GB2397565A

GB2397565A - An aerofoil sailing craft

Info

Publication number: GB2397565A
Application number: GB0401477A
Authority: GB
Inventors: Jonathan Sebastian Howes
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-01-25
Filing date: 2004-01-23
Publication date: 2004-07-28
Also published as: GB0301831D0; GB0401477D0; WO2004067378A1

Abstract

A sailing craft has a bouyant body (1) carrying at least one aerodynamic surface (2,9) disposed to provide stability and control, a hydrodynamic surface assembly (6) and an aerofoil (7). Body (1) and hydrodynamic surface assembly (6) are connected by a rigid beam (3) such their running axes remain parallel irrespective of the orientation of the beam (3) with respect to the longitudinal axis of the body (1). The aerofoil (7) is supported by the beam (3) and has rotational freedom such that any significant force generated by the aerofoil (7) will pass below the centre of mass of the craft when in operation and ensure dynamic stability. In addition, the running attitude of the hydrodynamic surface assembly (6) is controlled by the aerodynamic surface (2,9).

Description

TITLE:SAILING CRAFT

DESCRIPTION

The invention relates to a wind powered craft of the form À:. which, when under way, disposes an inclined aerodynamic A. . surface to leeward of a hull or body and a hydrodynamic À. -- surface to windward of the same body, the body being supported À À À by the water at low speeds and in light winds and above the e-.

water surface by the member interconnecting the hydrodynamic À and aerodynamic surfaces when sufficient aerodynamic force is À.e À . developed.

Sailing craft of this general form have been proposed and occasionally constructed with varying success. One of the earliest uses of a lifting sail was by the aviation pioneer Percy Sinclair Pitcher in the 1890's. This vessel used the hull as the hydrodynamic surface and, in spite of some control problems, was reasonably successful. A similar but developed concept was "Objectif 100", a craft designed by a naval architect, Jean Marie Finot, and constructed in 1988. This comprised an inclined aerofoil rig attached to the hull by a rigid strut and hydrodynamic surfaces directly beneath the hull.

The full separation of hull, aerodynamic and hydrodynamic surfaces was proposed by J G Hagedoorm in 1971. This concept comprised a free flying kite to leeward, the line of which was coupled to a freely flying hydrodynamic kite operating just below the water surface and displaced to windward, the crew being suspended by the interconnecting line and clear of the water surface.

More conventional approaches to high speed sailing have found control problems when the craft involved have approached speeds where cavitation can occur. Since most craft use at least two hydrodynamic surfaces, either both for lateral resistance or one for resistance and one for steering, when À ..cavitation occurs, or when one of these surfaces loses contact À.

.with the water surface due to wave effects, directional control À - .e and stability is generally impaired or lost. À

À À.Work by the current inventor led to a configuration À À20 similar to that of Hagedoorn, but replaced the flexible line between the aerodynamic surface and the hull and between the À .hull and the hydrodynamic surface with a structurally stiff member, the hull being equipped with its own aerodynamic stabilising surfaces. This solved all deployment and hydrodynamic stability problems and allowed the craft to tack and gybe by rotating the member around the hull.

In this early version the aerodynamic surface comprised a wing pivoted at the end of the beam with its own aerodynamic stabilising surfaces, such that it always pointed towards the apparent wind direction, load being applied to the wing as a result of control inputs to the wing's own pitch control. The hydrodynamic surface was disposed at the other end of the beam and comprised a hooked, ventilated foil, which form tends to naturally follow the water surface and, due to ventilation of the suction face, generated force predominantly via pressure face loading and was thus far less prone to inconsistent behaviour as a result of cavitation than a more conventional foil section. The present invention relates to improvements to sailing craft of this latter kind.

According to a first aspect, the invention consists in a sailing craft comprising: a hydrostatically-supportable body which carries at least one aerodynamic surface disposed to provide stability and control about the pitch axis of the body when in operation; a rigid member connected to the body by a first bearing, having a first rotational axis which is À:. generally vertical when in operation, the member extending when Àe . in operation in a generally horizontal plane away from the À.

first bearing and carrying, close to the end of the member À À À À remote from the first bearing, a second bearing of having a À.

second rotational axis which is generally vertical when in À operation; a hydrodynamic surface assembly mounted on the À second bearing and below the member when in operation, the assembly being constrained to maintain its own normal running axis generally parallel to that of the body irrespective of the orientation of the member with respect to the longitudinal axis of the body; the member having a portion that extends beyond the first bearing, away from the hydrodynamic surface assembly, and that is angled above the horizontal plane when in operation; and an aerofoil supported by the portion and spaced from the first bearing, the aerofoil having rotational freedom such that any significant force generated by that aerofoil will pass below the centre of mass of the craft when in operation and ensure dynamic stability. Accordingly, should the craft leave the water surface entirely, the resulting angular acceleration of the craft will be such that the hydrodynamic assembly is accelerated back towards the water surface.

