Wave-powered pump,systems and methods of use

Abstract

A wave-powered pump 100 is operable in a condition untethered from the seabed. The wave-powered pump 100 comprises an upper float assembly 110, a lower weight assembly 150 and a pump chamber 130 dispo

Description

Maritime operations such as aquaculture, desalination, energy production, mineral extraction, and blue carbon restoration, all require an appropriate means for pumping fluids (for example seawater). In aquaculture, water is pumped across different layers of the water column for the purpose of mixing water to distribute dissolved oxygen, fertilizers, and to prevent stratification of the water column. Typically pumping is by centrifugal pumps or piston pumps, which may be noisy, energy inefficient, and / or polluting to the surrounding environment. In blue carbon restoration programs, pumping water across different layers of the water column is also important for counteracting the risk to blue carbon ecosystems from increased stratification of the upper ocean layers and the reduction in available nutrients. In the renewable energy industry, wave energy is utilised to pump fluid, and this pumping of fluid can be used to drive turbines for electrical energy generation. US 4,326,840 A describes a system in which a piston is mounted between a buoyant wave follower and a mooring on the sea floor. The up and down motion in response to wave movements results in a pumping action which pumps water from a pumping chamber upstream from the piston. US 6,768,216 B1 describes a system in which an elongated cylinder is submerged below a water level in a vertical orientation, and where the pressure differential over the length of the cylinder, and the variation in response to passing waves, is used to drive a piston of an energy convertor. Many previously proposed systems are complex, comprising a number of interconnected mechanical components which require significant upkeep and maintenance. Many systems include rigid structures which are particularly vulnerable in harsh offshore conditions, where transverse forces from waves, wind, and currents impose significant stress. In addition, proposed systems commonly rely on the use of polluting substances such as hydraulic oil and lubricants, and therefore may not be suitable for use in environmentally sensitive marine areas. SE 459,684 B describes a system for utilising wave energy to provide a fluid flow through a nozzle and directed towards a turbine wheel to drive a generator to generate electricity for a signal buoy. A variable volume working chamber with a wall of an elastic matrix and a helically embedded reinforcement is arranged between a buoyant body at the upper surface of the water and a bottom anchorage. Movement of the waves results in changes to the volume of the working chamber, causing suction and discharge of the liquid through the system. The system is anchored to the seabed by a slack hanging chain. GB 2044843 discloses an energy generation system comprising a bellows tube for pumping water, where the bellows tube is connected to the surface of the water via a float and is submerged underneath the surface by a subsurface plate. WO 2011 / 058178 describes a braid pump for use in energy generation. The braid pump is supported by a buoyant float and is attached by a connecting line to a substantial weight or an anchor on the seabed. As a wave passes, the float has sufficient buoyancy to elongate the braid pump. As the braid pump is elongated, the volume decreases and water is forced out of the braid pump through an outlet valve, from which it may pass to a turbine or generator. As the crest of the wave passes, the braid pump contracts, increasing the volume and allowing water to enter an inlet valve and to fill the braid pump These known energy generation systems are energy efficient and mechanically simple but are not well suited for operating in untethered modes in which they are not anchored to the seabed. As such they are limited in their applications to deep water and in their ability to withstand high-energy events like storms. Furthermore, these known systems may not be well-suited for applications in which it is important for the system to be mobile, such as in aquaculture, where it may be desirable to provide mixing of water across different areas of the aquafarms, and / or may be necessary to move a whole or part of an aquafarm from time-to-time to comply with legislation, regulation, or best practice. Summary of the invention It is amongst the aims and objects of the invention to provide a wave-powered pump, system and method for pumping a liquid medium, which is an alternative to the methods and apparatus described in the prior art, and / or which addresses one or more of the problems of known apparatus and methods. It is amongst the aims and objects of the invention to provide a wave-powered pump, system and method for pumping a liquid medium, which obviates or mitigates one or more drawbacks or disadvantages of known apparatus and methods. It is amongst the aims and objects of the invention to provide a wave-powered pump, system and method for pumping a liquid medium, which addresses technical issues associated with operating a wave-powered pump in a condition untethered from the seabed. It is amongst the aims and objects of the invention to provide an improved wave-powered pump, system and method of use, which is an improvement of known apparatus and methods which operate in a condition untethered from the seabed. Further objects and aims of the invention will become apparent from the following description. According to a first aspect of the invention, there is provided a wave-powered pump comprising: an upper float assembly; a lower weight assembly; and a pump chamber disposed between the upper float assembly and the lower weight assembly, the pump chamber having a first opening with a first non-return valve and a second opening with a second non-return valve; wherein the pump chamber comprises a wall configured to define a variable volume during wave motion acting on the upper float assembly in a body of water to move a liquid medium through the first and second openings; 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 wherein the pump chamber is configured to be increased in length under a tension between a buoyant force on the float assembly and an opposing downward force on the lower weight assembly, and decreased in length by a relaxation of the tension; wherein the pump chamber is configured so that an increase or decrease in length of the pump chamber results in a change in volume of the pump chamber; wherein the pump is operable in a condition untethered from the seabed; and wherein the centre of gravity of the combined pump chamber and lower weight assembly is lower than the centre of buoyancy of the pump chamber. In one embodiment, the pump chamber may be configured to be increased in length and reduced in volume under a tension between a buoyant force on the float assembly and an opposing downward force on the lower weight assembly, and decreased in length and increased in volume by a relaxation of the tension. In an alternative embodiment, the pump chamber may be configured to be increased in length and increased in volume under a tension between a buoyant force on the float assembly and an opposing downward force on the lower weight assembly, and decreased in length and reduced in volume by a relaxation of the tension. The pump chamber may be elongated, and / or may extend in a longitudinal direction between the upper float assembly and the lower weight assembly. The pump chamber may have a pump chamber length, which may be defined as the length of the pump chamber in the longitudinal direction. The centre of buoyancy of the pump chamber may be located approximately at the middle point of the length of the pump chamber. In another embodiment, the centre of buoyancy of the pump chamber may be located at a distance Db above or below the middle point of the length of the pump chamber. The distance Db may be equal to or less than one quarter of the length of the pump chamber. The centre of gravity of the combined pump chamber and lower weight assembly may be located at a distance Dg below the centre of buoyancy of the pump chamber. The distance Dg may be equal to or less than one quarter of the length of the pump chamber. The centre of gravity of the combined pump chamber and lower weight assembly may be positioned at a distance Dg below the centre of buoyancy of the pump chamber, where the distance Dg is equal to or less than one eighth