GB2521015A

GB2521015A - Propulsion device for a watercraft

Info

Publication number: GB2521015A
Application number: GB1321727.8A
Authority: GB
Inventors: David Ronald Owen Evans
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-12-09
Filing date: 2013-12-09
Publication date: 2015-06-10
Anticipated expiration: 2033-12-09
Also published as: GB2521015B; GB201321727D0

Abstract

A propulsion device 100 for a watercraft that provides thrust in a first direction comprises a first wall 130 and a second wall 120, the first and second walls defining a first space and being movable relative to each other to vary the volume of the first space. The propulsion device further comprises an outlet opening 114 configured to allow liquid to be urged out of the first space along a direction opposite to the first direction and a one-way valve 140 and 150 configured to allow liquid into the first space as the volume of the first space is increased. The propulsion device is configured so that, as the volume of the first space is reduced, liquid is expelled only through the outlet opening.

Description

PROPULSION DEVICE FOR A WATERCRAFT

FIELD OF THE INVENTION

Embodiments of the present invention generally relate to methods and systems for propulsion of a watercraft.

BACKGROUND

Traditional methods of propulsion for boats generally involve pushing water in a rearward direction in order to generate forward thrust. This may be achieved by propellers, oars or paddles. For low powered water craft, such as rowboats or pedalos, the user may provide the drive to power the boat. Such traditional, user powered methods are generally inefficient, with much of the water being directed in directions other than the desired direction of thrust.

A further limitation for water-craft is the hull water-length wave effect where drag is increased greatly as a boat approaches its hull speed. This is caused by constructive interference between waves formed at the bow and stern of the boat.

In light of these limitations, there is a need for a new form of propulsion which is more efficient and which can reduce the effect of the hull water-length wave effect.

SUMMARY OF INVENTION

According to a first aspect of the invention there is provided a propulsion device for providing thrust in a first direction. The propulsion device comprises a first boundary member and a second boundary member, the first and second boundary member s defining a first space and being movable relative to each other to vary the volume of the first space. The propulsion device further comprises an outlet opening configured to allow liquid to be urged out of the first space along a direction opposite to the first direction and a one-way valve configured to allow liquid into the first space as the volume of the first space is increased. The propulsion device is configured to allow liquid to be expelled only through the outlet opening as the volume of the first space is reduced.

Embodiments of the present invention provide propulsion along a direction of thrust. This is achieved via a bellows like arrangement urging liquid through an outlet opening. As the fluid propulsion device is configured such that, as the volume of the first space is reduced, liquid is only allowed to exit the first space through the outlet opening, the full volume of liquid contained in the first space is utilised to produce thrust in the first direction without the risk of backflow.

Beneficially, the one-way valve is a non-retum valve, a check valve or a flap valve. The valve may be configured to limit the flow of liquid through the valve as the volume of the first space is reduced. The one-way valve may be located in the first boundary member. Altematively, or in addition, the propulsion device may comprise a one-way valve in the second wall configured to allow fluid into the first space as the first space is expanded.

Beneficially, the device is configured to be driven to increase the volume of the first space during a first cycle before decreasing the volume of the first space during a second cycle, the first and second cycles being consecutive.

Advantageously, the first and second surfaces are attached to each other along an axis and are configured to rotate relative to each other about the axis, wherein, the first and second surfaces are configured to be rotated towards each other and away from each other in consecutive cycles. The volume of the first space may be decreased as the first and second surfaces are rotated towards each other and increased as the first and second surfaces are rotated away from each other.

Advantageously, the first boundary member separates the first space from a second space and fluid propulsion device further comprises a means for limiting or substantially preventing fluid communication between the first and second spaces whilst the volume of the first space is reduced. The second space is located on the opposite side of the first boundary member to the first space. Ideally, the means for limiting fluid communication prevents fluid communication between the first and second spaces whilst the volume of the first space is reduced. The means for limiting fluid communication therefore prevents backflow between the first and second spaces.

The means for limiting fluid communication may be a sealing member.

The means for limiting or substantially preventing fluid communication is configured to be able transmit, to the first boundary member, a force that urges the first boundary member towards the second boundary member when applied to the first boundary member. The means for limiting or substantially preventing fluid communication therefore also provides a means to drive the first wall to increase and decrease the volume of the first space.

The one-way valve may be configured to allow fluid to pass from the second space into the first space as the volume of the first space is increased.