The terms 'vertical' and 'horizontal' refer to the orientation of the craft when in operation, viz: at low speeds or in light winds the body is supported by the water, in stronger winds or at higher speeds the body being supported by aerodynamic forces transmitted by the beam leaving the hydrodynamic surface assembly as the only point of water contact, in intermediate conditions the body is supported by a combination of hydrostatic, hydrodynamic and aerodynamic forces.

:. Preferably, the aerofoil has rotational freedom about a À.

third axis extending substantially from the centre of pressure of said aerofoil to beneath the centre of mass of the craft when À. À À

in operation, the axis lying close to a line which passes Àe through the centre of mass of the craft and which is generally À À . vertical when in operation. This third axis may substantially en..

À . intersect a line which passes through the centre of mass of the craft and which is generally vertical when in operation. In particular, it may be substantially coaxial with said first rotational axis of said first bearing. Furthermore, the aerofoil may have rotational freedom about an axis extending from substantially from the centre of pressure of the aerofoil and parallel to the transverse pitch axis of the aerofoil. The aerofoil assembly may be pivoted about its own pitch axis in conjunction with a yaw pivot, the axis of which generally intersects with the axis of the first bearing and below the centre of mass of the craft.

The aerofoil may form part of an aerofoil assembly including means for inducing rotational displacement about the bearing, the axis of which intersects with the first rotational axis of the first bearing which passes and below the centre of mass of the craft. Such means may be an aerodynamic control attached to that assembly.

As regards the hydrodynamic surface assembly, this may be surface piercing, i.e. the active hydrodynamic surface pierces the water surface and generally partially submerged during normal operation. In contrast, a submerged active surface is below the water surface and is generally supported from a parent structure by struts or the like, the primary purpose of which is support rather than generation of an hydrodynamic force.

The centre of mass of the craft may be longitudinally ee.e ahead of the aerodynamic centre of the craft so as to ensure stable operation. Similarly, at least one buoyant body and/or at À least one hydrodynamic surface may be disposed ahead of the Àe centre of mass, thereby to provide a pitching moment in Àe opposition to the nose-down pitching moment induced by the . À . aerofoil assembly during longitudinal acceleration when the craft is supported on the water surface. Combined buoyant, hydrodynamic elements may be used. Elements may also be disposed either side of the craft longitudinal axis, thereby to provide lateral stability during tacking and gybing manocuvres.

The hydrodynamic surface assembly may be provided with two hydrodynamic elements, one intended for each tack of the craft, and a rolling pivot, such that the hydrodynamic element designed for a given tack may be brought into service on that tack and the other hydrodynamic surface is lifted clear of the water surface, when on the same tack, by rolling of the assembly.

Furthermore, the hydrodynamic surface assembly may include an element that allows a vertical component of hydrodynamic force to be generated such that the running depth of the hydrodynamic surface may be regulated by changes to the incidence about the pitch axis.

In particular, incidence changes to the body of the craft induced by said at least one aerodynamic surface may be transmitted by the rigid member to the hydrodynamic surface assembly, thereby to change the incidence of said assembly and facilitating control of the running height of that assembly and allowing control of the vertical position of the point of action of the hydrodynamic forces with respect to the craft centre of mass thus generating a rolling moment component relative to the . body longitudinal axis in opposition to the rolling moment ^ generated by the aerofoil assembly. Advantageously, changes to the running height of the assembly allow changes in the area of the assembly that is active in the generation of hydrodynamic force. À

I * The aerofoil may comprise a wing with anhedral.

a, Additionally, the craft may comprise means for rotating the rigid member about said first rotational axis, thereby to vary the angle between the longitudinal axes of both the body and the hydrodynamic surface assembly, change the lines of action of the aerodynamic and hydrodynamic forces relative to the body axes and allow directional steering control. Advantageously, the body has an aerodynamic control surface deflectable in response to a directional control input to provide an aerodynamic moment complementary to the desired motion of the rigid member relative to the body.

According to a second aspect, the invention consists in a marine craft comprising a hydrodynamic surface assembly and at least one aerodynamic surface, wherein the running attitude of said hydrodynamic surface assembly is controlled by said at least one aerodynamic surface.