of the length of the pump chamber. The upper float assembly may be configured to operate on or at a surface of a body of water. Alternatively, or in addition, the upper float assembly may be configured to be operated under the surface of the water. The lower weight assembly may have a shape, mass, and / or composition which functions to restore the wave-powered pump towards a substantially vertical orientation, for example when acted on by forces from different weather and / or environmental conditions. The lower weight assembly may have an upper surface which extends horizontally. The lower weight assembly may have a surface configured to provide a hydrodynamic resistance to movement of the lower weight assembly in an upwards direction. The shape, mass, and / or composition of the lower weight assembly may be sufficient to act against a buoyant force from the float assembly and elongate the pump chamber. The wave-powered pump may be configured so that the lower weight assembly is positioned at depth below the surface of the water where it is substantially situated below the wave base of prevailing waves. The wave-powered pump may be configured so that an upwards buoyant force on the float assembly, when fully submerged, is less than a tensile strength of the pump chamber. The wave-powered pump may be configured so that the downwards force applied as a result of the mass of the lower weight assembly is less than a tensile strength of the pump chamber. The mass of the lower weight assembly may be between 15% and 60% of the mass of the pump chamber when filled with the liquid medium. In another embodiment, the mass of the lower weight assembly may be between 20% and 45% of the mass of the pump chamber when filled with liquid medium. In an embodiment, the mass of the lower weight assembly may be approximately 33% of the mass of the pump chamber when filled with liquid medium. The wave-powered pump may be configured so that the wave-powered pump tends to be restored towards a substantially vertical orientation, for example when acted on by forces from different weather and / or environmental conditions. The wave-powered pump may be configured to draw liquid into the pump chamber through the second opening, and output liquid from the pump chamber through the first opening. In an alternative embodiment, liquid may be output from the pump chamber from the second opening, and may be drawn into the pump chamber through the first opening. The first and second openings may be positioned at any location along the length or around the circumference of the pump chamber. In an embodiment, the first and second openings may be at different, spaced positions along the length of the pump chamber. For example, the first opening may be positioned towards the upper portion of the pump chamber whilst the second opening may be positioned towards the lower portion of the pump chamber. In an alternative embodiment, the first and second openings may be positioned at the same position on the length of the pump chamber, spaced around the circumference. The first opening and the second opening may comprise upper and lower openings. The wave-powered pump may be configured to pump liquid from a first location to a second location. The first location may be at a first depth in the body of water. The second location may be at a second, relatively shallower depth in the body of water. In an alternative embodiment, the second location may be at a second, relatively deeper depth in the body of water. Alternatively, or in addition, the first and / or the second location may be an offshore location or onshore location, which is not within the body of water. The wave-powered pump may be used for circulating water for aquaculture applications. The wave-powered pump may comprise a first extending conduit, which may be connected to the first opening. The first extending conduit may enable the liquid medium to be moved from and / or to a first location positioned at some distance, vertically and / or horizontally displaced, from the wave-powered pump. The first extending conduit may be a rigid tube or pipe. The first extending conduit may be a flexible tube or pipe. The first extending conduit may be an upper extending hose. The wave-powered pump may comprise a second extending conduit, which may be connected to the second opening. The second extending conduit may enable liquid to be moved from and / or to a second location positioned at some distance, vertically and / or horizontally displaced, from the wave-powered pump. The second extending conduit may be a rigid tube or pipe. The second extending conduit may be a flexible tube or pipe. The second extending conduit may be a lower extending hose. The pump chamber may be formed from durable and flexible material, such as an elastomeric material. The pump chamber may be formed from a rubber material. The pump chamber may be reinforced with filaments. The filaments may be formed from an appropriate material with properties of toughness and flexibility, such as steel. The filaments may be wound around the walls of the pump chamber. Filaments may be wound in opposing directions to each other around the walls of the pump chamber. In an embodiment, the pump chamber may be configured to reduce in volume when increased in length, and increase in volume when decreased in length. In this embodiment, the coil angle of the filaments may be greater than 35.2 degrees (or arccot degrees). The coil angle of the filaments may be defined as the angle the filaments make, when not under load, relative to a plane perpendicular to the axis of the pump chamber in the longitudinal direction. In this embodiment, the coil angle of the filaments may be in the range of 50 to 70 degrees. In this embodiment, the coil angle of the filaments may be in the range of 55 to 65 degrees. In an alternative embodiment, the pump chamber may be configured to increase in volume when increased in length, and reduce in volume when decreased in length. In this alternative embodiment, the coil angle of the filaments may be less than 35.2 degrees (or arccot degrees). Embodiments in which the coil angle of the filaments is greater than 35.2 degrees will decrease in volume when extending in length, and such embodiments have the advantage that the action of pumping liquid medium out of the pump chamber is provided during the lengthening of the pump chamber. The wave-powered pump may have a greater stability in a lengthened state as the restoring force and moment provided by the lower weight assembly is greater than when the wave-powered pump is in a shortened state. Therefore, a more stable and effective pumping action may be provided when the wave-powered pump pumps liquid during the lengthening of the pump chamber in contrast to the pump chamber pumping liquid during its shortening. Increasing coil angles will cause a greater volume decrease for a particular extension of the pump chamber. A higher coil angle will reduce the volume more effectively, but will also result in a stiffer pump chamber. This requires a greater force to extend or stretch the pump chamber. While effective coil angles will depend on various factors such as operating conditions and dimensions, coil angles in the range of approximately 50 to 70 degrees, and optionally between 55 degrees and 65 degrees, were found to provide a good balance between providing an effective pumping volume and being sufficiently compliant to extend the pump chamber under the action of passing waves. The pump chamber may comprise a non-linear spring rate when extended in the longitudinal direction. The non-linear spring rate may increase exponentially with the extension of the pump chamber in the longitudinal direction. The wave-powered pump may comprise at least one outlet to a body of water, where the outlet is configured as a propulsion outlet. Liquid that is directed through the propulsion outlet may provide a resultant force on the wave-powered pump which may be used to move the wave-powered pump. This force may be used to control the movement of the wave-powered pump in a lateral direction and / or the position of the pump in a body of water. The propulsion outlet may direct the liquid in a radially outwards direction relative to the wave-powered pump. The propulsion outlet may be directable. The propulsion outlet may be controlled to control the movement and / or position of the wave-powered pump. The propulsion outlet may be controlled to provide a resistance against the movement of the wave-powered pump and to keep the wave-powered pump at a particular