Wave compensator

Abstract

There is provided a wave compensator for a buoy, the wave compensator including a receptacle. The receptacle has an enclosing wall having an upper end and a lower end. The receptacle also includes a first opening and a second opening arranged at different heights and configured to allow the ingress of water into and the egress of water from the receptacle, in use.

Description

[0001] WAVE COMPENSATOR

[0002] This invention relates generally to wave compensators. More specifically, although not exclusively, this invention relates to wave compensators for damping the wave induced motion of buoys or other buoyancy structures, wave compensator assemblies for use with such buoys or buoyant structures, buoys comprising such wave compensators or wave compensator assemblies and a method of providing wave compensation for a buoyant structure.

[0003] Floating buoys are used for a range of purposes within seas and waterways. In particular, floating buoys have conventionally been used for navigation, hazard identification, mooring and research. Traditionally, floating buoys have a generally cylindrical body or hull containing a material arranged to provide buoyancy, for example a low density foam.

[0004] Floating buoys have more recently been used to provide offshore communications, for example to extend communications from land to offshore energy infrastructure. These communications buoys often include a mast, resulting in them being taller than floating buoys used for navigation and mooring. This additional height poses novel challenges when the buoy is exposed to waves and / or sea swell, as the height and mass of the mast can result in large destabilizing moments about the centre of gravity. It has been found that in order to maintain reliable communications it is desirable to minimise the overall displacement of the buoy or mast.

[0005] It is therefore a first non-exclusive object of the invention to provide a wave compensator for damping the wave induced motion of buoys, to help minimise the displacement of a mast of a buoy, and in particular a communications buoy.

[0006] According to an aspect of the invention, there is provided a wave compensator for a buoy, the wave compensator comprising: a receptacle comprising: an enclosing wall having an upper end and a lower end; and a first opening and a second opening arranged at different heights and configured to allow the ingress of water into and the egress of water from the receptacle, in use.

[0007] By providing a receptacle having first and second openings at different heights, the effective mass of the receptacle is varied in dependence on the amount of water within the receptacle and, by extension, on the size of a wave passing over or past it. For example, a large wave passing over the receptacle will result in the ingress of water via the higher of the first and second openings, thereby increasing the effective mass of the receptacle. When the wave has passed, the water may drain from the receptacle via the lower of the first and second openings. When the receptacle is attached to a buoyancy device, e.g. a float, the effective mass and effective inertia of the buoyancy device is changed in dependence on the effective mass of the receptacle.

[0008] The receptacle may be configured to receive water, in use.

[0009] The receptacle may define an internal volume.

[0010] The wave compensator may be for a seagoing buoy, floating buoy, a floatable buoy, a floatable structure, a floatable device or a buoyant structure. The buoy may be or may comprise a seagoing buoy, floating buoy, a floatable buoy, a floatable structure, a floatable device or a buoyant structure. The buoy may be or may comprise a communications buoy, for example a 5G communications buoy.

[0011] The second opening may be closer than the first opening to the upper end.

[0012] The first opening may be closer than the second opening to the lower end.

[0013] The second opening may be provided above the first opening, e.g. in use.

[0014] The second opening may be provided directly above the first opening.

[0015] The first opening and the second opening may be offset from one another.

[0016] The receptacle may comprise a sidewall.

[0017] The first and second openings may each be provided in the sidewall.

[0018] The first and second openings may each extend through the sidewall. The enclosing wall may comprise the sidewall. The enclosing wall may comprise a pair of end walls.

[0019] The sidewall may extend between the end walls.

[0020] A first end wall may define the upper end. A second end wall may define the lower end. The first end wall and / or the second end wall may be circular.

[0021] The sidewall may be tubular.

[0022] The first opening and second opening may be spaced from one another along the sidewall.

[0023] The first opening and the second opening may be offset with respect to one another around the circumference of the sidewall.