Such a marine craft may comprise means for transmitting the motion of said aerodynamic surface to said hydrodynamic surface assembly. Those means may comprise a rigid member connecting said aerodynamic surface to said hydrodynamic surface assembly. Advantageously, the hydrodynamic surface assembly includes an element configured, when in operation, to allow a vertical component of hydrodynamic force to be generated, thereby allowing the running depth of the hydrodynamic surface to be regulated by changes to the incidence about the pitch axis. In a preferred embodiment, the craft comprises a Abbe .'.. hydrostatically-supportable body, said aerodynamic surface being

-

mounted on said body. 4l.

À ' The various aspects of the invention improve the stability e. . of the vessel in the presence of an uneven water surface and provide means of stabilizing the aerodynamic surfaces and control of the hydrodynamic surfaces. Further specific problems solved by embodiments of this invention relate to the differing requirements for hydrodynamic surface area at low and high speed, the loss in performance due to excessive heeling to windward as speed and/or wind strength increase, control of the incidence and therefore power of the aerodynamic surface and directional control that reduces control forces as experienced by the crew.

Expressed differently, the present invention provides a sailing craft comprising a hull, or body, which carries aerodynamic surfaces disposed to provide stability and control about the pitch axis of the body. A beam which connects to this body by a bearing, the rotational axis of which is generally vertical and extends in a generally horizontal plane away from the bearing and carries, close to the end of this beam and displaced from the body bearing, another bearing of generally vertical axis on which, below the beam, is mounted a surface piercing hydrodynamic surface assembly that is constrained to maintain its own normal running axis generally parallel to that of the body irrespective of the orientation of the beam with respect to the longitudinal axis of the body. The extension of the beam beyond the body bearing and away from the hydrofoil assembly is angled above the horizontal plane and supports an aerofoil assembly, displaced from the body bearing, which is :'. provided with rotational freedom such that any significant . force generated by the aerofoil assembly will pass below the centre of mass of the craft when in normal use. In normal use ÀÀ the hydrofoil assembly is disposed to windward and the aerofoil assembly is disposed to leeward of the body.

A specific embodiment of the invention will now be À.,,' described by way of example with reference to the accompanying drawings in which: Figure 1 shows, in perspective, the general form and significant elements of the craft; Figures 2 to 5 show the balance of forces acting on the craft in steady operation over a range of speeds; Figures 6 and 7 show a preferred form of the hydrofoil assembly; Figure 8 illustrates one means of absorbing a range of aerodynamic force strengths and limiting heeling to windward; Figure 9 shows the method by which the foil area is varied for different running speeds; Figure 10 shows one preferred form of aerodynamic surface control and the preferred form of the attaching pivot of that surface; Figure 11 shows a preferred means by which the motion of the hydrofoil assembly is coupled to that of the body; Figure 12 is a schematic diagram of a preferred directional control; Figure 13 illustrates the concept of aerodynamic centre; Figures 14 and 15 illustrate the behaviour of a mechanical aerodynamic surface assembly pitch control; Figure 16 shows a sectional detail of a part of the aerodynamic surface assembly pitch control of figures 10, 14 and 15; and Figure 17 illustrates another means of controlling windward heeling moment.

Referring to Figure 1, the craft comprises a hull, or body (1), of a form conducive to hydrodynamic planing, that provides Àe À .accommodation for the crew and carries an aftward extension that supports aerodynamic stabilising and control surfaces providing À À control of the body pitch (2) and yaw (9) axes. The body is À hydrostatically-supportable, i.e. bouyant. The top of this body À À À . 25 supports a bearing (4) positioned close to the longitudinal À ...

À . position of the centre of gravity of the craft and of generally vertical axis on which is mounted a structurally stiff, i.e. rigid, member or beam (3) such that the beam may pivot above the body in a generally horizontal plane as indicated by the arrows (8).

At one end of this beam and displaced from the body, is a second bearing (5) of generally vertical axis that supports a hydrodynamic surface assembly (6) below the beam, the running axis of this assembly is mechanically constrained to remain generally parallel to that of the body at all times. The hydrodynamic surface assembly comprises a buoyant body (13) and a pair of hydrofoil surfaces (14). The extension of the other end of the beam (3) beyond the body bearing (4) is raised above the horizontal plane and carries a bearing assembly (10) which supports an aerodynamic surface assembly (7) and provides rotational freedom about an axis generally aligned with the major axis of the beam (3) adjacent to the point of attachment of the aerodynamic surface and also about the local pitch axis of the aerodynamic surface. This bearing assembly, in conjunction with the angle of the adjacent beam, constrains the line of action of any force of a magnitude such that it could, if incorrectly applied, destabilise the vessel, to pass below the centre of gravity of the craft and also, by means of a stabilising surface or surfaces (22), to align the chordwise . 20 axis of the aerodynamic surface assembly generally with the apparent wind axis. At the forward end of the body (1) are mounted two supporting members (11) that extend forward of the À À front of the body and laterally to each side, each of these members carries, at its outboard end, a buoyant body or float À 25 (12), the form of which is conducive to hydrodynamic planing. c

