WO2015198027A1

WO2015198027A1 - Improvements in or relating to watercraft

Info

Publication number: WO2015198027A1
Application number: PCT/GB2015/051816
Authority: WO
Inventors: Ian Henderson
Original assignee: Henderson Marine Services Limited
Priority date: 2014-06-23
Filing date: 2015-06-23
Publication date: 2015-12-30
Also published as: GB201411152D0; GB2527519A

Abstract

A keel system for a watercraft (12) comprising a first keel (10a), wherein the first keel is configured to be connectable to the watercraft and moveable between a stowed position and at least one deployed position and a second keel (10b), wherein the second keel is configured to be connectable to the watercraft and moveable between a stowed position and at least one deployed position.

Description

Improvements in or relating to watercraft

The present invention relates to a keel for a watercraft, a keel system for a watercraft and a watercraft incorporating the keel or keel system.

Swaying of watercraft during forward motion may be termed leeway. Leeway occurs, for example, if the watercraft is subject to a lateral force, such as a cross wind, during forward motion. The result of this leeway is that the watercraft must alter its heading, or course through the water, from its desired track, or course over the ground. This altered heading, means that the watercraft must have an angle of "set" that is required for the watercraft to maintain its desired track. By their nature, shallow draught and non-displacement watercraft suffer from reduced directional stability compared with deeper draught vessels. Consequently, the shallow draught and non-displacement craft are vulnerable to excessive leeway, whereby the heading of the craft is significantly different from the intended track. This reduces efficiency as a significant component of the propulsive thrust is required to maintain the intended track rather than drive the craft forward.

Running a motor powered watercraft with an altered heading is very inefficient, as the engine has to partially work against the cross wind. This increases the running cost of the watercraft, as the engine consumes additional fuel than would otherwise be required. It also places an undesired excess strain on the engine.

The addition of underwater keels provides some resistance to the lateral forces that the watercraft is exposed to. An underwater keel can reduce the angle between the watercraft's heading and desired track. This causes the watercraft' s sideways movement to be reduced, which thus reduces the propulsion required to maintain track.

While the use of underwater keels can reduce the angle between the watercraft's heading and desired track, which reduces the fuel consumed by the engine, the underwater keel adds drag to the watercraft.

The present inventor has appreciated the shortcomings in these known keels and keel systems.

According to a first aspect of the present invention there is provided a keel for a watercraft, wherein the keel is configured to be connectable to the watercraft and moveable between a stowed position and at least one deployed position.

The keel may be pivotably connectable to the watercraft. The keel may be pivotably connectable to the watercraft and moveable between the stowed position and the at least one deployed position. The keel may be translatably connectable to the watercraft. The keel may be translatably connectable to the watercraft and moveable between the stowed position and the at least one deployed position.

The keel may be pivotably connectable and translatably connectable to the watercraft. The keel may be configured to firstly translate from an initial stored position to the stowed position and then pivot from the stowed position to the at least one deployed position. The initial stored position may be within the hull of the watercraft. The keel may be configured to be connectable towards the bow end, or fore end, of the watercraft. The keel may be configured to be connectable towards the stern end, or aft end, of the watercraft. The keel may be configured to be connectable between the fore end and aft end of the watercraft.

The keel may be configured to be pivotably connectable towards the bow end, or fore end, of the watercraft. The keel may be configured to be pivotably connectable towards the stern end, or aft end, of the watercraft. The keel may be configured to be pivotably connectable between the fore end and aft end of the watercraft.

The keel may include a keel support member or keel support members; the keel support member, or support members, being attachable to the watercraft. The keel support member, or support members, may be configured to allow the keel to move between the stowed position and the deployed position.

The keel may include a keel pivot support member, the keel pivot support member being attachable to the watercraft. The keel pivot support member may be configured to allow the keel to pivot thereabout. The keel may be pivotably connectable to the keel pivot support member.

The keel pivot support member may be attachable to the bow end, or fore end, of the watercraft. The keel pivot support member may be attachable between the bow end, or fore end, and aft end of the watercraft.

The keel may be connectable to a side portion of the watercraft. The keel may be connectable to the starboard side of the watercraft. The keel may be connectable to the port side of the watercraft. The keel may be configured such that it is located on an outwardly facing side of the watercraft. The keel may be connectable to the watercraft between the starboard side and port side of the watercraft. In this arrangement the watercraft may, for example, be a multi-hulled watercraft.

The keel may be arranged along the centreline of the watercraft.

The keel may be configured to be rotatably moveable between the stowed position and the deployed position.

The keel may be a substantially planar member. The keel may have a front portion and a rear portion. The front portion of the keel may be pivotably connectable to the watercraft. The front portion of the keel may be pivotably connectable to the keel pivot support member. The keel may include a substantially planar portion between the front portion and the rear portion.

The keel may be substantially U-shaped. In this arrangement the front portion of the keel and the rear portion of the keel curve upwards from the mid portion of the keel. The keel may further include a keel support housing, the keel support housing being attachable to the watercraft and providing support to the keel as the keel moves between the stowed position and the deployed position. The keel support housing may support the rear portion of the keel. The keel support housing may be in the form of a collar, through which the keel may pass. The keel support housing may be a thrust collar. The keel may include one or more keel support housings.

The keel may have a longitudinal axis. The longitudinal axis runs between the front and rear portions of the keel.

The keel may be arranged such that the front portion of the keel and the rear portion of the keel lie on the longitudinal axis thereof. The keel may be configured such that its length is comparable to the length of the watercraft. The keel may be configured such that it is substantially the same length as the length of the watercraft. The keel may be configured such that it is at least two thirds of the length of the watercraft. The keel may be configured such that it is at least one half of the length of the watercraft.

The keel may include an extension portion that protrudes towards the stern end, or aft end, of the watercraft. In this arrangement the keel may be substantially the same length as the watercraft.

The keel may be of a height that is comparable to the height of the hull of the watercraft.

The keel may have a substantially rectangular cross-section. The cross- section of the keel in a plane normal to the longitudinal axis of the keel may be substantially rectangular. The keel may have a substantially rectangular cross-section in a plane that is normal to the longitudinal axis of the keel. The keel may have a substantially V-shaped lower portion. The lower portion of the keel may have a substantially V-shaped cross-section. The cross-section of the lower portion of the keel in a plane normal to the longitudinal axis of the keel may be substantially V-shaped. The lower portion of the keel may have a substantially V-shaped cross-section in a plane that is normal to the longitudinal axis of the keel.

The keel may be biased towards the stowed position. The keel may be spring biased towards the stowed position. The keel support member, or keel support members, may include a biasing device to bias the keel towards the stowed position. The keel pivot support member, or keel support members, may include a biasing device to bias the keel towards the stowed position. The biasing device may be a spring bias device. The keel may include one or more protruding portions that protrude from the outwardly facing surface of the keel. The keel may include one or more protruding portions that protrude from the outwardly facing side surface of the keel. The one or more protruding portions may be located towards the rear portion of the keel. The one or more protruding portions may be located between the rear portion and front portion of the keel. The one or more protruding portions may be located at an upper portion of the rear portion of the keel.

The one or more protruding portions may be curved surfaces that extend away from the outer surface of the keel. The one or more protruding portions may define at least a partially concave surface. The one or more protruding portions may define at least a partially spherical, or aspherical surface. The one or more protruding portions may be hydroplanes. The keel may include one or more hydroplanes. The keel may include one or more horizontal rudders. The one or more hydroplanes may be located on an outwardly facing surface of the keel. The one or more hydroplanes may be located on an outwardly facing side surface of the keel. The one or more hydroplanes may be located between the aft end and fore end of the keel. The one or more hydroplanes may have a front portion and a rear portion. The front portion of the hydroplane may be positioned lower than the rear portion of the hydroplane. In this arrangement the hydroplane is angled downwards with respect to the longitudinal axis of the keel, or watercraft. The rear portion of the one or more hydroplanes may protrude further from the outwardly facing surface of the keel than the front portion. The amount that the hydroplane protrudes from the outwardly facing of the surface of the keel may increase from the front portion of the hydroplane to the rear portion of the hydroplane. The amount that the hydroplane protrudes from the outwardly facing surface of the keel may increase linearly from the front portion of the hydroplane to the rear portion of the hydroplane. The amount that the hydroplane protrudes from the outwardly facing surface of the keel may increase non-linearly from the front portion of the hydroplane to the rear portion of the hydroplane.

The hydroplane may have a protective arrangement on its outwardly facing surface.

The hydroplane may be retractable. In this arrangement the hydroplane may retract into the keel. The hydroplane may move between a stowed position, where the hydroplane is entirely contained within the keel and a deployed position, where the hydroplane protrudes from the outwardly facing surface of the keel.

In the deployed position the rear portion of the hydroplane protrudes further from the outwardly facing surface of the keel than the front portion of the hydroplane.

The hydroplane may be configured to pivot between the stowed position and the deployed position.

The hydroplane may be biased towards the stowed position. The hydroplane may be spring biased towards the stowed position.

The hydroplane may pivot about a pivot point located towards the front portion of the hydroplane. The keel may be configured such that it may be moved to a plurality of deployed positions. Each deployed position may result in the keel being positioned at a different position relative to the watercraft.

The keel may be configured such that, when the keel is in the stowed position, the keel is located above the lowest portion of the hull, or hulls, of the watercraft. The keel may be configured such that, when the keel is in the stowed position, the keel is located above the lowest portion of the watercraft. In this arrangement, when the watercraft is in use, the lowest point of the keel is above the waterline of the watercraft. The keel may be configured such that, when the keel is in the deployed position, the keel is located below the lowest portion of the hull, or hulls, of the watercraft. The keel may be configured such that, when the keel is in the deployed position, the keel is located below the lowest portion of the watercraft. In this arrangement, when the watercraft is in use, the lowest point of the keel is below the waterline of the watercraft.

The keel may be configured such that the amount that the keel protrudes below the hull, or hulls, of the watercraft is adjustable. The deployed position of the keel may therefore be adjustable. The keel may be configured such that it is moveable between the stowed position and a maximum deployed position, and any deployed position therebetween.

The keel may include one or more moveable, or pivotable, hydroplanes, or rudders. The one or more moveable, or pivotable, hydroplanes, or rudders may be connected to the keel.

The one or more pivotable rudders may be pivotable about an axis, or axes, that are orthogonal to the longitudinal axis of the keel.

The keel may include a first pivotable rudder, or hydroplane, that is pivotable about a first axis that is perpendicular to the longitudinal axis of the keel, or watercraft. The keel may include a second pivotable rudder that is pivotable about a second axis that is perpendicular to the longitudinal axis of the keel, or watercraft. The first and second axes may be perpendicular to one another and perpendicular to the longitudinal axis of the keel, or watercraft. That is, the first axis, second axis and longitudinal axis of the keel, or watercraft, are orthogonally arranged with respect to one another. The keel may include a first pivotable rudder, or hydroplane, and a second pivotable rudder. The first pivotable rudder, or hydroplane, may be located on a side portion of the keel. The first pivotable rudder, or hydroplane, may be located on an outwardly facing side portion of the keel. The first pivotable rudder, or hydroplane, may be located between the front and rear portion of the keel. The first pivotable rudder, or hydroplane, may be pivotable about a horizontal plane relative to the longitudinal axis of the keel, or watercraft.

The second pivotable rudder may be located at the rear portion of the keel. The second pivotable rudder may be pivotable about a vertical plane relative to the longitudinal axis of the keel, or watercraft.

The second pivotable rudder may be located at the front portion of the keel. The second pivotable rudder may be pivotable about a vertical plane relative to the longitudinal axis of the keel, or watercraft.

The keel may include a third pivotable rudder that is pivotable about a third axis that is perpendicular to the longitudinal axis of the keel, or watercraft. The third pivotable rudder may be located at the front portion of the keel. The third pivotable rudder may be pivotable about a vertical plane relative to the longitudinal axis of the keel, or watercraft.

The first pivotable rudder, or hydroplane, may be biased towards its neutral position. The first pivotable rudder, or hydroplane, may be biased towards a position where the longitudinal axis of the rudder, or hydroplane, is substantially parallel to the longitudinal axis of the keel, or watercraft.

The second pivotable rudder may be biased towards its neutral position. The second pivotable rudder may be biased towards a position where the longitudinal axis of the rudder is substantially parallel to the longitudinal axis of the keel, or watercraft.

The third pivotable rudder may be biased towards its neutral position. The third pivotable rudder may be biased towards a position where the longitudinal axis of the rudder is substantially parallel to the longitudinal axis of the keel, or watercraft.

The keel may include one or more support wheels, the one or more support wheels being configured to provide support to the keel if the watercraft is operating on land. The one or more support wheels may be located on the lower portion of the keel. The one or more support wheels may be located between the fore end and aft end of the keel. The one or more support wheels may be pivotable relative to the keel. The one or more support wheels may be pivotably connected to the keel. The one or more support wheels may be pivotable about a vertical axis, the vertical axis being perpendicular to the longitudinal axis of the keel, or watercraft.