location. Thus, the propulsion outlet may be used as part of a dynamic positioning system for the pump. The outlet may function as a pump outlet (e.g. for the movement of the pumper medium) and a propulsion outlet. In an embodiment, there may be at least three outlets. The pump may comprise one or more controllable valves used to control the flow of liquid through the respective one or more outlets. The pump may comprise a controller, which may be used to control the controllable valves. The pump may comprise a GPS receiver configured to provide positional data to the controller. The positional data may be used by the controller to determine the operation of the controllable valves such that the liquid is directed in an appropriate direction in order to move the wave-powered pump in a desired direction. The positional data may be used by the controller to determine the operation of the controllable valves such that the liquid is directed in an appropriate direction to keep the wave-powered pump at or close to a particular location. The controller may provide dynamic positioning of the wave-powered pump. The operation of the controllable valves may be updated to dynamically position the wave-powered pump in response to updated positional data from the GPS receiver and / or in response to updated directions from an operator. According to a second aspect of the invention, there is provided a wave-powered pump comprising: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 an upper float assembly; a lower weight assembly; and a pump chamber disposed between the upper float assembly and the lower weight assembly, the pump chamber having a first opening with a first non-return valve and a second opening with a second non-return valve; wherein the pump chamber comprises a wall configured to define a variable volume during wave motion acting on the upper float assembly in a body of water to move a liquid medium through the first and second openings; wherein the pump chamber is configured to be increased in length under a tension between a buoyant force on the float assembly and an opposing downward force on the lower weight assembly, and decreased in length by a relaxation of the tension; wherein the pump chamber is configured so that an increase or decrease in length of the pump chamber results in a change in volume of the pump chamber; and wherein a tensile strength of the pump chamber is sufficient to withstand the buoyant force on the float assembly when fully submerged. The wave-powered pump may be operable in a condition untethered from the seabed. Embodiments of the second aspect of the invention may include one or more features of the first aspect of the invention or their embodiments, or vice versa. According to a third aspect of the invention, there is provided a wave-powered pump comprising: an upper float assembly; a lower weight assembly; and a pump chamber disposed between the upper float assembly and the lower weight assembly and configured to move a liquid medium via openings of the pump chamber; wherein the pump is operable in a body of water in a condition untethered from the seabed; and wherein the wave-powered pump is configured to direct at least some of the liquid that is output from the pump chamber to provide a propulsive force on the wave-powered pump in the body of water. The propulsive force may be used to control, adjust, maintain and / or change a position of the wave-powered pump in the body of water. The centre of gravity of the combined pump chamber and lower weight assembly may be lower than the centre of buoyancy of the pump chamber. Embodiments of the third aspect of the invention may include one or more features of the first or second aspects of the invention, or their embodiments, or vice versa. According to a fourth aspect of the invention, there is provided a wave-powered pump according to the first, second or third aspects of the invention, the wave-powered pump comprising a plurality of pump chambers disposed between the upper float assembly and the lower weight assembly. Each pump chamber may have a first opening with a first non-return valve and a second opening with a second non-return valve. Each pump chamber may comprise a wall configured to define a variable volume during wave motion acting on the upper float assembly in a body of water to move a liquid medium through the first and second openings. The plurality of pump chambers may be configured to be increased in length under a tension between a buoyant force on the float assembly and an opposing downward force on the lower weight assembly, and decreased in length by a relaxation of the tension. The wave-powered pump may be operable in a condition untethered from the seabed. The wave-powered pump may be configured so that the centre of gravity of the plurality of pump chambers and lower weight assembly combined may be lower than the centre of buoyancy of the combined plurality of pump chambers. The plurality of pump chambers may be configured so that the increase and decrease in length of each pump chamber results in a change in volume of each pump chamber. At least some of the plurality of pump chambers may be reinforced with filaments. In an embodiment, at least some of the plurality of pump chambers may be configured to reduce in volume when increased in length, and increase in volume when decreased in length. In this embodiment, the coil angle of the filaments may be greater than 35.2 degrees. In an alternative embodiment, at least some of the plurality of pump chambers may be configured to increase in volume when increased in length, and reduce in volume when decreased in length. In this alternative embodiment, the coil angle of the filaments may be less than 35.2 degrees. In an embodiment, at least some of the plurality of pump chambers may be configured to reduce in volume when increased in length, and increase in volume when decreased in length, and at least some of the plurality of pump chambers may be configured to increase in volume when increased in length, and reduce in volume when decreased in length. Therefore, the coil angle of the filaments in at least some of the plurality of pump chambers may be greater than 35.2 degrees, and the coil angle of the filaments in at least some of the plurality of pump chambers may be less than 35.2 degrees. Embodiments of the fourth aspect of the invention may include one or more features of the first to third aspects of the invention, or their embodiments, or vice versa. According to a fifth aspect of the invention, there is provided a wave-powered pump system comprising at least one wave-powered pump according to the first to fourth aspects of the invention. Embodiments of the fifth aspect of the invention may include one or more features of the first to fourth aspects of the invention, or their embodiments, or vice versa. According to a sixth aspect of the invention, there is provided a method of using a wave-powered pump to move a liquid medium, the method comprising using the wave-powered pump of the first to fifth aspects of the invention. The method may comprise operating the pump in a condition untethered from the seabed in the body of water. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 The method may comprise increasing the length and decreasing the volume of the pump chamber under a tension between a buoyant force on the float assembly and an opposing downward force on the lower weight assembly, and may comprise decreasing the length and increasing the volume of the pump chamber by a relaxation of the tension. The method may comprise fully submerging the upper float assembly under wave action acting on the upper float assembly, for at least some of operation of the wave power pump. A tensile strength of the pump chamber may therefore be sufficient to withstand the buoyant force on the float assembly when fully submerged. The centre of gravity of the combined pump chamber and lower weight assembly may be lower than the centre of buoyancy of the pump chamber. The method may comprise directing at least some of the liquid from the pump chamber to provide a propulsive force on the wave-powered pump in the body of water. The method may comprise controlling, adjusting, maintaining and / or changing a position of the wave-powered pump in the body of water. Embodiments of the sixth aspect of the invention may include one or more features of the first to fifth aspects of the invention or their embodiments, or vice versa. According to a seventh aspect of the invention, there is provided a method of moving water from a first depth to a