is too small to cause significant movement of those buoyant bodies.

[0018] Each buoyant body may be substantially the same size (e.g. length, optionally width, optionally depth, optionally weight) as each other buoyant body. The first buoyant body may be larger than the second buoyant body (e.g. longer, optionally wider, optionally deeper, optionally heavier). The second buoyant body may be larger than the first buoyant body (e.g. longer, optionally wider, optionally deeper, optionally heavier). The first buoyant body may have a length greater than that of the second buoyant body by at least 10%, optionally at least 50%, optionally at least 100%, optionally at least 150%, typically not more than 500%, e.g. not more than 200%. The second buoyant body may have a length greater than that of the first buoyant body by at least 10%, optionally at least 50%, optionally at least 100%, optionally at least 150%, typically not more than 500%, e.g. not more than 300%. The first buoyant body may have a width greater than that of the second buoyant body by at least 10%, optionally at least 20%, typically not more than 200%, e.g. not more than 100%. The second buoyant body may have a width greater than that of the first buoyant body by at least 10%, optionally at least 20%, typically not more than 200%, e.g. not more than 100%. The first buoyant body may have a depth greater than that of the second buoyant body by at least 5%, optionally at least 10%, optionally at least 50%, typically not more than 200%, e.g. not more than 100%. The second buoyant body may have a depth greater than that of the first buoyant body by at least 5%, optionally at least 10%, optionally at least 50%, typically not more than 200%, e.g. not more than 100%. The first buoyant body may have a weight greater than the second buoyant body by at least 5%, optionally at least 20%, optionally at least 50%, optionally at least 100%, typically not more than 500%, e.g. not more than 200%. The second buoyant body may have a weight greater than the first buoyant body by at least 5%, optionally at least 20%, optionally at least 50%, optionally at least 100%, typically not more than 500%, e.g. not more than 200%.

[0019] In an apparatus with one buoyant body larger than the other buoyant body, the larger buoyant body will typically be more stable (i.e. less susceptible to rolling, pitching, yawing, and particularly to movement around the hinge, etc., as a result of wave motion) than the smaller buoyant body. This stability allows for ease of access for maintenance of the WEC and particularly access which requires a person to board the larger buoyant body. This stability can also reduce mooring loads.

[0020] The second buoyant body may comprise (e.g. have) a buoyancy chamber defined therein, for example such that the first buoyant body is less buoyant than the second buoyant body. Thus, the second buoyant body may move more (e.g. around the hinge) in response to wave action than the first buoyant body. The second buoyant body may be configured to move more (e.g. around the hinge) in response to wave action than the first buoyant body.

[0021] Each of the buoyant bodies may have a buoyancy such that at least some (e.g. at least 5%, optionally at least 10%, optionally at least 20%, typically less than 95%, e.g. less than 80%) of the mass of the or each buoyant body is above the water line in a still water rest position. The or each buoyant body may have a buoyancy such that at least 50% of the mass of the buoyant body is below the water line in a still water rest position. Each of the buoyant bodies may have a buoyancy such that at least some (e.g. at least 5%, optionally at least 10%, optionally at least 20%, typically less than 95%, e.g. less than 80%) of the volume of the or each buoyant body is above the water line in a still water rest position. The or each buoyant body may have a buoyancy such that at least 50% (e.g. at least 20%, optionally at least 30%, optionally at least 40%, typically less than 90%, e.g. less than 80%) of the volume of the buoyant body is below the water line in a still water rest position. In an example, the or each buoyant body may have a buoyancy such that between 50% and 70% is below the water line in a still water rest position. It will be understood that the water line in the still water rest position is (on average, e.g. mean, over at least 5 minutes and when viewed across an area of 5 m2) coincident with the horizontal plane.

[0022] The hinge may be a buoyant hinge. For example, the hinge may have a buoyancy such that at least some (e.g. at least 5%, optionally at least 10%, optionally at least 20%, typically less than 95%, e.g. less than 80%) of the mass of the hinge is above the water line in a still water rest position. The hinge axis may be at least partially submerged beneath the still water surface, however, it may in some embodiments float (e.g. be)above the still water surface.

[0023] Thus, a greater proportion (e.g. mass, optionally volume) of the mass or volume of the hinge may lie above the water line than the proportion of the mass or volume of at least one of (optionally each of) the buoyant bodies, allowing rotation about the hinge with less resistance from water such that the bodies may more freely rotate.

[0024] The first buoyant body may comprise fibre glass. The first buoyant body may comprise metal (e.g. aluminium or steel). The first buoyant body may comprise plastics material(s). The first buoyant body may comprise concrete. The second buoyant body may comprise fibre glass. The second buoyant body may comprise metal (e.g. aluminium or steel). The second buoyant body may comprise plastics material(s). The second buoyant body may comprise concrete. The hinge may comprise fibre glass. The hinge may comprise metal (e.g. aluminium or steel). The hinge may comprise plastics material(s). The hinge may comprise concrete. The hinge axis may be coincident with the mean plane of the lower surfaces of the first and second bodies. The hinge axis may be at least partially submerged beneath the still water surface (e.g. in use) however, it may in some embodiments float (e.g. be) above the still water surface. The hinge may be buoyant. The linkage mechanism may be coupled to a power take off (PTO) system. The PTO system may generate power as a result of the rotation of the first and second buoyant bodies around the hinge. Typically, the PTO system generates power as a result of the rotation of the first linkage member around the second axis of rotation (which is typically driven by the rotation of the first and second buoyant bodies around the hinge). It may be that the PTO system is housed in the first buoyant body. It may be that the PTO system is housed in the second buoyant body. It may be that a first portion of the PTO system is housed in the first buoyant body, and a second portion of the PTO is housed in the second buoyant body. It may be that the PTO system is housed in a linkage member, for example the first linkage member. It may be that a portion of the PTO system is housed in a linkage member, for example the first linkage member. It may be that a linkage member, e.g. the first linkage member comprises the PTO system. It may be that a linkage member, e.g. the first linkage member comprises at least a portion of the PTO system. It may be that the apparatus comprises an umbilical to allow for the removal of generated power therefrom. It may be that the umbilical is in electrical connection with the PTO system. It may be that the umbilical extends from the first buoyant body. It may be that the umbilical extends to the sea floor. Typically the power generated by the PTO system is transferred elsewhere, e.g. to a power grid.