[0024] The first opening and the second opening may have a different circumferential position on the sidewall or receptacle.

[0025] The first opening and the second opening may be offset with respect to one another around the enclosing wall, sidewall or circumference thereof.

[0026] The first opening and the second opening may be have a different circumferential position on the enclosing wall, sidewall or receptacle.

[0027] The first opening and second opening may be provided on different levels.

[0028] The first opening or the second opening may be located to define a minimum volume of water with the receptacle. The first opening or the second opening may provide or define an overflow.

[0029] The second opening may formed on an end surface of the receptacle, e.g. a surface of the upper end.

[0030] The openings may be arranged to vary the mass of the buoyancy device in dependence on a sea state, in use. The second opening may comprise an inlet.

[0031] The first opening may comprise an outlet.

[0032] The first and second openings may be spaced from the ends of the receptacle.

[0033] The first and second openings may be located between the upper end and the lower end of the receptacle.

[0034] The first opening and the second opening may each provide fluid communication with the receptacle, e.g. an internal volume of the receptacle.

[0035] The first opening and / or the second opening may comprise an aperture.

[0036] The first opening and / or the second opening may comprise a slot.

[0037] The first opening and the second opening may be identical.

[0038] The first opening and the second opening may be different. The first opening and the second opening may have a different shape.

[0039] The first opening and the second opening may have a different size, flow area or cross- sectional area.

[0040] The first opening may be larger or smaller than the second opening. The first opening may have a larger or smaller flow area or cross-sectional area than the second opening.

[0041] The wave compensator may comprise a valve on, e.g. mounted on or across, the first opening and / or second opening configured to control the ingress of water into and egress of water from the receptacle, e.g. in use.

[0042] The wave compensator may comprise a respective valve on, e.g. mounted on or across, the first opening and / or second opening configured to control the ingress of water into and egress of water from the receptacle, e.g. in use. The valve may be bolted to a portion of the wave compensator, e.g. a portion of the enclosing wall and / or end wall, adjacent the opening.

[0043] The or each valve may comprise a manual valve.

[0044] The or each valve may be configured to be remotely actuated.

[0045] The or each valve may be located downstream of the first opening and / or second opening.

[0046] The wave compensator may comprise a seal between a valve and the opening on or across which the valve is mounted, e.g. such that the ingress of water into or egress of water from the receptacle passes through the valve.

[0047] The or each valve may be located within the receptacle. The or each valve may be on an internal side of the first opening and / or second opening.

[0048] The or each valve may be located externally of the receptacle. The or each valve may be on an external side of the first opening and / or second opening.

[0049] The wave compensator may comprise an energy harvesting means. The energy harvesting means may be configured to convert the flow of water into and / or out of the receptacle into electrical energy.

[0050] The energy harvesting means may comprise a turbine. The energy harvesting means may comprise a turbine, e.g. a respective turbine, on the first opening and / or the second opening.

[0051] The energy harvesting means may be located downstream of a valve on the first opening. The energy harvesting means may be located within the receptacle.

[0052] The energy harvesting means may be located downstream of a valve on the second opening. The energy harvesting means may be located externally of the receptacle. The wave compensator may comprise an energy storage means. The energy storage means may be configured to store the electrical energy generated by the energy harvesting means.

[0053] The energy storage means may comprise an electrochemical cell or battery.

[0054] The receptacle may comprise a drum, e.g. a cylindrical drum. The receptacle may comprise a cuboid.

[0055] The receptacle, cuboid, drum or cylindrical drum may be hollow.

[0056] The receptacle may comprise a bracing or reinforcement element. The bracing or reinforcement member or structure may be located within the receptacle, e.g. an internal volume thereof.

[0057] The bracing or reinforcement member may be connected to an internal surface of the enclosing wall, e.g. at its ends. The bracing or reinforcement member may be connected to each of the end walls.

[0058] The wave compensator may further comprise a buoyancy device, a buoyancy pod or buoyancy module (hereinafter buoyancy device).