second depth in an aquaculture environment in a body of water, using a wave-powered pump comprising an upper float assembly; a lower weight assembly; and a pump chamber disposed between the upper float assembly and the lower weight assembly and configured to move a liquid medium via openings of the pump chamber; wherein the method comprises: under wave action acting on the upper float assembly, increasing a length of the pump chamber under a tension between a buoyant force on the float assembly and an opposing downward force on the lower weight assembly, and decreasing the length of the pump chamber by a relaxation of the tension; wherein the increasing and decreasing of the length of the pump chamber results in a changing volume of the pump chamber; wherein the changing volume of the pump chamber causes water to be drawn into the pump chamber from the first depth and output from the pump chamber at a second depth. The method preferably comprises operating the pump in a condition untethered from the seabed in the body of water. The method may comprise increasing the length and decreasing the volume of the pump chamber under a tension between a buoyant force on the float assembly and an opposing downward force on the lower weight assembly, and may comprise decreasing the length and increasing the volume of the pump chamber by a relaxation of the tension. The method may comprise fully submerging the upper float assembly under wave action acting on the upper float assembly, for at least some of operation of the wave power pump. A tensile strength of the pump chamber may therefore be sufficient to withstand the buoyant force on the float assembly when fully submerged. The centre of gravity of the combined pump chamber and lower weight assembly may be lower than the centre of buoyancy of the pump chamber. The method may comprise directing at least some of the liquid from the pump chamber to provide a propulsive force on the wave-powered pump in the body of water. The method may comprise controlling, adjusting, maintaining and / or changing a position of the wave-powered pump in the body of water. Embodiments of the seventh aspect of the invention may include one or more features of the first to sixth aspects of the invention or their embodiments, or vice versa. Brief description of the drawings There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which: Figure 1 is a schematic representation of a wave-powered pump, according to an embodiment of this invention; Figure 2A and Figure 2B are schematic representations of the wave-powered pump, in a shortened and lengthened state respectively, according to an embodiment of this invention; Figure 3 is a schematic representation of the wave-powered pump, according to an embodiment of this invention; Figure 4 is a schematic representation of the wave-powered pump, according to an embodiment of this invention; Figure 5A is a schematic representation of a method of using the wave-powered pump, according to an alternative embodiment of this invention; and Figure 5B is a schematic representation of the wave-powered pump, according to an alternative embodiment of this invention. Detailed description of preferred embodiments By way of example, embodiments of the invention will be described in the context of the circulation of water for aquaculture applications. It will be appreciated that in at least some of its aspects and embodiments, the invention is generally applicable to other applications. For example, embodiments of the invention are applicable where liquid is pumped either to an offshore or onshore location, used for energy generation, and / or to pump water onshore for onshore fish farming applications. Embodiments of the invention are also applicable for desalination, mineral or salt extraction applications, and for providing artificial upwelling or downwelling in marine environments to counteract the increasing risk to blue carbon ecosystems from increased stratification of upper ocean layers. Referring firstly to Figure 1, there is shown generally at 100 a wave-powered pump in accordance with an embodiment of the invention. The wave-powered pump 100 comprises a float shown generally at 110 which comprises an outer shell 111 and a core 112. The float 110 has a lower surface 113, and in the embodiment shown has a substantially cylindrical shape. The float 110 is constructed from materials which have an appropriate buoyancy and durability, for example one or more of marine-grade plastics such as polyethylene and polyvinyl chloride, composites such as fiberglass or carbon fibre, and metals such as anodized aluminium. In the embodiment shown, the float 110 has a core 112 which defines a hollow volume filled with a gas such as air, or alternatively a foam. In alternative embodiments, the float 110 may be formed from a single solid buoyant material. The float 110 is connected via upper lines 120 to a pump chamber shown generally at 130. The upper lines 120 may be chains, wires, rods, or some other appropriate connecting means. The upper lines 120 are connected between the lower surface 113 of the float 110 and an upper portion 125 of the pump chamber 130. Three or more upper lines 120 connect the float 110 to the pump chamber 130, and each individual upper line 120 is connected between a point towards the outer circumference of the float 110 and a corresponding point towards the outer circumference of the upper portion 125 of the pump chamber 130. The upper lines 120 are connected at equidistant points around the circumference of the float 110 and at corresponding equidistant points around the circumference of the upper portion 125 of the pump chamber 130. The pump chamber 130 has a substantially cylindrical tubular form and comprises a chamber wall 131 configured to define a variable internal chamber volume 132. A first (upper) opening 135 and a second (lower) opening 136 are fluidly connected to the internal chamber volume 132. The upper opening 135 and lower opening 136 contain first (upper) and second (lower) non-return valves 137 and 138 respectively. The upper opening 135 is positioned towards the upper portion 125 of the pump chamber 130, and the lower opening 136 is positioned towards a lower portion 139 of the pump chamber 130. A weight assembly 150, which in the embodiment shown is disc shaped, is suspended below the pump chamber 130 via lower lines 140. The lower lines 140 may be chains or some other appropriate connecting means. The weight assembly 150 is constructed from a dense material such as a steel, which may or may not be coated, or may be constructed from another suitable material, for example a composite material such as concrete. This material is ideally an environmentally friendly material which can be used in sensitive marine environments, and should ideally be able to withstand harsh marine conditions without corroding or degrading. The lower lines 140 are connected between the lower portion 139 of the pump chamber 130 and an upper surface 151 of the weight assembly 150. Three or more lower lines 140 connect the weight assembly 150 to the pump chamber 130, and each individual lower line 140 is connected between a point towards the outer circumference of the weight assembly 150 and a corresponding point towards the outer circumference of the lower portion 139 of the pump chamber 130. The lower lines 140 are connected at equidistant points around the circumference of the weight assembly 150 and at corresponding equidistant points around the circumference of the lower portion 139 of the pump chamber 130. In the embodiment described, the float 110 has a radius of around 2.5 to 3 metres, a height of around 3 metres, a mass of around 4000 kg, and a total buoyant force on the float 110 when fully submerged of around 600 to 700 Kilonewtons (kN). The pump chamber 130 has a length of around 10 metres and a radius of 0.5 metres. In approximate terms, the pump chamber has a dry mass of around 1000 kg, and can contain a mass of water of around 7000 kg. The pump chamber 130 provides a total negative buoyant force of around 4 Kilonewtons (kN). The lower weight assembly 150 has a radius of 3 to 4 metres, a thickness of around 0.01 metres and a density of around 6 to 10 g / cm3. The lower weight assembly 150 provides a total negative buoyant force of around 20 to 25 Kilonewtons (kN). These parameters are provided as examples only, and it is appreciated that the invention can operate with dimensions and parameters other than those disclosed herein. The pump chamber 130 is made of an elastomeric material such as rubber, which gives