The one or more support wheels may be biased towards a position where the axis of rotation of the one or more support wheels is perpendicular to the longitudinal axis of the keel or watercraft. The rotational axis of the one or more support wheels is perpendicular to the pivotal axis of the support wheel. The one or more support wheels may be swivel wheels, or caster wheels.

The one or more support wheels may be sprung to support the weight, or at least a portion of, the weight of the keel or watercraft. The one or more support wheels may be at least partially located within the keel. The keel may include one or more chambers, each chamber being configured to receive at least a portion of the one or more support wheels therein. The one or more support wheels may be configured so that their outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel.

The one or more support wheels may include one or more braking devices, the one or more braking devices being operable to exert a braking force on the wheels to prevent rotation thereof.

The second pivotable rudder may include a first wheel, the first wheel being configured to provide support to the keel if the watercraft is operating on land. In this arrangement the first wheel may be configured to provide rolling support to the keel if the watercraft is operating on land. The first wheel prevents the lower portion of the keel contacting the ground. The first wheel is configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel.

The first wheel may be rotatably attached to the second pivotable rudder. The first wheel may be attached to the lower portion of the second pivotable rudder. The first wheel may be at least partially located within the second pivotable rudder.

The second pivotable rudder may be a wheel. The second pivotable rudder may be a combined wheel and wheel housing. The wheel may be housed within a housing. The housing may at least partially surround the wheel. The wheel may be configured to provide support to the keel if the watercraft is operating on land. In this arrangement the wheel may be configured to provide rolling support to the keel if the watercraft is operating on land. The wheel prevents the lower portion of the keel contacting the ground. The wheel is configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel. The wheel may be pivotably attached to the keel. The wheel may be rotatably attached to the keel or housing. The wheel may be biased towards a position where its axis of rotation is perpendicular to the longitudinal axis of the keel or watercraft. The keel may include a second wheel, the second wheel being configured to provide support to the keel if the watercraft is operating on land. The second wheel may be located on the lower portion of the keel. The second wheel may be located towards the fore end, or front end, of the keel.

The second wheel may be pivotable relative to the keel. The second wheel may be pivotably connected to the keel. The second wheel may be pivotable about an axis that is perpendicular to the longitudinal axis of the keel, or watercraft.

The second wheel may be biased towards a position where the axis of rotation of the second wheel is perpendicular to the longitudinal axis of the keel or watercraft. The rotational axis of the second wheel is

perpendicular to the pivotal axis of the second wheel. The second wheel may be a swivel wheel, or caster wheel.

The second wheel may be at least partially located within the keel. The keel may include a chamber, the chamber being configured to receive at least a portion of the second wheel therein. The second wheel may be configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel.

The second wheel may include one or more braking devices, the one or more braking devices being operable to exert a braking force on the wheel to prevent rotation thereof.

The second wheel may be sprung to support a portion of the weight, or the entire weight, of the keel or watercraft.

The second wheel may be the third pivotable rudder in the fore part of the keel. The third pivotable rudder may be a combined wheel and wheel housing. The wheel may be housed within a housing. The housing may at least partially surround the wheel. The wheel may be configured to provide support to the keel if the watercraft is operating on land. In this arrangement the wheel may be configured to provide rolling support to the fore part of the keel if the watercraft is operating on land. The wheel prevents the lower portion of the keel contacting the ground. The wheel is configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel. The wheel may be pivotably attached to the keel. The wheel may be rotatably attached to the keel or housing. The wheel may be biased towards a position where its axis of rotation is perpendicular to the longitudinal axis of the keel or watercraft.

Where the second wheel forms part of the third pivotable rudder, it may be biased towards a position where its axis of rotation is parallel to the tiller controlling the third pivotable rudder. The wheel may be sprung to support a portion of the weight of the keel or watercraft

The wheel forming part of the third pivotable rudder may include one or more braking devices, the one or more braking devices being operable to exert a braking force on the wheel to prevent rotation thereof.

The second wheel may be a spherical wheel. The spherical wheel may rotate in any direction relative to the keel. The spherical wheel may be biased towards a position where the axis of rotation of the spherical wheel is perpendicular to the longitudinal axis of the keel or watercraft. The spherical wheel may be at least partially located within the keel. The keel may include a chamber, the chamber being configured to receive at least a portion of the spherical wheel therein. The spherical wheel may be configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel. The spherical wheel may include one or more braking devices, the one or more braking devices being operable to exert a braking force on the wheel to prevent rotation thereof.

The keel may include a third wheel, the third wheel being configured to provide additional support to the keel if the watercraft is operating on land. The third wheel may be located on the lower portion of the keel. The third wheel may be located towards the fore end, or front end, of the keel. The third wheel may be located either side of the second wheel. The third wheel may be located behind the second wheel. That is, the third wheel may be located closer to the aft end, or stern end, of the keel than the second wheel. The third wheel may be fixed relative to the keel. The third wheel may have a horizontal axis of rotation that is perpendicular to the longitudinal axis of the keel, or the watercraft. The third wheel may be at least partially located within the keel. The keel may include a chamber, the chamber being configured to receive at least a portion of the third wheel therein. The third wheel may be configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel. The third wheel may be configured such that it protrudes from the lowest portion of the lower portion of the keel less than the second wheel. That is, the second wheel protrudes further from the lower portion of the keel than the third wheel.

The third wheel may include one or more braking devices, the one or more braking devices being operable to exert a braking force on the third wheel to prevent rotation thereof.

The third wheel may be sprung to support at least a portion of the weight of the keel or watercraft.

The keel may further include a control apparatus, the control apparatus being operable to control the movement of the keel between the stowed position and the deployed position, or positions. The control apparatus may be configured to work against the biasing force that biases the keel towards the stowed position.

The control apparatus may be hand operated. The control apparatus may be foot operated. The control apparatus may be power-assisted. The control apparatus may be attachable to the watercraft.

The control apparatus may be engagable with the keel to control the movement of the keel between the stowed position and the deployed position, or positions.

The control apparatus may comprise a linkage mechanism. The linkage mechanism may be connected between the keel and a control arm of the control apparatus.

The linkage mechanism may be pivotably connected to the keel.

The linkage mechanism may include a push rod and a control plate. The push rod may be pivotably connected to the control plate and the control plate may be pivotably connected to the keel.

The control apparatus may be configured to transfer a translational motion of at least a part of the linkage mechanism to a pivotal motion of the keel. The control apparatus may be configured to transfer a vertical motion of at least a part of the linkage mechanism to a pivotal motion of the keel.

The linkage mechanism may be configured to transfer a vertical motion of the push rod to a pivotal motion of the control plate and keel.

The control apparatus may also be operable to control the movement of the first pivotable rudder, or hydroplane. The control apparatus may also be operable to control the movement of the second pivotable rudder. The control apparatus may also be operable to control the movement of the third pivotable rudder. The control apparatus may also be operable to control the movement of the first and second pivotable rudders. The control apparatus may also be operable to control the movement of the first, second and third pivotable rudders. The control apparatus may also be operable to control the movement of the first and second pivotable rudders simultaneously. The control apparatus may also be operable to control the movement of the first, second and third pivotable rudders simultaneously.

The control apparatus may be operable to control the movement of the first pivotable rudder, or hydroplane, from a first neutral position to a second active position. In the first neutral position the longitudinal axis of the first pivotable rudder, or hydroplane, is substantially parallel to the longitudinal axis of the keel, or watercraft. In the second active position longitudinal axis of the first pivotable rudder, or hydroplane, is angled downwards with respect to the longitudinal axis of the keel, or watercraft.

The control apparatus may be operable to control the movement of the second pivotable rudder from a first neutral position to a second active position. In the first neutral position the longitudinal axis of the second pivotable rudder is substantially parallel to the longitudinal axis of the keel, or watercraft. In the second active position the longitudinal axis of the second pivotable rudder is substantially non-parallel, or angled, with respect to the longitudinal axis of the keel, or watercraft. The control apparatus may be operable to control the movement of the third pivotable rudder from a first neutral position to a second active position. In the first neutral position the longitudinal axis of the third pivotable rudder is substantially parallel to the longitudinal axis of the keel, or watercraft. In the second active position the longitudinal axis of the third pivotable rudder is substantially non-parallel, or angled, with respect to the longitudinal axis of the keel, or watercraft.

The linkage mechanism may also be connected to the first pivotable rudder, or hydroplane. The linkage mechanism may also be connected to the second pivotable rudder. The linkage mechanism may also be connected to the third pivotable rudder. The linkage mechanism may also be connected to the first and second pivotable rudders. The linkage mechanism may also be connected to the first, second and third pivotable rudders.

The linkage mechanism may be pivotably connected to the first pivotable rudder, or hydroplane. The control plate may also be pivotably connected to the first pivotable rudder, or hydroplane. In this arrangement the linkage mechanism is configured to transfer a vertical motion of the push rod to a pivotal motion of both the keel and the first pivotable rudder, or hydroplane, via the control plate.

The linkage mechanism may further include a steering arm. The steering arm may be connected between the control plate and the second pivotable rudder. The steering arm may be pivotably connected to the control plate. The steering arm may be horizontally arranged with respect to the keel or watercraft. The steering arm may be pivotably connected to the second pivotable rudder. The steering arm may be pivotably connected to the second pivotable rudder via a tiller. The tiller may be pivotably connected to the steering arm and directly fixed to the second pivotable rudder.

The linkage mechanism may further include another steering arm. The steering arm may be connected between the control plate and the third pivotable rudder. The steering arm may be pivotably connected to the control plate. The steering arm may be horizontally arranged with respect to the keel or watercraft. The steering arm may be pivotably connected to the third pivotable rudder via a tiller. The tiller may be pivotably connected to the steering arm and directly fixed to the third pivotable rudder.

Where the linkage mechanism is connected to the keel, first pivotable rudder, or hydroplane, and second pivotable rudder, operation of the control apparatus to move the keel from its stowed position to its deployed position also moves both the first and second pivotable rudders from their neutral position to their active position. This is as a result of the linkage mechanism being connected to the keel, first pivotable rudder, or hydroplane, and second pivotable rudder.

Where the linkage mechanism is connected to the keel, first pivotable rudder, or hydroplane, second pivotable rudder and third pivotable rudder, operation of the control apparatus to move the keel from its stowed position to its deployed position also moves both the first, second and third pivotable rudders from their neutral position to their active position. This is as a result of the linkage mechanism being connected to the keel, first pivotable rudder, or hydroplane, second pivotable rudder and third pivotable rudder.

The operation of the control apparatus and linkage mechanism may have two stages: the first stage may move the keel from its stowed position to its deployed position, this may be, for example, directional stability of the watercraft; the second stage may be further movement of the keel towards a maximum deployed position, in which the control apparatus and linkage mechanism moves the first, second and third pivotable rudders from their neutral position to their active position. In this arrangement the keel is lowered initially for directional stability and then, with further lowering of the keel, the rudders move from their neutral position to their active position.

The control apparatus may be operable to control the movement of the retractable hydroplane between the stowed position and the deployed position.

The control apparatus may be engagable with the retractable hydroplane to control the movement of the retractable hydroplane between the stowed position and the deployed position.

The linkage mechanism may be connected between the retractable hydroplane and a control arm of the control apparatus. The push rod may be pivotably connected to the control plate and the control plate may be configured to be in contact with the retractable hydroplane.

The control apparatus may be configured to transfer a translational motion of at least a part of the linkage mechanism to a pivotal motion of the retractable hydroplane.

The control apparatus may be configured to transfer a vertical motion of at least a part of the linkage mechanism to a pivotal motion of the retractable hydroplane.

The linkage mechanism may be configured to transfer a vertical motion of the push rod to a pivotal motion of the control plate and retractable hydroplane. According to a second aspect of the present invention there is provided a keel system for a watercraft comprising:

a first keel, wherein the first keel is configured to be connectable to the watercraft and moveable between a stowed position and at least one deployed position; and

a second keel, wherein the second keel is configured to be connectable to the watercraft and moveable between a stowed position and at least one deployed position. The first and second keels may be pivotably connectable to the watercraft. The first and second keels keel may be pivotably connectable to the watercraft and moveable between the stowed position and the at least one deployed position. The first and second keels may be translatably connectable to the watercraft. The first and second keels may be translatably connectable to the watercraft and moveable between the stowed position and the at least one deployed position. The first and second keels may be pivotably connectable and translatably connectable to the watercraft. The first and second keels may be configured to firstly translate from an initial stored position to the stowed position and then pivot from the stowed position to the at least one deployed position. The initial stored position may be within the hull of the watercraft.

The first and second keels may be configured to be connectable towards the bow end, or fore end, of the watercraft. The first and second keels may be configured to be connectable towards the stern end, or aft end, of the watercraft. The first and second keels may be configured to be connectable between the fore end and aft end of the watercraft.