À., . Use of the vessel over an uneven water surface can result in frequent high speed contact with wave crests. Significant sideslip angles under these conditions can result in high lateral force being developed that can often destabilize the vessel and cause loss of control. In order to prevent the body of the vessel from impacting the water surface at a significant sideslip angle it is essential that the running axis of the hydrodynamic surface assembly be maintained in general alignment with the longitudinal axis of the body.

Use of the vessel over an uneven water surface or when speeds are such that the hydrodynamic behaviour is inconsistent, due to cavitation or other effects, is facilitated by the presence of only one point of water contact when the body is aerodynamically supported. Temporary disturbance of this single point of contact from a trimmed equilibrium condition merely results in a transient lateral acceleration which is corrected as the hydrodynamic surface re-enters the water.

In accordance with the first aspect of the invention, the aerodynamic force vector passes below the centre of gravity of the vessel. If, for any reason, the hydrodynamic surface assembly loses contact with the water surface, or suffers an interruption in its operation such that the hydrodynamic force is suddenly reduced, the aerodynamic force will generate an immediate unbalanced moment about the longitudinal axis of the . 20 body (rolling axis). If the aerodynamic force vector is below the centre of gravity this moment will tend to roll the vessel such that the hydrodynamic surface assembly is returned to, or À À . lowered further into, the water and stable operation is re À.

established. If the converse is permitted such that the À Àe À . 25 aerodynamic vector passes above the centre of gravity the À . hydrodynamic surface assembly will be rolled away from the water surface and a loss of control is likely to follow.

To provide for stable behaviour about the pitch axis, the longitudinal location of the centre of gravity is advantageously located ahead of the aerodynamic centre of the vessel. The aerodynamic centre is defined as that point about which, for a constant wind speed relative to the longitudinal axis of the ' body the aerodynamic pitching moment of the vessel is constant. I This is a well known aeronautical concept and is further clarified by reference to figure 13. The graph at the top of this figure shows three examples of variation of pitching moment (M) with incidence of the vehicle (a), the scale of a is approximate but typical of real values. A stable vehicle must respond to increasing incidence by generating a reduced nose-up pitching moment. By convention, nose-up moment is positive and so a stable response over the working range of incidence is indicated by a negative gradient, a response of this character is marked Stable on the figure. By changing the reference point about which the moment is evaluated the gradient of the working range of moment with incidence (designated in this case, but not exclusively in reality, by the linear portion of the curve) may be changed. An aft movement of the reference point results in the gradient becoming less negative and when the gradient is zero there is no pitching moment variation with : 20 incidence and the vehicle is neutrally stable, in this situation

the reference point coincides with the vehicle aerodynamic centre, also sometimes referred to as the "neutral point". If À À the reference point is moved still further aft the vehicle becomes unstable. The lower half of figure 13 depicts À. 25 diagrammatically movement of the reference point with respect to À e À. the aerodynamic centre for a vehicle, the reference point in this situation is the centre of inertial forces, the centre of gravity. The airflow is indicated by a feathered arrow to the left of the figure and is shown as impacting the vehicle at an angle such that a transient lift increment (AL) is generated. If the aerodynamic centre (ac) is behind the cg (reference point forward) by a distance +Xac, a moment increment, -AM is generated leading to a pitch acceleration to reduce the transient incidence, this response is marked 'stable'. In a similar manner, the remaining two diagrams show the effect of coincidence of ac and cg (neutral) and of placing the ac ahead of the cg (unstable)...DTD: Vessels of this form are vulnerable to pitchpole capsize at low speeds due to a combination of light weight and a point of application of forward thrust displaced above the centre of resistance. To prevent this it is preferable to supply a means of generating an additional hydrostatic or hydrodynamic or combined hydrodynamic and hydrostatic vertical force ahead of the beam body bearing (4). A preferred means of achieving this is by means of floats (12) displaced forward and laterally from the main body, these floats also provide lateral stability when tacking and gybing the vessel.

Another preferred means of resisting or preventing a pitchpole capsize is by application of a hydrofoil surface or :20 surfaces displaced forward of, or towards the front of the main À À . À . body of the vessel and, in any case, ahead of the centre of gravity of the vessel.