Beneficially, the propulsion device may further comprise a third wall, the second space being defined between the first and third boundary members and the first and third boundary members being movable relative to each other to vary the volume of the second space. The propulsion device may further comprise an inlet opening configured to allow liquid into the second space.

The propulsion device may be configured so that the volume of the second space is increased as the volume of the first space is reduced.

Advantageously, the propulsion device may be configured to allow liquid to be drawn into the second space through the inlet opening along a second direction substantially opposite to the first direction as the volume of the second space increases. The second direction may be substantially opposite to the first direction. As the water being drawn in travels in the same direction as the water being expelled, there is an increased net change in momentum. The ingress of water therefore provides additional propulsion in the first direction.

Advantageously, the propulsion device may comprise inlet and outlet chambers separated by the first wall. The one-way valve may be located in the first wall to allow liquid to pass from the second space into the first space. Beneficially, the first wall is movable relative to the second and third walls in order to increase and decrease the volume of the first and second spaces.

The propulsion device may be arranged such that the first and second spaces may have an inverse relationship, that is, the volume of the first space increases as the volume of the second space decreases and the volume of the first space decreases as the volume of the second space increases. The outlet chamber may form the outlet opening and the inlet chamber may form the inlet opening configured to allow liquid into the inlet chamber.

By allowing liquid to be drawn into the propulsion device as the volume of the first space is decreased, embodiments of the device further utilise the power exerted in decreasing the volume of the first space to produce additional thrust. Furthermore, drawing in liquid to the second space readies it to be transferred through the one-way valve, into the first space. In addition, as shall be discussed later, embodiments of the invention may be used to reduce the hull water-length wave effect for a boat by delaying wave formation towards the front of the boat.

Advantageously, the geometry of the outlet opening can be changed in use to change the direction in which fluid is expelled from the first space. This be achieved, for example, by allowing the entire outlet opening to be movable in use to adjust the first direction thereby controlling the direction of thrust. By controlling the direction of thrust, the propulsion device may be used to steer a vessel.

Advantageously, there is provided a watercraft comprising the propulsion device.

According to a second aspect of the invention there is provided a method of providing thrust in a first direction comprising, in a propulsion device comprising a first boundary member and a second boundary member, the first and second boundary members defining a first space and being movable relative to each other to vary the volume of the first space, increasing the volume of the first space to allow liquid into the first space via a one-way valve. The method further comprises reducing the volume of the first space to urge liquid out of the first space only through an outlet opening in the propulsion device. The liquid is urged in a direction opposite to the first direction.

Beneficially, the first boundary member separates the first space from a second space and the method further comprises using a means for limiting or substantially preventing fluid communication between the first and second spaces whilst the volume of the first space is reduced to limit or substantially prevent fluid communication between the first and second spaces whilst the volume of the first space is reduced.

The limitation or substantial prevention of fluid communication may be by a sealing member of the fluid propulsion device.

Advantageously, the reduction in the volume of the first space is through urging the first boundary member towards the second boundary member by applying a force to the means for limiting or substantially preventing fluid communication and transmitting the force to the first boundary member.

The method may further comprise allowing fluid to pass from the second space into the first space through the one-way valve as the volume of the first space is increased.

The method may further comprise increasing the volume of the second space as the volume of the first space is reduced to draw liquid into the second space through an inlet opening in the propulsion device.

The liquid may be drawn into the second space along a second direction substantially opposite to the first direction.

The one-way valve may be located in the first boundary member to allow liquid to pass from the second space into the first space.

The method may further comprise changing the geometry/moving the outlet opening relative to the propulsion device to adjust the first direction thereby controlling the direction of thrust.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the present invention will be described by way of example only and with reference to the drawings in which: Figure 1 shows a fluid propulsion device 100; Figure 2A shows a first inlet valve 140; and, Figure 2B shows a second inlet valve 150.

DETAILED DESCRIPTION

The purpose of embodiments of the present invention is to permit the efficient utilisation of force to provide propulsion. Embodiments of the present invention may be utilised to move a water craft more easily through the water, both inland on lake or river and in the sea, wherever rowing or paddling is the traditional means of propulsion. It is moreover foreseen that the embodiments of the invention also provide efficiency gains in situations where, other than as set out in the description below the propulsion device is power by muscle power, the propulsion device is powered by an engine. Embodiments of the invention consequently also encompass such a situation.