The first and second keels may be configured to be pivotably connectable towards the bow end, or fore end, of the watercraft. The first and second keels may be configured to be pivotably connectable towards the stern end, or aft end, of the watercraft. The first and second keels may be configured to be pivotably connectable between the fore end and aft end of the watercraft.

The keel system may include a keel support member, the keel support member being attachable to the watercraft. The keel support member may be configured to allow the first and second keels to move between the stowed position and the deployed position. There may be one or more keel support members along the length of the keel.

The keel system may include a keel pivot support member, the keel pivot support member being attachable to the watercraft. The keel pivot support member may be configured to allow the first and second keels to pivot thereabout. The first and second keels may be pivotably connectable to the keel pivot support member.

The first and second keels may be connectable to a side portion of the watercraft. The first keel may be connectable to the starboard side of the watercraft and the second keel may be connectable to the port side of the watercraft. The first and second keels may be configured such that they are located on an outwardly facing side of the watercraft. The first and second keels may be connectable to the watercraft between the starboard side and port side of the watercraft. In this arrangement the watercraft may, for example, be a multi-hulled watercraft.

The keels may be arranged along the centreline of the watercraft.

The first and second keels may be configured to be rotatably moveable between the stowed position and the deployed position.

The first and second keels may be substantially planar members. The first and second keels may have a front portion and a rear portion. The front portion of each keel may be pivotably connectable to the watercraft. The front portion of each keel may be pivotably connectable to the keel pivot support member. The first and second keels may include a substantially planar portion between the front portion and the rear portion thereof.

The first and second keels may be substantially U-shaped. In this arrangement the front portion of each keel and the rear portion of each keel curve upwards from the mid portion of the keel. The keel system may further include two or more keel support housings, the keel support housings being attachable to the watercraft and providing support to each keel as each keel moves between the stowed position and the deployed position. The keel support housings may support the rear portion of the keel. The keel support housings may support the mid portion of the keel. The keel support housings may be in the form of collars, through which the keels may pass. The keel support housings may be thrust collars. The keel may include one or more keel support housings. The first and second keels may have a longitudinal axis. The longitudinal axis runs between the front and rear portions of the keel.

The first and second keels may be arranged such that the front portion of each keel and the rear portion of each keel lie on the respective

longitudinal axis thereof.

The first and second keels may be configured such that their length is comparable to the length of the watercraft. The first and second keels may be configured such that they are substantially the same length as the length of the watercraft. The first and second keels may be configured such that they are at least two thirds of the length of the watercraft. The keel may be configured such that it is at least one half of the length of the watercraft. The first and second keels may include an extension portion that protrudes towards the stern end, or aft end, of the watercraft. In this arrangement each keel may be substantially the same length as the watercraft.

The first and second keels may be of a height that is comparable to the height of the hull of the watercraft.

The first and second keels may have a substantially rectangular cross- section. The cross-section of the keel in a plane normal to the longitudinal axis of each keel may be substantially rectangular. The first and second keels may have a substantially rectangular cross-section in a plane that is normal to the longitudinal axis of each keel.

The first and second keels may have a substantially V-shaped lower portion. The lower portion of each keel may have a substantially V- shaped cross-section. The cross-section of the lower portion of each keel in a plane normal to the longitudinal axis of the keel may be substantially V-shaped. The lower portion of each keel may have a substantially V- shaped cross-section in a plane that is normal to the longitudinal axis of each keel.

The first and second keels may be biased towards the stowed position. The first and second keels may be spring biased towards the stowed position. The keel support member may include a biasing device to bias the keels towards the stowed position. The keel pivot support member may include a biasing device to bias the keels towards the stowed position. The biasing device may be a spring bias device.

The first and second keels may include one or more protruding portions that protrude from the outwardly facing surface of each keel. The first and second keels may include one or more protruding portions that protrude from the outwardly facing side surface of each keel. The one or more protruding portions may be located towards the rear portion of the keel. The one or more protruding portions may be located between the rear portion and front portion of the keel. The one or more protruding portions may be located at an upper portion of the rear portion of the keel.

The one or more protruding portions may be curved surfaces that extend away from the outer surface of the keel. The one or more protruding portions may define at least a partially concave surface. The one or more protruding portions may define at least a partially spherical, or aspherical surface.

The one or more protruding portions may be hydroplanes.

The first and second keels may include one or more hydroplanes. The first and second keels may include one or more horizontal rudders.

The one or more hydroplanes may be located on an outwardly facing surface of the keel. The one or more hydroplanes may be located on an outwardly facing side surface of the keel. The one or more hydroplanes may be located between the aft end and fore end of the keel.

The one or more hydroplanes may have a front portion and a rear portion. The front portion of the hydroplane may be positioned lower than the rear portion of the hydroplane. In this arrangement the hydroplane is angled downwards with respect to the longitudinal axis of the keel, or watercraft.

The rear portion of the one or more hydroplanes may protrude further from the outwardly facing surface of the keel than the front portion. The amount that the hydroplane protrudes from the outwardly facing surface of the keel may increase from the front portion of the hydroplane to the rear portion of the hydroplane. The amount that the hydroplane protrudes from the outwardly facing surface of the keel may increase linearly from the front portion of the hydroplane to the rear portion of the hydroplane. The amount that the hydroplane protrudes from the outwardly facing surface of the keel may increase non-linearly from the front portion of the hydroplane to the rear portion of the hydroplane. The hydroplane may have a protective arrangement on its outwardly facing surface.

The hydroplane may be retractable. In this arrangement the hydroplane may retract into the keel.

The hydroplane may move between a stowed position, where the hydroplane is entirely contained within the keel and a deployed position, where the hydroplane protrudes from the outwardly facing surface of the keel.

The hydroplane may pivot about a pivot point located towards the front portion of the hydroplane. The first and second keels may be configured such that they may be moved to a plurality of deployed positions. Each deployed position may result in the keel being positioned at a different position relative to the watercraft. The first and second keels may be configured such that, when the keels are in the stowed position, the keels are located above the lowest portion of the hull, or hulls, of the watercraft. The first and second keels may be configured such that, when the keels are in the stowed position, the keels are located above the lowest portion of the watercraft. In this

arrangement, when the watercraft is in use, the lowest point of the keels are above the waterline of the watercraft.

The first and second keels may be configured such that, when the keels are in the deployed position, the keels are located below the lowest portion of the hull, or hulls, of the watercraft. The first and second keels may be configured such that, when the keels are in the deployed position, the keels are located below the lowest portion of the watercraft. In this arrangement, when the watercraft is in use, the lowest point of the keels are below the waterline of the watercraft.

The first and second keels may be configured such that the amount that each keel protrudes below the hull, or hulls, of the watercraft is adjustable. The deployed position of the keels may therefore be adjustable. The keels may be configured such that they are moveable between the stowed position and a maximum deployed position, and any deployed position therebetween.

The first and second keels may include one or more moveable, or pivotable, hydroplanes, or rudders. The one or more moveable, or pivotable, hydroplanes, or rudders may be connected to the keel.

The one or more pivotable rudders may be pivotable about an axis, or axes, that are orthogonal to the longitudinal axis of the keel, or watercraft. The first and second keels may include a first pivotable rudder, or hydroplane, that is pivotable about a first horizontal axis that is

perpendicular to the longitudinal axis of the keel, or watercraft. The first and second keels may include a second pivotable rudder that is pivotable about a second vertical axis that is perpendicular to the longitudinal axis of the keel, or watercraft.

The first and second keels may include a third pivotable rudder that is pivotable about a second axis that is perpendicular to the longitudinal axis of the keel, or watercraft.

The first and second axes may be perpendicular to one another and perpendicular to the longitudinal axis of the keel, or watercraft. That is, the first horizontal axis, second vertical axis and longitudinal axis of the keel, or watercraft, are orthogonally arranged with respect to one another. The first and second keels may include a first pivotable rudder, or hydroplane, and a second pivotable rudder. The first and second keels may include a first pivotable rudder, or hydroplane, a second pivotable rudder and third pivotable rudder.

The first pivotable rudders, or hydroplanes, may be located on a side portion of each keel. The first pivotable rudders, or hydroplanes, may be located on an outwardly facing side portion of each keel. The first pivotable rudders, or hydroplanes, may be located between the front and rear portion of each keel. The first pivotable rudders, or hydroplanes, may be pivotable about a horizontal plane relative to the longitudinal axis of the keel, or watercraft. The second pivotable rudders may be located at the rear portion of each keel. The second pivotable rudders may be pivotable about a vertical plane relative to the longitudinal axis of the keel, or watercraft. The second pivotable rudders may be located at the front portion of each keel. The second pivotable rudders may be pivotable about a vertical plane relative to the longitudinal axis of the keel, or watercraft.

The first and second keels may include a third pivotable rudder that is pivotable about a third axis that is perpendicular to the longitudinal axis of the keel, or watercraft. The third pivotable rudder may be located at the front portion of the keel. The third pivotable rudder may be pivotable about a vertical plane relative to the longitudinal axis of the keel, or watercraft.

The first pivotable rudders, or hydroplanes, may be biased towards their neutral position. The first pivotable rudders, or hydroplanes, may be biased towards a position where the longitudinal axis of each rudder, or hydroplane, is substantially parallel to the longitudinal axis of the keel, or watercraft.

The second pivotable rudders may be biased towards their neutral position. The second pivotable rudders may be biased towards a position where the longitudinal axis of each rudder is substantially parallel to the longitudinal axis of the keel, or watercraft.

The third pivotable rudder may be biased towards its neutral position. The third pivotable rudder may be biased towards a position where the longitudinal axis of the rudder is substantially parallel to the longitudinal axis of the keel, or watercraft. The first and second keels may include one or more support wheels, the one or more support wheels being configured to provide support to the keels if the watercraft is operating on land. The one or more support wheels may be located on the lower portion of each keel. The one or more support wheels may be located between the fore end and aft end of each keel.

The one or more support wheels may be pivotable relative to the keel. The one or more support wheels may be pivotably connected to the keel. The one or more support wheels may be pivotable about a vertical axis, the vertical axis being perpendicular to the longitudinal axis of the keel, or watercraft. The one or more support wheels may be biased towards a position where the axis of rotation of the one or more support wheels is perpendicular to the longitudinal axis of the keel or watercraft. The rotational axis of the one or more support wheels is perpendicular to the vertical pivotal axis of the one or more support wheels. The one or more support wheels may be swivel wheels, or caster wheels.

The one or more support wheels may be sprung to support the weight, or at least a portion of, the weight of the keel or watercraft. The one or more support wheels may be at least partially located within each keel. The keel may include one or more chambers, each chamber being configured to receive at least a portion of the one or more support wheels therein. The one or more support wheels may be configured so that their outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of each keel. The one or more support wheels may include one or more braking devices, the one or more braking devices being operable to exert a braking force on the wheels to prevent rotation thereof.

The second pivotable rudders may include a first wheel, the first wheel being configured to provide support to the keel if the watercraft is operating on land. In this arrangement the first wheel may be configured to provide rolling support to the keel if the watercraft is operating on land. The first wheel prevents the lower portion of the keel contacting the ground. The first wheel is configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel. The first wheels may be rotatably attached to the second pivotable rudders. The first wheels may be attached to the lower portion of the second pivotable rudders. The first wheels may be at least partially located within the second pivotable rudders. Each second pivotable rudder may be a wheel. The second pivotable rudder may be a combined wheel and wheel housing. The wheel may be housed within a housing. The housing may at least partially surround the wheel. The wheel may be configured to provide support to the keel if the watercraft is operating on land. In this arrangement the wheel may be configured to provide rolling support to the keel if the watercraft is operating on land. The wheel prevents the lower portion of the keel contacting the ground. The wheel is configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel. The wheel may be pivotably attached to the keel. The wheel may be rotatably attached to the keel or housing. The wheel may be biased towards a position where its axis of rotation is perpendicular to the longitudinal axis of the keel or watercraft.

The first and second keels may include a second wheel, the second wheel being configured to provide support to the keel if the watercraft is operating on land. The second wheel may be located on the lower portion of the keel. The second wheel may be located towards the fore end, or front end, of the keel. The second wheels may be pivotable relative to the keels. The second wheels may be pivotably connected to the keels. The second wheels may be pivotable about an axis that is perpendicular to the longitudinal axis of the keels, or watercraft. The second wheels may be biased towards a position where the axes of rotation of the second wheels are perpendicular to the longitudinal axis of the keel or watercraft. The rotational axis of each second wheel is perpendicular to the vertical pivotal axis of each second wheel. The second wheel may be a swivel wheel, or caster wheel.

The second wheels may be at least partially located within each keel. Each keel may include a chamber, the chamber being configured to receive at least a portion of the second wheel therein. The second wheel may be configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel.