the pump chamber 130 flexibility and resilience. The pump chamber 130 is reinforced with filaments made of a tough and flexible material with high tensile strength, such as steel or synthetic fibres, which are helically wound around the chamber wall 131 of the pump chamber 130. These filaments enhance the structural integrity of the pump chamber 130 improving the ability to withstand the dynamic loads imposed by wave action and other operational stresses. The pump chamber 130 has a non-linear spring rate, which increases exponentially as the pump chamber is stretched in a longitudinal direction. The pump chamber 130 includes filaments which are wound around the internal chamber volume 132 in opposite directions to each other. The coil angle or pitch of the filaments is chosen according to a particular application of the wave-powered pump 100 so that the longitudinal extension of the pump chamber 130 results in a desired change in volume of the internal chamber volume 132. In general, when the coil angle of the filaments is greater than approximately 35.2 degrees (or arccot ^2 degrees), the pump chamber will decrease in volume when extending in length, and all such embodiments have the advantage that the action of pumping liquid medium out of the pump chamber is provided during the lengthening of the pump chamber. The wave-powered pump may have a greater stability in a lengthened state as the restoring force and moment provided by the lower weight assembly is greater than when the wave-powered pump is in a shortened state. However, the inventor also recognises that the wave-powered pump is operable when the coil angle of the filaments is less than approximately 35.2 degrees (or arccot ^2 degrees). In such an alternative configuration, the volume of the internal chamber volume 132 will instead increase as the pump chamber is stretched longitudinally. A higher pitch angle, while reducing the internal chamber volume 132 more effectively, will also requires a stronger force to extend or stretch the pump chamber 130. As such, this may be advantageous in scenarios where a powerful pump action is needed for example when there are lower prevailing wave heights. In the embodiment described, the coil angle of the filaments is in the range of 55 degrees to 65 degrees (described from a plane perpendicular to the longitudinal axis of the pump chamber). This range of coil angles is found to provide a good balance between providing an effective pumping volume and being sufficiently compliant to extend the pump chamber under the action of passing waves, for the described embodiment. In other embodiments the coil angle of the filaments may advantageously be in the range of 50 to 70 degrees. In use, the wave-powered pump 100 is positioned within a body of water W with the float 110 positioned at or towards the surface of the water S. The float 110 may be partially or fully submerged within the body of water, depending on the buoyancy of the wave-powered pump 100. In normal use, the wave-powered pump 100 is configured to maintain a substantially vertical orientation within the body of water W, with the weight assembly 150 positioned at the deepest point within the body of water W and the pump chamber 130 positioned at a depth between the weight assembly 150 and the float 110. The wave-powered pump 100 uses the natural motion of the waves in a marine environment to pump water W. The water is pumped as a result of the relative movement between the float 110 and the weight assembly 150, and the corresponding lengthening and shortening of the pump chamber 130.The weight assembly 150 has a shape and weight to provide a force which resists the upward movement of the float 110 during wave action. During passing waves, a tensile force acts on the pump chamber 130 increasing the distance between the float 110 and the weight assembly 150. The resulting increase in length of the pump chamber 130, leads to a decrease in volume of the internal chamber volume 132. Once the wave has passed, the tensile forces are reduced and the distance between the float 110 and the weight assembly 150 decreases, resulting in a decrease in length of the pump chamber 130. This decrease in length of the pump chamber 130 results in an increase in volume of the internal chamber volume 132. This process of the lengthening and shortening of the pump chamber 130 of the wave-powered pump 100, as a result of passing wave action, is shown schematically in Figures 2A and 2B. Figure 2A illustrates the pump chamber 130 in a shortened state, for example when the wave-powered pump 100 is towards the trough of a passing wave. In contrast, Figure 2B illustrates the pump chamber 130 in a lengthened state, for example when the wave-powered pump 100 is towards the crest of a passing wave. The upper and lower valves 137 and 138, disposed at the upper opening 135 and the lower opening 136 of the pump chamber 130, respectively, are one-way valves. These one-way valves ensure unidirectional flow through the internal chamber volume 132 of the pump chamber 130 during passing wave action. As an example application of the wave-powered pump 100, a configuration will be described in which the upper and lower valves 137 and 138 are configured such that the water enters the internal chamber volume 132 at the lower opening 136 and exits the internal chamber volume 132 at the upper opening 135. Such a configuration may be used in applications where water needs to be pumped from a first depth to a second relatively shallow depth, for example when circulating water in a body of water for aquaculture applications. In this example configuration, the lower valve 138 is non-return or one-way valve which allows water to flow only in a direction into the internal chamber volume 132 and the upper valve 137 is a one-way valve which allows water to flow only in a direction out of the internal chamber volume 132 and into the body of water W. In this configuration, when the length of the pump chamber 130 decreases, for example when the wave-powered pump 100 moves from the crest to a trough of a wave, the increasing volume of the internal chamber volume 132 will result in water being drawn in through the lower valve 138 of the lower opening 136 from the body of water W and into the internal chamber volume 132. When the length of the pump chamber 130 increases, for example as the wave-powered pump 100 moves from the trough to the crest of a wave, the decreasing volume of the internal chamber volume 132 will result in water being output through the upper valve 137 of the upper opening 135 from the internal chamber volume 132 into the body of water W. In an alternative configuration, the direction of flow of water through the pump chamber 130 may be in the opposite direction, in that, water is drawn into the internal chamber volume 132 through the upper opening 135 and is output from the variable volume through the lower opening 136. This alternative configuration is achieved through appropriately positioning the one-way valves at the respective upper and lower openings 135 and 136, and may be used in applications to pump water from a first relatively shallower depth to a second relatively deeper depth. Figure 3 illustrates a wave-powered pump 100 in use, where it is subjected to different weather and / or environmental conditions, which result in the float 110 and weight assembly 150 moving in opposing lateral directions to each other relative to the surface S. If this occurs, the ability of the wave-powered pump 100 to pump water is limited. Such weather and / or environmental conditions may include currents, winds and / or waves, all of which may result in transverse forces being applied across the wave-powered pump 100. The present invention addresses these issues by being designed so that the wave-powered pump 100 has increased stability during operation in weather and / or environmental conditions that will be encountered during typical use in a marine environment. In particular, the wave-powered pump 100 is designed such that a centre of gravity 155 of the combined pump chamber 130 and lower weight assembly 150, is a distance 157 (Dg) lower than a centre of buoyancy 156 of the pump chamber 130. In the embodiment shown, the centre of buoyancy 156 is positioned at the middle point of the length of the pump chamber 130. In other embodiments, the centre of buoyancy 156 of the pump chamber may not be located at the middle point of the length of the pump chamber 130, and may instead be located at a distance Db above of below this middle point, where the distance Db may, for