Traditional rowing requires strength and skill, embodiments of the present invention permit a vertical movement which better utilises the strength and weight of the rower and requires less practice on the part of the rower and paddler to become proficient. The user of the propulsion device will face forward in the direction of travel, a clear advantage over the traditional rowing method. Embodiments of the present invention minimise the hull water-length wave effect' thereby minimising drag. The hull water-length wave effect is a significant limitation to the speed that may be attained by low powered water-craft. Embodiments of the present invention also minimise drag at the rear of the water craft by controlling the speed of the water exiting the device.

Figure 1 shows a propulsion device 100. The propulsion device 100 comprises a housing. The housing comprises a hollow tube 110 with an inner surface which forms an inlet opening 112 at one open end and an outlet opening 114 at the opposite open end. In this embodiment the hollow tube 110 is a rectangular parallelepiped having a rectangular cross-section. The inner surface of the hollow tube 110 forms a central cavity extending from the inlet opening 112 to the outlet opening 114 along a longitudinal axis of the hollow tube 110. The central cavity is a channel through which fluid is pumped by the propulsion device 100 during use in order to provide thrust.

A movable panel 130 is hingedly connected to an inner surface of the hollow tube 110. The movable panel 130 divides the space contained within the hollow tube 110 into two chambers, an outlet chamber (seen at the left hand side of Figure 1) and an inlet chamber (seen at the right hand side of Figure 1). In use the propulsion device 100 is attached to the underside of a watercraft and is consequently submerged so that the hollow tube contains liquid. When the movable panel 130 is urged towards the inner surface of the hollow tube 110 to which it is connected, the volume of the outlet chamber is reduced allowing liquid contained within the outlet chamber to be urged out of the hollow tube 110 through the outlet opening 114 in the hollow tube 110, thereby providing thrust. In this way, the propulsion system 100 ads like a bellows in order to provide propulsive force. The propulsion device 100 may be attached to a boat or other vessel and submerged in order to provide thrust.

The central cavity has a substantially uniform cross-section running along its longitudinal axis.

The inner surface comprises two side faces 116, a top face 118 and a bottom face 120. The two side faces 116 run parallel to each other and are located on opposing sides of the central cavity. The top 118 and bottom 120 faces run parallel to each other and are located on opposing sides of the central cavity. The top 118, bottom 120 and side 116 faces define a tubular cavity with a rectangular cross-section having a width and a height. An opening 122 for a driving member is formed in the top face 118 of the hollow tube 110, passing from the inside of the hollow tube 110 to the outside of the hollow tube 110. The driving member opening 122 forms a slit which runs perpendicular to the longitudinal axis of the hollow tube 110, across the full width of the top face 118 of the hollow tube 110.

It should be noted that the fluid propulsion device 100 may be oriented in any way suitable for use and therefore the words "top" and bottom" are relative terms and do not constrain the orientation of the device, whether during use or otherwise, as long as the inlet and outlet opening of the propulsion device are, in use, aligned with the intended direction of travel of the watercraft. It will of course be appreciated that, in arrangements where the propulsion device is not oriented in the manner shown in Figure 1 the way in which a force is applied to the moveable panel 130 may differ from the way shown in Figure 1.

A movable panel 130 is located within the central cavity. The movable panel 130 is a paddle for urging water out of the outlet opening 114. In the embodiment the movable panel 130 is a substantially planar rectangular panel. The movable panel 130 has a transverse axis running perpendicular to the longitudinal axis of the hollow tube 110. The transverse axis defines the width of the movable panel 130. The width of the movable panel is substantially the same as the width of the central cavity. That is, the width of the movable panel 130 is substantially the same as the distance between the two side faces 116 of the hollow tube 110 whilst still allowing relative movement of the moveable panel 130 along the side faces 116. This ensures minimal or substantially no leakage between the edges of the movable panel 130 and the side walls 116, whilst the movable panel 130 is still able to be moved within the cavity.

A hinge 132 hingedly connects one end of the movable panel 130 the bottom face 120 close to the inlet opening 112. The length of the bottom face 120, along the longitudinal axis of the propulsion device 100, is greater than or equal to the length of the movable panel 130. The movable panel 130 can, for example, be attached to the inner surface via an axle allowing the movable panel to rotate about an axis of rotation. The axis of rotation runs perpendicular to the longitudinal axis of the hollow tube 110. In other words, the axis of rotation runs perpendicular to the side walls 116 of the hollow tube 110. The axis of rotation runs parallel to a hinged edge of the movable panel 130. As the movable panel 130 and the bottom face 120 are moved relative to each other, the volume defined between the two surfaces varies.