[0025] Thus, the energy of the waves may be converted into other forms of useable energy (e.g. electrical energy).

[0026] The power take off system may comprise a generator. The generator may be configured to be driven by rotation of the first linkage member relative to the first buoyant body around the second axis of rotation through the second angle. The generator may be configured to be driven by rotation of the second linkage member relative to the second buoyant body around the second axis of rotation through the second angle. The generator may be a linear generator. The generator may be configured to be driven via a crank mechanism. The generator may be configured to be driven by rotation of the linkage mechanism via a crank mechanism.

[0027] The rotation of the buoyant bodies relative to one another through a first angle (e.g. caused by wave motion) causes a rotation of the first linkage member through a second angle. Typically, the rotational velocity of the buoyant bodies is lower than is useful for generators, which require higher rotational velocities to function efficiently. The linkage mechanism therefore provides a way for the lower rotational velocity caused by wave motion to be converted to a higher rotational velocity of the first linkage member, which may then be used to drive the generator. Thus, the mechanical power of the waves can be more efficiently converted into electrical power by way of increasing the velocity of the generator via the linkage mechanism.

[0028] The first buoyant body may comprise the power take off system. Thus, in embodiments where the first buoyant body is more stable than the second buoyant body, the power take off system can be accessed from the more stable buoyant body, allowing easier access for maintenance of the power take off system. The power take off system may be mounted on the first buoyant body. The power take off may be housed within the first buoyant body. Thus, the power take off system is protected from the external environment by the first buoyant body. The second buoyant body may comprise the power take off system. The power take off system may be mounted on the second buoyant body. The power take off may be housed within the second buoyant body. The hinge may comprise the power take off system. The power take off may be housed within the hinge.

[0029] The first buoyant body may comprise (e.g. have) a first end proximal to the second buoyant body (e.g. proximal to, optionally connected to the hinge). The first buoyant body may comprise (e.g. have) a second end distal to the second buoyant body (e.g. distal to the hinge). The second buoyant body may comprise (e.g. have) a first end proximal to the first buoyant body (e.g. proximal to, optionally connected to the hinge). The second buoyant body may comprise (e.g. have) a second end distal to the first buoyant body (e.g. distal to the hinge). In an example, the first buoyant body may comprise one or more features which extend beyond the first end of the first buoyant body. One or more linkage members may extend beyond the first end of the first buoyant body. The second buoyant body may comprise one or more features which extend beyond the first end of the second buoyant body. One or more linkage members may extend beyond the first end of the second buoyant body.

[0030] In other words, the first end of the first buoyant body may be a first end region (e.g. rather than an extreme end point). The second end of the first buoyant body may be a second end region (e.g. rather than an extreme end point). The first end of the second buoyant body may be a first end region (e.g. rather than an extreme end point). The second end of the second buoyant body may be a second end region (e.g. rather than an extreme end point). The linkage mechanism may be configured such that the second axis of rotation is between the first axis of rotation and the second end of the first buoyant body. The linkage mechanism may be configured such that the first axis of rotation is between the first end (e.g. end region) of the first buoyant body and the first end (e.g. end region) of the second buoyant body. The first end (e.g. end region) of the first buoyant body and the first end (e.g. end region) of the second buoyant body may be overlapping regions.

[0031] The linkage mechanism may be configured such that the first axis of rotation is located between the first end of the first buoyant body and the second end of the first buoyant body. The location of the first axis of rotation may be configured to prevent the first angle from exceeding a predetermined maximum. The geometry of the first buoyant body may be configured to prevent the first angle from exceeding a predetermined maximum. The geometry of the second buoyant body may be configured to prevent the first angle from exceeding a predetermined maximum. In an example, the location of the first axis of rotation and the geometry of the first and second buoyant bodies may (e.g. together) be configured to prevent the first angle from exceeding a predetermined maximum.

[0032] Thus, in extreme weather conditions the apparatus is prevented from excess damage. The expected extent of the hinge angle range is calculated using the size of the floating bodies relative to the wavelengths of the waves. Wave conditions are monitored to determine the maximum extent the hinge angle will reach in such conditions. The apparatus is then designed (e.g. configured, e.g. the geometries of the first and / or second floating bodies and / or the linkage mechanism may be configured) such that the hinge angle will encompass this maximum extent, so as to prevent the first and second buoyant bodies from over rotation about the hinge into a position from which it is possible that the apparatus may not naturally return (e.g. under further wave action).

[0033] The generator may be located between the first end of the first buoyant body and the first axis of rotation. Thus, the mass of the generator is offset from the hinge joint allowing the hinge to be more buoyant and thus reducing the resistance to rotation of the buoyant bodies relative to one another. The generator may be located between the first end of the first linkage member and the first axis of rotation. The generator may be located between the first end of the second buoyant body and the first axis of rotation. The generator may be located aft of the hinge. The generator may be located fore of the hinge. The generator may be located above the hinge. The generator may be located below the hinge. The generator may be located between the first end of the first buoyant body and the second linkage member. The second linkage member may comprise the generator. The generator may be housed within a linkage member, for example within the first linkage member or within the second linkage member.

[0034] One or more of the linkage members may have a length which is variable. The second linkage member may have a length which is variable.