Figures 6 and 7 illustrate the preferred form of the hydrodynamic surface assembly. Figure 6 is a head on view and À. 25 figure 7 is a perspective view of this assembly. Figure 6 shows, A. À. from left to right, the method by which the assembly is rolled such that a hydrofoil surface designed for the current tack of the vessel is brought into service, this allows an asymmetric foil section to be employed. The three views, from left to right, represent starboard tack, a neutral condition that may be encountered in light winds or during manoeuvres and port tack respectively. This behaviour is explained by reference to figures 6 and 7 and is achieved by loading the assembly and allowing it to rotate about a generally longitudinal roll axis, on bearings (21) supplied for the purpose, until a stop (19) is encountered. The foils are of hooked form such that the root surface (15) can generate an upwards force component on immersion whereas the mid span (16) and tip (17) areas tend to develop a downwards vertical component, this results in the lo water surface generally settling in the hook region (20) such that the float (13) is clear of the water surface. At higher speeds, an auxiliary hydrofoil (18), in an approximately horizontal plane, is employed to provide sufficient vertical force to lift the assembly until this auxiliary hydrofoil is planing on the water surface, this allows the active hydrodynamic area to be reduced as the velocity through the water becomes closer to the apparent wind velocity. The useful range of values of this reduced area (17) has been found to be between 0.5% and 0.25% of the aerodynamic surface area although greater or lesser areas can be used with the possible loss of À..

À .some performance.

Figures 8 and 9 illustrate one preferred means of À . Àe preventing excessive heeling to windward. As aerodynamic force À:.

is increased with vessel speed, the aerodynamic surface is À. : 25 caused by its own stabilising surfaces to align its chordwise À. axis generally with the apparent wind axis. For a given true wind speed, at lower vessel speeds the aerodynamic force vector, denoted by Fal, is such that the projection of this vector towards the body passes well below the centre of gravity of the vessel, the corresponding hydrodynamic force vector, denoted by Fh1, intersects with the aerodynamic vector directly below the centre of gravity and the angle between these two vectors, l, is low indicating a low tension in the beam (3). At higher speeds the aerodynamic vector is rotated due to the smaller apparent wind angle and this results in the vector moving closer to the horizontal plane such that its projection towards the body passes more closely below the centre of gravity (Fa2). In order for equilibrium to be maintained the hydrodynamic vector must still intersect with the aerodynamic vector directly beneath the centre of gravity. To achieve this while generating the maximum possible aerodynamic and hydrodynamic forces it is advantageous to apply the hydrodynamic force at a point that is vertically displaced below the original point of action of Fh1, this is shown as Fh2. The angle, +2, is now increased indicating much greater tension within the beam without applying an unbalanced heeling moment. This is achieved by provision of an auxiliary hydrofoil surface (18) on the hydrodynamic surface assembly such that a change in body pitch angle will, via the beam (3) change the incidence angle of this auxiliary surface and so partially lift the hydrodynamic surface assembly above the mean water surface. Reference to the parallelogram of forces À À À, À. to the top right of the figure illustrates the typical magnitude of the force changes involved, Fa2 and Fh2 being, in this example, in excess of twice the magnitude of Fal and Fh1 although À À . À À both sets of forces are still in equilibrium with the weight of À À ..

the vessel and no unbalanced rolling moment is present.

Figure 9 illustrates the preferred means by which the incidence of the auxiliary hydrofoil surface is adjusted in accordance with the second aspect of the invention. The body aerodynamic pitch control (2) is moved such as to alter the steady running pitch angle of the body (1). This pitch angle motion is transmitted via the rigid beam (3) to the hydrofoil assembly (6) and hence to the auxiliary surface (18) causing a change in the angle of incidence, denoted by ah, of this surface, this, in turn causes a variation in the vertical force generated by this component and allows the active hydrodynamic surface to lift until the auxiliary surface planes on the water surface.

Another means of controlling excessive windward heeling is by means of an aerodynamic control surface applied to the aerodynamic surface assembly such that control about the local yaw axis of that assembly is provided. If this control is applied such that the aerodynamic surface assembly is yawed away from the true wind direction the two degrees of freedom provided by the bearing assembly (10) are such that the aerodynamic force vector is rotated both towards the horizontal plane and towards the forward longitudinal axis of the vessel. This both reduces the vertical (lifting) component of the force and increases the forward (thrust) component. This is shown diagrammatically by À...