[0059] The buoyancy device may comprise a float.

[0060] The buoyancy device may be configured to provide positive buoyancy, e.g. in use. The buoyancy device may be configured to provide positive buoyancy when deployed in water or sea water.

[0061] The buoyancy device may be configured to provide buoyancy to a buoy, in use

[0062] The receptacle and buoyancy device may be attached or connected, e.g. by welding and / or fixing means.

[0063] The receptacle may be attached or connected to the buoyancy device, e.g. by welding and / or fixing means. The receptacle may be provided on the buoyancy device.

[0064] The receptacle may be provided within the buoyancy device.

[0065] The receptacle and buoyancy device may be unitary or may comprise a unitary structure.

[0066] The unitary structure may comprise a buoyancy chamber and the receptacle

[0067] The receptacle and buoyancy device may be fixed, attached or connected to one another such that the receptacle moves with the buoyance device, in use.

[0068] The receptacle and buoyancy device may be configured to move, translate and or rotate with one another.

[0069] The wave compensator may comprise a motion sensor. The motion sensor may be configured to detect and / or measure movement or displacement of the buoyancy device and / or receptacle, in use.

[0070] The motion sensor may comprise an accelerometer and / or inertial measurement unit.

[0071] The wave compensator may comprise a control means. The control means may be configured to control the valve to control the ingress of water into and / or egress of water from the receptacle in dependence on the detected and / or measured movement of the buoyancy device and / or receptacle.

[0072] The energy storage means may be configured to power one or more onboard systems of a buoy, in use. The energy storage means may be configured to power the control means, motion sensor and / or valve(s).

[0073] The wave compensator may comprise means for attachment or connection to a buoy.

[0074] The wave compensator may be configured to be attached to connected to a buoy by welding and / or fixing means. The fixing means may comprise one or more clamps and / or bolts. The wave compensator may be configured to be attached or connected to a buoy via the buoyancy device.

[0075] Another aspect of the invention provides a wave compensator assembly comprising a plurality wave compensators as described above.

[0076] The wave compensator assembly may comprise three wave compensators arranged in a triangle. The wave compensators may be located at the vertices of the triangle. The triangle may be an equilateral triangle. The triangle may be an isosceles triangle. The triangle may be a scalene triangle, an acute triangle, a right triangle or an obtuse triangle.

[0077] The plurality of wave compensators may be connected within a frame.

[0078] The plurality of wave compensators may be connected to one another within a frame.

[0079] The frame may be or may comprise a mounting frame.

[0080] The plurality of wave compensators may be tethered to one another.

[0081] The wave compensator assembly may comprise means for attachment to a buoy or floatable device.

[0082] The wave compensator assembly may comprise four wave compensators arranged in a square. The wave compensators may be located at the vertices of the square. The buoyancy assembly may comprise four buoyancy devices arranged in a quadrilateral, rectangle, diamond, trapezoid, rhomboid or parallelogram. The buoyancy devices may be located at the vertices of the quadrilateral, rectangle, diamond, trapezoid, rhomboid or parallelogram.

[0083] The wave compensator assembly may comprise five wave compensators arranged in a pentagon. The wave compensators may be located at the vertices of the pentagon.

[0084] The wave compensator assembly may comprise six wave compensators arranged in a hexagon. The wave compensators may be located at the vertices of the hexagon. The wave compensator assembly may comprise a plurality of wave compensators arranged in a circle.

[0085] Another aspect of the invention provides a buoy comprising a wave compensator as described above or a wave compensator assembly as described above.

[0086] The buoy may be or may comprise a seagoing buoy, floating buoy, a floatable buoy, a floatable structure, a floatable device or a buoyant structure. The buoy may be or may comprise a communications buoy, e.g. a 5G communications buoy.