The second wheels may include one or more braking devices, the one or more braking devices being operable to exert a braking force on the wheel to prevent rotation thereof. The second wheels may be a part of the third pivotable rudders, the second wheels being configured to provide support to the keel if the watercraft is operating on land. In this arrangement the second wheels may be configured to provide rolling support to the keel if the watercraft is operating on land. The second wheels prevent the lower portion of the fore end of the keel contacting the ground. The second wheels are configured so that the outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel. The second wheels may be rotatably attached to the third pivotable rudders. The second wheels may be attached to the lower portion of the third pivotable rudders. The second wheels may be at least partially located within the third pivotable rudders. Each third pivotable rudder may be a wheel. The third pivotable rudder may be a combined wheel and wheel housing. The wheel may be housed within a housing. The housing may at least partially surround the wheel. The wheel may be configured to provide support to the keel if the watercraft is operating on land. In this arrangement the wheel may be configured to provide rolling support to the keel if the watercraft is operating on land. The wheel prevents the lower portion of the keel contacting the ground. The wheel is configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel. The wheel may be pivotably attached to the keel. The wheel may be rotatably attached to the keel or housing. The wheel may be biased towards a position where its axis of rotation is parallel to the tiller of the third pivotable rudder.

The wheel may be sprung to support a portion of the weight of the keels or watercraft. The second wheels may be spherical wheels. The spherical wheels may rotate in any direction relative to the keel. The spherical wheels may be biased towards a position where the axis of rotation of each spherical wheel is perpendicular to the longitudinal axis of the keel or watercraft. The spherical wheels may be at least partially located within each keel. Each keel may include a chamber, the chamber being configured to receive at least a portion of the spherical wheel therein. The spherical wheel may be configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel. The spherical wheel may include one or more braking devices, the one or more braking devices being operable to exert a braking force on the wheel to prevent rotation thereof. The wheel may be sprung to support a portion of the weight of the keels or watercraft.

The first and second keels may include a third wheel, the third wheel being configured to provide additional support to the keel if the watercraft is operating on land. The third wheel may be located on the lower portion of the keel. The third wheel may be located towards the fore end, or front end, of the keel. The third wheel may be located either side of the second wheel on each keel. The third wheel may be located behind the second wheel of each keel. That is, the third wheel may be located closer to the aft end, or stern end, of the keel than the second wheel on each keel.

The third wheel may be fixed relative to the keel. The third wheel may have a horizontal axis of rotation that is perpendicular to the longitudinal axis of the keel, or the watercraft. The third wheel may be at least partially located within the keel. Each keel may include a chamber, each chamber being configured to receive at least a portion of the third wheel therein. The third wheel may be configured so that its outermost surface, or ground contacting surface, protrudes from the lowest portion of the lower portion of the keel. The third wheel may be configured such that it protrudes from the lowest portion of the lower portion of the keel less than the second wheel. That is, the second wheel protrudes further from the lower portion of the keel than the third wheel. The third wheel may include one or more braking devices, the one or more braking devices being operable to exert a braking force on the third wheel to prevent rotation thereof.

The keel system may include a control apparatus, the control apparatus being operable to control the movement of the first and second keels between the stowed position and the deployed position, or positions.

The control apparatus may be configured to work against the biasing force that biases the first and second keels towards the stowed position.

The first and second keels may be independently operable from one another. The control apparatus may be configured to operate each keel individually.

The control apparatus may be configured to operate the keels jointly. The first and second keels may be operable jointly. The control apparatus may be configured such that the first and second keels move in synchronisation. The first and second keels may be operable in synchronisation. The control apparatus may be configured such that the first and second keels are both deployed and stowed in synchronisation. In this

arrangement both keels are stowed and deployed at the same time.

The control apparatus may be configured to operate such that when the first keel is stowed, the second keel is deployed, and vice versa.

The control apparatus may be engagable with the first and second keels to control the movement of the keels between the stowed position and the deployed position, or positions.

The control apparatus may comprise a linkage mechanism. The linkage mechanism may be connected between the first and second keels and a control arm of the control apparatus. The control arm may be pivotably connectable to the watercraft. The control arm may be pivotably connectable to the keel pivot support member.

The control arm may be connectable to the watercraft via a universal joint. The control arm may be connectable to the keel pivot support member via a universal joint. The control arm may engage the keel pivot support member via a universal joint.

The linkage mechanism may be pivotably connected to the first and second keels.

The linkage mechanism may include two push rods and two control plates. Each push rod may be pivotably connected to a control plate and each control plate may be pivotably connected to a keel.

The control apparatus may be configured to transfer a translational motion of at least a part of the linkage mechanism to a pivotal motion of the first and second keels. The control apparatus may be configured to transfer a vertical motion of at least a part of the linkage mechanism to a pivotal motion of the first and second keels.

The linkage mechanism may be configured to transfer a vertical motion of the push rods to a pivotal motion of the control plate and the first and second keels.

The control arm and linkage mechanism may be configured to allow the first and second keels to be deployed and stowed at the same time.

The control arm and linkage mechanism may be configured such that the first keel is stowed when the second keel is deployed and vice versa. The control arm may be a rocker arm, the rocker arm being configured to operate the linkage mechanism such that the first keel is deployed when the second keel is stowed and vice versa. The rocker arm may be connected to the watercraft via a universal joint.

The control apparatus may also be operable to control the movement of the first pivotable rudders, or hydroplanes. The control apparatus may also be operable to control the movement of the second pivotable rudders. The control apparatus may also be operable to control the movement of the third pivotable rudders. The control apparatus may also be operable to control the movement of the first and second pivotable rudders. The control apparatus may also be operable to control the movement of the first and second pivotable rudders simultaneously. The control apparatus may also be operable to control the movement of the first, second and third pivotable rudders simultaneously.

The control apparatus may be operable to control the movement of the first pivotable rudders, or hydroplanes, from a first neutral position to a second active position. In the first neutral position the longitudinal axis of the first pivotable rudder, or hydroplane, is substantially parallel to the longitudinal axis of the keel, or watercraft. In the second active position longitudinal axis of the first pivotable rudder, or hydroplane, is angled downwards with respect to the longitudinal axis of the keel, or watercraft.

The control apparatus may be operable to control the movement of the second pivotable rudders from a first neutral position to a second active position. In the first neutral position the longitudinal axis of the second pivotable rudder is substantially parallel to the longitudinal axis of the keel, or watercraft. In the second active position the longitudinal axis of the second pivotable rudder is substantially non-parallel, or angled, with respect to the longitudinal axis of the keel, or watercraft.

The control apparatus may be operable to control the movement of the third pivotable rudder from a first neutral position to a second active position. In the first neutral position the longitudinal axis of the third pivotable rudder is substantially parallel to the longitudinal axis of the keel, or watercraft. In the second active position the longitudinal axis of the third pivotable rudder is substantially non-parallel, or angled, with respect to the longitudinal axis of the keel, or watercraft.

The linkage mechanism may also be connected to the first pivotable rudders, or hydroplanes. The linkage mechanism may also be connected to the second pivotable rudders. The linkage mechanism may also be connected to the third pivotable rudders. The linkage mechanism may also be connected to the first and second pivotable rudders. The linkage mechanism may also be connected to the first, second and third pivotable rudders. The linkage mechanism may be pivotably connected to the first pivotable rudders, or hydroplanes. The control plates may also be pivotably connected to the first pivotable rudders, or hydroplanes. In this

arrangement the linkage mechanism is configured to transfer a vertical motion of the push rods to a pivotal motion of both the first and second keels and the first pivotable rudder, or hydroplane, thereof via the control plate.

The linkage mechanism may further include steering arms. The steering arms may be connected between the control plates and the second pivotable rudders. The steering arms may be connected between the control plates and the third pivotable rudders. Each steering arm may be pivotably connected to the control plate. The steering arms may be horizontally arranged with respect to the keel or watercraft. The steering arms may be pivotably connected to the second pivotable rudders. The steering arms may be pivotably connected to the second pivotable rudders via a tiller. The tiller may be pivotably connected to the steering arm and directly fixed to the second pivotable rudder.

The steering arms may be pivotably connected between the control plates and the third pivotable rudders. Each steering arm may be pivotably connected to the control plate. The steering arms may be horizontally arranged with respect to the keel or watercraft. The steering arms may be pivotably connected to the third pivotable rudders. The steering arms may be pivotably connected to the third pivotable rudders via a tiller. The tiller may be pivotably connected to the steering arm and directly connected to the third pivotable rudder.

Where the linkage mechanism is connected to a keel, first pivotable rudder, or hydroplane, and second pivotable rudder, operation of the control apparatus to move the keel from its stowed position, or mid- deployed position, to its maximum deployed position also moves both the first and second pivotable rudders from their neutral position to their active position. This is as a result of the linkage mechanism being connected to the keel, first pivotable rudder, or hydroplane, and second pivotable rudder.

Where the linkage mechanism is connected to a keel, first pivotable rudder, or hydroplane, second pivotable rudder and third pivotable rudder, operation of the control apparatus to move the keel from its stowed position, or mid-deployed position, to its maximum deployed position also moves the first, second and third pivotable rudders from their neutral position to their active position. This is as a result of the linkage mechanism being connected to the keel, first pivotable rudder, or hydroplane, second pivotable rudder and third pivotable rudder.

Where the linkage mechanism is connected to the keel, first pivotable rudder, or hydroplane, second pivotable rudder and third pivotable rudder, operation of the control apparatus to move the keel from its stowed position to its deployed position also moves the first, second and third pivotable rudders from their neutral position to their active position. This is as a result of the linkage mechanism being connected to the keel, first pivotable rudder, or hydroplane, second pivotable rudder and third pivotable rudder. The operation of the control apparatus and linkage mechanism may have two stages: the first stage may move the keel from its stowed position to its deployed position, this may be, for example, directional stability of the watercraft; the second stage may be further movement of the keel towards a maximum deployed position, in which the control apparatus and linkage mechanism moves the first, second and third pivotable rudders from their neutral position to their active position. In this arrangement the keel are lowered initially for directional stability and then, with further lowering of the keel, the rudders move from their neutral position to their active position.

The control apparatus may be operable to control the movement of the retractable hydroplane between the stowed position and the deployed position. The control apparatus may be engagable with the retractable hydroplane to control the movement of the retractable hydroplane between the stowed position and the deployed position. The linkage mechanism may be connected between the retractable hydroplane and a control arm of the control apparatus.

The push rod may be pivotably connected to the control plate and the control plate may be configured to be in contact with the retractable hydroplane.

The control apparatus may be configured to transfer a vertical motion of at least a part of the linkage mechanism to a pivotal motion of the retractable hydroplane. The linkage mechanism may be configured to transfer a vertical motion of the push rod to a pivotal motion of the control plate and retractable hydroplane.

Embodiments of the second aspect of the invention may include one or more features of the first aspect of the invention or its embodiments.

Similarly, embodiments of the first aspect of the invention may include one or more features of the second aspect of the invention or its embodiments.

According to a third aspect of the invention there is provided a watercraft comprising a keel according to the first aspect of the invention. The watercraft may be a non-displacement craft. The watercraft may be a hovercraft, including hovercraft or air cushion vehicle mainly or solely operated on land, naviplane, shallow draught watercraft such as paddle driven vessels, airboats or fan boats, jon boats, air thrust boats or air propeller powered boats.

The watercraft may be human powered or propelled by machinery. Embodiments of the third aspect of the invention may include one or more features of the first or second aspects of the invention or its embodiments.

According to a fourth aspect of the invention there is provided a watercraft comprising a keel system according to the second aspect of the invention.

The watercraft may be a non-displacement craft. The watercraft may be a hovercraft, including hovercraft, or air cushion vehicle mainly or solely operated on land, naviplane, shallow draught watercraft such as paddle driven vessels, airboats or fan boats, jon boats, air thrust boats or air propeller powered boats.

The watercraft may be human powered or propelled by machinery.

Embodiments of the fourth aspect of the invention may include one or more features of the first, second or third aspects of the invention or its embodiments.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompany drawings, in which:- Figure 1 is a side view of a keel for a watercraft, keel system and a watercraft according to the present invention;

Figure 2a is a front view of the keel and watercraft of figure 1 ;

Figure 2b is a rear view of the keel and watercraft of figure 1 ;

Figure 3 is a side view of an alternate embodiment of the keel and watercraft;

Figure 4 is a further alternate embodiment of the keel and watercraft;

Figure 5 is a partial end view of an alternate embodiment of the keel of figure 1 ;

Figure 6 is a partial perspective side view of an alternate embodiment of the keel of figure 1 ;

Figures 7a and 7b are end views of an alternate embodiment of the keel and watercraft of figure 1 with both keels deployed and only one keel deployed;

Figure 8 is a side view of a linkage mechanism of a control apparatus engaged with a rotatable hydroplane;

Figure 9 is a top view of a linkage mechanism of a control apparatus engaged with a rotatable rudder;

Figure 10a is a front view of a control apparatus of the keel; Figure 10b is a partial side view of the linkage mechanism of the control apparatus of figure 10a;

Figure 1 1 is an end view of an alternate control apparatus of the keel;

Figure 12 is a side view of an alternate embodiment of the keel, keel system and watercraft of figure 1 ;

Figure 13a is a partial side view of a wheel and rudder system located on the rear portion of the keel;

Figure 13b is a partial top view of the wheel and rudder system of figure 13a; Figure 14a is a partial side view of a wheel located on the lower portion of the keel;

Figure 14b is a partial side view of an alternate wheel arrangement located on the lower portion of the keel;

Figure 15 is a is a partial perspective side view of an alternate

embodiment of the keel of figure 1 ;

Figure 16 is a side view of the keel of figure 15; and

Figure 17 is a cross-sectional end view of a linkage mechanism of a control apparatus engaged with a retractable hydroplane.

