Hydrodynamic Fin

Abstract

A hydrodynamic fin, such as a keel or a rudder of a watercraft, in particular a sailing craft or surfboard, which fin comprises at least two fin sections ( 20,21 ), which are each connectable to the watercraft ( 31 ) in a manner permitting rotation, in which the fin sections are rotatable in between two extreme positions around an axis ( 22,23 ) which is substantially parallel to the longitudinal symmetrical plane of the hull, in which extreme positions the fin sections provide a mainly cambered shape to the fin, with the characteristic that the fin sections can move with a substantially constant resistance from one extreme position to the other extreme position and the hydrodynamic fin is also provided with an end-stop ( 26 ) in order to stop a rotation of the fin sections when rotating from one extreme position to the other extreme position, such that the fin sections in use take either one extreme position or the other extreme position as a result of the hydrodynamic load.

1 . A hydrodynamic fin, for a watercraft, having a hull, comprising:
 at least two fin sections, which are each connectable to the watercraft in a manner permitting rotation, wherein the fin sections are rotatable between a first position and a second position around an axis which is substantially parallel to a longitudinal symmetrical plane of the hull, and wherein, in the first and second positions, the fin sections provide a substantially cambered shape to the fin, and   wherein the fin sections can move with a substantially constant resistance from one of the positions to the other position and the hydrodynamic fin further comprises an end-stop to stop rotation of the fin sections when rotating from one position to the other position, such that the fin sections in use take either one position or the other position as a result of the hydrodynamic load.   
   
   
       2 . A hydrodynamic fin according to  claim 1 , wherein the fin sections are connected to each other. 
   
   
       3 . A hydrodynamic fin according to  claim 1 , wherein the fin comprises two fin sections. 
   
   
       4 . A hydrodynamic fin according to  claim 1 , where the fin sections are mainly rigid. 
   
   
       5 . A hydrodynamic fin according to  claim 1 , wherein the fin sections are connected to each other by means of at least one hinges having a backlash. 
   
   
       6 . A hydrodynamic fin according to  claim 5 , wherein the hinge incorporates a pin and a slotted hole, and wherein the pin is connected to one of the fin sections and extends through a slotted hole that is made in another fin section. 
   
   
       7 . A hydrodynamic fin according to  claim 6 , wherein the pin of the hinge is slidable longitudinally inside the slotted hole. 
   
   
       8 . A hydrodynamic fin according to  claim 6 , wherein the slotted hole has end surfaces that form an end-stop for the pin in the hinge, wherein the distance between the end-surfaces of the slotted hole determines the first and second positions of the fin sections. 
   
   
       9 . A hydrodynamic fin according to  claim 1 , wherein a gap exists between the sections, which gap is filled with a soft flexible material. 
   
   
       10 . A hydrodynamic fin according to  claim 9 , wherein the soft flexible material is a silicon rubber. 
   
   
       11 . A hydrodynamic fin according to  claim 1 , wherein the fin comprises a pin which forms an end-stop, which acts at the fin section in the first or second position. 
   
   
       12 . A hydrodynamic fin according to  claim 11 , wherein the position of the pin can be adjusted, such that the first and second positions of the fin sections are adjustable. 
   
   
       13 . A hydrodynamic fin according to  claim 1 , wherein at least two fin sections have rotation shafts that are supported in bearings permitting rotation of the shafts inside a connection head. 
   
   
       14 . A hydrodynamic fin according to  claim 13 , wherein the connection head is of the tuttle-box type. 
   
   
       15 . A hydrodynamic fin according to  claim 11 , wherein the pin is mounted in a connection head. 
   
   
       16 . A hydrodynamic fin according to  claim 1 , wherein the fin comprises a controllable fixation system to lock the fin sections in a position in between the first and second positions. 
   
   
       17 . A hydrodynamic fin according to  claim 13 , wherein the two rotation shafts supported in bearings are fitted with a fixation system such that at least one of the fin sections may be selectively fixed in any one of the first position, the second position and a position between the first and second positions. 
   
   
       18 . A hydrodynamic fin according to  claim 5 , wherein the hinge between the fin sections is constructed from two profiles having a U-shape and made of a hard material, which are mounted at the fin sections, between which a flexible material is glued or vulcanized. 
   
   
       19 . A watercraft provided with a fin according to  claim 1 .