Hydrofoil watercraft

Abstract

A hydrofoil section comprises first and second faces that create, in operation at speeds above a ventilation speed, a ventilated cavity defined by a first cavity face which departs from the first hydrofoil face and a second cavity face which departs from the second hydrofoil face. Each cavity face represents a free surface and each face separating from the said free surface at a discontinuity on that surface, the separated faces forming a continuation of the faces of arbitrary shape and enclosed by the free surfaces without contacting the said free surfaces. Below the speed at which full ventilation occurs the arbitrarily shaped portion of each face is configured to provide a modified flow configuration resulting in changed lift and or drag and or pitching moment under partial, or unventilated operation.

1 - 27 . (canceled) 
     
     
         28 . A hydrofoil watercraft having a normal pitch attitude, the watercraft comprising:
 at least one buoyant body,   at least one strut extending below the or each buoyant body,   a hydrofoil secured to the or each strut beneath the buoyant body, the hydrofoil being for lifting the buoyant body of the watercraft above the surface of the water and   means for driving the watercraft forwards;   
       wherein the hydrofoil is adapted to plane when the watercraft is driven above a planing speed and has:
 a leading edge, 
 a trailing edge, 
 a first, lower surface between the leading edge and the trailing edge, the lower surface being:
 smoothly curved and shaped:
 to plane on the surface of the water when the watercraft is driven forwards at or above the planing speed with the lower surface wetted at normal pitch attitude and 
 to generate lift when submerged with the watercraft being driven at less than planing speed at normal pitch attitude and 
 
 
 a second, upper surface between the leading edge and the trailing edge, the upper surface having:
 at least one discontinuity between the leading edge and the trailing edge, providing a fore portion between the leading edge and the discontinuity and an aft portion between the discontinuity and the trailing edge and being shaped:
 at the fore portion to generate negligible lift in comparison with that of the lower surface when submerged at normal pitch attitude and 
 at the aft portion to slope down towards the trailing edge when submerged at normal pitch attitude, whereby:
 the aft portion generates lift when the watercraft is driven at a speed lower than a super-ventilation speed with the aft portion wetted and 
 the aft portion generates less lift when the watercraft is driven at a speed above the super-ventilation speed to allow formation of super-ventilation over at least part of the aft portion. 
 
 
 
 
     
     
         29 . The hydrofoil watercraft according to  claim 28 , wherein the strut is provided with ventilation means for atmospheric air communication to the discontinuity. 
     
     
         30 . The hydrofoil watercraft according to  claim 28 , wherein the discontinuity is an aft facing step. 
     
     
         31 . The hydrofoil watercraft according to  claim 28 , wherein:
 the fore portion of the second upper surface is substantially flat,   the aft portion of the second upper surface is substantially flat   the aft portion is angled down with respect to the fore portion from the discontinuity to the trailing edge.   
     
     
         32 . The hydrofoil watercraft according to  claim 28 , wherein the aft portion of the second upper surface has at least one second discontinuity dividing the aft portion into facets. 
     
     
         33 . The hydrofoil watercraft according to  claim 32 , wherein:
 the fore portion of the second upper surface is substantially flat,   a fore one of the facets of the aft portion is substantially flat and is angled down with respect to the fore portion and   an after one of the facets is substantially flat and is angled down with respect to the fore one of the facets.   
     
     
         34 . The hydrofoil watercraft according to  claim 32 , wherein the strut is provided with ventilation means for atmospheric air communication to the second discontinuity. 
     
     
         35 . The hydrofoil watercraft according to  claim 32  where the second discontinuity is an aft facing step. 
     
     
         36 . The hydrofoil watercraft according to  claim 28 , wherein the hydrofoil has a swept profile such that the discontinuity has a spanwise component. 
     
     
         37 . The hydrofoil watercraft according to  claim 28 , wherein the aft facing step has a depth tapering towards a tip of the hydrofoil. 
     
     
         38 . The hydrofoil watercraft according to  claim 29 , wherein the strut is substantially vertical and has
 a forward strut portion   an aft strut portion, and   an intersection between the forward and aft strut portions extending from the buoyant body to the hydrofoil, the intersection providing the ventilation means for atmospheric air communication to the discontinuity.   
     
     
         39 . The hydrofoil watercraft according to  claim 38 , wherein the intersection is an aft facing step. 
     
     
         40 . The hydrofoil watercraft according to  claim 28 , wherein:
 the aft portion of the second upper surface has at least one second discontinuity dividing the aft portion into facets,   the strut is substantially vertical and has
 a forward strut portion 
 an aft strut portion, 
 an intersection between the forward and aft strut portions extending from the buoyant body to the hydrofoil, the intersection providing ventilation means for atmospheric air communication to the discontinuity and 
 a second intersection between fore and aft facets of the after strut portion, the second intersection providing ventilation means for atmospheric air communication to the second discontinuity. 
   
     
     
         41 . The hydrofoil watercraft according to  claim 40 , wherein the second intersection is an aft facing step. 
     
     
         42 . The hydrofoil watercraft according to  claim 28 , wherein the leading edge of the hydrofoil has an armour surface. 
     