À.20 figure 17 with the aerodynamic surface assembly at two positions À.designated Half and Elba. In position Half the assembly is .feathered into the apparent wind and incidence applied to it . generates a force indicated by Fatal. If the aerodynamic surface assembly yaw control (22) is deflected by an angle (e) to yaw À . À. À 25 the assembly away from the true wind the force generated by the À

. À..DTD: À. assembly is rotated toward the horizontal plane and further forward of the vertical axis of the vessel as indicated by Fan and the vertical component of the force is thus reduced and the driving component is increased.

The behaviour of the craft is described by reference to figures 2 to 5, the wind in these examples is on the port beam, i.e., the vessel is on the port tack. The following notation is employed in these figures: Fb1 Hydrostatic buoyant force applied close to the centre of the main body (1) Fb2 Hydrostatic buoyant force applied close to the location of the hydrodynamic surface assembly (6) Fa The aerodynamic force generated by the aerodynamic surface assembly Fh The hydrodynamic force generated by the hydrodynamic surface assembly cg The location of the centre of gravity (centre of mass) of the craft as a whole (rather than just the body); W The force due to the mass of the craft under the influence of gravity Theangle between the main body (1) and the beam (3) Vw The true wind velocity vector Vv The vessel velocity vector VA The apparent wind velocity vector free D The combined aerodynamic and hydrodynamic drag of the vessel À a.

À. Figure 2 shows, at left, a head on view of the craft a. almost at rest, a plan view of this condition is shown to the À Àe . right of this figure. There is no development of any significant aerodynamic force, the aerodynamic surfaces are at close to zero À À' À 25 incidence to the wind and are pointing directly into the true À a. .

wind as constrained by their stabilising surfaces. The vessel is almost wholly supported by hydrostatic forces.

In a similar manner to Figure 2, figures 3 to 5 show both head on and plan views of the craft operating at progressively higher speeds. Figure 3 illustrates the condition in which the support of the craft is shared between hydrostatic, hydrodynamic and aerodynamic forces, the beam angle, ó, is small relative to the angle achieved under full aerodynamic support and this relates directly to the need to overcome the high hydrodynamic resistance of hull contact with the water. The hydrodynamic surfaces are operating at a low speed when compared to the apparent wind speed as shown by the velocity triangle to the right of this figure, this results in a need for a large hydrodynamic area to avoid stalling of this surface while resisting the lateral component of the aerodynamic force, Fa and this is achieved by deeply immersing the active hydrofoil (14) and hence exposing more hydrofoil area to the flow. At very low speeds this happens naturally as there is insufficient dynamic pressure for the foil to overcome the weight induced loads, at intermediate speeds the mechanism described earlier in conjunction with figure 9 is employed and the spur (18 in figure 7) is maintained at low incidence by means of the aerodynamic body control (2 in figure 9). The resistance of the vessel in this configuration is typically dominated by the hull and this À.20 is indicated in figure 3 by the positioning of the drag vector À ..

À.close to the hull centreline.

Figure 4 shows the vessel operating at the point where the hull is just clear of the water surface. The line of action of aerodynamic force passes well below the centre of mass of the vessel and to achieve equilibrium it is necessary for the a..

a'' hydrodynamic surface assembly to provide a vertical lift component, the speed is increasing but is still significantly below the apparent wind speed and so the hydrodynamic surface is immersed to the level of the hook (20). The overall drag is reduced and the drag vector has moved away from the hull and towards the hydrodynamic surface assembly, correspondingly, the beam angle, ó, has increased.

Figure 5 illustrates the vessel operating close to its performance limits. The aerodynamic force vector is still below the vessel centre of gravity but by a smaller margin and the hydrodynamic surface is now running with the auxiliary hydrofoil (18) close to the water surface. The drag is now at a minimum relative to the other forces acting on the vessel and the beam angle, ó, is at the maximum steady state value. The vessel velocity is now at its greatest possible fraction of the apparent wind velocity.