example, be equal to or less than one quarter of the length of the pump chamber. In the embodiment shown, the distance 157 of the centre of gravity 155 below the centre of buoyancy 156 of the pump chamber 130 is approximately an eighth (12.5%) of the total length of the pump chamber 130. The inventor has identified that having the centre of gravity 155 of the combined pump chamber 130 and lower weight assembly 150 positioned lower than the centre of buoyancy 156 of the pump chamber 130 aids in the restoration of the wave-powered pump 100 to a substantially vertical orientation when subjected to different weather and / or environmental conditions. Consequently, during operation, the wave-powered pump 100 is in a more stable position, enabling efficient operation whilst benefitting from the lower weight assembly 150 not being tethered or anchored to the sea floor. A larger distance 157 between the centre of gravity 155 and the buoyancy 156 will result in an increased stability of the wave-powered pump 100 when subjected to transverse forces, as it will result in a larger restoring force and restoring moment acting on the wave-powered pump 100, facilitating the restoration of the wave-powered pump to a substantially vertical orientation. In order to keep the centre of gravity 155 at an optimal distance below the centre of buoyancy 156, the inventor has identified that the weight of the lower weight assembly 150 is preferably approximately one third of the weight of the pump chamber 130, when filled with water. Having an appropriate weight of the lower weight assembly 150, helps provide stability to the wave-powered pump 100 when subjected to different transverse forces during operation. There are a number of other features of the wave-powered pump 100, which contribute to its ability to operate effectively whilst not being tethered to the sea floor. The weight of the lower weight assembly 150 is sufficiently high that the pump chamber 130 is pre-stretched and is subject to a sufficient tensile force so that the pump chamber 130 is not slack when the wave-powered pump 100 is not subjected to wave action. This pre-loading of the pump chamber 130 provides improved responsiveness and pumping of the wave-powered pump 100 when subjected to wave-induced movements. The lower weight assembly 150 exerts a downwards force counteracting the upwards force from the buoyancy of the float 110, where the downwards force depends on the mass of the lower weight assembly 150, as well as the resistive drag forces during rising wave action created as a result of the shape of the lower weight assembly 150. The weight and shape of the lower weight assembly 150 may be optimised to provide sufficient resistance to counteract the upward buoyant force provided by the float 110 during wave action. In particular, the shape of the lower weight assembly 150 may provide a high drag coefficient and hydrodynamic resistance to movement in an upward direction, enhancing the ability of the float 110 to move relative to the lower weight assembly 150 during wave action. This hydrodynamic resistance is provided by the large surface area provided by the upper surface 151 of the weight assembly 150. It has been identified as being beneficial to the stability of the wave-powered pump 100 for the weight assembly 150 to be positioned at a depth below the surface S, where it is predominantly situated below the wave base of prevailing waves and thus is not significantly affected by the action of prevailing waves. There are certain operating scenarios where the wave-powered pump 100 may be subjected to particularly high forces, which are not encountered during normal operating conditions. These operating scenarios may include when the wave-powered pump 100 is subjected to particularly strong wave action, such as during storms, or where a portion of the wave-powered pump 100 becomes entangled in something. The wave-powered pump 100 is designed to minimise the risk of the wave-powered pump 100 from being damaged in these scenarios and from being exposed to forces which may cause damage to the wave-powered pump 100 and result in structural overload. The wave-powered pump 100 is designed such that the upward force provided by the buoyancy of the float 110 when fully submerged is less than the tensile strength of the pump chamber 130. In addition, the wave-powered pump 100 is designed such that the tensile force applied to the pump chamber 130 by the weight of the lower weight assembly 150 is less than the tensile strength of the pump chamber 130. The wave-powered pump 100 is also designed so the tensile force applied to the pump chamber 130 by the drag provided by the lower weight assembly 150 is unlikely to be greater than the tensile strength of the pump chamber 130. By designing the wave-powered pump 100 in this way, under large forces the lower weight assembly 150 would pull upwards, or the float 110 would be pulled underwater, effectively limiting the maximum tensile force that can be exerted on the pump chamber 130. This provides a mechanism for the protection of the wave-powered pump 100 under extreme hydrodynamic conditions, and also facilitates the operation of the wave-powered pump 100, even under these extreme scenarios. Taking into account the above considerations, and the limitations to the tensile forces that may be applied to the pump chamber 130, the wave-powered pump 100 is designed such that the tensile forces applied to the pump chamber 130 during normal operation are above the level required for the wave-powered pump 100 to operate through the lengthening of the pump chamber 130 during wave action. In addition, the progressive non-linear spring rate of the pump chamber 130, which increases exponentially as the pump chamber is stretched in a longitudinal direction, acts as a buffer against over-extension of the pump chamber 130 in high-energy conditions and extreme scenarios. This contributes to protecting the integrity of the wave-powered pump 100 and contributes to effective and stable operations. Where the resistance of the pump chamber 130 to being stretched, increases non-linearly with extension, this helps dampen unwanted oscillations and provides additional stability to the wave-powered pump 100. Figure 4 illustrates a wave-powered pump 200, which is similar to the wave-powered pump 100, with like features indicated by like reference numerals. In contrast to the wave-powered pump 100, the wave-powered pump 200 has a first (upper) and second (lower) extending hose 160 and 165. The upper extending hose 160 has an upper hose connection point 161 connecting the upper extending hose 160 to the pump chamber 130, and an upper hose opening 162 which is positioned at some distance away from the wave-powered pump 200. The lower extending hose 165 has a lower hose connection point 166 connecting the lower extending hose 165 to the pump chamber 130 and a lower hose opening 167 which is positioned at some distance away from the wave-powered pump 200. The wave-powered pump 200 operates in a similar manner to the wave-powered pump 100. The addition of the upper and lower extending hoses 160 and 165 enables fluid to be input from a location at a distance from the wave-powered pump 200 and / or to be output from the wave-powered pump 200 at a distance from the wave-powered pump 200. This enables the wave-powered pump 200 to be used for a variety of alternative applications. As an example, the lower hose opening 167 of the lower extending hose 165 may extend to depths below the wave-powered pump 200 such that the water can be extracted from deeper depths for water circulation applications. In some applications, the upper extending hose 160 may extend to a location external to the body of water W. This may be useful, for example, where water is directed towards a turbine for the purpose of generating electrical energy from the pumped water. It will be appreciated that there may be embodiments where the upper extending hose 160 and the lower extending hose 165 extend to a location external to the body of water W, and this location may include an onshore or offshore location. There may also be embodiments where one of the upper extending hose 160 or the lower extending hose 165 extends to a location within the body of water W and another extending hose extends to a location external to the body of water W, which may include an onshore or offshore location. It is further appreciated that there may be embodiments where only one of the upper openings 135 or the lower opening 136 has the extending hose 160 or 165 attached, and the