[0035] It will be understood that a “bifurcation point” arises when the point of connection of the first linkage member and the first buoyant body (A); the point of connection between the first linkage member and the second linkage member (B); and the point of connection between the second linkage member and the second buoyant body (C) form a substantially straight line (ABC) (e.g. the angle between A, B, and C may be approximately 180°). This is considered a bifurcation point, because at this point there are two possible paths via which the linkage mechanism may return to the working angular range. Bifurcation points can lead to high joint loads being applied and to uncertainty in the behaviour of the linkage mechanism. Similarly, it will be understood that the “working angular range” includes angles which are not bifurcation points. The apparatus may be configured to work in conditions including relative pitch angles of ±90°, e.g. ±100°, e.g. ±120° (e.g. above or below the neutral position).

[0036] Accordingly, to limit the conditions in which a bifurcation point may arise, the length of the second linkage member may be configured to increase at the extremes of the working angular range (for example, when the magnitude of the angle between the first and second buoyant bodies is less than 90 degrees, e.g. less than 80 degrees). Thus, the range of motion of the mechanism can increase to pass through bifurcation points in a controllable path. An extension of the second linkage member in angular ranges nearing the bifurcation points (and thus an increase in the distance between the point of connection between the first linkage member and the second linkage member (B) and the point of connection between the second linkage member and the second buoyant body (C)) allows bifurcation points to be passed through in a greater range of conditions, by causing an increase in the range of motion of the linkage mechanism.

[0037] For example, the second linkage member may comprise an extension portion, such that the length of the second linkage member can be increased by at least 5%, optionally at least 10%, optionally at least 20%, optionally at least 30%, typically less than 80%, e.g. less than 70%, e.g. less than 50%.

[0038] It may be that the second linkage member has an extended configuration, wherein the extension portion is extended from a main body portion of the second linkage member. It may be that the second linkage member has an unextended configuration wherein the extension portion is retracted within a main body portion of the second linkage member. It may be that the second linkage member is configured to be in the extended configuration when the magnitude of the angle between the first and second buoyant bodies is less than a first predetermined angle. It may be that the second linkage member is configured to be in the unextended configuration when the magnitude of the angle between the first and second buoyant bodies is greater than a second predetermined angle. It may be that the second linkage member is configured to transition between the extended and unextended configurations when the magnitude of the angle between the first and second buoyant bodies is greater than the first predetermined angle and less than the second predetermined angle.

[0039] Thus, the second linkage member may be normally retracted through the majority of the working angular range and may only extend where and by an amount necessary for a particular arrangement of the linkage mechanism. The extension portion allows a simple means of extending the length at the extremes of the working angular range while maintaining the predictability of the linkage mechanism through the typical range of angles within the working angular range.

[0040] One or more of the buoyant bodies may comprise an endstop. The or each endstop may be configured to limit the angular ranges in which a bifurcation point may be reached.

[0041] The first axis of rotation may be parallel to the second axis of rotation. The first axis of rotation may be separated from the second axis of rotation by a distance of at least 0.2 meters, optionally at least 0.5 meters, e.g. at least 1 meter, e.g. at least 2 meters, typically less than 50 meters, e.g. less than 20 meters, e.g. less than 10 meters.

[0042] Thus, by offsetting the first and second axes of rotation from one another, the system is less constrained by the level of tolerancing which would be required if the first and second axes of rotation were aligned. This allows for greater flexibility in the configuration of the apparatus.

[0043] The linkage mechanism may comprise a permanent magnet electrical machine, e.g. a vernier hybrid machine.

[0044] The or each of the first and second bodies may comprise (e.g. have) a sloped surface extending in a direction away from the hinge. The or each sloped surface may be configured such that at least a portion of the sloped surface is under the waterline at least when the device is in a still water rest position. It will be understood that a sloped surface will be inclined with respect to the horizontal (e.g. in the still water rest position). The sloped surface may be configured such that water in waves flows from the body of water (e.g. the sea), up and onto the buoyant body via the sloped surface, stop when the water runs out of kinetic energy, and then flow down and off the buoyant body via the sloped surface to return to the sea. This movement of water waves encourages (e.g. may help to drive or promote) movement of the buoyant bodies and is a particularly efficient way of extracting energy from waves for conversion to other useful forms of energy.

[0045] The sloping base may extend upwards at a mean angle of at least 10 degrees relative to the horizontal, when the apparatus is at rest (e.g. in a still water rest position), optionally at least 20 degrees, e.g. at least 30 degrees, e.g. at least 50 degrees, e.g. at least 70 degrees, typically less than 90 degrees, e.g. less than 85 degrees.

[0046] The sloping base may comprise one or more curved portions. The sloping base may comprise one or more flat regions in addition to sloping regions, such that there is a net slope. The sloping base may comprise a first, flat or sloping, region and a second region, between the first region and the second end of the buoyant body, in which the second region is more sloped than the first region.

[0047] The first body may comprise a wave receiving channel. The second body may comprise a wave receiving channel. The or each wave receiving channel may comprise (e.g. have) a wave receiving opening. The or each wave receiving channel may comprise (e.g. have) one or more side walls. The or each wave receiving channel may comprise (e.g. have) a sloping base. The or each sloping base may comprise (e.g. be) a (e.g. the) sloped surface. The or each buoyant body may comprise a rear wall, e.g. at the opposite end of the wave receiving channel to the wave receiving opening. The or each wave receiving channel may be (e.g. at least partly) defined by one or more (e.g. first and second) side walls and the sloping base, e.g. the sloped surface and optionally the rear wall.

[0048] Although the sloping base may extend from above the still water surface to below the still water surface in a still water rest position, this is not essential. The sloping base may be entirely below the still water surface in the still water rest position.

[0049] Advantageously, the provision of a wave receiving channel allows for more wave energy to be converted, as a greater proportion of the water entering the channel will flow up the sloping base and then back down, rather than flowing off the sides of the buoyant body (which is limited by the provision of the side walls). This allows energy which would normally be lost when water flows off the side of the buoyant body to instead be converted into useful forms of energy.

