Planing hydrofoils for marine craft

Abstract

A hydrofoil ( 20 ) for mounting to a high speed surface vessel arranged for planning operation at least at higher craft speeds and in which the trailing edge ( 202 ) remain substantially fully wetted at all craft speeds when operating under calm conditions.

1 . A hydrofoil for mounting to a high speed surface vessel arranged for planing operation at least at higher craft speeds and in which the trailing edge remains substantially fully wetted at all craft speeds when operating under calm conditions. 
     
     
         2 . A hydrofoil according to  claim 1  in which the ratio of the wetted chord at the tip to the wetted chord at the centre of the hydrofoil is in the range of 15% to 75% in the design condition and preferentially under all normal high speed operating conditions due to the fact that the drag coefficient rises substantially outside this range. 
     
     
         3 . A hydrofoil according to  claim 1  in which the planing surfaces are prismatic and are arranged such that the angle of attack, the angel of dihedral and the forward spray root line ensure that the underside planing surface of the hydrofoil extends out to substantially the full span of the hydrofoil under all normal operational conditions. 
     
     
         4 . A hydrofoil according to  claim 1  in which the dihedral angle β is zero such that the root spray angle is ninety degrees. 
     
     
         5 . A hydrofoil according to  claim 1  being a rectangular hydrofoil with no dihedral. 
     
     
         6 . A hydrofoil according to  claim 1  comprising a cambered planing surface. 
     
     
         7 . A hydrofoil according to  claim 1  comprising a new hydrofoil section which comprises a forward downwards inclined generally straight section, an intermediate upwards cambered section, an aft downwards cambered section and a downwards inclined trailing edge section. 
     
     
         8 . A hydrofoil according to  claim 1  comprising a new hydrofoil section which comprises a forward generally straight section, an aft downwards cambered section and a downwards inclined trailing edge section. 
     
     
         9 . A hydrofoil according to  claim 6  in which the spray root line is adapted to the cambered section and in which such modified spray root line extends out to substantially the full span under all desirable operating conditions. 
     
     
         10 . A hydrofoil according to  claim 1  in which any part of the hydrofoil is constituted by any fixed part of the hull. 
     
     
         11 . A hydrofoil according to  claim 1  in which any part of the hydrofoil is constituted by any part attached to the hull. 
     
     
         12 . A hydrofoil according to  claim 10  in which the adjacent hull surfaces serve to increase the effective aspect ratio of the hydrofoil. 
     
     
         13 . A hydrofoil according to  claim 1  which further comprises at least one trailing edge flap. 
     
     
         14 . A hydrofoil according to  claim 13  in which any trailing edge flaps is arranged with a control mechanism and a controller for adaptive lift control. 
     
     
         15 . A hydrofoil according to  claim 1  which is adapted to provide a significant amount of lift due to the principle of ground effect. 
     
     
         16 . A hydrofoil according to  claim 15  which is adapted to provide at least 10% of the lift required due to the principle of ground effect. 
     
     
         17 . A hydrofoil according to  claim 1  in which the relationship between the root spray angle, the angle of attack and the dihedral angle for prismatic surfaces is given by the expression below 
       
         
           
             
               γ 
               - 
               
                 
                   tan 
                   
                     - 
                     1 
                   
                 
                  
                 
                   ( 
                   
                     
                       π 
                       2 
                     
                     · 
                     
                       
                         tan 
                          
                         
                             
                         
                          
                         τ 
                       
                       
                         tan 
                          
                         
                             
                         
                          
                         β 
                       
                     
                   
                   ) 
                 
               
             
           
         
       
     
     
         18 . A hydrofoil according to  claim 7  in which the spray root line is adapted to the cambered section and in which such modified spray root line extends out to substantially the full span under all desirable operating conditions. 
     
     
         19 . A hydrofoil according to  claim 8  in which the spray root line is adapted to the cambered section and in which such modified spray root line extends out to substantially the full span under all desirable operating conditions. 
     
     
         20 . A hydrofoil according to  claim 11  in which the adjacent hull surfaces serve to increase the effective aspect ratio of the hydrofoil.