A driving member 134 protrudes from the movable panel 130. The driving member 134 allows a driving force to be applied to the movable panel 130 from outside/above the hollow tube 110.

The driving member 134 is located at the opposite end of the movable panel 130 to the hinged end and protrudes towards the top face 118 of the hollow tube 110. The driving member 134 passes through the driving member opening 122 in the hollow tube 130. The driving member 134 and the driving member opening 122 fit tightly to prevent water from passing through the driving member opening 122, whilst still allowing the driving member 134 to move within the driving member opening 122. The driving member 134 comprises a separator wall 136 and a force application member, in this particular embodiment a pedal 138. The separator wall 136 is a curved protrusion from the movable panel 130 shaped to pass through the driving member opening 122. The separator wall 136 extends across the whole width of the movable panel 130.

The movable panel 130 and the separator wall 136 divide the central cavity into two chambers.

An inlet chamber is located in between the inlet opening 112 and the movable panel 130 and separator wall 136. An outlet chamber is located in between the outlet opening 114 and the movable panel 130 and separator wall 136. The separator wall 136 maintains the separation between the inner and outer chambers as the movable panel 130 is moved towards the bottom face 120 of the hollow tube 110. The separator wall 136 fits tightly with the outflow side edge of the driving member opening 122 of the hollow tube 110 to ensure that water may only pass between the inner and outer chambers via the second set of inlet valves 150. The separator wall 136 is a sealing member which limits or substantially prevents fluid communication between the inlet and outlet chambers whilst the volume outlet chamber is reduced.

Whilst in practice, a small amount of leakage may occur between the movable panel 130 and separator wall 136, any such leakage is limited. The relative size of any leakage to the amount of water which passes into and out of the outlet chamber means that, for all intents and purposes, the propulsion device 100 may be considered to only allow water into the outlet chamber from the inlet chamber through the second set of inlet valves 150 and to only allow water to be expelled from the outlet chamber through the outlet opening 114.

The driving member 134 is configured to receive a driving force. The driving member is shaped such that, as it is urged into the hollow tube 110, the movable panel 130 is urged towards the face of the hollow tube 110 to which it is hingedly attached, i.e. the bottom face 120. The movable face 130 and the bottom face 120 define an internal space which is located between the two faces. As the moveable face 130 is moved towards the bottom face 120, volume between the movable face 130 and the bottom face 120 is reduced. In use, liquid is contained within this internal space and reduction in volume urges the liquid out of the outlet opening 114 in the direction indicated in Figure 1 resulting in thrust in an opposite direction.

A first set of inlet valves 140 are located in the bottom face 120 of the hollow tube 110. A second set of inlet valves 150 are located in the movable panel 130. The first 140 and second sets of inlet valves are one-directional valves which are configured to allow fluid to pass into the outlet chamber. The first set of inlet valves 140 allow fluid to pass into the outlet chamber from an area located outside/below of the hollow tube 110. The second set of inlet valves 150 allow fluid to pass into the outlet chamber from the inlet chamber. The first 140 and second 150 sets of inlet valves are configured to prevent liquid from passing through them out of the outlet chamber. The first 140 and second 150 sets of inlet valves are configured to provide a much smaller resistance to water flow into the outlet chamber than the outlet opening 114. This limits the amount of water that is drawn into the outlet chamber through the outlet opening 114 as the volume of the internal space increases thereby reducing drag as water is drawn into the outlet chamber.

In use, the propulsion device 100 is submerged in water so that both of the inlet and outlet chamber are at least partially or completely filled with water. As a downward force is applied to the driving member 134 the driving member urges the movable panel 130 towards the bottom face 120 of the hollow tube 110 thereby reducing the volume of the internal space contained between the movable panel 130 and the bottom face 120. This causes water being urged out of the outlet opening 114 creating a propulsive force in the opposite direction. In this way, the movable panel 130 acts like a paddle, squeezing water against the bottom face 120, acting like a stationary paddle, in an action much like a bellows.