Figures 1 , 2a and 2b illustrate two keels 10 for a watercraft 12 (an example of a keel for a watercraft and a keel system for a watercraft). In the embodiment illustrated and described here, the watercraft 12 is a shallow draught watercraft such as an airboat, fan boat, jon boat, air thrust boat or air propeller powered boat. However, it should be appreciated that the keels 10 may be used with any suitable type of watercraft, such hovercraft or air cushion vehicles mainly or solely operated on land, shallow draught watercraft such as paddle driven vessels, airboats or fan boats, jon boats, air thrust boats or air propeller powered boats.

The watercraft 12 includes a first keel 10a and a second keel 10b. The first keel 10a is pivotably connected to the starboard side 12a of the watercraft 12 and the second keel 10b is pivotably connected to the port side 12b of the watercraft 12. The keels 10a, 10b may be made from wood, marine plywood, steel, aluminium, glass reinforced plastic or composite material or combination thereof.

The watercraft also includes an air fan 13. The air fan 13 being used supply propulsion to the watercraft 12.

As illustrated in figures 2a and 2b, the keels 10a, 10b are moveable between a stowed position, as illustrated in figure 2b, and a deployed position, as illustrated in figure 2a.

When the keels 10a, 10b are in the stowed position, the keels 10a, 10b are located above the lowest portion of the hull 12c of the watercraft 12. In this arrangement, when the watercraft 12 is in use, the keels 10a, 10b are above the waterline 14 of the watercraft 12.

When the keels 10a, 10b are in the deployed position, the keels 10a, 10b are located below the lowest portion of the hull 12c of the watercraft 12. In this arrangement, when the watercraft 12 is in use, the keels 10a, 10b are below the waterline 14 of the watercraft 12.

As illustrated in figure 1 , the keels 10a, 10b are pivotably connected to the watercraft 12 at the bow end 12d thereof. The keels 10a, 10b are pivotably connected to the watercraft 12 via two keel pivot support members 16. Each keel pivot support member 16 is located on a side portion 12h of the watercraft 12. The keel pivot support members 16 may be detachably removable from the watercraft 12.

The keel pivot support members 16 allow the keels 10a, 10b to pivot about a pivot point 16a. The keels 10a, 10b pivot about a horizontal pivot axis 16b of the pivot point 16a. The keels 10a, 10b are arranged to run from the keel pivot support members 16 along the sides 12a, 12b of the watercraft 12.

The keels 10a, 10b are substantially planar members. The keels 10a, 10b have a front portion 10c and a rear portion 10d. The front portion 10c of each keel 10a, 10b is pivotably connected to the pivot support members 16.

As illustrated in figure 1 , the keels 10a, 10b are generally U-shaped, with the front and rear portions 10c, 10d curving upwardly from the lower mid- portion 10e.

The watercraft 12 also includes two keel support housings 18. The keel support housings 18 provide support to the keels 10a, 10b as they pivot between the stowed and deployed positions. The keel support housings 18 are attached to the watercraft 12 between the bow end 12d and the stern end 12e. The keel support housings 18 support the rear portions 10d of the keels 10a, 10b. The keel support housings 18 are in the shape of collars (thrust collars) and allow the keels 10a, 10b to pass

therethrough.

The keels 10a, 10b have a longitudinal axis 10f that runs between the front portion 10c and rear portion 10d of the each keel 10a, 10b. The keels 10a, 10b are arranged such that the front portion 10c and the rear portion 10d of each keel 10a, 10b lie on the respective longitudinal axis 10f. In this arrangement the keels 10a, 10b are substantially planar members.

As illustrated in figure 1 , in the embodiment illustrated and described here, the keels 10a, 10b are a significant portion of the length of the watercraft 10. However, it should be appreciated that the keels 10a, 10b may be longer or shorter than the embodiment illustrated in figure 1.

As illustrated in figures 2a and 2b, the keels 10a, 10b are substantially rectangular in a cross section that is normal to the longitudinal axis 10f of the keels 10a, 10b. Although not illustrated here, the keels 10a, 10b may have a substantially V-shaped cross-sectional lower portion. That is, at least the lower mid-portion 10e of each keel 10a, 10b may extend to a point, the point facing downwards.

The keels 10a, 10b are biased towards the stowed position. In the embodiment illustrated and described here the keels 10a, 10b are spring biased. However, it should be appreciated that any suitable biasing means or devices could be used to bias the keels 10a, 10b towards the stowed position. The keel support members 18 include the spring biasing device. The spring biasing device is connected between each keel support member and each keel 10a, 10b. Figure 3 illustrates an alternate embodiment of the keel 10 and keel system 100. The keel 10' of figure 3 differs from the keel 10 of figures 1 and 2 in that it includes an extension portion 10g that extends towards the stern end 12e of the watercraft 12. The keel 10' of figure 3 also differs from the keel 10 of figures 1 and 2 in that each keel 10a, 10b has a rudder located at the rear portion 10d thereof, as described further below.

Figure 4 illustrates an alternate embodiment of the keel 10 and keel system 100. The keel 10" of figure 4 differs from the keel 10' of figure 3 in that it includes a hydroplane located on the outwardly facing side portion 10h thereof, as described further below.

With reference to figures 5 and 6, the keels 10a, 10b may include one or more protruding portions that protrude from the outwardly facing side surface 10h of each keel 10a, 10b. Figure 5 illustrates an embodiment of the keel 10 where the protruding portion 10i is a curved surface that curves outwards and away from the outwardly facing side surface 10h of each keel 10a, 10b. Figure 6 illustrates an embodiment of the keel 10 where the protruding portion is a hydroplane 20. In the embodiment illustrated and described in figure 6 the hydroplane 20 is fixed, non- moveable, with respect to the keel 10. The hydroplane 20 has a front portion 20a and a rear portion 20b. The rear portion 20b protrudes further from the outwardly facing surface of the keel 10 than the front portion 20a. As illustrated in figure 6, the hydroplane 20 initially tapers in a curved manner outwardly from the outwardly facing surface of the keel 10. The hydroplane 20 then extends linearly towards the rear portion 20b thereof. The hydroplane 20 is also angled "nose down". That is, the front portion 20a of the hydroplane 20 is lower than the rear potion 20b. In figures 5 and 6 the protruding portions are fixed relative to the keels 10a, 10b. In the embodiment illustrated in figure 4, each keel 10a, 10b includes a horizontally pivotable hydroplane 22 (an example of a first pivotable rudder, or hydroplane) and a vertically pivotable rudder 24 (an example of a second pivotable rudder), which is also illustrated in figure 3.

The horizontally pivotable hydroplane 22 is pivotable about a horizontal axis 22a. The horizontal axis 22a is arranged to be perpendicular to the longitudinal axis 10f of the keel 10, or the longitudinal axis 12f of the watercraft 12. The vertically pivotable rudder 24 is pivotable about a vertical axis 24a. The vertical axis 24a is arranged to be perpendicular to the longitudinal axis 10f of the keel 10, or the longitudinal axis 12f of the watercraft 12. In this arrangement the longitudinal axis of the keel 10a, 10b, or the longitudinal axis 12f of the watercraft 12 the horizontal axis 22a and the vertical axis 24a are orthogonal.

The horizontally pivotable hydroplane 22 is located on the outwardly facing surface 10h of the keel 10a, 10b and, in the embodiment illustrated and described here, is located around the mid-point of the keel 10/watercraft 12. The vertically pivotable rudder 24 is located at the rear portion 10d of the keel 10a, 10b. In the embodiment illustrated and described here, the vertically pivotable rudder 24 is essentially formed as part of the keel 10a, 10b. That is, the vertically pivotable rudder 24 is an extension of the keel 10a, 10b, following the same shape and lines of the keel 10a, 10b.

With reference to figures 8 and 9, the horizontally pivotable hydroplane 22 is biased towards its neutral position. In the neutral position the longitudinal axis 22b of the hydroplane 22 is substantially parallel to the longitudinal axis 10f of the keel 10a, 10b, or the longitudinal axis 12f of the watercraft 12. The hydroplane 22 may be spring biased towards its neutral position. The vertically pivotable rudder 24 is also biased towards its neutral position. In the neutral position the longitudinal axis 24b of the rudder 24 is substantially parallel to the longitudinal axis 10f of the keel 10a, 10b, or the longitudinal axis 12f of the watercraft 12. The rudder 24 may be spring biased towards its neutral position.

With reference to figures 7a to 9, the keels 10a, 10b include a control apparatus 26. The control apparatus 26 is operable to control the movement of the keels 10a, 10b between their stowed and deployed positions, as illustrated in figures 7a and 7b. In the embodiment illustrated and described here the control apparatus 26 operates as a rocker arm. That is, the control apparatus 26 operates such that when one keel 10a, 10b is in the deployed position, the other keel 10a, 10b is in the stowed position, and vice versa, as illustrated in figures 7a and 7b. However, depending on the desired use of the keels 10a, 10b or watercraft 12, the control apparatus 26 could be configured to allow joint deployment or stowage of the keels 10a, 10b. It should be appreciated that in an alternative arrangement, the keels 10a, 10b may be configured such that they are independently operable. In this arrangement the control apparatus 26 is configured to allow individual control of the keels 10a, 10b to control the movement between the stowed and deployed positions.

The control apparatus 26 is attachable to the watercraft 12 and is configured to work against the biasing forces of the keels 10a, 10b. The control apparatus 26 may be hand-operated, foot operated, or power assisted, as described below.

The control apparatus 26 is connected to each keel 10a, 10b via a control arm 26a and a linkage mechanism 26b. The linkage mechanism 26b is pivotably connected to the control arm 26a and the keels 10a, 10b. As described further below, the linkage mechanism 26b includes push rods 26c, control plates 26d and steering arms 26e. Each push rod 26c, control pate 26d and steering arm 26e operates on a single keel 10a, 10b. As illustrated in figures 7a and 7b, and described above, the control apparatus 26 operates as a rocker arm, such that when one keel 10a, 10b is in the deployed position, the other keel 10a, 10b is in the stowed position, and vice versa. The linkage mechanism 26b facilitates the movement of the keels 10a, 10b in this manner.

In addition to the control apparatus 26 being configured to control the operation of the keels 10a, 10b, the control apparatus 26 also controls the operation of the a horizontally pivotable hydroplane 22 and the vertically pivotable rudder 24.

Operation of the horizontally pivotable hydroplane 22 and the vertically pivotable rudder 24 is illustrated in figures 8 and 9. With reference to figure 8, the push rod 26c of the linkage mechanism 26b is pivotably connected to the control plate 26d. The control plate 26d is pivotably connected to the keel 10a, 10b. The control plate 26d is also pivotably connected to the horizontally pivotable hydroplane 22 and the steering arm 26e, and moves with the control plate 26d, directly attached, or on the same axle. With reference to figure 9, the steering arm 26e is pivotably connected to the vertically pivotable rudder 24. The steering arm 26e is pivotably connected to the vertically pivotable rudder 24 via a tiller 26f. The tiller 26f is pivotably connected to the steering arm 26e and fixed directly to the rudder 24. The control apparatus 26 also includes a keeper plate 26g to prevent the vertically pivotable rudder 24 from turning towards the hull 12c. As illustrated in figures 8 and 9, downward motion of the push rod 26c causes the control plate 26d to pivot (clockwise). Since the control plate 26d is pivotably connected to the keel 10a, 10b and directly connected to the horizontally pivotable hydroplane 22, the keel 10a, 10b is pushed downwards, rotating about pivot point 16a, and the hydroplane 22 pivots (clockwise) about its horizontal axis 22a (pivot point 22a'). At the same time, since the control plate 26d is pivotably connected to the steering arm 26e and the steering arm 26e is pivotably connected to the vertically pivotable rudder 24, via the tiller 26f, the steering arm 26e is moved forward towards the bow end 12d of the watercraft 12 and the rudder 24 pivots (anti-clockwise) about its vertical axis 24a (pivot point 24a').