     
         43 . The hydrofoil watercraft according to  claim 28 , including flow fences on the second upper surface. 
     
     
         44 . The hydrofoil watercraft according to  claim 28 , including:
 a rudder and   a stabilising, submerged hydrofoil is attached to the rudder.   
     
     
         45 . The hydrofoil watercraft according to  claim 28 , including:
 a rudder and   a secondary, surface running, ventilated hydrofoil is attached to the rudder at a foil-borne waterline.   
     
     
         46 . The hydrofoil watercraft according to  claim 28 , wherein the hydrofoil is located close to the longitudinal centre of gravity of the watercraft and the watercraft includes a submerged stabilising foil positioned aft, the combination forming a stable, surface following combination. 
     
     
         47 . The hydrofoil watercraft according to  claim 28 , wherein the hydrofoil is located close to the longitudinal centre of gravity of the watercraft and the watercraft includes a surface-running stabilising foil positioned fore, the combination forming a stable, surface following combination. 
     
     
         48 . The hydrofoil watercraft according to  claim 47 , wherein the surface-running stabilising foil has an aspect ratio of less than two. 
     
     
         49 . The hydrofoil watercraft according to  claim 47 , wherein the surface-running stabilising foil is swept by more than 45 degrees. 
     
     
         50 . The hydrofoil watercraft according to  claim 28 , wherein the first lower surface of the hydrofoil has a dihedral angle when viewed in a vertical plane transverse to the longitudinal axis of the watercraft. 
     
     
         51 . The hydrofoil watercraft according to  claim 28 , wherein the strut extends below the hydrofoil to provide stabilisation against leeway. 
     
     
         52 . The hydrofoil watercraft according to  claim 51 , wherein the strut extends behind the hydrofoil as well as below the hydrofoil to provide stabilisation against leeway. 
     
     
         53 . The hydrofoil watercraft according to  claim 28 , wherein the watercraft is a sail board. 
     
     
         54 . The hydrofoil watercraft according to  claim 28 , wherein the watercraft is a sail boat. 
     
     
         55 . The hydrofoil watercraft according to  claim 28 , wherein the watercraft is a motor boat. 
     
     
         56 . A hydrofoil watercraft comprising:
 a buoyant body,   a strut extending below the buoyant body,   a hydrofoil secured to the strut beneath the buoyant body for lifting the buoyant body above the surface of the water when travelling at a surface running speed and   means for driving the watercraft forwards;   
       wherein the hydrofoil has:
 a first, lower surface shaped to generate a distributed pressure for supporting the watercraft with the hydrofoil running at the surface of the water at surface running speed and 
 a second, upper surface having:
 at least one discontinuity between a leading edge and a trailing edge, dividing the upper surface into fore and aft portions and being shaped 
 at the fore portion to generate negligible lift and 
 at the aft portion to provide lift tending to raise the watercraft when travelling at speeds at which the aft portion is wetted by water flow in contact with it and to allow ventilation at intermediate speeds higher than the wetted speeds and below surface running speeds and 
 
 
       wherein both the strut and hydrofoil are provided with
 ventilation means for atmospheric communication from above the surface of the water to the discontinuity in the upper surface of the hydrofoil. 
 
     
     
         57 . The hydrofoil watercraft according to  claim 56 , wherein the ventilation means are aft facing steps in the strut and the second, upper face of the hydrofoil. 
     
     
         58 . The hydrofoil watercraft according to  claim 56 , wherein:
 the fore portion of the second upper surface is substantially flat,   the aft portion of the second upper surface is substantially flat   the aft portion is angled down with respect to the fore portion from the discontinuity to the trailing edge.   
     
     
         59 . The hydrofoil watercraft according to  claim 57 , wherein the aft portion of the second upper surface has at least one second discontinuity dividing the aft portion into facets. 
     
     
         60 . The hydrofoil according to  claim 59 , wherein:
 the fore portion of the second upper surface is substantially flat,   a fore one of the facets of the aft portion is substantially flat and is angled down with respect to the fore portion and   an after one of the facets is substantially flat and is angled down with respect to the fore one of the facets.   
     
     
         61 . A hydrofoil watercraft having lift inducing lower surface and a top surface which is substantially flat from a leading edge to a first discontinuity and substantially flat and angled down from the first discontinuity to a trailing edge. 
     
     
         62 . The hydrofoil watercraft according to  claim 61 , wherein the discontinuity is an aft facing step. 
     
     
         63 . The hydrofoil watercraft according to  claim 61 , wherein the strut is provided with ventilation means for atmospheric air communication to the discontinuity. 
     
     
         64 . The hydrofoil watercraft according to  claim 61  further comprising a second discontinuity, wherein the top surface which is substantially flat from the leading edge to the first discontinuity and further is substantially flat and angled down from the first discontinuity to a second discontinuity and substantially flat and angled further down from the second discontinuity to the trailing edge. 
     
     
         65 . The hydrofoil watercraft according to  claim 64 , wherein the first and second discontinuities are aft facing steps. 
     
     
         66 . The hydrofoil watercraft according to  claim 64 , wherein the strut is provided with ventilation means for atmospheric air communication to the discontinuities.