Further propulsive force is provided by water being sucked into the inlet chamber by the expansion of the space contained within the inlet chamber as the movable panel 130 is moved towards the bottom face 120. As the volume of the space between the movable panel 130 and the bottom face 120 is decreased, the volume of the space between the movable panel 130 and the top face 118 is increased. The expansion of the inlet chamber allows liquid to be drawn into the inlet chamber through the inlet opening 112. By drawing liquid in along a second direction, some further thrust is provided via suction. In the present embodiment, the direction of expulsion of liquid from the outlet opening 114 is parallel to the direction of ingress of liquid into the inlet opening 112. The two actions are therefore complimentary, producing combined thrust.

The separator wall 136 prevents the backflow of water into the inlet chamber from the outlet chamber as the movable panel 130 is moved towards the bottom face 120. The separator wall 136 is at least as tall as the height of the inner cavity. This means that the separator wall separates the inner and outer chambers across the whole range of motion of the movable panel 130.

The movable panel 130 may then be moved away from the bottom face 120 in order to allow water into the outlet chamber. This may be achieved through the natural buoyancy of the movable panel 130 and/or may be achieved via a pulling force received at the driving member 134. Water passes into the outlet chamber via the first 140 and second 150 inlet valves due to external water pressure as well as the pressure difference caused by the increase in the volume of the internal space and the reduction in the volume of the space contained within the inlet chamber.

In one embodiment, the propulsion device 100 is attached to the bottom of boat or other vessel, below the waterline of the vessel. It will be appreciated that the propulsion device 100 does not need to include the upper face 118 of the tube. The propulsion device 100 may be located in an opening in the base of the watercraft, similar in the manner in which engines for watercrafts are located in engine wells. In one embodiment the moveable panel 130 and water in the inlet chamber can be seen from inside of the watercraft but the engine well arrangement ensures flooding of the watercraft is nevertheless avoided. As the moveable panel 130 is exposed, driving force may be applied directly to the moveable panel 130. Having said this, the incorporation of the top face 118 provides improved efficiency due to further propulsive force being provided by the water being drawn into the inlet chamber by suction as water is expelled from the outlet chamber. In an alternative embodiment, the propulsion device 100 does not include the upper face 118 and the upper face 118 is provided by the bottom surface of the boat to which it is attached.

The propulsion device 100 may be attached to the boat so that the pedal 138 is located within the boat allowing the user to provide a driving action. In one embodiment, the pedal 138 may be a handle or any other means suitable for applying a driving force to the movable panel 130.

In an alternative embodiment, the driving member 134 is connected to an actuator to allow a rotary force, such as from a rotary pedal system or a motor, to drive the movable panel 130.

In an alternative embodiment, the position of the driving member 134 relative to the movable panel 130 is reversed such that a pulling, as opposed to pushing, driving action urges water out of the outlet opening 114. It will be appreciated that, in this embodiment, the outlet chamber is located on top of the moveable panel 130 and the inlet chamber below the moveable panel 130.

The one way valves in the moveable panel 130 still have to allow one-way flow from the inlet to the outlet chamber, that is, they will need to allow flow in the direction opposite to the direction discussed above with reference to Figure 1.

In one embodiment, a reverse gear may be incorporated by moving the hinge 132 of the movable panel 130 towards the top face 118 of the hollow tube 110. The hinge 132 may configured to disengage from the side walls 118 to allow it to be moved into position adjacent to the top face 118. In a further embodiment, the hinge 132 is located within channels in the side walls 118 running from the bottom face 120 to the top face 118. In addition, a handle may be connected to the hinge 132 and may pass through an opening in one of the side walls 118 to provide a means for the hinge 132 to be moved towards the top face 118. With the hinge 132 located next to the top face 118, water may be urged out of the inlet opening by urging the movable panel 130 towards the bottom face 120 thereby producing reverse thrust.

Multiple propulsion devices 100 may be attached to the boat, for instance, one for each leg of a user. In addition, propulsion devices 100 may be provided for multiple users. Multiple propulsion devices 100 may be located in different engine wells or in a single engine well of the boat.

