Patent Description:
Watercraft with a catamaran arrangement (i.e. with two symmetrical hulls which are joined together) are well known in the art. However, when such watercraft are used in rough water conditions, the craft may have poor seakeeping, and be subject to large movements in response to waves. In order to improve seakeeping, small waterplane area twin hull (SWATH) vessels can be used. However, such crafts are typically sensitive to changes in loading of the watercraft, for example when being used to transport heavy equipment. This may cause the trim of the craft to be affected, and may make it impractical for such craft to carry large payloads.

Monohull boats are known to have improved response to changes in loading. The drag of monohull boats can be reduced by making the hull shape more slender (i.e. increasing its length relative to its width, or beam). Such boats may be provided with an outrigger which is used to stabilise the boat. Such a boat may be known as a "proa" configuration boat. However, such boats may have high drag in the water due to the outrigger, and reduced efficiency. <CIT> and <CIT> disclose various arrangements of boats with outriggers.

It is an aim of the present invention to at least partially address the problems noted above.

According to the present invention as claimed, there is provided a motorised outrigger stabilised watercraft comprising a main hull extending in a fore-aft direction, a single outrigger arranged to stabilise the main hull, extending substantially parallel to the main hull and spaced laterally from the main hull and at least one hydrofoil mounted at or proximate the stern of the main hull. This may provide good seakeeping, improved response to changes in loading, and low drag, resulting in improved fuel efficiency. The outrigger may also allow a more slender hull to be used, which may also reduce drag, whilst the presence of the outrigger may provide improved static stability even when a slender hull is used.

The hydrofoil is dynamically adjustable and arranged to apply a variable force to the main hull. This may provide improved response to changes in loading and improve seakeeping of the watercraft, and allow control of the trim of the watercraft.

Optionally, the outrigger is a small waterplane area hull. This may reduce drag whilst maintaining stability.

According to the invention, the outrigger comprises a first portion arranged to be submerged below the waterline during operation. This may provide buoyancy whilst avoiding a large increase in drag.

The outrigger comprises a joining portion joining the first portion to the watercraft. The joining portion has a width perpendicular to the fore-aft direction which is less than that of the first portion. The joining portion may also have a length which is shorter in the fore-aft direction than the first portion. This may provide a small waterplane area, which may reduce drag.

The outrigger further comprises a second portion arranged to float during operation. The joining portion joins the first portion to the second portion.

Optionally, the watercraft further comprises an arm connecting the second portion to the main hull.

Optionally, the first portion has substantially the same length as the second portion in the fore-aft (or front-rear) direction.

Optionally, the length of the outrigger parallel to the fore-aft direction is between <NUM>% and <NUM>% of the length of the main hull, preferably between <NUM>% and <NUM>% of the length of the main hull.

Optionally, the extent of the outrigger in the fore-aft direction is between the stern and a point <NUM>% of the total length of the main hull forward of the stern.

Optionally, the hydrofoil is mounted aft of the stern.

Optionally, the dynamically adjustable hydrofoil mounted at or proximate the stern of the main hull is arranged to be adjusted such that the hydrofoil supports between <NUM>% and <NUM>% of the total displacement of the vessel, preferably between <NUM>% and <NUM>% of the total displacement of the vessel.

Optionally, the hydrofoil comprises a main hydrofoil body and a trailing edge flap arranged to move relative to the main body to thereby vary the force applied to the main hull. This may provide improved control over the lift produced by the hydrofoil. In some arrangements, more than one trailing edge flap may be provided.

The angle of attack of the hydrofoil is adjustable to thereby vary the force applied to the main hull. This may provide improved control over the lift produced by the hydrofoil.

Optionally, the hydrofoil is retractable. This may prevent damage to the hydrofoil when it is not in use and/or during shallow water operation.

Optionally, the width of the hydrofoil is larger than the beam of the main hull.

Optionally, the hydrofoil is further joined to the outrigger. This may increase the lift of the hydrofoil and improve seakeeping.