[0050] The wave receiving channel may have one or more channel resonant modes. The buoyant body (optionally the wave receiving channel) may be configured to encourage the excitation of the channel resonant modes. For example, the dimensions of one or more of the buoyant body, sloping base, side walls, wave receiving opening, and rear wall may be selected to encourage the excitation of the channel resonant modes by waves in a wavelength range. The angle of the sloping base may be selected to encourage the excitation of the channel resonant modes by waves in the wavelength range. The angles of the side walls and / or rear wall may be selected to encourage the excitation of the channel resonant modes by waves in the wavelength range. The buoyancy of the buoyant bodies and thus the proportion of the sloping base (e.g. and wave receiving channel) which is submerged below the water line in a still water rest position) may be selected to encourage the excitation of channel resonant modes by waves in the wavelength range. The apparatus may be installed in a body of water known to generate waves in the wavelength range.

[0051] The apparatus may be configured such that the wave motion excites one or more resonant modes of the buoyant bodies. It may be that the resonance of the buoyant bodies corresponds with resonance of the fluid within either or both of the wave channels (e.g. with the one or more channel resonant modes). The excitation of the one or more channel resonant modes may be caused by excitation of the wave receiving channel at one or more corresponding channel resonant frequencies. The one or more channel resonant frequencies may be at least partly defined by the sloping base. The one or more channel resonant frequencies may be at least partly defined by the or each side wall. The one or more channel resonant frequencies may be at least partly defined by the rear wall. In other words, the (e.g. geometry of the) wave receiving channel may be configured such that incoming waves cause resonance of the wave receiving channel.

[0052] While the invention allows for improved efficiencies in wave energy conversion even where no channel resonant modes are excited, it has been surprisingly found that exciting the channel resonant modes via wave action leads to further enhanced wave energy extraction.

[0053] In accordance with a further aspect of the present invention, there is provided a method of extracting energy from wave motion, the method comprising providing the apparatus as described hereinabove in a body of water, the body of water comprising waves. The body of water may be an ocean. The body of water may be a sea. The body of water may be a lake. The body of water may be a loch. The body of water may be a reservoir.

[0054] The second linkage member may comprise an extension (e.g. extendible) portion. The extension (e.g. extendible) portion may be configured such that the (e.g. total) length of the second linkage member can be increased by at least 10%, optionally at least 20%, optionally at least 30%, typically less than 80%, e.g. less than 70%, e.g. less than 50%. The method may comprise allowing (e.g. causing) the extendible portion to extend in response to a predetermined set of wave conditions.

[0055] The method may comprise an (e.g. initial) step of measuring the properties of the waves at a location. Measuring the properties of the waves at a location may comprise measuring the properties averaged over a period of time (e.g. a year). The method may comprise selecting the apparatus from amongst a plurality of possible apparatuses having different sizes and configurations, taking into account the measured properties.

[0056] In extreme weather conditions the method may be configured to prevent excess damage to the apparatus. The method may comprise determining (e.g. estimating, optionally calculating) an expected extent of the hinge angle range using the size of the floating bodies relative to the wavelength of the waves. The method may comprise monitoring the wave conditions to determine the maximum extent the hinge angle will reach in such conditions. The method may comprise selecting the apparatus from amongst a plurality of possible apparatuses having different sizes and configurations (e.g. selecting the geometries of the first and / or second floating bodies and / or the linkage mechanism) such that the hinge angle will encompass this maximum extent, to thereby prevent the first and second buoyant bodies from over rotation about the hinge joint into a position from which it is possible that the apparatus may not naturally return.

[0057] Thus, the size and configuration of the apparatus can be selected based on the conditions of the waves in order to maximise the power extracted therefrom.

[0058] Description of the Drawings

[0059] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0060] Figure 1 is a perspective elevation view diagram of a linkage mechanism according to an example embodiment of the invention;

[0061] Figure 2 is a side elevation view of the linkage mechanism of the example embodiment of Figure 1 ;

[0062] Figures 3a to 3d are side elevation view diagrams of the linkage mechanism of Figures 1 and 2 and illustrate a series of rotational positions as the second buoyant body rotates around the hinge, alongside corresponding plots indicating the relevant angles of rotation;

[0063] Figure 4 is a perspective elevation view diagram of an apparatus according to an example embodiment of the invention;

[0064] Figures 5a and 5b are side elevation view diagrams of a second example linkage mechanism according to a further example embodiment of the invention; and Figure 6 is a flow chart including steps in a method according to an example embodiment of the invention.

[0065] Detailed Description of an Example Embodiment

[0066] It will be understood by those skilled in the art that any dimensions and relative orientations such as lower and higher, above and below, and directions such as vertical, horizontal, upper, lower, longitudinal, axial, radial, lateral, circumferential, etc. referred to in this description refer to, and are within expected structural tolerances and limits for, the technical field and the apparatus and methods described, and these should be interpreted with this in mind.

[0067] Figure 1 and Figure 2 are perspective and elevation view diagrams, respectively, of a first example embodiment of a linkage mechanism 101 of an apparatus according to the invention. The linkage mechanism 101 includes a first buoyant body 102 and a second buoyant body 104 connected via a hinge 106. Here, the apparatus is shown in the neutral position, with the first and second buoyant 102, 104 bodies extending away from each other in opposite directions, on either side of the hinge 106, as would be the case if the apparatus were floating in still water.

[0068] The first and second buoyant bodies 102, 104 depicted in Figures 1 and 2 will be understood to provide illustrative examples only, and the skilled person will appreciate that these buoyant bodies 102, 104 may extend beyond that which is shown in Figures 1 and 2 (e.g. they may have greater lengths and / or further features which are omitted from these figures for clarity).