The propulsion device 100 may be mounted to the boat or vessel via an axle or hinge allowing steering via rotation of the propulsion device about the vertical direction. Alternatively, or in addition, the outlet opening 114 may be configured so that the direction in which water is expelled can be controlled in order to provide steering, such as, for example, through the use of a flexible pipe. In one embodiment, the outlet openings 114 for two or more propulsion devices are connected to a single flexible pipe. All outlet channels would lead to a single channel which could be of flexible material to aid steering by means of cables and pulleys attached to a steering wheel or rudder handle. Where two or more propulsion devices 100 are mounted to a vessel, the vessel may be steered by providing propulsion through a subset of the propulsion devices 100. For instance, only one propulsion device may be driven.

Figures 2A and 2B show first 140 and second 150 one-way inlet valves in accordance with embodiments of the invention.

Figure 2A shows a first inlet valve 140. In one embodiment, the first inlet valve 140 comprises a floating louvre 142. The floating louvre 142 comprises a flap which is hingedly secured within an opening. The flap has a lower density than water and therefore floats when no external forces are applied to it.

Figure 2B shows a second inlet valve 150 in accordance with an embodiment of the invention.

In one embodiment, the first inlet valve 150 comprises a sinking louvre 152. The sinking louvre 152 comprises a weighted flap which is hingedly secured within an opening. The weighted flap has a higher density than water and therefore sinks when no external forces are applied to it.

The flaps have cross sections which are the same, or greater than their respective openings so that when each flap is forced closed its respective opening is sealed and water is prevented from passing through the opening. In one embodiment, the flaps and openings are rectangular.

When the movable panel 130 is stationary the floating 142 and sinking 152 louvres are under no pressure and therefore will open to allow water to pass through the first 140 and second 150 inlet valves. When the movable panel 130 is being urged towards the bottom face 120, that is, when the volume of the internal space is reduced, the increased pressure within the outlet chamber will force the floating 142 and sinking 152 louvres closed. Therefore, water may not pass out of the outlet chamber through the first 140 and second 150 inlet valves when the volume of the internal space located between the movable panel 130 and the bottom face 120 is being reduced.

In one embodiment, the movable panel 130 has a lower density than water. Accordingly, when no force is applied to the movable panel 130 it will float away from the bottom face 120 and the floating 142 and sinking 152 louvres will open to allow water into the outlet opening as the internal space expands. In addition, if the movable panel 130 is urged away from the bottom face 120 then there will be a reduced pressure within the outlet chamber and the floating 142 and sinking 152 louvres will be forced open, allowing water to be sucked into the outlet chamber.

Of course, whilst the first 140 and second 150 inlet valves are described as floating 142 and sinking 152 louvres respectively, this may be reversed in a situation where the propulsion device is inverted during use. In this scenario, the first inlet valves 150 located in the movable panel 130 would be sinking louvres 152 and the second inlet valves 140 located in the bottom face 120 would be floating lourvres 142. Furthermore, the louvres 142, 152 may be made orientation independent by using springs, or any other elastic or resilient material, instead of buoyancy to urge the lourves 142, 152 open. In this scenario, inlet valves may be located in the side faces 116 of the propulsion device 100. Alternatively, the first 140 and second 150 inlet valves may be check valves, clack valves, non-return valves or any of the one-way valves generally known in the art.

The use of an embodiment of the invention shall now be described. A user of the watercraft will sit on a bench located above an engine well of the boat. Two propulsion devices 100 will be located within the engine well, one for each leg of the rower. The propulsion devices 100 shall be submerged underwater, allowing the inlet and outlet chambers to fill with water. Each of the user's feet will rest on a pedal 138 of the two propulsion devices 100. The user presses down in turn on each pedal 138. As a pedal 138 is urged towards the main body of the propulsion device 100, the water which is contained in the internal space located between the movable panel 130 and its matching bottom face 120 will be expelled though the outlet opening 114 at the rear of the internal cavity. By equal and opposite reaction the water craft will be propelled forward. One foot will alternate with another building up forward momentum. At the same time that water is expelled from the channel to the rear by the reduction in the volume of the internal space underneath the movable panel 130, the space between the movable panel 130 and the top face 118 is expanded thereby drawing water into this space through the inlet opening 112.

This suction will help to pull the boat forward, adding to the forward thrust provided by the propulsion device.