[0087] The buoy may comprise a communications mast. The communications mast may be a 4G or 5G communications mast. Additionally or alternatively, the communications mast may be an optical wireless communications mast. Additionally or alternatively, the communications mast may be a microwave communications mast.

[0088] The buoy and / or communications mast may have a height between 5 and 30 metres, for example, between 10 and 25 metres, between 15 and 20 metres. The buoy and / or communications mast may have a height between 12 and 25 metres.

[0089] The first opening and / or the second opening may be configured to be positioned above the water line, in use, e.g. in the absence of waves.

[0090] Another aspect of the invention provides a method of providing wave compensation for a buoyant structure, the method comprising attaching a wave compensator as described above or a wave compensator assembly as described above to a floatable device.

[0091] The floatable device may be or comprise a buoy.

[0092] Another aspect of the invention provides a buoy power generation system comprising a receptacle as described above, an energy harvesting means as described above and an energy storage means as described above.

[0093] The energy harvesting means may comprise a turbine. The energy harvesting means may comprise a turbine, e.g. a respective turbine, on the first opening and / or the second opening of the receptacle. The energy storage means may be operatively connected with the energy harvesting means.

[0094] For the avoidance of doubt, any of the features described herein apply equally to any aspect of the invention. For example, the wave compensator assembly may comprise any one or more features of the wave compensator relevant to the wave compensator assembly and / or the method may comprise any one or more features or steps relevant to one or more features of the wave compensator or the wave compensator assembly.

[0095] Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. For the avoidance of doubt, the terms “may”, “and / or”, “e.g.”, “for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.

[0096] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

[0097] Figure 1 is a schematic side view of a first embodiment communications buoy comprising a wave compensator;

[0098] Figure 2 is a schematic plan view of the communications buoy of Figure 1 ;

[0099] Figure 3 is a schematic perspective view of a wave compensator according to an embodiment of the invention; Figure 4 is a schematic side view of the communications buoy of Figure 1 with a wave in a first position as it moves left to right;

[0100] Figure 5 is a schematic side view of the communications buoy of Figure 4 with the wave in a second position as it moves left to right;

[0101] Figure 6 is a schematic side view of the communications buoy of Figure 4 with the wave in a third position as it moves left to right;

[0102] Figure 7 is a schematic side view of a second embodiment communications buoy comprising a wave compensator; and

[0103] Figure 8 is a schematic side view of a third embodiment communications buoy comprising a wave compensator.

[0104] Referring now to Figures 1 and 2, there is shown a communications buoy 10, configured to be deployed within a waterway or at sea and arranged to extend communications from land to offshore energy infrastructure. The communications buoy 10 includes a hull or base 12 (hereinafter hull) from which extends a communications mast 14. The communications buoy 10 has a central axis C that extends centrally through the communications mast 14, hull 12 and centre of gravity G in this embodiment. The communications buoy 10 is shown in a level state in Figure 1 .

[0105] A wave compensator assembly 20 is attached to the communications buoy 10 and includes three wave compensators 30 arranged in a triangle when viewed in plan (Figure 2). The wave compensators 30 are located at the vertices of the triangle and each includes a respective receptacle 40 attached to a buoyancy device 60. Each of the receptacles 40 is configured to receive water, in use. As will be described in greater detail below, the buoyancy devices 60 are configured to provide positive buoyancy to the communications buoy 10 when deployed in water and the receptacles 40 are configured to dampen wave induced motion of the buoyancy devices 60, and therefore the communications buoy 10.

[0106] The wave compensator assembly 20 includes a mounting frame 22 having three elongate connecting spars 24 connecting each of the wave compensators 30 to one another. In particular, each connecting spar 24 is connected at each of its ends to a respective receptacle 40. The connecting spars 24 are elongate hollow tubes in this embodiment and have been omitted from Figure 1 for the sake of clarity.