A preferred means of controlling the pitch angle of the aerodynamic surface assembly and of providing the desired degrees of rotational freedom is shown in figures 10,14,15 and 16. The beam (3) is extended from outboard of the body bearing (4) initially as a beam curved above the horizontal plane and then as a more slender hollow strut (22) on which are mounted bearings (23) with the rotational axis aligned with the major axis of the member. A fairing (24) is mounted on these bearings (23) and carries at its upper end a bearing (25) which provides À Àe rotational freedom about the local pitch axis of the aerodynamic À ... surface assembly. A control cable or other flexible tensile À. member (26) passes through the strut (22), at the upper end of this strut (detailed to a greater scale by figure 16) the cable or flexible tensile member contains a swivel coupling (39) and then passes over a pulley (27) displaced above the axis of the strut and free to rotate about the z axis (defined on figure 10) on bearings (40 in figure 16) and thence to an anchorage (28) towards the nose of the aerodynamic surface assembly, the section of cable (37) between the pulley and the anchorage acting as a link of fixed length during rotation about the strut bearings (23). Figures 14 and 15 illustrate the rotation of the aerodynamic surface assembly about the strut axis. The small drawings to the right of the main figures indicate by arrow (A and B) the direction of view of the sectional drawings to the left of the figures. The offset of the pulley (27), results in the section of cable between the pulley (27) and the anchorage (28), designated 37 in figures lo, 14 and 15, acting as a link of fixed length and applying a force to anchorage (28) such that the incidence of the aerodynamic surface assembly is moved in a nose-up sense about the bearing (25) when the assembly is rotated to bring its own forward longitudinal axis towards the front of the vessel. Correct geometrical proportioning of this pulley (27) offset and the location of the anchorage (28) causes the aerodynamic surface assembly to remain generally aligned with the apparent wind at all steady running conditions of the vessel, this is indicated by the angle O on figure 15 being representative of the typical apparent wind direction as experienced by the aerodynamic surface assembly when the vessel À . . . À.20 is operating. Positive incidence can be applied to the A. À À.aerodynamic surface assembly by shortening the cable or flexible .tensile member from an extension to within the body (1).

Another preferred means of controlling the pitch angle of the aerodynamic surfaces is by means of the bearing system À' À 25 described above and by figure 10 in conjunction with an . . À À''. aerodynamic pitch control (38 in figure 17) directly attached to the aerodynamic surface assembly and controllable from within the vessel body (1).

In conjunction with the two degree of freedom bearing for the aerodynamic surface assembly described above, a preferred method of achieving both a stable aerodynamic surface assembly and accommodating variations of the apparent wind angle with height above the water surface due to wind gradient effects is to form the aerodynamic assembly as a wing with anhedral, i.e., to angle the tips of the wing below the mean plane of the wing surface. Another preferred approach is to apply forward sweep to the mean quarter chord line of the wing. Another preferred method is to use both anhedral and forward sweep in conjunction.

Figure 11 illustrates a preferred means of maintaining the running axis of the hydrodynamic surface assembly in general alignment with the longitudinal axis of the body. A pulley, sprocket or other generally similar positive drive component (29) is earthed to the body (1) and operates within the beam (3). A similar pulley, sprocket or positive drive component (30) is earthed to the hydrodynamic surface assembly (6). Both of these components are linked by a continuous loop of cable, chain or positive drive tensile member such that the movement of the beam (3) relative to the body (1) does not generally affect the relative alignment of the hydrodynamic surface assembly to the -,,' 20 body. .

Another preferred means of maintaining the running axis of the hydrodynamic surface assembly in general alignment with the À longitudinal axis of the body is by use of bevel gearing at À:.

both the hydrodynamic surface assembly bearing (5) and at the : 25 main body bearing (4). These gear assemblies both have the same ,..

ratio and are linked with a torsion member. It is advantageous to arrange for the gear ratio to be such that the torsion member rotates much more rapidly than the rotation of the beam relative to the body to reduce the effects of any torsional deflection that this member will have on the accuracy of alignment of the body with the hydrodynamic surface assembly.

Figure 12 provides a schematic view of the directional control system. The objective of any control system for this type of vessel is to rotate the beam (3) relative to the longitudinal axis of the body (1) and hence also to the running axis of the hydrodynamic surface assembly (6) and thus to change the relative positions of the aerodynamic and hydrodynamic force vectors. When the wheel (31) is rotated, resulting tension in the cable (35) causes torque to be applied to the servo yoke (33). This is resisted by the spring (34) and the deflection of this spring allows some motion to be transmitted via the cables (36) to the aerodynamic rudder (9) .

The tension in the cable (35) also transmits torque to the beam pulley (38) which is directly attached to the beam (3).

Aerodynamic force on the rudder (9) and mechanical force on the beam (3) are both in the same sense with respect to alteration of the beam to body angle (from figure 11) and hence the aerodynamic forces are used to servoassist the beam movement. :e *e e $ 1 . a f *. .e $ a À

Claims

1. A sailing craft comprising: a hydrostatically-supportable body which carries at least one aerodynamic surface disposed to provide stability and control about the pitch axis of the body when in operation; a rigid member connected to the body by a first bearing, having a first rotational axis which is generally vertical when in operation, the member extending when in operation in a generally horizontal plane away from the first bearing and carrying, close to the end of the member remote from the first bearing, a second bearing of having a second rotational axis which is generally vertical when in operation; a hydrodynamic surface assembly mounted on the second bearing and below the member when in operation, the assembly being constrained to maintain its own normal running axis generally parallel to that of the body irrespective of the orientation of the member with respect to the longitudinal axis of the body; the member having a portion that extends beyond the first Àeae bearing, away from the hydrodynamic surface assembly, and that is angled above the horizontal plane when in operation; an aerofoil supported by the portion and spaced from the first bearing, the aerofoil having rotational freedom such that : 25 any significant force generated by that aerofoil will pass below . a.

the centre of mass of the craft when in operation and ensure dynamic stability.