remaining upper of lower opening 135 or 136 may be left as embodied in the wave-powered pump 100. Figure 5A illustrates a method 301 for controlling the position of a wave-powered pump 300 and Figure 5B illustrates a sectional view through the pump chamber 130 of the wave-powered pump 300 positioned towards the surface S of a body of water. The wave-powered pump 300 is similar to the wave-powered pumps 100 and 200, with like features indicated by like reference numerals. However, the wave-powered pump 300 includes at least three upper openings 135a, 135b and 135c, in contrast to the single upper opening 135 of the pump 100. Additionally, the wave-powered pump 300 includes a GPS receiver 383, which may be connected to the float 110, and first, second and third controllable valves 382a, 382b and 382c disposed in the respective upper openings 135a, 135b and 135c. The wave-powered pump 300 operates in a similar manner to the wave-powered pumps 100 and 200, and pumps water through the movement of the float 110 relative to the weight assembly 150, and the corresponding lengthening and shortening of the pump chamber 130. The upper openings 135a, 135b and 135c are fluidly connected to the internal chamber volume 132. As such, water enters the wave-powered pump 300 at the lower opening 136 or the lower hose opening 167 and this water exits through the upper openings 135a, 135b and / or 135c. The wave-powered pump 300 uses the force of the water that is ejected from the upper openings 135a, 135b and / or 135c to control the lateral movement and / or position of the wave-powered pump 300. The upper openings 135a, 135b and / or 135c direct water in a radial direction outwards from the wave-powered pump 300, in an approximate direction as indicated by the arrows on Figure 5B. By controlling the first, second and third controllable valves 382a, 382b and 382c, the flow of water through the respective upper openings 135a, 135b and / or 135c can be controlled, facilitating the movement of the wave-powered pump 300 in a desired direction, and / or maintaining the pump on station or in a desired operating region. Any combination of the controllable valves 382a, 382b and 382c may be opened or closed to move the wave-powered pump 300 in a desired direction. In addition, the controllable valves 382a, 382b and 382c may be partially opened or closed to provide a partial flow of fluid through the respective upper openings 135a, 135b and / or 135c. The GPS receiver 383 provides positional data for the wave-powered pump 300, such as geolocation data, to the controller 385. Based on this positional data, if it is determined that the wave-powered pump 300 needs to be moved to a new location or needs to be returned to a previous location, the controller 385 will open at least one of the controllable valves 382a, 382b and / or 382c, and close the remaining controllable valves 382a, 382b and / or 382c, in order to move the wave-powered pump 300 to a desired location. In an alternative embodiment, upper extending hoses 160a, 160b and 160c may be connected to the upper openings 135a, 135b and 135c of the wave-powered pump 300. These upper extending hoses 160a, 160b and 160c may be used to direct the flow of water to an alternative location. As an example, the upper extending hoses 160a, 160b and 160c may be connected to the float 110, and the respective upper hose openings 162a, 162b and 162c are positioned such that in use they direct water in a radial direction outwards from the wave-powered pump 300. There may also be alternative embodiments in which the upper extending hoses 160a, 160b and 160c are not connected to the float 110 and instead are positioned independently in or above the body of water and / or where they are connected to and supported by a single or multiple further submerged or floating structures not described herein. As such, whilst in the described embodiments, water is directed in an outwards direction relative to the wave-powered pump 300, there are embodiments where the wave-powered pump 300 outputs the water below the surface S, and also embodiments where the wave-powered pump 300 outputs the water above the surface S. In such alternative embodiments, the upper extending hoses 160a, 160b and 160c may be connected to and separate from a single upper opening 135 of the wave-powered pump 300. Alternatively, each of the upper extending hoses 160a, 160b and 160c may be connected to their own respective upper opening 135a, 135b and 135c positioned on the pump chamber 130. In the embodiment described, water enters the wave-powered pump 300 at the lower opening 136 or the lower hose opening 167. It is also appreciated that there may be embodiments in which the water instead enters the wave-powered pump 300 at the upper opening 135 or the upper hose opening 162. In such alternative embodiments, water will then be pumped out of one or more lower openings 136 or lower hose openings 167, and this water will be used for controlling the direction of movement of the wave-powered pump 300. Additionally, whilst in the embodiments described herein, there are at least three openings through which water is directed, it is appreciated that the wave-powered pump 300 may also operate using only a single upper or lower hose opening 162 or 167. In such an embodiment, the direction of the single upper or lower hose opening 162 or 167 may be directable, for example controlled and rotated using an additional controller. Therefore, using this single upper or lower hose opening 162 or 167, water may be directed in any radial direction outwards from the wave-powered pump, and the movement and / or position of the wave-powered pump may be controlled using the water output from only a single upper or lower hose opening 162 or 167. The invention provides a wave-powered pump which is operable in a condition untethered from the seabed. The wave-powered pump comprises an upper float assembly, a lower weight assembly and a pump chamber disposed between the upper float assembly and the lower weight assembly. The pump chamber comprises a wall configured to define a variable volume during wave motion acting on the upper float assembly in a body of water to move a liquid medium through a first and second opening in the pump chamber. The pump chamber is configured so that an increase or decrease in length of the pump chamber results in a change in volume of the pump chamber. The invention provides an improved solution for pumping water using wave motion, where the wave-powered pump is untethered from the seabed. In particular, the wave-powered pump is configured to maintain stability and functionality in the varying environmental and weather conditions that are experienced in marine environments. The wave-powered pump provides an improved solution, whereby the wave-powered pump is configured so that it maintains a substantially vertical orientation when subjected to different weather and / or environmental conditions. There are a number of advantages and benefits to being able to operate in a condition untethered from the seabed. Avoiding seabed anchoring reduces the cost and complexity of the associated installation and maintenance. Seabed installations often require specialised ships and equipment, further increasing the cost. Avoiding seabed anchoring also reduces environmental disruption and provides environmental benefits as installation processes like seabed drilling or embedding structures in the sea floor are not required. By having a wave-powered pump which is not tethered to the seabed, the wave-powered pump is also more adaptable and is better suited to adjusting to changes in water level, such as tides and storm surges. This improved adaptability can enhance the efficiency and survivability of the system in various sea conditions. Furthermore, by having an untethered system, retrieving, servicing and performing maintenance on the system, or upgrading components, can be more straightforward and less costly. An untethered system also enables the wave-powered pump to be more easily moved to another location, which can be beneficial in applications such as aquaculture applications, where it can be beneficial to move the system to different locations to provide water circulation in these different locations, and also where a whole aquafarm may need to be moved from time to time, for example due to legislative requirements. Various modifications to the above-described embodiments may be made within the scope of the invention, and the invention extends to combinations of features other than those expressly claimed herein.