After a movable panel 130 has been fully depressed against its respective bottom face 120, the applied driving force is removed permitting the movable panel 130 to float upwards. Water ingresses through the inlet valves 140, 150 which were previously closed under the force of water pressure while the movable panel 130 was depressed. Both the first 140 and second 150 sets of inlet valves will open to allow the space between the bottom face 120 and the movable panel 130 to fill with water causing the movable panel 130 to rise up to its starting position. The cycle is then repeated to build up momentum. To provide an even greater driving force, the user may stand up to apply their full body weight to each pedal 138 in turn. Straps may be located on each pedal 138 to allow the rower to urge the movable panel 130 away from the bottom face 120 to speed up the driving cycle.

It will be appreciated that, instead of providing moveable panels 130 that rely on buoyancy to return from the fully depressed position to the position shown in Figure 1 (or indeed for other embodiments in which a driving force is applied in an upward direction and for which a recovering force' must consequently act downwardly) the moveable member may instead be biased in a direction that is opposite to the direction in which force is applied by the user. It is also envisaged that, if more than one propulsion device is used in a watercraft, the actuation cycles of these propulsion devices are out of phase with each other, for example so that when the moveable member 130 of one propulsion device is pushed in a downward direction by the user the moveable member 130 of another propulsion device is required to move in the upward direction. The moveable members 130 of two or more such propulsion devices may be mechanically coupled in a manner that causes a part of a downwardly extending pushing force applied to one moveable member 130 to be converted in to an upwardly extending pushing force that, coupled to the moveable member 130 of the other propulsion device, moves the moveable member 130 of the other propulsion device upwardly to the position shown in Figure 1.

In an alternative embodiment, the top face 118 of the tubular structure 110 is omitted. In this embodiment, the housing of the propulsion device 100 has a cross-section which is substantially u" shaped. The upper portion of the propulsion device 100 is therefore open.

In a further embodiment, the top face 118 of the tubular structure 110 is provided by the bottom surface of a watercraft to which is it attached. The top face 118 of the tubular structure is omitted. In use, the propulsion device 100 is attached to the hull of a watercraft. In use, the inlet chamber is therefore defined by the movable panel 130, the side walls 118 and the separator wall 138 of the propulsion device, and the hull of the watercraft.

Embodiments of the present invention provide a system of propulsion which is easier than traditional rowing and paddling, and may be applied to boats, paddle boards or any other vessel. The system provides more efficient use of body strength and weight to move a water craft. In contrast to traditional rowing, the movable panels 130, being hingedly secured within the propulsion device 100, are always presented at an ideal angle to urge water out of the outlet opening 114 and to draw water in through the inlet opening 112 along a fixed longitudinal axis of the propulsion device 100. The contained inlet and outlet chambers allow the ingress and expulsion of water to be directed in order to focus the total volume of water pumped into one or more controlled directions to provide a more efficient method of propulsion.

It will be appreciated that the driving force provided to the useable members does not solely have to originate from a single source, say the legs of a user. Instead it is envisaged that the user may further be enabled to provide driving force(s) in additional ways, for example by allowing actuation by the user's arm, say through a lever connection or actuation members that can be gripped by user's hands to the moveable member 130.

In addition to the above benefits, embodiments of the present invention allow the user to face the direction of travel for ease of use and safety. Various embodiments of the invention may be applied to lifeguard rescue wherein allowing a user to adopt a standing position raises the line of sight for a lifeguard thereby aiding the search for distressed swimmers.

In some applications, embodiments of the invention reduce the hull water-length wave effect' which limits the speed at which a low powered water-craft may travel. The hull water-length wave effect causes increased resistance to the acceleration of a vessel as the speed of the vessel approaches the vessel's hull speed. At the hull speed of a vessel, the waves formed at the bow of the vessel constructively interfere with waves formed at the stern. At this point, the vessel's bow wave is equal to the length of the vessel. The large waves caused by the vessel as it approaches hull speed results in increased drag thereby impeding further acceleration.

Without wishing to be bound by theory it is believed that, as the above described propulsion device sucks water in through the inlet opening and expels it through the outlet the wave pattern created by the watercraft is altered and the speed at which the bow and stern waves created by the vessel constructively interfere with each other increases, so that increased resistance to movement is only experienced at higher speeds.

In one embodiment, two propulsion devices fitted on the bottom of a vessel are fed water from the front of the watercraft through a single aperture. The single aperture may be shaped to minimise drag, say, for example, be round in profile. This aperture may be positioned to suck water from the front at such a rate such that the formation of the front part of the hull wave is delayed; thereby increasing the speed of travel obtainable by the boat before the waves formed at the bow and stern of the vessel constructively interfere. By delaying the formation of the hull wave drag is reduced. To overcome the hull wave effect is particularly advantageous in low powered boating where the hull-wave effect is more problematic.