[0069] The first buoyant body 102 is provided with a first clevis portion 108 and a second clevis portion 110. Each clevis portion 108, 110 has a first end attached to the first buoyant body 102 and extends beyond a first end 112 of the first buoyant body 102 and the hinge 106 to a second end of the clevis portion. A clevis pin (not shown) is attached to the first clevis portion 108 at a first connection region (e.g. point of connection 160) and extends through the second buoyant body 104 to attach to the second clevis portion 110, forming the hinge 106. The centre of the clevis pin defines a first axis of rotation 116 around which the first and second buoyant bodies 102, 104 may rotate relative to one another. The second end of the first clevis portion 108 is provided with a first linkage member in the form of an eccentric cam 118 pivotably attached thereto at a second connection region (e.g. point of connection) 162 such that the first eccentric cam 118 may rotate around a second axis of rotation 120.

[0070] In the present example embodiment, the first eccentric cam 118 has a teardrop shape, with a main disc centred on the second axis of rotation 120 and a tapered portion extending radially from the main disc. A first end of a second linkage member in the form of a first connecting rod 122 is pivotably attached to the tapered portion at a third connection region (e.g. point of connection) 164 such that the first connecting rod 122 may rotate relative to the first eccentric cam 118 around a third axis of rotation 124. The second buoyant body 104 is provided with a first protruding portion 126 to which a second end of the first connecting rod 122 is pivotably attached at a fourth connection region (e.g. point of connection) 166. Thus, the first connecting rod 122 may rotate relative to the second buoyant body around a fourth axis of rotation 128. The connections between the first clevis portion 108, first eccentric cam 118, first connecting rod 122, and second buoyant body 104 create a first four-bar linkage system 130, illustrated more clearly in Figure 2 where the four bars are indicated by broken lines. Similarly, on the opposite side of the first buoyant body 102, the second clevis portion 110 is provided with a second eccentric cam 119 connected to a second connecting rod (not shown), which is further connected to a second protruding portion 127 of the second buoyant body 104, thus creating a second four-bar linkage system, the configuration and operation of which is substantially equivalent to that of the first four-bar linkage system 130 with the same axes of rotation 116, 120, 124, 128.

[0071] In this example embodiment, the first, second, third, and fourth axes of rotation 116, 120, 124, 128 are substantially parallel to each other.

[0072] Figures 3a to 3d are side elevation view diagrams of the linkage mechanism 101 of Figures 1 and 2 and illustrate a series of rotational positions as the second buoyant body 104 rotates around the hinge, alongside corresponding plots 103a, 103b, 103c, 103d indicating the relevant angles of rotation, as seen from the frame of reference of the first buoyant body 102. From Figures 3a to 3d it can be seen that the linkage mechanism 101 is configured such that when there is a rotation of the second buoyant body 104 relative to the first buoyant body 102 through an angle 0, there is a corresponding rotation of the eccentric cam 118 though an angle (p and that 0 and (p are not the same angle (and that in most cases, and typically those where the bodes 102, 104 pass through the neutral position, (p will be greater than 0). The skilled person will appreciate that rotations of the first and second buoyant bodies 102, 104 through more extreme angles (e.g. where 0 includes an angular range from more than 40° to greater angles, optionally from more than 60°, optionally more than 80° to greater angles above or below the neutral position, or from angles above or below the neutral position by more than 80° to smaller angles but not reaching the neutral position) may, across some subranges of rotation, result in (p being smaller than 0.

[0073] Figure 4 is a perspective view diagram of an example embodiment of an apparatus 200 according to the invention. In this example embodiment, the apparatus is a hinged raft wave energy conversion apparatus. The apparatus 200 comprises a linkage mechanism 201 which is substantially similar to the linkage mechanism 101 of the previous figures apart from the hereinafter described differences. Like features are illustrated with like reference numbers, with the first digit changing from 1 to 2 to indicate that the feature is relevant to the second embodiment depicted in Figure 4, rather than the first embodiment shown in previous figures (e.g. the first connecting rod 122 of Figure 1 corresponds to the first connecting rod 222 of Figure 4). Specifically, the linkage mechanism 201 includes a buoyant hinge 206, first and second clevis portions (not labelled), a first connecting rod 222, a second connecting rod 223, and first and second protruding portions 226, 227. The first and second buoyant bodies of the linkage mechanism of Figure 1 have been replaced by a first buoyant body in the form of a fore hull 242 and a second buoyant body in the form of an aft hull 244, respectively.

[0074] The fore hull 242 is hingedly connected to the aft hull 244 via the hinge 206 at a first end and extends away from the hinge to a second end distal to the hinge 206. The aft hull 244 is likewise hingedly connected to the fore hull 242 via the hinge at a first end and extends away from the hinge to a second end distal to the hinge. Thus, the fore hull 242 and the aft hull 244 extend away from the hinge in opposite directions. The fore hull 242 and the aft hull 244 can rotate relative to each other around a first axis of rotation (not labelled in Figure 4) which is located between the first end of the fore hull 244 and the second end of the fore hull 244 (closer to the first end), through a working angular range. This positioning of the first axis of rotation means that there is a maximum angular range through which the fore hull 242 and the aft hull 244 can rotate relative to each other (e.g. before the two hulls 242, 244 are brought into contact). The fore hull 242 is an elongate buoyant hull having a fore wave receiving channel 246 into which (and out of which) water may flow, the fore wave receiving channel 246 having a wave receiving opening 251 , a sloping base 253, a sloping end wall 255, and first and second side walls 257a, 257b. In the example embodiment in Figure 4, the aft hull 244 is also a buoyant hull having an aft wave receiving channel 248 having a wave receiving opening, a sloping base and a sloping end wall (not labelled). The sloping bases 253 are provided in the form of sloped surfaces which extend in a direction away from the hinge and the fore and aft hulls 242, 244 and the wave receiving channels 246, 248 are configured so that the sloped surface is beneath the waterline in the still water rest position. The wave receiving channels 246, 248 are configured such that waves may enter via the wave receiving openings 251 , and thereby enhance rotation of the fore and aft hulls 242, 244 via the hinge 206.