Optionally, the hydrofoil is arranged to control the trim of the watercraft.

Optionally, the hydrofoil is arranged to compensate for changes in loading of the watercraft.

Optionally, the main hull comprises a plurality of hydrofoils.

Optionally, the outrigger further comprises at least one hydrofoil. This may provide improved control over roll of the watercraft.

Optionally, the hydrofoil located on the outrigger is dynamically adjustable and arranged to apply a variable force to the outrigger. This may allow the roll response of the watercraft to be adjusted.

Optionally, the hydrofoil located on the outrigger is located at or proximate the stern of the first portion.

Optionally, the hydrofoil located on the outrigger extends toward the main hull.

Optionally, the hydrofoil located on the outrigger is arranged to control roll of the watercraft.

Optionally, the main hull supports <NUM>% or more of the total static displacement of the watercraft, preferably <NUM>% to <NUM>% of the total static displacement of the watercraft.

Optionally, the outrigger supports <NUM>% or less of the total static displacement of the watercraft, preferably <NUM>% to <NUM>% of the total static displacement of the watercraft.

Optionally, the watercraft further comprises a control system arranged to dynamically adjust the hydrofoil. The control system may optionally comprise an inertial measurement unit.

Optionally, the watercraft further comprises a motorised propulsion device arranged to propel the watercraft, wherein the motorised propulsion device is positioned forward of the hydrofoil in the fore-aft direction.

The present invention will now be described, by way of non-limitative example only, with reference to the accompanying drawings, in which:.

The present invention relates to an outrigger stabilised watercraft. As shown in <FIG>, the watercraft comprises a main hull <NUM> and an outrigger <NUM>. The main hull <NUM> extends in a fore-aft direction, and the outrigger <NUM> extends substantially parallel to this direction, spaced laterally (i.e. separated in a direction perpendicular to the fore-aft direction) from the main hull <NUM>. The outrigger <NUM> is a single outrigger. That is, the watercraft has only one outrigger and does not have a second outrigger, as in the case of a trimaran. The main hull <NUM> and the outrigger <NUM> are joined by an arm <NUM>. The watercraft further comprises a hydrofoil <NUM> mounted at or proximate the stern of the main hull <NUM>, as shown in <FIG>. During operation, the hydrofoil <NUM> is submerged (i.e. below the waterline) so that flow around the hydrofoil causes a resultant lift force, which is in turn transmitted to the main hull <NUM>. The watercraft (and thus the main hull) may be used in a displacement mode, a semi-planing mode, or a fully planing mode, and may transition between these modes, depending, for example, on the speed of the vessel.

In the configuration shown in <FIG>, it will be noted that the hydrofoil is shown as mounted aft of the stern (i.e. aft of the transom, or the rear-most part of the main hull <NUM>). However, it will be understood that the hydrofoil <NUM> (which may be referred to as the main hull hydrofoil <NUM>) may also be located at a position near, but not at the rear-most part, (i.e. the stem) of the main hull <NUM>. For example, the hydrofoil may be located at a position in the rear <NUM>% of the main hull <NUM>. It will also be understood that the point at which the hydrofoil is mounted (i.e. attached) to the main hull <NUM> may be the same in the front-rear (i.e. fore-aft) direction as the position in the front-rear direction of the hydrofoil itself, or that these two locations may be offset from each other. For example, the hydrofoil <NUM> may be mounted to the main hull <NUM> using struts, which may extend vertically downwards, or at a different angle to the vertical.

In the arrangement shown in <FIG> (which is not according to the claimed invention), the outrigger has the form of a conventional displacement hull, in which the lower part of the outrigger hull is submerged, and the upper part of the outrigger hull is above the waterline. In other words, the hull of the outrigger <NUM> can be considered to act like a small displacement hull, being smaller than the main hull <NUM>. However, as will be described below, other arrangements of outrigger <NUM> are possible, such as the arrangement shown in <FIG>.