Therefore, as the push rod 26c is pushed downwards by the control arm 26a of the control apparatus 26, three movements occur: (i) the keel 10a, 10b is moved downwards, pivoting (anti-clockwise) about pivot point 16a, (ii) the horizontally pivotable hydroplane 22 pivots (clockwise) about its horizontal axis 22 (pivot point 22a'), and the vertically pivotable rudder 24 pivots (anti-clockwise) about its vertical axis 24a (pivot point 24a'). It should be appreciated that figures 8 and 9 relate to the operation of the starboard side keel 10a. The operation of the port side keel 10b is identical to the starboard side 12a operation, only the pivoting directions will be opposite if viewed from the port side 12b of the watercraft 12.

It should be appreciated that in the embodiment illustrated and described here the keels 10a, 10b include both horizontally moveable hydroplanes 22 and vertically pivotable rudders 24. However, it should be appreciated that the keels 10a, 10b may include one or the other of the horizontally moveable hydroplanes 22 and vertically pivotable rudders 24.

Not illustrated, is the operation of vertically pivoted rudders at the fore end of the keels 10a, 10b. These would be arranged in a similar fashion to the rudder 24 in Figure 9 with the exception being that steering arm in Figure 8 would be pivotably connected to the control plate 26d where the push rod 26c is connected and lead towards the fore part of the keel 10c. The downward motion of the push rod 26c causes the control plate 26d to pivot (clockwise) since the control plate 26d is pivotably connected to the keel 10a, 10b. At the same time, since the control plate 26d is pivotably connected to the forward steering arm (not illustrated) and the steering arm is pivotably connected to the vertically pivotable forward rudder, via a tiller, the steering arm is moved aft towards the stern end 12e of the watercraft 12 and the forward rudder pivots (clockwise) about its vertical axis.

Figures 10a and 10b illustrate an alternate embodiment of the control apparatus 26. Figure 10a is a front view of the control apparatus 26'. As described further below, the solid lines indicate the stowed position of the keels 10a, 10b and the dashed lines indicate a position where the starboard side keel 10a is deployed and the port side keel 10b is stowed. The control apparatus 26' of figures 10a and 10b differs from the control apparatus 26 of figures 7a and 7b in that the control arm 26a' is pivotably connected to the watercraft 12 via a universal joint 28 and the control arm 26a' includes handles 27 for operation by a user. The handles 27, may also operate the control for air propulsion steering, having an

independently rotatable shaft within the column. As illustrated in figure 10a the control arm 26a' is able to pivot about a longitudinal axis 28a of the universal joint 28. In this arrangement the keels 10a, 10b are operable in the same manner as the control apparatus 26 of figures 7a and 7b, in that they are moveable between the stowed position and the deployed position. However, in addition to the ability of the control arm 26a' to pivot about the longitudinal axis 28a of the universal joint 28, the control arm 26a' is also capable of pivoting about a horizontal axis 28b of the universal joint 28. Figure 10b is a partial side view of the linkage mechanism 26b' of the control apparatus 26'. In the stowed position A, the handles 27 of the control apparatus 26' are pushed fully forward towards the bow end 12d of the watercraft 12. In this arrangement both keels 10a and 10b are in the stowed position A. As the handles 27 of the control apparatus 26' are pulled backwards towards the stern end 12e of the watercraft, the keels 10a and 10b move from the stowed position A towards a first deployed position B. As the handles 27 of the control apparatus 26' are pulled fully back towards the stern end 12e of the watercraft 12 the keels 10a and 10b move to a fully deployed position C. As illustrated in figure 10b, the control arm 26a' of the linkage mechanism 26b' is slidably engagable with the top portions of push pads 27c'. The push pads 27c' are directly connected to the tops of the keels 10a, 10b.

The ability of the control arm 26a' of the control apparatus 26' to be able to pivot about the longitudinal axis 28a of the universal joint 28 and the horizontal axis 28b of the universal joint 28 allows the keels 10a, 10b to be deployed jointly, such as when the handles 27 are pulled rearwards along the longitudinal axis 28a of the universal joint 28, and for the keels 10a, 10b to be deployed selectively, or alternatively, such as when the handles 27 are pivoted about the longitudinal axis 28a of the universal joint 28.

Figure 11 illustrates a further alternative embodiment of the control apparatus 26". Figure 1 1 is a rear view of the control apparatus 26". In this arrangement the movement of the keels 10a, 10b is illustrated by the dashed and solid lines. As illustrated, the keels 10a, 10b can be raised and lowered (stowed and deployed) via the foot operated pedals 50.

The control apparatus 26" of figures 1 1 differs from the control apparatus 26 of figures 7a and 7b and the control apparatus 26' of figures 10a and 10b in that it is foot-operated and the control arm 26a" is pivotable about a pivot point 26"c. The operation of the control apparatus 26" is otherwise very similar to the operation of the control apparatus 26 of figures 7a and 7b.

Figure 12 illustrates an alternate embodiment of the keel 10 and keel system 100. Figure 12 illustrates the keels 10a', 10b' being used with a hovercraft watercraft 12'. Operation of the keels 10a, 10b of the hovercraft 12' is essentially identical to previous embodiments. The main difference between the keels 10a' and 10b' of the figure 12 embodiment is that the keels 10a' and 10b' include a number of support wheels. For clarity, the same reference numbers have been used for components that are common to all embodiments of the keels 10 and keel system 100. In terms of operation of the keels 10a', 10b', the keels are operable to be deployed to a position that the lower portions thereof are located below the skirt 15 of the hovercraft in use, as illustrated in figure 12.

With reference to figures 12, 13a and 13b, each second pivotable rudder 24' includes a first wheel 30. The first wheel 30 is configured to provide support to the keel 10a', 10b' when the watercraft 12' is operated on land. The first wheel 30 prevents the lower portion 10e' of the keel 10a', 10b' contacting the ground. The first wheel 30 is configured so that its ground contacting surface protrudes from the lowest portion of the lower portion of the keel 10a', 10b'. As illustrated in figures 13a and 13b, the second pivotable rudder 24' is a combined wheel 30 and wheel housing 32. As illustrated, the housing 32 includes trailing brackets 32a and bracket extensions 32b. The wheel 30 is partially housed in the housing 32 and the outer surface 32a, 32b of the housing 32 provides the operating surface of the rudder. The combined wheel 30 and housing 32 (rudder 24') is biased towards its neutral position by tension springs 34. As above, the neutral position of the combined wheel 30 and housing 32 is such that its longitudinal axis 24b' is substantially parallel to the longitudinal axis of the keel 10a', 10b' or watercraft 12', or the rotational axis 30a of the wheel 30 is perpendicular to the longitudinal axis of the keel 10a', 10b' or watercraft 12'. Figures 13a and 13b also illustrate the steering arm 26e' and tiller 26f, the operation of which is the same as described above. Figures 14a and 14b are detailed views of the supporting wheels 36 of figure 12 and illustrate two variants for second supporting wheels 36 that are positioned towards the front portion 10c' of the keels 10a', 10b'. The second supporting wheels are configured to provide support to the keels 10a', 10b' if the watercraft 12' is being operated on land.

With reference to figure 14a, the second wheel 36 is pivotable with respect to the keel 10a', 10b'. In this embodiment the second wheel is a castor wheel and is pivotable about a vertical axis 36a that is perpendicular to the longitudinal axis 10f' of the keels 10a', 10b' or longitudinal axis 12f of the watercraft 12'. The second wheel 36 is also biased towards a position where the axis of rotation 36b of the wheel is perpendicular to the longitudinal axis 10f of the keels 10a', 10b' or longitudinal axis 12f of the watercraft 12'. The second wheel 36 may be at least partially located within a chamber 38 within each keel 10a', 10b'. The second wheel 36 is also sprung to support a portion of the weight of the keels or the craft. The second wheel 36 may also include a braking device (not illustrated). The braking device being configured to exert a braking force on the wheel 36 to prevent rotation thereof. With reference to figure 14b, the second wheel 36' may be a spherical wheel. The spherical wheel 36' may be able to rotate in any direction relative to the keel 10a', 10b'. The spherical wheel 36' is also biased towards a position where the axis of rotation 36b' of the wheel is perpendicular to the longitudinal axis 10f of the keels 10a', 10b' or longitudinal axis 12f of the watercraft 12'. The spherical wheel 36' is at least partially located within a chamber 38' of the keel 10a', 10b'. The second wheel 36' may also include a braking device (not illustrated). The braking device being configured to exert a braking force on the wheel 36' to prevent rotation thereof.

With reference to figure 14a, the second wheel 36 may include an associated third support wheel 40, the third support wheel 40 being configured to provide additional support to the keel 10a', 10b' if the watercraft 12' is operating on land. The third support wheel 40 is located beside the second support wheel 36, 36'. The third wheel 40 is fixed relative to the keel 10a', 10b' and has an axis of rotation 40a that is perpendicular to the longitudinal axis 10f of the keels 10a', 10b' or longitudinal axis 12f of the watercraft 12'. The third wheel 40 may also be located within a chamber 42 in the keel 10a', 10b'. The third wheel 40 is configured so that its ground contacting surface protrudes from the lower portion of the keel 10a', 10b'. The third wheel 40 is configured such that it protrudes from the lower portion of the keel 10a', 10b' less than the second wheel 36, 36'. That is, the second wheel 36, 36' protrudes further from the lower portion of the keel 10a', 10b' than the third wheel 40. The third wheel 40 also includes one or more braking devices (not illustrated). The one or more braking devices being operable to exert a braking force on the third wheel 40 to prevent rotation thereof.

The third wheel 40 may also by sprung to support a portion of the weight of the keels or the craft.

Figures 15 to 17 illustrate an alternate embodiment of the keel 10 and keel system 100. Figures 15 to 17 illustrates a retractable hydroplane 22'. The retractable hydroplane 22' is configured to be moveable from a stowed position to a deployed position, as illustrated in figure 17. The retractable hydroplane 22' is spring biased to its stowed position. As illustrated in figures 15 and 16 the retractable hydroplane 22' is pivotably connected to the keels 10a, 10b. The retractable hydroplane 22' pivots about a pivot axis 23. The pivot point 23a is located towards the front portion 22a' of the retractable hydroplane 22'. The retractable hydroplane 22' is arranged to be pointed "nose down", i.e. the front portion 22a' of the retractable hydroplane 22' is positioned lower than the rear portion 22b' of the retractable hydroplane 22'. In use, if the pushrod 26c is lifted above the neutral position, the retractable hydroplane 22' remains in the stowed position. It is spring biased to remain stowed and is only deployed when the pushrod 26c moves below the "neutral position", thus activating the control plate 26d. The pushrod 26c is not mechanically connected to the control plate 26d. The pushrod 26c is arranged to engage with the control plate 26d by impinging thereon to cause the rotation (or pivoting) thereof. The control plate 26d has a pivot point 29 (or pivot axis 29) outboard of the pushrod 26c, which may be parallel to the retractable hydroplane 22' or parallel to the longitudinal axis of the keels 10a, 10b or watercraft 12. This is the only fixing to the keels 10a, 10b. The control plate 26d will impinge on a different part of the inboard side of the retractable hydroplane 22' due to a difference in the angle of the retractable hydroplane 22' and the keel 10a, 10b itself. A set of guides 31 (inboard of the slot 31 a) maintain the correct angle of the retractable hydroplane 22' as it translates outwards, pivoting around the forward end. Therefore, the distance by which the retractable hydroplane 22' is deployed is dependent on the distance the push rod 26c is moved downwards. Retaining stops (not illustrated) prevent the retractable hydroplane 22' from being deployed to the extent that it may suffer undue forces.

Therefore, the retractable hydroplane 22' will only be deployed when activated by the pushrod 26c, during a turn. It will be retracted when the watercraft 12 is travelling in a straight line when there is no differential between the distance the keels 10a, 10b are deployed; and when the keels 10a, 10b are in the stowed position.

With reference to figures 1 and 2, the operation of the keel 10 and keel system 100 will now be described. The keels 10a, 10b are designed to improve the manoeuvring

characteristics of watercraft, including non-displacement craft, for example air-boats, hovercraft and variations thereof. The keels 10a, 10b are vertically retractable and depth adjustable longitudinal keels, which may extend for all or part of the underwater length of the watercraft 12. The keels 10a, 10b may be operated in shallow water. Variations may include relatively shallow, retractable bilge keels.

For directional stability, the keels 10a, 10b are lowered sufficiently to resist undesirable lateral forces caused, for example, by cross winds during forward motion or centrifugal force during turning of the watercraft 12. This resistive force is transferred to the main structure of the watercraft 12. The keels 10a, 10b are shaped such that any shock loads to the watercraft's structure on initial contact with the water surface are minimised. This may be accomplished by a shallow angle, narrow cross section, V-shaped cross section, or combination.