[0107] The mounting frame 22 also includes an annular mounting bracket 26 extending around the hull 12 for connecting the wave compensator assembly 20 to the communications buoy 10. A respective radially extending mounting beam 28 is connected to the annular mounting bracket 26 at a first end and is connected to a respective buoyancy device 60 via a mounting bracket (not shown) at a second end. As is shown in Figure 2, the communications buoy 10 is positioned centrally of the triangle defined by the wave compensator assembly 20, such that each wave compensator 30, and in particular the central axis D of each receptacle 40 (Figure 3) is positioned an equal distance from the central axis C.

[0108] It will be appreciated that instead of each respective mounting beam 28 being connected to a respective buoyancy device 60, it may instead be connected to a respective receptacle 40 via a mounting bracket.

[0109] The receptacle 40 is a hollow cylindrical drum in this embodiment and is shown in greater detail in Figure 3. The receptacle 40 is configured to receive water, in use, and includes an upper end 42 having an upper circular end wall 42a and a lower end 44 having a lower circular end wall 44a. A tubular sidewall 46 extends between the upper and lower end walls 42a, 44a.

[0110] A first opening 48 and a second opening 50 are provided in the sidewall 46, spaced from the upper and lower ends 42, 44, and are configured to allow the ingress of water into and the egress of water from the receptacle 40, in use. The first opening 48 and second opening 50 are identical in size and shape and are each a generally rectangular slot in this embodiment with their longitudinal axes parallel to each other and perpendicular to the longitudinal axis D, wherein the first opening 48 provides an outlet and the second opening 50 provides an inlet, in use.

[0111] The first opening 48 and the second opening 50 are spaced from one another and arranged at different heights, with the first opening 48 being located closer than the second opening 50 to the lower end 44. Furthermore, the second opening 50 is provided directly above the first opening 48, such that the first opening 48 and the second opening 50 have the same position around the circumference of the sidewall 46. The first and second openings 48, 50 are positioned diametrically opposite the respective mounting beam 28 and buoyancy device 60. As shown in Figure 1 in particular, each of the first opening 48 and second opening 50 is positioned above the water line L, in use and in the absence of waves.

[0112] The receptacle 40 and buoyancy device 60 are connected via a mounting bracket 52 positioned on the sidewall 46 at a diametrically opposed portion of the receptacle 40 to the first and second openings 48, 50. The receptacle 40 and buoyancy device 60 are connected such that they move with one another, in use. The buoyancy devices 60 are positioned between the respective receptacles 40 and the hull 12.

[0113] Each of the buoyancy devices 60 contains a low density foam in this embodiment. However, it will be appreciated that each of the buoyancy devices 60 may instead be a cylindrical drum that may be hollow or provided with a low density foam.

[0114] Figures 4 to 6 show the operation of the wave compensator 30 as a wave W passes the communications buoy 10. In the absence of wave W passing, it will be understood that the communications buoy 10 will be provided in the level state of Figure 1.

[0115] Referring to Figure 4, the wave W is shown in a first position with the crest X of the wave W passing over the leftmost wave compensator 30. As the wave W passes over the wave compensator 30, the buoyancy device 60 generates an upwards thrust T causing a clockwise moment A about the centre of gravity G of the communications buoy 10.

[0116] However, the inertia of the buoyancy device 60, increased at least in part by the attached receptacle 40, means the wave compensator 30 does not immediately rise to the crest of the wave X. Therefore, the level of the water at the crest of the wave X is above the second opening 50, which provides an inlet for the ingress of water into the receptacle 40. As water flows into the receptacle 40 via the second opening 50, the fill level F is raised and the effective mass of the receptacle 40 is increased. As the receptacle 40 is connected to the buoyancy device 60 the effective mass of the buoyancy device 60 is also increased. The effect on the buoyancy device 60 is that its response to the passing wave W is slowed, and the generated thrust T is reduced. Therefore, the overall displacement of the wave compensator 30 in response to the passing crest X is reduced. Referring to Figure 5, the wave W is shown in a second position with the crest X of the wave W having passed the leftmost wave compensator 30. The receptacle 40 contains water, of which a minimal amount is able to drain as the first opening 48 remains below the water level.

