TECHNICAL DOMAIN

The present invention relates to, in embodiment, a hydrofoil boat with improvements that increased its manoeuvrability, especially in restricted spaces or where the water depth is limited.

RELATED ART

Hydrofoil boats are known since several decades and have been used both in transport, sports, and leisure. In essence, they have a water-displacing hull that ensures that the boat stays afloat at low speed or when it is not moving, and underwater appendages that generate a vertical lift when the craft is in motion. Above a minimum speed, that is determined by the lift of the immersed structures and the speed, hydrofoils "fly", the hull raised from the water.

Hydrodynamic resistance in a flying hydrofoil can be much lower than in a conventional displacement or planing hull at the same speed. Consequently, hydrofoils can use much less energy, produce a very reduced wake and create much less noise than conventional motorboats. Hence, hydrofoils are especially suitable for "green" application, using electric propulsion, wind, or other renewable forms of propulsion. They can move speedily in areas where other power watercrafts would not be tolerated, because of their noise and of the waves that they produce.

The lift appendages can assume a multitude of shapes and configurations in hydrofoils. It is known to use "T" foils that have a symmetric winglike lifting foil at the lower end of a vertical underwater mast lying in the median plane of the boat.

As any other underwater appendage, the lifting foils are a liability when the boat must manoeuvre in shallow water, for example in marinas or close to beaches. Also, high-performance foils can be rather large, especially if they are configured to operate at low or moderate speed and can exceed the beam of the hull. This is a problem when the boat must move in restricted spaces, for example when docked. Water weeds and loose lines can also snag on underwater appendages, and this is a common problem in marinas. SHORT DISCLOSURE OF THE INVENTION

An aim of the present invention is the provision of a hydrofoil boat that overcomes the shortcomings and limitations of the state of the art.

According to the invention, these aims are attained by the object of the attached claims.

The present disclosure will refer to terms like "up", "down", "longitudinal", "transversal", following the customary meaning that these words have in relation with boats, "up" and "down" designate the vertical directions perpendicular to that of a surface of calm water. "Longitudinal" is the direction of the centreline of the boat, that is a line that from the bow joins the transom and is also the direction along which the boat is generally supposed to travel. "Fore-and-aft" may be a synonym of "longitudinal". A "longitudinal plane" is a vertical plane containing that line, and is, almost always, a symmetry plane for the general shape of the hull. The "transverse" direction is that of a line perpendicular to the longitudinal plane, usually parallel to the maximum beam of the hull.

SHORT DESCRIPTION OF THE DRAWINGS

Exemplar embodiments of the invention are disclosed in the description and illustrated by the drawings in which:

Figures la and lb show schematically a boat according to the invention, seen from the side, in a deep-water configuration and flying, respectively in a shallow-water configuration at slow speed.

Figures 2a to 2c illustrate the transition from the deep-water configuration to the shallow-water configuration, from below and in three steps

Figures 3a and 3b show the boat in the deep-water configuration, respectively in the shallow-water configuration, as seen from the bow.

EXAMPLES OF EMBODIMENTS OF THE PRESENT INVENTION

Figures la shows a watercraft 100 in motion, sustained by the vertical lift of its underwater appendages, which are, in this embodiment, a horizontal elongated hydrofoil 47 and a rudder-mounted horizontal stabilizer 57. The hydrofoil 47 is at the lower end of an underwater mast 41, while the horizontal stabilizer 57 is at the lower end of a rudder 51 abaft the underwater mast 41. Preferably, these appendages are configured to provide a high lift/drag ratio at moderate speed and, to this end, are slender elongated hydrodynamic bodies with a high aspect ratio, as it can be seen in figure 2a where the watercraft 100 is represented as seen from below.

Returning to figure la, the hydrofoil 47 is at the lower end of an underwater mast 41 that extends from the centreline below the hull 10 in an essentially vertical direction. The mast inserts a distance between the hull and the hydrofoil such that the boat can fly above the waterline 31 with the desired clearance.

Either or both the underwater mast 41 and the rudder 51 may have propulsion pods 43, 53 with an electric motor and a propeller 45, 55. This is not essential for the invention, however, and the watercraft 100 may have any suitable means of propulsion including propellers connected to the hull or to other appendages, sails or kites, bow propellers for manoeuvring, water jets, and so on.