As the keels 10a, 10b are lowered initially, the increase in drag is minimised as described above. Increased depth will increase the drag, which can be harnessed as a steering force. As described further below, steering mechanisms may be added at one or both ends of the watercraft 12 to increase turning forces further. As described further below, hydroplaning arrangements (horizontal hydroplanes 22) may also be fitted to compensate for the additional buoyancy when the keels 10a, 10b are immersed and to allow the watercraft 12 to bank into a turn. Addition of the hydroplanes 22 increases the manoeuvring characteristics and efficiency by reducing drift and advance during turning and allows controlled turns to be undertaken at higher speeds. For non-displacement craft which may also traverse land, such as hovercrafts, the wheels 30, 36 of the keels 10a, 10b allow the keels 10a, 10b to remain deployed. As described above, the wheels 30, 36 may have a certain freedom to rotate in the vertical axis 24a, 36a. A steering and/or braking system may also be added to increase effectiveness on land. This allows the keels 10a, 10b to continue to improve directional control over land and prevent damage thereto.

With reference to figures 2a and 2b, when both keels 10a and 10b are deployed, the keels 10a, 10b allow the watercraft 12 to resist any lateral forces exerted thereon by, for example, cross winds, with only a modest increase in the watercraft's drag. This allows the keels 10a, 10b to be effective in shallow water depths. Furthermore, when both keels 10a and 10b are deployed, the buoyancy of the keels 10a, 10b resists any heeling, or rolling, of the watercraft 12. If the watercraft 12 is heeled by an external force, the hull 12c is immersed on the low side. The buoyancy of the immersed keel 10a, 10b and the lack of buoyancy of the non-immersed keel 10a, 10b causes an up thrust, or a "righting moment" of the hull 12c. This arrangement of keels 10a, 10b reduces "rolling" of the watercraft 12 in a rough sea, as the additional up thrust from the differential buoyancy is exerted on alternating keels 10a, 10b.

With reference to figures 2a and 2b, the keels 10a, 10b are also used to assist in the turning of the watercraft 12. By lowering (deploying) one keel 10a, 10b and lifting the other keel 10a, 10b a turning force is caused by the differential in drag on either side of the watercraft 12.

It is generally regarded that a vessel's pivot turn for turning, is

approximately one third of the distance from forward during normal forward motion without other forces. Vessels generally steer by operating rudders or by turning the propulsion on a vertical axis. The result is to move the stern in the opposite direction to that required.

Therefore, while longitudinal keels will resist lateral (sway) and yawing forces which improve directional stability, if they extend a significant distance aft of the pivot point, they will impair the turning effect of the crafts own steering. By fitting active or passive steering arrangements, this problem can be mitigated whilst retaining the benefit of directional stability, especially at high speed. With reference to figures 3 and 4, the vertically pivotable rudder 24 operates by redirecting the flow of air or water flowing thereover, causing a turning or yawning force. Similarly, the horizontally pivotable hydroplane 22 operates by redirecting the flow of air or water flowing thereover, causing an upward or downward thrust. If the hydroplane 22 is set "nose down", i.e. the leading edge of the plane is below the pivot point 22a' (and the trailing edge is therefore above the pivot point 22a'), a downward force is exerted when water flows over the hydroplane 22. This can be utilised to counteract up thrust caused by an increase in buoyancy. By adding hydroplanes to the keels 10a, 10b, a banking or inward roll force can be exerted during turning. This assists with the turning of the watercraft 12.

With reference to figure 3, for turning, only the inside rudder 24 may operate: this is more effective as it pivots away from the watercraft 12. This turning force is augmented by a differential in depths of keels 10a, 10b, which would lift the outer keel 10a, 10b. If lifted clear of the water, the rudder 24 would have no effect. The lower keel 10a, 10b on the inside will have the rudder 24 submerged to a greater distance, increasing its effective area.

With reference to figure 4, the hydroplane 22 is fitted just above the operational waterline level 14 of the keel 10a, 10b, as it is only required to be submerged during turning. This reduces drag under normal conditions when providing directional control and stability. If both keels 10a, 10b are immersed further, the hydroplane 22 only has a drag effect over its surface area. If a turning force is required, and the rudders 24 are supplemented with a differential of keel depths, the inside keel 10a, 10b is lowered. This results in increased buoyancy, combined with the reduction of buoyancy of the raised keel 10a, 10b on the outboard side, causing a tendency for the craft to heel outwards, which is undesirable. By immersing the inside keel hydroplane 22 and operating a nose down attitude this serves the two fold purpose of increasing drag and exerting a downward force on the inside keel 10a, 10b. The imbalance of buoyancy is thus eliminated. By increasing the nose down angle, the downward force is increased, resulting in the watercraft 12 banking in to the turn, such as an aircraft or motorcycle.

With reference to figure 5, the standard construction of the keel may be modified above the dashed centre horizontal line 17 to provide a fixed or passive steering system. The upper edge has been curled outwards from the outwardly facing surface of the keel 10a, 10b. There are no moving parts on the keel 10a, 10b; increased immersion with forward movement deflects the flow of water. The flow of water is deflected away from the watercraft 12, pushing the stern and assisting the turn. In this way, more effective use can be made of the differential of immersion. This also increases drag on the lower (inner most) side. Another benefit is that this allows the keels 10a, 10b to extend along most of the length of the watercraft 12, improving directional stability and control, yet still allow steering when deployed. Consequently, to be effective, the keels 10a, 10b can operate at lesser depth, only increasing to any extent for higher speed turns.

With reference to figure 6, the dashed line indicates the normal waterline 14 for the keel 10a, 10b to be effective for directional purposes. At this depth, the fixed hydroplane 20, in the "nose down" attitude is clear of the water and does not affect the hydrodynamics of the keel 10a, 10b. If a large wave makes contact with the hydroplane 20, the downward force will be counteracted by the increased buoyancy from the immersion of the keel 10a, 10b. The hydroplane 20 is shaped to increase downwards force gradually with immersion. If the keel 10a, 10b is lowered to the full extent, indicated by the dotted line 19 above the hydroplane 20, the flow of water will pull the keel 10a, 10b downwards as the flow of water over the full area of the hydroplane will exert a greater force than the added buoyancy, if the watercraft 12 is moving forward. This downward force will increase with speed. The keel 10a, 10b illustrated in figure 6 would be lowered for a turn to the starboard side 12a. The watercraft 12 would be heeled to the starboard side 12a by the hydroplane 20 and therefore lean into the turn. This allows the watercraft 12 to make tighter turns at higher speeds and with a relatively small increase in draught. This also significantly reduces the drift of the watercraft 12 during the turn. On smaller watercraft, this may be operated by the pilot moving their body weight into the turn, also termed kinaesthetic steering as used on small hovercraft. As described above and with reference to figures 7a and 7b, by exerting a downward force on one keel 10a, 10b (inside keel for turning), the rocker assembly of the control arm 26a lifts the outer keel 10a, 10b by the same distance. With reference to figures 8 and 9, the pushrods 26c of the linkage mechanism 26b augment the turning and banking forces by operating the hydroplanes 22 and rudders 24, as described above. Downward force on the pushrods 26c causes the pushrod to move downwards and move the control plate 26d. As described above, the control plate 26d, which is fixed by a pivot to the keel 10a, 10b, rotates clockwise. As this is the starboard side 12a and is being pushed down, the desired effect is a banked turn to starboard. The steering arm 26e is pulled forward, causing the rudder 24 to be turned for a starboard turn, as illustrated in figure 9. The hydroplane 22 is directly coupled to the control plate 26d, or to the same axle. It is rotated clockwise into a "nose down" attitude which, with forward motion, will cause the keel 10a, 10b to be pulled lower in the water. The increased depth will also cause increased drag on one side of the watercraft 12, assisting the turn. With reference to figure 9, the arrows 44 depict a turn to starboard. The steering arm 26e is pulled forward, causing the rudder 24 to deflect the flow of water. The steering arm 26e operates in tension only (such as rope). The keeper plate 26g is fitted to prevent the rudder 24 from hitting the sides of the watercraft's hull 12c. For amphibious watercraft, this may also take the form of a caster wheel, spring biased in the fore and aft direction, with the pivot point 24a' being the swivel of the caster wheel.

As described above and with reference to figures 12 to 14b, variations may be made to the keels 10a, 10b to allow for the keels 10a, 10b to be effective when traversing land as well as over water. The amphibious watercraft 12' uses supporting wheels 30, 36. In order to avoid damage of making landfall at an oblique angle due to a sudden change of heading, the wheels 30, 36 allow rotation about the vertical axis 24a, 36a. The wheels 30, 36 are placed such that they would be, or as close as practicable to being, the first point of contact when making landfall. The tension springs 34 of figure 13b bias the wheel 30 in the fore and aft direction (longitudinal axis 24b'). The bracket extensions 32b are shaped to improve water flow when the wheel 30 is immersed and becomes a rudder in the water.

The aim of the present invention is to improve directional control and stability of shallow draught and non-displacement watercraft during forward motion and to provide a substantial improvement in turning by considerably reducing the turning diameter. By doing so, the craft will be more efficient. The apparatus may be utilised as a supplementary or emergency steering system for deeper draught vessels.

The underwater area of the keels 10a, 10b is primarily longitudinal and only sufficiently deep enough to affect the manoeuvring characteristics as described above. The keels 10a, 10b can, therefore, be used in shallow waters. This arrangement is different from keels used on sailing vessels as the underwater area is primarily vertical and consequently cannot be used in shallow waters due to the increased draught. Also, sailing vessel keels are not designed specifically to improve directional stability nor assist in turning. The purpose of a sailing vessel keel is to reduce the deliberate leeway caused by the force of wind on the sails. Applications of the present invention envisaged include non-displacement craft, such as hovercraft, including hovercraft mainly or solely operated on land, shallow draught watercraft such as paddle driven vessels, airboats or fan boats.

By improving directional control, a watercraft can operated more efficiently as less corrective rudder movements are required to maintain course. In addition, as the magnitude of the rudder angle is also reduced, efficiency is increased as the main propulsive effort is to drive the watercraft forward and not to correct for yawing. Another characteristic of shallow draught and non-displacement watercraft is the increase in bodily drift and advance caused by centrifugal force when turning, compared with a deeper draught vessel. This can be quite considerable and, if not sufficiently anticipated by the coxswain or pilot, may lead to an

unfavourable situation.

By operating the keels 10a, 10b as an additional steering system, the advance of the turn is reduced. This increases efficiency as tighter turns may be performed at higher speeds. As described above, where two keels are used, an imbalance of drag can be utilised to create a turning force by operating the keels at different depths. Maximum turning force will be experienced with inboard keel at maximum depth (causing maximum drag) and the outboard keel lifted clear (zero drag in the water). By operating the keels at different depths, the turning effect will be augmented by the addition of a steering system which is operated by this differential. A steering system may also be fitted at the forward end of the keel.

By building a steering system in to the keels, the keels 10a, 10b may be deployed along the full length of the watercraft 12, thereby increasing their effectiveness at a much shallower draught. The addition of hydroplanes 22 operated by the differential in immersion will assist in "banking" the watercraft into a turn. These may be active; or passive hydrofoils/hydroplanes. This overcomes the issue of when two keels 10a, 10b are utilised to create a turning force, the differential in buoyancy will cause a moment pushing the watercraft 12 to lean outwards in a turn. If two keels 10a, 10b are deployed at the same depth and the watercraft 12 is heeled over due to external forces, such as wind or waves, the increase in immersion, and consequently buoyancy, on the lower side will cause a righting moment. For watercrafts which may spend some time in deeper waters, a variation in the form of retractable bilge keels may be used. The differential of distance of deployment of the keels 10a, 10b can be used to actively operate a steering system and/or hydroplanes 22. The keels 10a, 10b are fitted with sufficiently strong fittings such that the lateral resistance forces can be transferred to the hull 12c or structure of the watercraft 12. The fore and aft spring biased swivel caster wheels 30, 36 can be utilised as the steering system on water as well as on land. Likelihood of damage is reduced by having the keels 10a, 10b spring biased in the retracted position, this being a "fail safe" position. This fail safe position may be augmented by the inherent buoyancy. A braking effect will be experienced if both keels 10a, 10b are deployed to the full extent. This property is of benefit where reverse thrust on the watercraft's main propulsion is limited and in case of an emergency when a higher rate of deceleration is required.

As described above, for smaller watercraft, a direct mechanical linkage connected to the pilot's controls operates deployment/retraction of the keels 10a, 10b and, in conjunction with intuitive kinaesthetic steering, operates the keels 10a, 10b for steering. Mechanised arrangements are required for larger watercraft. If fitted with a suitable braking arrangement, with application of braking force proportional to the downward force exerted, this system will operate on land and water. If lateral movement is desired, for example a hovercraft moving down a beach to the water, the keels 10a, 10b may be retracted during operation, thereby still retaining desirable manoeuvring characteristics.

The keels 10a, 10b and the keel system 100 incorporating the keels 10a, 10b are designed such that they may be retrofitted to existing watercraft. No modifications are required to be made to the underwater hull, air cushion and propulsion by retrofitting the keels 10a, 10b or keel system 100.