In the arrangement shown in <FIG>, the outrigger <NUM> has the form of a small waterplane area hull. The small waterplane area hull comprises a first portion <NUM> which is completely submerged during operation. This portion may be known as a "submarine" portion. The small waterplane area hull may further comprise a joining portion <NUM> joining the first portion to the rest of the watercraft. In particular, the joining portion <NUM> is a thin joining portion, having a width in the beamwise direction (i.e. the horizontal direction perpendicular to the fore-aft direction) that is smaller than that of the first portion <NUM>. That is, in the view shown in <FIG>, the width of the joining portion <NUM> is less than that of the first portion <NUM>. The joining portion may also have a length which is shorter in the fore-aft direction than the first portion. In some arrangements, the length of the joining portion may vary with height. During normal operation, the thin joining portion is at the waterline, which provides a small cross sectional area at the waterline. This provides the "small waterplane area" of this hull type.

The small waterplane area hull further comprises a second portion <NUM> which is above the waterline, and may float (during operation). The second portion <NUM> may come into contact with the water, and thus float, producing a righting moment, when the boat is at a large heel (i.e. list) angle. Such a large heel angle may occur due to wave motion, or during a turn in the direction which causes the main hull <NUM> to roll towards the outrigger <NUM>. The second portion is joined to the first portion by the joining portion, and the second portion may be joined to the rest of the watercraft by the arm <NUM>. It will also be understood that the second portion <NUM> may be omitted. When the second portion <NUM> is omitted, the joining portion <NUM> may be joined directly to the arm <NUM>.

As best seen in <FIG>, the first portion <NUM> of the outrigger and the second portion <NUM> of the outrigger may have substantially the same length as each other in the front-rear direction. Alternatively, in some arrangements, the lengths of the first portion <NUM> and the second portion <NUM> may be different to each other. For example, the first portion <NUM> may be longer than the second portion <NUM>. These relative lengths can be varied according to the desired volume of the first portion <NUM>, which may be chosen depending on the distance between the outrigger <NUM> and the main hull <NUM>.

Conventionally, small waterplane area hulls are typically used in vessels with a small waterplane area twin hull (SWATH) configuration, with two hulls of this type joined together. However, the present invention provides arrangements in which only the outrigger <NUM> has a small waterplane area hull, and the main hull <NUM> has a different hull form. For example, the configuration of the arrangement of outrigger stabilised watercraft shown in <FIG> has an outrigger <NUM> with a small waterplane area hull configuration, and a main hull <NUM> with a conventional hull.

The combination of a conventional hull <NUM> (such as a displacement hull, a semi-displacement/semi-planing hull, or a planing hull) with a small waterplane area outrigger may give particularly good stability and seakeeping, for example in rough water conditions, whilst allowing changes in loading (e.g. from cargo) to be accommodated without the trim or efficiency of the vessel being compromised. Further, this configuration, when combined with the hydrofoil <NUM> mounted at or proximate the stern of the main hull <NUM>, may give particularly good seakeeping due to the effect of the hydrofoil, whilst at the same time reducing fuel consumption due to the reduced drag associated with a small waterplane area hull outrigger. Further still, the use of an outrigger may allow the main hull to be longer than that of a conventional catamaran for a given construction area (i.e. amount of material used in the construction) or deck area, which may in turn reduce resistance and improve seakeeping.

It will be understood that all of the options and variations as set out below are equally applicable to the embodiments of hull and outrigger shown in <FIG> and <FIG>.

The main hull <NUM> may have a slender hull shape. In some arrangements, the outrigger <NUM> and hydrofoil <NUM> may allow the use of main hull shapes which, due to their slenderness (which can be measured by the ratio of length to displacement or length to beam) would otherwise be unstable and impractical to use. That is, the outrigger <NUM> and hydrofoil arrangement of the present invention may allow the reduced drag that such slender hull shapes provide, whilst providing increased stability and improved seakeeping.