In one embodiment the propulsion device 100 may be configured to control the speed at which the water arrives at the rear of the boat to permit the minimisation of drag. The outlet opening 114 may end at the rear of the boat, or may be connected to a channel ending at the rear of the boat.

Whilst the hollow tube 110 is described as having a rectangular cross-section, in alternative embodiments the hollow tube 110 may have a different shaped cross section. Whilst the above embodiments are described in relation to water, the embodiments of the invention are suitable for use with any type of liquid.

Whilst certain embodiments have been described above, the embodiments have been presented by way of example only and are not intended to limit the scope of protection. It should be understood that the invention is not limited to the specific aspects and embodiments described above and that a variety of modifications, additions and deletions are within the scope of the invention as defined by the following claims.

Claims

CLAI MS: 1. A propulsion device for providing thrust in a first direction comprising: a first boundary member and a second boundary member, the first and second boundary members defining a first space and being movable relative to each other to vary the volume of the first space; an outlet opening configured to allow liquid to be urged out of the first space along a direction opposite to the first direction; and a one-way valve configured to allow liquid into the first space as the volume of the first space is increased; wherein the propulsion device is configured to allow liquid to be expelled only through the outlet opening as the volume of the first space is reduced.
2. The fluid propulsion device of claim 1 wherein the first boundary member separates the first space from a second space and wherein the fluid propulsion device further comprises a means for limiting or substantially preventing fluid communication between the first and second spaces whilst the volume first space is reduced.
3. The fluid propulsion device of claim 2 wherein the means for limiting or substantially preventing fluid communication comprises a sealing member.
4. The fluid propulsion device of claims 2 or 3 wherein the means for limiting or substantially preventing fluid communication is configured to be able transmit, to the first boundary member, a force that urges the first boundary member towards the second boundary member when applied to the first boundary member.
5. The fluid propulsion device of one of claims 2 to 4 wherein the one-way valve is configured to allow fluid to pass from the second space into the first space as the volume of the first space is increased.
6. The fluid propulsion device of any of claims 2 to 5 further comprising: a third boundary member, the second space being defined between the first and third boundary members, the first and third boundary members being movable relative to each other to vary the volume of the second space; and an inlet opening configured to allow liquid into the second space, wherein, the fluid propulsion device is configured so that the volume of the second space is increased as the volume of the first space is reduced.
7. The propulsion device of claim 6 configured to allow liquid to be drawn into the second space through the inlet opening along a second direction substantially opposite to the first direction as the volume of the second space increases.
8. The propulsion device of any preceding claim wherein the geometry of the outlet opening can be changed in use to change the direction in which fluid is expelled from the first space.
9. A watercraft comprising a propulsion device according to any preceding claim.
10. A method of providing thrust in a first direction comprising, in a propulsion device comprising a first boundary member and a second boundary member, the first and second boundary members defining a first space and being movable relative to each other to vary the volume of the first space: increasing the volume of the first space to allow liquid into the first space via a one-way valve; and reducing the volume of the first space to urge liquid out of the first space only through an outlet opening in the propulsion device, wherein the liquid is urged in a direction opposite to the first direction.
11. The method of claim 10 wherein the first boundary member separates the first space from a second space and wherein the method further comprises using a means for limiting or substantially preventing fluid communication between the first and second spaces whilst the volume of the first space is reduced to limit or substantially prevent fluid communication between the first and second spaces whilst the volume of the first space is reduced.
12. The method of claim 11 further comprising urging the first boundary member towards the second boundary member by applying a force to the means for limiting or substantially preventing fluid communication
13. The method of claim 11 or 12 wherein the second space is located between the first boundary member and a third boundary member of the propulsion device, the first and third boundary members being movable relative to each other to vary the volume of the second space and the method comprises increasing the volume of the second space as the volume of the first space is reduced to draw liquid into the second space through an inlet opening in the propulsion device.
14. The method of claim 13 wherein the liquid is drawn into the second space along a second direction substantially opposite to the first direction.
15. The method of any of claims 10 to 14 further comprising changing the geometry of the outlet opening relative to the propulsion device to control the direction of thrust.
16. A fluid propulsion device as hereinbefore described with reference to the figures.