When the keels 10a, 10b and the keel system 100 incorporating the keels 10a, 10b, complete with support wheels 30, 36, 40 or combination thereof, are fitted to a hovercraft or air-cushion vehicle, they may be used to provide rolling support to the craft when on land so that the craft may be pushed, pulled or towed either by the craft's own forward propulsion only or by an external propulsive force provided by, for example, a land based vehicle. This obviates the need to inflate the air cushion, thereby saving the operation of the engines required to inflate the air cushion. Therefore, this will save fuel, reduce running hours on the air cushion fan engines and may be a contingency in the event of a mechanical failure.

Another case where underwater keels improve handling characteristics of shallow draught and non-displacement craft is when conducting an alteration of course. The reduced "presence" in the water leads to the craft being unable to conduct turns at high speed without excessive bodily drift and advance in the turning diameter. The keels 10a, 10b and keel system 100 obviate or mitigate the above- referenced problems identified with known keels or keel systems.

Modifications and improvements may be made to the above without departing from the scope of the present invention. For example, although the keels 10a, 10b have been illustrated and described above as being pivotably connectable to the watercraft 12. It should be appreciated that the keels 10a, 10b may be translatably connected to the watercraft 12. In this arrangement the keels 10a, 10b may, for example, may be linearly translated or rotated between the stowed position and the deployed position.

Also, although the keels 10a, 10b have been illustrated and described above as being located on the outer sides of the watercraft 12, it should be appreciated that the keels 10a, 10b may be located between the hulls of the multi-hulled watercraft, or on the underside of the watercraft. Furthermore, although the keel system has been illustrated and described above as comprising two keels, it should be appreciated that the keel system may include two or more keels, or a plurality, of keels.

Also, although the specific description illustrates and describes the use of two keels, it should be appreciated that the present invention in its broadest sense relates to a single keel and the keel system may include a single keel.

Claims

1. A keel system for a watercraft comprising:

a second keel, wherein the second keel is configured to be connectable to the watercraft and moveable between a stowed position and at least one deployed position.

2. A keel system according to claim 1 , wherein the first and second keels are pivotably connectable to the watercraft.

3. A keel system according to claim 1 or claim 2, wherein the first and second keels are configured to be connectable towards the bow end of the watercraft.

4. A keel system according to any preceding claim, wherein the keel system includes a keel pivot support member, the keel pivot support member being attachable to the bow end of the watercraft and the first and second keels being pivotably connectable to the keel pivot support member.

5. A keel system according to any preceding claim, wherein the first keel is connectable to the starboard side of the watercraft and the second keel is connectable to the port side of the watercraft.

6. A keel system according to any preceding claim, wherein the first and second keels are substantially planar members.

7. A keel system according to any of claims 4 to 7, wherein the first and second keels have a front portion and a rear portion, the front portion of each keel being pivotably connected to the keel pivot support member.

8. A keel system according to any preceding claim, wherein the keel system further includes two keel support housings, the keel support housings being attachable to the watercraft and providing support to each keel as each keel moves between the stowed position and the deployed position.

9. A keel system according to claim 7 or claim 8, wherein the keel support housings supports the rear portion of the keel.

10. A keel system according to any preceding claim, wherein the first and second keels are biased towards the stowed position.

1 1. A keel system according to any preceding claim, wherein the first and second keels are configured such that, when the keels are in the stowed position, the keels are located above the lowest portion of the hull, or hulls, of the watercraft and when the keels are in the deployed position, the keels are located below the lowest portion of the hull, or hulls, of the watercraft.

12. A keel system according to any preceding claim, wherein the first and second keels include one or more hydroplane or rudder portions that protrude from the outwardly facing surface of each keel.

13. A keel system according to claim 12, wherein the one or more hydroplanes or rudders are pivotable with respect to the keels.

14. A keel system according to claim 13, wherein the first and second keels include a first pivotable hydroplane, the first pivotable hydroplane being pivotable about a first horizontal axis that is perpendicular to a longitudinal axis of the keel, or longitudinal axis of the watercraft.

15. A keel system according to claim 13 or claim 14, wherein the first and second keels include a second pivotable rudder, the second pivotable rudder being pivotable about a second vertical axis that is perpendicular to a longitudinal axis of the keel, or longitudinal axis of the watercraft.

16. A keel system according to any of claims 13 to 15, wherein the first and second keels include a third pivotable rudder, the third pivotable rudder being pivotable about a second vertical axis that is perpendicular to a longitudinal axis of the keel, or longitudinal axis of the watercraft

17. A keel system according to any of claims 14 to 16, wherein the first pivotable hydroplanes are located on an outwardly facing side portion of each keel and are pivotable about a horizontal plane relative to the longitudinal axis of the keel, or watercraft.

18. A keel system according to any of claims 14 to 17, wherein the second pivotable rudders are located at the rear portion of each keel and are pivotable about a vertical plane relative to the longitudinal axis of the keel, or watercraft.

19. A keel system according to any of claims 16 to 18, wherein the third pivotable rudders are located at the forward portion of each keel and are pivotable about a vertical plane relative to the longitudinal axis of the keel, or watercraft.

20. A keel system according to any of claims 13 to 19, wherein the first pivotable rudders and the second pivotable rudders are biased towards their neutral position.

21. A keel system according to any of claims 16 to 19, wherein the first pivotable rudders, the second pivotable rudders and the third pivotable rudders are biased towards their neutral position.

22. A keel system according to any preceding claim, wherein the first and second keels include one or more support wheels, the one or more support wheels being located on the lower portion of each keel and configured to provide support to the keels if the watercraft is operating on land.

23. A keel system according to claim 22, wherein the one or more support wheels are pivotably connected to the keel such that the one or more wheels pivot about a vertical axis, the vertical axis being

perpendicular to the longitudinal axis of the keel, or watercraft.

24. A keel system according to claim 22, wherein the one or more support wheels are biased towards a position where the axis of rotation of the one or more support wheels is perpendicular to the longitudinal axis of the keel, or watercraft.

25. A keel system according to any of claims 22 to 24, wherein the one or more support wheels are at least partially located within a chamber in each keel.

26. A keel system according to any of claims 22 to 25, wherein the one or more support wheels include one or more braking devices, the one or more braking devices being operable to exert a braking force on the wheels to prevent rotation thereof.

27. A keel system according to any of claims 22 to 26, wherein the one or more support wheels are sprung to support at least a portion of the weight of the watercraft.

28. A keel system according to any of claims 16 to 27, wherein the second pivotable rudders and/or the third pivotable rudders include a first wheel, the first wheel being configured to provide support to the keel if the watercraft is operating on land.

29. A keel system according to any preceding claim, wherein the first and second keels include a second wheel located towards the fore end of the keel, the second wheel being configured to provide support to the keel if the watercraft is operating on land.

30. A keel system according to claim 29, wherein the second wheel is pivotably connected to the keels.

31. A keel system according to claim 29 or claim 30, wherein the second wheels are biased towards a position where the axes of rotation of the second wheels are perpendicular to the longitudinal axis of the keel, or watercraft.

32. A keel system according to any of claims 29 to 31 , wherein the second wheels are at least partially located within a chamber in each keel.

33. A keel system according to any of claims 29 to 32, wherein the second wheels include one or more braking devices, the one or more braking devices being operable to exert a braking force on the wheel to prevent rotation thereof.

34. A keel system according to claim 29, wherein the second wheels are spherical wheels.

35. A keel system according to claim 34, wherein the spherical wheels are biased towards a position where the axis of rotation of each spherical wheel is perpendicular to the longitudinal axis of the keel, or watercraft.

36. A keel system according to claim 34 or claim 35, wherein the spherical wheels are at least partially located within a chamber in each keel.

37. A keel system according to any of claims 34 to 36, wherein the spherical wheels include one or more braking devices, the one or more braking devices being operable to exert a braking force on the wheel to prevent rotation thereof.

38. A keel system according to any of claims 34 to 37 wherein the spherical wheels are sprung to support at least a portion of the weight of the watercraft.

39. A keel system according to any of claims 29 to 38, wherein the first and second keels include a third wheel, the third wheel being configured to provide additional support to the keel if the watercraft is operating on land.

40. A keel system according to claim 39, wherein the third wheel is located adjacent the second wheel and is configured such that it protrudes from the lowest portion of the lower portion of the keel less than the second wheel.

41. A keel system according to claim 39 or claim 40, wherein the third wheel includes one or more braking devices, the one or more braking devices being operable to exert a braking force on the third wheel to prevent rotation thereof.

42. A keel system according to any of claims 39 to 41 , wherein the third wheel is sprung to support at least a portion of the weight of the watercraft.

43. A keel system according to any preceding claim, wherein the keel system includes a control apparatus, the control apparatus being operable to control the movement of the first and second keels between the stowed position and the deployed position, or positions.

44. A keel system according to claim 43, wherein the control apparatus is attachable to the watercraft.

45. A keel system according to claim 43 or claim 44, wherein the control apparatus comprises a linkage mechanism, the linkage mechanism being connected between the first and second keels and a control arm of the control apparatus and being configured to transfer a vertical motion of at least a part of the linkage mechanism to a pivotal motion of the first and second keels.

46. A keel system according to claim 45, wherein the control arm is pivotably connectable to the watercraft.

47. A keel system according to claim 45, wherein the control arm is connectable to the watercraft via a universal joint.

48. A keel system according to any of claims 45 to 47, wherein the linkage mechanism is pivotably connected to the first and second keels.

49. A keel system according to claim 48, wherein the linkage mechanism includes two push rods and two control plates, each push rod being pivotably connected to a control plate and each control plate being pivotably connected to a keel.

50. A keel system according to any of claims 45 to 49, wherein the control arm and linkage mechanism is configured to allow the first and second keels to be deployed and stowed at the same time.

51. A keel system according to any of claims 45 to 49, wherein the control arm and linkage mechanism is configured such that the first keel is stowed when the second keel is deployed and vice versa.

52. A keel system according to claim 51 , wherein the control arm is a rocker arm, the rocker arm being configured to operate the linkage mechanism such that the first keel is deployed when the second keel is stowed and vice versa.

53. A keel system according to claim 52, wherein the rocker arm is connected to the watercraft via a universal joint.

54. A keel system according to any of claims 43 to 53, when dependent upon any of claims 15 to 42, wherein the control apparatus is operable to control the movement of the first pivotable hydroplane and the second pivotable rudder of each keel.

55. A keel system according to any of claims 43 to 54, when dependent upon any of claims 16 to 42, wherein the control apparatus is operable to control the movement of the first pivotable hydroplane, the second pivotable rudder and the third pivotable rudder of each keel.

56. A keel system according to claim 54 or claim 55, wherein the control apparatus is operable to control the movement of the first pivotable hydroplane from a first neutral position to a second active position and the second pivotable rudder from a first neutral position to a second active position.

57. A keel system according to claim 55 or claim 56, wherein the control apparatus is operable to control the movement of the first pivotable hydroplane from a first neutral position to a second active position, the second pivotable rudder from a first neutral position to a second active position and the third pivotable rudder from a first neutral position to a second active position.

58. A keel system according to any of claims 54 to 57, wherein the linkage mechanism is pivotably connected to the first pivotable hydroplane and operation of the linkage mechanism causes movement of the first pivotable hydroplane from a first neutral position to a second active position.

59. A keel system according to claim 58, wherein the linkage mechanism is pivotably connected to the second pivotable rudder and operation of the linkage mechanism causes movement of the second pivotable rudder from a first neutral position to a second active position.

60. A keel system according to any of claims 55 to 59, wherein the linkage mechanism is pivotably connected to the third pivotable rudder and operation of the linkage mechanism causes movement of the third pivotable rudder from a first neutral position to a second active position.

61. A keel system according to any of claims 12 to 60, wherein the one or more hydroplanes are retractable.

62. A keel system according to claim 61 , wherein the one or more hydroplanes are moveable between a stowed position and a deployed position.

63. A keel system according to claim 62, wherein in the stowed position the hydroplane is at least partially located within the keel, and in the deployed position the hydroplane protrudes from an outwardly facing surface of the keel.

64. A keel system according to any of claims 43 to 63, wherein the control apparatus is operable to control the movement of the hydroplane between the stowed position and the deployed position.

65. A watercraft comprising a keel system according to any of claims 1 to 64.

66. A watercraft according to claim 65, wherein the watercraft is a non- displacement craft.

67. A watercraft according to claim 66, wherein the non-displacement craft is a hovercraft, including hovercraft mainly or solely operated on land, or a shallow draught watercraft such as paddle driven vessels, airboats or fan boats.

68. A keel for a watercraft, wherein the keel is configured to be connectable to the watercraft and moveable between a stowed position and at least one deployed position.

69. A watercraft comprising a keel according to claim 68.

70. A watercraft according to claim 69, wherein the watercraft is a non- displacement craft.

71. A watercraft according to claim 70, wherein the non-displacement craft is a hovercraft, including hovercraft mainly or solely operated on land, or a shallow draught watercraft such as paddle driven vessels, airboats or fan boats.