In some arrangements, the hydrofoil <NUM> may be dynamically adjustable. In other words, the position of the hydrofoil when submerged in the water may be varied, such that it applies a variable force to the main hull <NUM>. This may allow yet improved seakeeping, and may allow the trim of the boat to be actively controlled, in response to, for example, changes in water conditions (e.g. waves) and/or changes in loading of the boat due to, for example, the cargo being carried.

During operation, the main hull hydrofoil <NUM> may typically support between <NUM>% and <NUM>% of the total displacement (i.e. weight of the vessel), and preferably between <NUM>% and <NUM>% of the total displacement of the vessel. It will be understood that, when a dynamically adjustable hydrofoil <NUM> is used, the proportion of the displacement of the vessel supported by the hydrofoil (i.e. the force applied to the main hull <NUM> by the hydrofoil <NUM>) may vary as the hydrofoil is dynamically adjusted. In some circumstances, the hydrofoil <NUM> may also provide a negative lift. For example, in some arrangements, the hydrofoil <NUM> at the stern of the main hull <NUM> may typically support between -<NUM>% and <NUM>% of the total displacement, depending on the water conditions.

In some arrangements, the hydrofoil <NUM> may comprise a main hydrofoil body and a trailing edge flap arranged to move relative to the main hydrofoil body. In this arrangement, the main hydrofoil may be fixed. The trailing edge flap may be moved relative to the main body to provide dynamic adjustment of the force applied to the main hull <NUM> by the hydrofoil <NUM>. Further, in some arrangements, multiple trailing edge flaps may be used on the hydrofoil <NUM> along its length (i.e. along the span of the hydrofoil). This may provide improved control over the force applied by the hydrofoil and thus over the displacement of the vessel carried by the hydrofoil <NUM>, by allowing the lift produced by the hydrofoil to be varied along its span. In particular this may allow roll and trim to be independently controlled.

Alternatively or additionally, the angle of attack of the hydrofoil <NUM> itself may be variable. In other words, the position (or angle) of the hydrofoil when submerged may be varied such that the force applied to the main hull <NUM> by the hydrofoil <NUM> changes.

In some arrangements, the hydrofoil <NUM> may be arranged so that it can move to a position out of the water when the vessel is in the water. For example, the hydrofoil may be arranged to rotate aft about a pivot point such that it is lifted out of the water. The hydrofoil may also be retractable into the main hull <NUM> or to a position near the main hull. In the retracted position the foil may preferably still be below the waterline, though a retracted position at or above the waterline is possible. This may allow the boat to be operated in shallow water even if the water depth is such that the hydrofoil cannot be used. This may also allow the hydrofoil to be protected when not in use (e.g. when the boat is berthed, moored or otherwise stored).

In some arrangements, the span of the hydrofoil <NUM> (i.e. the width as shown in <FIG>) may be larger than the beam (i.e. the width) of the main hull <NUM>. This may provide improved control over stability. In the arrangement shown in <FIG> and <FIG>, the hydrofoil <NUM> extends inboard of the main hull toward the outrigger. It will be understood that the hydrofoil may alternatively or additionally extend outboard of the main hull <NUM> (i.e. in a direction away from the outrigger <NUM>, and to the left in the view shown in <FIG> and <FIG>).

Further, in some arrangements, and as shown in <FIG>, the hydrofoil <NUM> may extend from the main hull <NUM> to the outrigger, and be joined to the outrigger <NUM>. In other words, the hydrofoil <NUM> may span between the main hull <NUM> and outrigger <NUM>.

In some arrangements, a plurality of hydrofoils may be mounted on the main hull. When more than one hydrofoil is present on the main hull, each hydrofoil may be used in any of the arrangements described above. For example, a plurality of hydrofoils may be mounted at or proximate the stern of the main hull. In such an arrangement, the hydrofoils may be mounted in the beamwise direction, with each hydrofoil being separately controllable (i.e. dynamically adjustable). In other arrangements, there may be a mixture of fixed and dynamically adjustable hydrofoils.