[0117] Whilst the wave compensator 30 has been displaced upwards as a result of the thrust T, as described above the ingress of water into the receptacle 40 slowed the response of the buoyancy device 60 meaning the wave compensator 30 did not fully rise to the crest X. Therefore, the overall displacement is less than would have been the case if only a buoyancy device 60 had been provided.

[0118] Referring to Figure 6, the wave W is shown in a third position with the crest X of the wave W having passed and the leftmost wave compensator 30 located within a trough Y. The receptacle 40 contains water which, as discussed above, has an effect on the effective mass of the buoyancy device 60.

[0119] Due to the mass of the wave compensator 30, a downward thrust T’ is generated causing an anti-clockwise correcting moment A’ about the centre of gravity G of the communications buoy 10

[0120] However, the first opening 48 is located above the water level within the trough Y, allowing the egress of water from the receptacle 40 and thereby lowering the fill level F. As the receptacle 40 is connected to the buoyancy device 60, the effective mass of the buoyancy device 60 is reduced as the effective mass of the receptacle 40 is also reduced. The effect on the buoyancy device 60 is that its displacement is slowed, meaning the wave compensator 30 does not immediately fall to, or below, the trough Y of the wave W. Therefore, the overall displacement of the wave compensator 30 in response to the passing trough Y is reduced.

[0121] From the described operation of the wave compensator 30 with respect to Figures 4 to 6, it will be appreciated that the wave compensators 30 provide damping of wave induced motion of the communications buoy 10.

[0122] Referring now to Figure 7, there is shown a communications buoy 110 according to a second embodiment of the invention, configured to be deployed within a waterway or at sea and arranged to extend communications from land to offshore energy infrastructure. The communications buoy 110 is similar to communications buoy 10 of Figures 1 and 2, wherein like features are denoted by like references incremented by ‘100’ and in the interests of brevity on the differences will be described in detail hereinafter.

[0123] In the present embodiment, and referring to the receptacle 140a shown on the left, the first opening 148 and the second opening 150 are each provided with a respective manual valve 170. Each valve 170 has a handle 172 arranged to manually adjust the flow area through a respective opening 148, 150. The handles 172 may be manually actuated in order to manually control the ingress of water into, and the egress of water from, the receptacle 140a, in use.

[0124] Now referring to the receptacle 140b shown on the right, the first opening 148 and the second opening 150 are each provided with a remotely actuated valve 180. Each remotely actuated valve 180 includes a controller 182 configured to adjust the valve in order to adjust the flow area through a respective opening 148, 150.

[0125] The communications mast 114 includes a transceiver 116 arranged to receive a control signal from a location remote from the communications buoy 110, and send a control signal 118 to each of the valves 180 in order to control the ingress of water into, and the egress of water from, the receptacle 140, in use. The controller 182 also includes a receiver (not shown) arranged to receive the control signal from the transceiver 116.

[0126] It will be appreciated that instead of the communications mast 110 including a transceiver 116, it may instead include a receiver and a controller, and each of the valves 180 may include a wired connection to the receiver and / or controller.

[0127] It will also be appreciated that whilst the leftmost and rightmost buoyancy modules 140a, 140b shown in Figure 7 each have different valves, this is merely for illustration and it is also possible that all buoyancy modules 140 of a communications buoy 110 have the same valves, e.g. they may all have manual valves 170 or they may all have remotely actuated valves 180.

[0128] Referring now to Figure 8, there is shown a communications buoy 210 according to a third embodiment of the invention, configured to be deployed within a waterway or at sea and arranged to extend communications from land to offshore energy infrastructure. The communications buoy 210 is similar to communications buoy 10 of Figures 1 and 2, wherein like features are denoted by like references incremented by ‘200’ and in the interests of brevity on the differences will be described in detail hereinafter.