Claims

1. A wave-powered pump comprising: an upper float assembly;a lower weight assembly; anda pump chamber disposed between the upper float assembly and the lower weight assembly, the pump chamber having a first opening with a first non-return valve and a second opening with a second non-return valve;wherein the pump chamber comprises a wall configured to define a variable volume during wave motion acting on the upper float assembly in a body of water to move a liquid medium through the first and second openings;wherein the pump chamber is configured to be increased in length under a tension between a buoyant force on the float assembly and an opposing downward force on the lower weight assembly, and decreased in length by a relaxation of the tension;wherein the pump chamber is configured so that an increase or decrease in length of the pump chamber results in a change in volume of the pump chamber;wherein the pump is operable in a condition untethered from the seabed; and wherein the centre of gravity of the combined pump chamber and lower weight assembly is lower than the centre of buoyancy of the pump chamber.

2. The wave-powered pump according to claim 1, wherein the pump chamber is configured to be increased in length and reduced in volume under a tension between a buoyant force on the float assembly and an opposing downward force on the lower weight assembly, and decreased in length and increased in volume by a relaxation of the tension.

3. The wave-powered pump according to claim 1 or claim 2, wherein the centre of buoyancy of the pump chamber is located at a distance Db above or below the middle point of the length of the pump chamber, where the distance Db is equal to or less than one quarter of the length of the pump chamber.

4. The wave-powered pump according to claim 3, wherein the centre of buoyancy of the pump chamber is located approximately at the middle point of the length of the pump chamber.

5. The wave-powered pump according to claim 3 or claim 4, wherein the centre of gravity of the combined pump chamber and lower weight assembly is located at a distance Dg below the centre of buoyancy of the pump chamber, and where the distance Dg is equal to or less than one quarter of the length of the pump chamber.

6. The wave-powered pump according to claim 5, wherein the distance Dg is equal to or less than one eighth of the length of the pump chamber.

7. The wave-powered pump according to any preceding claim, wherein the lowerweight assembly has an upper surface which extends horizontally and the upper surface is configured to provide a hydrodynamic resistance to movement of the lower weight assembly in an upwards direction.

8. The wave-powered pump according to any preceding claim, wherein the wave-powered pump is configured so that the lower weight assembly is positioned at depth below the surface of the water where it is substantially situated below the wave base of prevailing waves.

9. The wave-powered pump according to any preceding claim, wherein the wave-powered pump is configured so that the tensile strength of the pump chamber is sufficient to withstand the buoyant force on the float assembly when fully submerged.

10. The wave-powered pump according to any preceding claim, wherein the mass of the lower weight assembly is between 20% and 40% of the mass of the pump chamber when filled with water.

11. The wave-powered pump according to claim 10, wherein the mass of the lower weight assembly is approximately one third of the mass of the pump chamber when filled with water.

12. The wave-powered pump according to any preceding claim, wherein the wave-powered pump is configured to pump liquid from a first location to a second location, where the first location is at a first depth in the body of water.

13. The wave-powered pump according to claim 12, wherein the second location is at a second, relatively shallower depth in the body of water.

14. The wave-powered pump according to claim 12, wherein the second location is at a second, relatively deeper depth in the body of water.

15. The wave-powered pump according to claim 12, wherein the second location is an offshore location or onshore location, which is not within the body of water.

16. The wave-powered pump according to any preceding claim, wherein the pump chamber is reinforced with filaments which are wound around the walls of the pump chamber in opposing directions to each other.

17. The wave-powered pump according to claim 16, wherein the coil angle of the filaments is greater than approximately 35.2 degrees.

18. The wave-powered pump according to claim 17, wherein the coil angle of the filaments is in the range of 50 to 70 degrees.

19. The wave-powered pump according to any preceding claim, wherein the pump chamber has a non-linear spring rate which increases exponentially with the extension of the pump chamber in the longitudinal direction.

20. The wave-powered pump according to any preceding claim, wherein the wave-powered pump is configured to direct at least some of the liquid that is output from the pump chamber to provide a propulsive force on the wave-powered pump in the body of water.

21. The wave-powered pump according to claim 20, comprising at least one propulsion outlet to the body of water.

22. The wave-powered pump according to claim 21, wherein the propulsion outlet is directable.

23. The wave-powered pump according to claim 21 or claim 22, wherein the propulsion outlet functions as a pump outlet and a propulsion outlet.

24. The wave-powered pump according to any of claims 21 to 23, comprising at least three propulsion outlets and a system of valves, wherein the controllable valves are used to control the flow of liquid through the respective propulsion outlets.

25. The wave-powered pump according to any of claims 20 to 24, comprising a dynamic positioning system, the dynamic positioning system controlling the propulsive force on the wave-powered pump.

26. A method of using a wave-powered pump to move a liquid medium, the method comprising using the wave-powered pump according to any preceding claim.s

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