The combined lift of the hydrofoil 47 and of the stabilizer 57 is such that the boat 100 flies at the desired height above the waterline and remains level. Preferably, this is achieved automatically, by a computer control that receives information about the instantaneous height and attitude of the boat, and acts on suitable control surfaces of the underwater appendages, as it will be shown later.

Preferably, the boat has means to detect the height of flight above the water, for example height sensors 71 and its position with respect to other vessels and obstacles, for example by a LIDAR 75, and this information is provided to the computer control as input.

Figure lb shows the boat 100 at low speed, when the lift generated by the appendages is not enough to overcome the weight, and the boat is sustained essentially by its buoyancy. The appendages are lifted closer to the hull to reduce the water draft. The underwater mast 41 is raised inside the hollow post 49, while the rudder is lifted vertically. In this case, the aft propeller 55 is underwater and provides propulsion and direction at low speed, but other solutions are possible. Preferably, the boat allows a third configuration, not shown, where the rudder can be raised even higher, lifting the pod 53 above the waterline. Figures 2a to 2c show the transition between the deep-water configuration of figure la to the shallow-water configuration of figure lb in three steps. While the hydrofoil 47 is lifted close to the hull, at the same time it rotates along a vertical axis towards the longitudinal plane L. In the example shown the rotation is quite complete and, in the final configuration of figure 2c, the hydrofoil 47 is aligned with the longitudinal plane L, but this is not an essential requirement.

Advantageously, turning the hydrofoil fore-and-aft reduces its side encumberment. In the example, the width 'w', or wingspan of the foil exceeds the beam 'b' of the hull, and the boat could not safely dock to a wall in the deep-water configuration. By rotating the hydrofoil towards the midplane L, the hydrofoil is no longer an encumberment. In this configuration the risk of snagging with the foil to weeds or loose lines is also greatly reduced.

Preferably, the hydrofoil 47 is connected rigidly to the underwater mast 41, which has a flattened section to minimize the drag and, in the shallow-water configuration, the hydrofoil 47 and the mast 41 rotate together as a body. This is not the only option, however.

The combined movement of the mast 41 and of the hydrofoil 47 can be obtained in several ways, all comprised in the invention. In a preferred solution, the underwater mast is guided helically inside the post 49 along at least a part of its travel such that, as it rises, it necessarily turns of the desired angle. The total angle a of rotation of the foil 47 may be 90°, as shown in figure 2c, but even a lesser rotation would procure a useful reduction of the underwater beam.

Figures 2a-2c show also the control surfaces 48, 58 of the hydrofoil 47, respectively the stabilizer 57. This is just an example, however, and the control surfaces could be configured otherwise, without leaving the invention. Possibly, the lift of the hydrofoil and of the stabilizer could be controlled by pitching the whole wing, rather than a smaller surface. In can be said, in this case that each of the wings of the hydrofoil is a control surface.

Left-right differential control of the surfaces 48, 58 causes a change in the roll angle of the boat 100, while a differential setting of the hydrofoil surfaces 48 with respect to the additional surfaces 58 influences the pitch of the boat. These actions are interlinked in a complex manner that depends on the dynamic state of the boat, and can be controlled by a skilful skipper, or by an automatic control unit using a dynamic model, as it is known in the art.

Figures 3a and 3b show the boat in the two configurations of figures la and lb, as seen from the bow. Advantageously, the hydrofoil 47 tucks inside a tunnel 11 of the hull when it is raised in the shallow-water configuration. This minimizes the chances of a snag and, if the tunnel is deep enough, the pod 43 can be lifted above the waterline to reduce fouling, as represented in figure 3b.

Reference symbols in the figures

9 superstructure

10 hull

11 tunnel

31 waterline

41 mast

43 centre pod

45 centre propeller

47 hydrofoil

48 control surfaces

49 hollow post

51 rudder

53 aft pod

55 aft propeller

57 horizontal stabilizer

58 additional control surfaces

71 height sensor

75 lidar

100 boat, watercraft