[0129] In the present embodiment, the communications buoy 210 includes an energy harvesting means 290 including a respective turbine 292 provided on the second opening 250 of each of the receptacles 240. Each turbine 292 is connected to an energy storage means in the form a battery unit 294 in this embodiment, located within the hull or base 212 of the communications buoy 210. Each turbine 292 is connected to the battery unit 294 by a respective wire 296.

[0130] In use, each turbine 292 is rotated as water enters the receptacle 140 on which it is provided or installed. The rotation of the turbine 292 is used to generate electricity that is transferred to the battery unit 294 in order to power one or more onboard systems of the communications buoy 210, or to be stored as a back-up power source.

[0131] It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention.

[0132] It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and / or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.

Claims

CLAIMS1 . A wave compensator for a buoy, the wave compensator comprising: a receptacle comprising: an enclosing wall having an upper end and a lower end; and a first opening and a second opening arranged at different heights and configured to allow the ingress of water into and the egress of water from the receptacle, in use.

2. A wave compensator according to claim 1 , wherein the second opening is closer than the first opening to the upper end.

3. A wave compensator according to claim 1 or claim 2, wherein the second opening comprises an inlet and the first opening comprises an outlet.

4. A wave compensator according to claim 2 or claim 3, wherein the first and second openings are spaced from the ends of the receptacle.

5. A wave compensator according to any preceding claim, wherein the receptacle comprises a sidewall and the first and second openings are each provided in the sidewall.

6. A wave compensator according to any preceding claim, comprising a valve on the first opening and / or second opening configured to control the ingress of water into and egress of water from the receptacle.

7. A wave compensator according to claim 6, wherein the or each valve comprises a manual valve.

8. A wave compensator according to claim 6, wherein the or each valve is configured to be remotely actuated.

9. A wave compensator according to any preceding claim, comprising an energy harvesting means configured to convert the flow of water into and / or out of the receptacle into electrical energy.

10. A wave compensator according to claim 9, wherein the energy harvesting means comprises a turbine on the first opening and / or second opening.

11. A wave compensator according to claim 9 or claim 10, comprising an energy storage means configured to store the electrical energy generated by the energy harvesting means.

12. A wave compensator according to any preceding claim, wherein the or each receptacle comprises a cylindrical drum.

13. A wave compensator according to any preceding claim, further comprising a buoyancy device.

14. A wave compensator according to claim 13, wherein the receptacle and buoyancy device are attached.

15. A wave compensator according to claim 13, wherein the receptacle is provided within the buoyancy device.

16. A wave compensator according to any one of claims 13 to 15, wherein the receptacle and buoyancy device are fixed to one another such that the receptacle moves with the buoyance device, in use.

17. A wave compensator according to claim 16, comprising a motion sensor configured to detect movement of the buoyancy device, in use.

18. A wave compensator according to claim 17, wherein the motion sensor comprises an accelerometer and / or inertial measurement unit.

19. A wave compensator according to claim 17 or claim 18 when dependent on claim 6, comprising a control means configured to control the valve to control the ingress of water into and / or egress of water from the receptacle in dependence on the detected movement of the buoyancy device.

20. A wave compensator according to any preceding claim, comprising means for attachment to a buoy.21 . A wave compensator assembly, comprising a plurality wave compensators according to any of the preceding claims.

22. A wave compensator assembly according to claim 21 , comprising three wave compensators arranged in a triangle.

23. A buoy comprising a wave compensator according to any one of claims 1 to 20 or a wave compensator assembly according to claim 21 or 22.

24. A buoy according to claim 23, wherein the buoy comprises a communications mast.

25. A method of providing wave compensation for a buoyant structure, the method comprising attaching a wave compensator according to any one of claims 1 to 20 or a wave compensator assembly according to claim 21 or 22 to a buoy.

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