2. Sailing craft according to claim 1, said aerofoil having rotational freedom about a third axis extending substantially from the centre of pressure of said aerofoil to beneath the centre of mass of the craft when in operation, the axis lying close to a line which passes through the centre of mass of the craft and which is generally vertical when in operation.

3. Sailing craft according to claim 2, wherein said third axis substantially intersects a line which passes through the centre of mass of the craft and which is generally vertical when in operation.

4. Sailing craft according to claim 2 or 3, wherein said line is substantially coaxial with said first rotational axis of said first bearing.

5. Sailing craft according to any preceding claim, said aerofoil having rotational freedom about an axis extending from substantially from the centre of pressure of the aerofoil and À . : parallel to the transverse pitch axis of the aerofoil. Àe À e À...

6. Sailing craft according to any one of claims 2 to 5, À Àe wherein said aerofoil forms part of an aerofoil assembly including means for inducing rotational displacement about the À À. bearing, the axis of which intersects with the first rotational Àee A axis of the first bearing and which passes below the centre of mass of the craft.

7. Sailing craft according to any preceding claim, wherein said hydrodynamic surface assembly is surface piercing.

8. Sailing craft according to any preceding claim, wherein the centre of mass of the craft is longitudinally ahead of the aerodynamic centre of the craft.

9. Sailing craft according to any preceding claim, wherein at least one buoyant body and/or at least one hydrodynamic surface is disposed ahead of the centre of mass, thereby to provide a pitching moment in opposition to the nose-down pitching moment induced by the aerofoil assembly during longitudinal acceleration when the craft is supported on the water surface.

10. Sailing craft according to claim 9 and comprising combined buoyant, hydrodynamic elements.

11. Sailing craft according to claim 10, wherein said elements are disposed either side of the craft longitudinal axis, thereby to provide lateral stability during tacking and gybing manoeuvres. À:.. Àe.e Àe.e

À .

12. Sailing craft according to any preceding claim, wherein the hydrodynamic surface assembly is provided with two À Àe hydrodynamic elements, one intended for each tack of the craft, and a rolling pivot, such that the hydrodynamic element designed À À. for a given tack may be brought into service on that tack and e À. the other hydrodynamic surface is lifted clear of the water surface, when on the same tack, by rolling of the assembly.

13. Sailing craft according to any preceding claim, wherein the hydrodynamic surface assembly includes an element that allows a vertical component of hydrodynamic force to be generated such that the running depth of the hydrodynamic surface may be regulated by changes to the incidence about the pitch axis.

14. Sailing craft according to any preceding claim, wherein said aerofoil comprises a wing with anhedral.

15. Sailing craft according to any preceding claim and comprising means for rotating said rigid member about said first rotational axis, thereby to vary the angle between the longitudinal axes of both the body and the hydrodynamic surface assembly, change the lines of action of the aerodynamic and hydrodynamic forces relative to the body axes and allow directional steering control.

16. Sailing craft according to claim 15, wherein the body has an aerodynamic control surface deflectable in response to a directional control input to provide an aerodynamic moment À complementary to the desired motion of the rigid member relative À.

À .. to the body. À À Àe

17. Marine craft comprising a hydrodynamic surface assembly À:.

and at least one aerodynamic surface, wherein the running attitude of said hydrodynamic surface assembly is controlled by À . À. said at least one aerodynamic surface.

18. Marine craft according to claim 17, wherein the craft comprises means for transmitting the motion of said aerodynamic surface to said hydrodynamic surface assembly.

19. Marine craft according to claim 18, wherein said means comprises a rigid member connecting said aerodynamic surface to said hydrodynamic surface assembly.

20. Marine craft according to any one of claims 17 to 19, I wherein the hydrodynamic surface assembly includes an element configured, when in operation, to allow a vertical component of hydrodynamic force to be generated, thereby allowing the running depth of the hydrodynamic surface to be regulated by changes to the incidence about the pitch axis.

21. Marine craft according to any one of claims 17 to 20, wherein the craft comprises a hydrostatically-supportable body, said aerodynamic surface being mounted on said body. À... À - . À e. À À... Àe À À.e À:' À a.

I À À