As shown in <FIG> and <FIG>, the outrigger may also comprise a hydrofoil <NUM>. That is, as well as the hydrofoil <NUM> provided on the main hull, a separate hydrofoil <NUM> (i.e. an outrigger hydrofoil) may be provided on the outrigger <NUM>. The outrigger hydrofoil <NUM> may be located at any suitable location on the outrigger. In some arrangements, the outrigger hydrofoil <NUM> may be located at or proximate the stern of the outrigger <NUM>. In other arrangements, the outrigger hydrofoil may be located at or proximate the midships position of, or the centre of gravity of, the watercraft. This may provide improved roll control of the watercraft.

As described above in relation to the main hull hydrofoil <NUM>, the angle of attack of the outrigger hydrofoil <NUM> may be controllable so as to vary the force applied to the outrigger by the outrigger hydrofoil <NUM>, and/or one or more trailing edge flaps may be provided on the outrigger hydrofoil <NUM>. It will be understood that the arrangement in <FIG> in which the hydrofoil <NUM> is also connected to the outrigger <NUM>, may also be considered as a main hull hydrofoil <NUM> and an outrigger hydrofoil <NUM> which are joined together. It will also be understood that arrangements are possible in which the main hull hydrofoil <NUM> extends to the outrigger <NUM>, and the outrigger hydrofoil <NUM> extends to the main hull <NUM>, such that there are two full width hydrofoils spanning between the main hull <NUM> and the outrigger <NUM>. Further, one of either of the main hull hydrofoil <NUM> and the outrigger hydrofoil <NUM> may span the full width of the vessel (and thus join the outrigger or main hull respectively), and the other may span only part of the width of the vessel, and not be joined to another component. Further still, additional hydrofoils may be added such that there are three or more hydrofoils. Such additional hydrofoils may be mounted to the main hull <NUM>, the outrigger <NUM>, or span between both the main hull and the outrigger.

The outrigger hydrofoil <NUM> may be of any suitable configuration. In the arrangements shown in <FIG>, the outrigger hydrofoil <NUM> is located inboard of the outrigger <NUM>. That is, the span of the outrigger hydrofoil <NUM> extends from the first portion of the outrigger <NUM> toward to main hull <NUM> in the beamwise direction. However, it will be understood that the hydrofoil outrigger <NUM> may also be provided on the outboard side of the outrigger <NUM> (i.e. extending in a direction away from the main hull <NUM>). The outrigger hydrofoil <NUM> may provide improved control over the attitude of the watercraft, in particular, the balance (roll) of the watercraft and the heave amplitude of the outrigger. In arrangements where the outrigger hydrofoil <NUM> extends and is joined to the main hull, the outrigger foil may carry some of the main hull weight, reducing the resistance of the vessel.

In some arrangements, one or both of the hydrofoils <NUM>, <NUM> may have an anhedral or dihedral arrangement. That is, the span of the hydrofoil may not be horizontal when in use, but rather be at an angle to the horizontal. In the case of a dihedral arrangement, the hydrofoil may have two parts which slope upward, and in the case of an anhedral arrangement, the hydrofoil may have two parts which slope downward.

The watercraft may further comprise a control system arranged to provide dynamic control of the position of the hydrofoil <NUM>, and where present, the outrigger hydrofoil <NUM>. As explained above, the angle of attack of the hydrofoil(s) may be controlled by the control system, and/or the angle of a trailing edge flap on one or more of the hydrofoil(s) may be controlled by the control system. The control may be optimised so as to control at least one of the trim of the watercraft, rotational motions of the boat (i.e. pitch, roll and yaw), translational motions of the boat (heave, sway and surge), and/or to compensate for changes in loading of the watercraft. The control system may be arranged to provide the control above automatically and/or in response to an input by a user. The control system may use an inertial measurement unit in order to measure the state of the vessel, and command the hydrofoils accordingly. The control system may use, for example, at least one of rudder angle, input steering angle, yaw angle from the inertial measurement unit, and velocity (e.g. from a GPS unit) in order to command the hydrofoils.