[0075] In this example embodiment the fore hull 242 is larger than the aft hull 244. The fore hull 242 is 20 meters in length and at its widest the wave receiving channel 246 of the fore hull 242 is 4 meters in width. The aft hull 244 is 3 meters in length and at its widest extent the wave receiving channel 248 of the aft hull 244 is 4 meters in width.

[0076] The wave receiving channels 246, 248 are sized and shaped such that resonant modes are excited when waves of a suitable wavelength and frequency flow into the channel. This resonant effect leads to enhanced wave energy extraction. The choice of dimensions of the wave receiving channels 246, 248 are particularly important as they affect the resonant modes and, as a result, the energy which may be generated. Of particular importance are the angle of slope of the sloping base of the wave receiving channel 246, 248, and the length-to-width ratio (i.e. the ratio of the length of the base to the width of the base (distance between side walls) of the wave receiving channel. For example, a longer and narrower base will excite a stronger fluid resonance within the channel and at a longer wavelength than will a shorter and wider base.

[0077] In this example embodiment, the first and second eccentric cams function as first and second generators 260, 261 located between the first end of the fore hull 242 and the first end of the aft hull 244. The first and second generators 260, 261 are each coupled to a power take off system (not shown) housed within the fore hull. The fore hull 242 has first and second buoyancy cavities 254, 256 positioned close to the generators for providing additional buoyancy to the hinge 206, such that the additional mass of the power take off system is offset.

[0078] The fore hull 242 is provided with a mooring point 258 in electrical connection with the power take off system to allow for extraction of generated electrical energy.

[0079] Figures 5a and 5b are two side elevation view diagrams of a further example embodiment of a linkage mechanism 301 in accordance with the present invention. The linkage mechanism 301 is substantially similar to the linkage mechanism 101 Figures 1 , 2, and 3a through 3d apart from the hereinafter described differences. Like features are illustrated with like reference numbers, with the first digit changing from 1 to 3 to indicate that the feature is relevant to Figures 5a and 5b rather than Figure 1 , 2, or 3a through 3d (e.g. the first clevis portion 108 of Figure 5a corresponds to the clevis portion 308 of Figure 5b). Additionally, though only one side of the linkage mechanism 301 is shown, it will be understood that the linkage mechanism 301 includes two four-bar linkage systems as in previous embodiments. Specifically, the linkage mechanism 301 includes first and second buoyant bodies 302, 304, a clevis portion 308, a first linkage member provided in the form of an eccentric cam 318, a first protruding portion 326, and first, second, and third connection regions (e.g. points of connection) (not shown in Figures 5a and 5b). The linkage mechanism 301 is shown in an unextended configuration 303 in Figure 5a and is shown in an extended configuration 305 in Figure 5b.

[0080] The linkage mechanism 301 differs from the previous examples through the replacement of the connecting rod 122 (second linkage member) with an extendible connecting rod 370 (second linkage member) having a main body 372 and an extendible portion 374. This is an optional feature which can be used to replace the connecting rods of other embodiments, which has a number of advantages, including reducing strain on the linkage mechanism, increasing the workable hinge angle, avoiding overloading during a fault condition, and to provide ease of installation and removal of the PTO.

[0081] In the example embodiment of Figures 5a and 5b, the extendible portion 374 of the connecting rod 370 is provided by a spring-loaded additional rod portion positioned within a hollow distal end of the connecting rod 370, such that when a certain angle of rotation is reached the forces on the spring are sufficient to cause the spring to extend and the additional rod portion to move out of the hollow distal end of the connecting rod 370.

[0082] In normal operation of the linkage mechanism 101 depicted in Figures 1 , 2, and 3a through 3d, the first and second buoyant bodies 102, 104 are placed in a body of water containing waves (in this example, a location in open ocean) such that the linkage mechanism 101 is at least partially above the still water surface. The motion of the waves causes the first and second buoyant bodies 102, 104 to rotate relative to one another about the hinge 106, which causes a rotation of the first and second eccentric cams 118, 119 via the first and second four-bar linkage systems 130. The four-bar linkage systems 130 cause the eccentric cams 118, 119 to rotate through a greater angle around the second axis of rotation than the rotation of the first and second buoyant bodies 102, 104 around the first axis of rotation 116 caused by the waves, as depicted in Figures 3a through 3d (e.g. at least in cases where the rotation of the first and second buoyant bodies 102, 104 means that they pass through the neutral position; the skilled person will appreciate that rotations of the first and second buoyant bodies through more extreme angles (e.g. from more than 40° to greater angles, optionally from more than 60°, optionally more than 80° to greater angles above or below the neutral position, or from angles above or below the neutral position by more than 80° to smaller angles but not reaching the neutral position) may, across some subranges of rotation, lead to rotation of the eccentric cams 118, 119 through smaller angles).