The upper surface of the arm <NUM> may be arranged so that it forms part of the deck of the vessel. For example, it may be continuous with the deck of the main hull. This may allow a larger usable deck space, providing for increased vessel capacity.

The outrigger <NUM> may be of any suitable length, but is typically between <NUM>% and <NUM>% of the length of the main hull <NUM>, and preferably between <NUM>% and <NUM>% of the length of the main hull <NUM>. The outrigger may be positioned so that it is located between the stern of the main hull <NUM> and a point <NUM>% of the total length of the main hull <NUM> forward of the stern.

It will be understood that the static displacement (i.e. weight) of the watercraft is carried by the main hull and the outrigger. In some arrangements, the main hull supports <NUM>% or more of the total static displacement of the watercraft, and preferably <NUM>% to <NUM>% of the total static displacement. Thus, in such arrangements, the outrigger may support <NUM>% or less of the total static displacement of the watercraft, and preferably <NUM>% to <NUM>% of the total static displacement. It will be understood that the proportions of the total static displacement carried by the main hull and the outrigger are not fixed, and may vary due to loading conditions (which may change due to changes in external load such as cargo, due to the use of fuel and stores, and due to the movement of the crew) and dynamically when the craft is travelling through water.

The watercraft is a motorised watercraft (i.e. a powerboat). In such an arrangement, the watercraft may be predominantly propelled by any suitable motorised propulsion system. For example, one or more propellers, water jets or pod drives may be located on the main hull <NUM>, in any suitable configuration. The type of propulsion system and location thereof may be chosen to take account of the position of the main hull hydrofoil <NUM> such that the hydrofoil and propulsion unit do not interfere with each other. In particular, in some arrangements, the propulsion system (and in particular, a propulsion device thereof) is positioned forward of the hydrofoil in the fore-aft direction, or level with the hydrofoil in the fore-aft direction. It will be appreciated that other arrangements with different relative positions of propulsion device and hydrofoil are also possible.

Further, an additional propulsion unit may be provided on the outrigger. Again, the propulsion unit on the outrigger may use any known suitable propulsion system. In arrangements with a propulsion unit on the outrigger (i.e. an additional propulsion unit), the additional propulsion unit may be used to provide extra propulsive force to propel the watercraft, and/or to provide additional manoeuvring capability (e.g. to act as a bow thruster).

The watercraft according to the present invention has been described as a monohull watercraft which is stabilised by an outrigger. However, it will be understood that the watercraft could also be considered to be an "asymmetric catamaran", with the main hull <NUM> and the outrigger <NUM> forming two hulls of a catamaran. It will be understood that the watercraft of the present invention incorporates the advantages of both monohull watercraft (which can readily accommodate changes in loading), and multi-hull watercraft, which may have improved seakeeping characteristics and reduced drag.

Claim 1:
A motorised outrigger stabilised watercraft comprising:
a main hull (<NUM>) extending in a fore-aft direction;
a single outrigger (<NUM>) arranged to stabilise the main hull, extending substantially parallel to the main hull and spaced laterally from the main hull; and
at least one hydrofoil (<NUM>) located at or proximate the stern of the main hull characterised in that the outrigger comprises:
a first portion (<NUM>) arranged to be submerged below the waterline during operation;
a joining portion (<NUM>) joining the first portion to the watercraft, the joining portion having a width perpendicular to the fore-aft direction which is less than that of the first portion; and
a second portion (<NUM>) arranged to float during operation, the joining portion joining the first portion to the second portion; and
wherein the angle of attack of the hydrofoil is dynamically adjustable and arranged to
apply a variable force to the main hull.