[0083] The example apparatus 200 depicted in Figure 4 is an example of how a linkage mechanism 201 according to the present invention is used in a wave-energy converter. The apparatus 200 is placed in a body of water containing waves. When the apparatus 200 is provided in a body of water such that the fore and aft hulls 242, 244 extends in a direction aligned with the direction of propagation of the waves of the body of water, each hull 242, 244 encounters oncoming waves independently, such that the motion of the fore hull 242 is out of phase with the motion of the aft hull 244. The first axis of rotation (not labelled in Figure 4) is arranged parallel to the horizontal (e.g. parallel to the still water surface) and transverse to the direction of wave propagation. The difference in phase of the motion of the hulls 242, 244 upon interaction with a wave induces a rotation of the hulls 242, 244 relative to one another about the hinge. More specifically, an oncoming wave entering and diffracting around the fore wave receiving channel 246 of the fore hull 242 causes the fore and aft hulls 246, 242 to rotate relative to one another around the hinge, thus capturing the energy of the wave. In typical conditions, the rotation of the fore and aft hulls 246, 242 around the hinge will cause a corresponding greater rotation of the first and second generators 250, 251 via the four-bar linkage systems (e.g. where rotation of the fore and aft hulls 246, 242 includes movement of the hulls through the neutral position). This increased rotational velocity of the generators increases the efficiency of the power generation of the generators than that which would be possible if generator velocity were equal to hinge velocity. The generated power is extracted via the power take off system where it may be transferred for use elsewhere. The skilled person will appreciate that rotations of the fore and aft hulls 246, 242 through more extreme angles (e.g. from more than 40° to greater angles, optionally from more than 60°, optionally more than 80° to greater angles above or below the neutral position, or from angles above or below the neutral position of more than 80° to smaller angles but not reaching the neutral position) may, across some subranges of rotation, cause a smaller rotation of the first and second generators 250, 251 via the four-bar linkage systems).

[0084] Figures 5a and 5b depict an alternative embodiment of a linkage mechanism 301 with an extendible connecting rod 370. In typical conditions, the linkage mechanism 301 will be in the unextended configuration 303 depicted in Figure 5a. However, in some circumstances (e.g. during extreme weather), the first and second buoyant bodies may rotate through greater angles and thereby reach a bifurcation point. As discussed hereinabove, it will be understood that a bifurcation point arises when the connection regions (e.g. points) 362 (A), 364 (B), and 366 (C) form a substantially straight line (ABC). This is considered a bifurcation point, because at this point there are two possible paths via which the linkage mechanism 301 may return to a working angular range.

[0085] A view of the linkage mechanism 301 at a rotational position which would be a bifurcation point for the embodiments of Figures 1 to 3d is depicted in Figure 5a. In the embodiment of Figures 5a and 5b, once this point is reached, the extendible portion 374 of the connecting rod 370 extends from the main body portion 372, thus increasing the total effective length of the connecting rod 370. The increased length of the connecting rod 370 allows for further rotation of the first and second bodies relative to one another beyond the bifurcation point of the unextended connecting rod as depicted in Figure 5a. Figure 5b depicts the theoretical point at which a bifurcation point would be reached in an extended configuration 305, with angle eBof Figure 5b greater than angle eAof Figure 5a. The shape and configuration of the first and second buoyant bodies 302, 304 restricts the extent of their relative rotation such that they will be prevented from reaching the bifurcation point depicted in Figure 5b. In practice, the size (e.g. length) of the floating bodies relative to the wavelength of the waves of the body of water in which the device is placed is such that neither of the bifurcation points depicted in Figures 5a and 5b are likely to be reached.

[0086] Thus, by providing a linkage mechanism 301 with an extendible connecting rod 370, the linkage mechanism may avoid the stresses on the system and uncertainties of pathing associated with bifurcation points.

[0087] Figure 6 is a flow chart including steps in a method 400 of extracting energy from wave motion according to an example embodiment of the invention. The method 400 comprises measuring 410 properties of waves of a body of water at a location, averaging 420 those properties over a period of time, selecting 430 an apparatus from amongst a plurality of possible apparatuses having different sizes and configurations, providing 440 that apparatus in the body of water, and extracting 450 energy from the waves of the body of water.

[0088] In this example embodiment, the body of water is a location in open ocean. The properties of the waves are measured over a year-long period of time. The apparatus is selected in dependence on the measured wave properties (e.g. measured wavelengths, frequencies, and amplitudes), in particular to have a fore and aft hull and linkage mechanism which will be of an appropriate size and shape to maximise the amount of energy extracted over at least a year’s worth of wave exposure. The apparatus is then installed in the location in open ocean with the result that wave motion at that location causes rotation of the fore and aft hulls relative to each other around the hinge. Energy is thereby extracted from the waves.

[0089] In the examples of Figures 1 and 2, the buoyant bodies are formed of steel and have buoyancy chambers defined therein. The linkage members are formed of steel. The apparatus is coated in a paint system which includes cathodic protection. Advantageously, by providing a linkage mechanism 101 , 201 , 301 as described herein, a gearing is created between the rotation of the buoyant bodies (e.g. the fore and aft hulls) 102, 104, 242, 244, 302, 304, and the rotation of the eccentric cams 118, 318 such that the rotational velocity of the buoyant bodies 102, 104, 242, 244, 302, 304 causes a rotation of the eccentric cams 118, 318 with a rotational velocity different to that of the buoyant bodies 102, 104, 242, 244, 302, 304 (and typically greater than that of the buoyant bodies 102, 104, 242, 244, 302, 304 at least for rotations of the buoyant bodies wherein the buoyant bodies pass through the neutral position).

[0090] Although in the example embodiment of Figure 4 the fore hull 242 is 20 meters in length and at its widest the wave receiving channel 246 of the fore hull 242 is 4 meters in width, other dimensions are contemplated within the scope of the invention. Similarly, while the aft hull 244 is 3 meters in length and at its widest extent the wave receiving channel 248 of the aft hull 244 is 4 meters in width the aft hull 244 may be a different size. Indeed, other sizes and shapes for both hulls would typically be selected in dependence on the specific use case and expected wave conditions.

[0091] Although in the example embodiment of Figure 4, the fore hull 242 is longer than the aft hulls 244, this is not required and the reverse may be true, or both hulls may be substantially the same size. Similarly, it will be appreciated that while in the example embodiment of Figure 4, the fore hull 242 is provided with buoyancy cavities 254, 256, mooring point 258, and power take off system, this is also not required and any of these features may be provided elsewhere in the apparatus 200, for example in the aft hull 244. In an example, both hulls 242, 244 may be elongate. It will be understood that a body (e.g. a hull) is elongate if it has a length greater than its breadth and greater than its width.

[0092] In some example embodiments, only one of the fore hull 242 and the aft hull 244 may have a wave receiving channel 246, 248. Conversely, in some embodiments additional walls may be provided within one or both of the wave receiving channels 246, 248 to thereby define a plurality of sub-channels. The wave receiving channels 246, 248 may have different dimensions, for example in order to have different resonant wavelengths. They may for example have different beams, and / or bases which slope at different angles. In summary, there is provided a hinged raft wave energy conversion apparatus 200 comprising: a first buoyant body 102, 242, 302; a second buoyant body 104, 244, 304; and a linkage mechanism, wherein the linkage mechanism 101 , 201 , 301 comprises a hinge 106 and wherein the first buoyant body is hingedly connected to the second buoyant body via the hinge, such that the first and second buoyant bodies can rotate relative to each other around a first axis of rotation through a working angular range, the first axis of rotation being arranged parallel to the horizontal and transverse to the direction of wave propagation, in use, and wherein the first and second bodies extend away from the hinge in opposite directions, the linkage mechanism further comprising: a first linkage member 118, 318 and a second linkage member 122, 222, 370, the first linkage member pivotably connected to the first buoyant body such that the first buoyant body and the first linkage member can rotate relative to each other around a second axis of rotation, the first linkage member further pivotably connected to the second linkage member, the second linkage member pivotably connected to the second buoyant body, wherein a rotation of the buoyant bodies relative to each other about the first axis of rotation through a first angle within the working angular range causes a rotation of the first linkage member relative to the first buoyant body around the second axis of rotation through a second angle, wherein the magnitude of the second angle and the magnitude of the first angle are different.

[0093] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to and do not exclude other components, integers, or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0094] Features, integers, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

Claims1. A hinged raft wave energy conversion apparatus comprising: a first buoyant body; a second buoyant body; and a linkage mechanism, wherein the linkage mechanism comprises a hinge and wherein the first buoyant body is hingedly connected to the second buoyant body via the hinge, such that the first and second buoyant bodies can rotate relative to each other around a first axis of rotation through a working angular range, wherein, when the apparatus is in a neutral position, the first and second bodies extend away from the hinge in opposite directions, the linkage mechanism further comprising: a first linkage member and a second linkage member, the first linkage member pivotably connected to the first buoyant body such that the first buoyant body and the first linkage member can rotate relative to each other around a second axis of rotation, the first linkage member further pivotably connected to the second linkage member, the second linkage member pivotably connected to the second buoyant body, wherein a rotation of the buoyant bodies relative to each other about the first axis of rotation through a first angle within the working angular range causes a rotation of the first linkage member relative to the first buoyant body around the second axis of rotation through a second angle, and wherein, for a rotation of the buoyant bodies relative to each other about the first axis of rotation wherein the buoyant bodies pass through the neutral position, the magnitude of the second angle is greater than the magnitude of the first angle.

2. The apparatus according to claim 1 , wherein the first and second buoyant bodies are elongate buoyant bodies having a largest dimension extending from the hinge by a distance of at least two meters.

3. The apparatus according to any preceding claim, wherein the first buoyant body is larger than the second buoyant body.

4. The apparatus according to any preceding claim, wherein the linkage mechanism is coupled to a power take off system.

5. The apparatus according to claim 4, wherein the power take off system comprises a generator, the generator configured to be driven by rotation of the first linkage member relative to the first buoyant body around the second axis of rotation through the second angle.

6. The apparatus according to claim 4 or claim 5, wherein the first buoyant body comprises the power take off system.

7. The apparatus according to any preceding claim, wherein the first buoyant body has a first end proximal to the second buoyant body and a second end distal to the second buoyant body, wherein the second buoyant body has a first end proximal to the first buoyant body and a second end distal to the first buoyant body, wherein the location of the first axis of rotation and the geometry of the first and second buoyant bodies are configured to prevent the first angle from exceeding a predetermined maximum.

8. The apparatus according to claim 7 when dependent on claim 5 or claim 6, wherein the generator is located between the first end of the first buoyant body and the second linkage member, optionally housed within a linkage member.

9. The apparatus according to any preceding claim, wherein the second linkage member has a length which is variable.

10. The apparatus according to any preceding claim, wherein the second linkage member comprises an extension portion, such that the length of the second linkage member can be increased by at least 10%.

11. The apparatus according to any one preceding claim, wherein the first axis of rotation is parallel to the second axis of rotation and is separated from the second axis of rotation by a distance of at least 0.2 meters.

12. The apparatus according to any one preceding claim wherein the linkage mechanism comprises a permanent magnet electrical machine, optionally a vernier hybrid machine.

13. The apparatus according to any preceding claim, wherein at least one of the first and second bodies has a sloped surface extending in a direction away from the hinge, at least a portion of the sloped surface being under the waterline at least when the device is in a still water rest position.

14. The apparatus according to any one preceding claim, wherein the first body comprises a wave receiving channel, the wave receiving channel having a wave receiving opening, side walls, and a sloping base.

15. The apparatus according to claim 14, wherein the said wave receiving channel has one or more channel resonant modes, the excitation of the one or more channel resonant modes being caused by excitation of the wave receiving channel at one or more corresponding channel resonant frequencies being at least partly defined by the sloping base.

16. A method of extracting energy from wave motion, the method comprising providing the apparatus according to any one preceding claim in a body of water, the body of water comprising waves.

17. A method according to claim 16, wherein method comprises causing the extendible portion to extend.

18. A method according to claim 17, comprising the initial step of measuring the properties of the waves at a location, averaged over a period of time, and selecting the apparatus from amongst a plurality of possible apparatuses having different sizes and configurations, taking into account the measured properties.

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