Fin Unit with Elastic Attachment System on an Underside of a Marine Apparatus

Abstract

The invention relates to a fin unit ( 2 ) with elastic attachment system on an underside ( 1 ) of a marine apparatus, such as a wind surf, kite surf, fly surf, wakeboard, knee board and particularly a surfboard. The fin in the mounting thereof is partially made to self-align in the flow of liquid medium with the aim of avoiding the hydrodynamic stall caused by the passage of high turbulence and/or large lateral movements caused by the surfer in extreme motion. The possibility for self-orientation is due to three fundamental parameters which are: the type of elasticity of the attachment system ( 3 - 4 - 5 - 27 ), the forward position of the centre of gravity G towards the leading edge ( 15 ) and the form of the root profile ( 9 ) of the fin ( 2 ) which has a thickening ( 7 ) of the trailing edge thereof.

1 . Removable fin unit with system of fastener on careen of a marine apparatus ( 1 ) such as surfboard, kite surfing, fly surfing, wake board, knee board, windsurf board or similar, characterised by the fact that the fin ( 2 ) is partially made self directional in its evolution in fluid environment in order to push back the hydrodynamic stall caused by the crossing of large turbulences and/or the strong lateral movements applied by the surfer in extreme motion, thanks to elastic means of fastening (3-4-5-27) combined with the forward position of the centre of gravity G and the form of the profile ( 7 ) out of root ( 9 ) of the fin ( 2 ). 
   
   
       2 . Fin unit according to  claim 1 , characterised in that the form of the profile of the fin ( 2 ) out of root ( 9 ) includes a thickening ( 7 ) of the trailing edge ( 8 ) of a value equal or lower than the maximum cross section thickness situated at approximately 25% of the airfoil cord, the said thickening being built on a height H of value at least equal to that of the said maximum cross section. 
   
   
       3 . Fin unit according to  claim 1 , characterised in that the means of fastening units are represented by an insert ( 5 ) embedded in the careen ( 1 ) including an elastic matter ( 4 ) coating a sleeve ( 27 ) in order to hold at least a tenon ( 3 ) out of root ( 9 ) of the fin ( 2 ), which assembly allows a partial elastic mobility of the fin around OZ axis and OX axis. 
   
   
       4 . Fin unit according to  claim 1 , characterised in that the fin ( 2 ) assembled with its means of fastening (3-4-5-27) is brought as to be able to have angular displacement (Ai and Aj), in the case of over lift pressure of hydrodynamic nature ΔP, around vertical axis OZ in yawning Mz and around longitudinal axis OX in rolling Mx. 
   
   
       5 . Fin unit according to  claim 1 , characterised in that the fin ( 2 ) equipped with tenon ( 3 ) is manufactured in such a way that it can float in the water, that is to say it is composed by a profiled core ( 16 ) made of very light material covered with a skin ( 17 ) of great strength with a leading edge ( 15 ) reinforcement by successive layers, which includes according to the needs a ballast ( 6 ) to adjust the natural frequencies HP, to position the centre of gravity (G) of the fin close to the root ( 9 ) and in front of OZ axis. 
   
   
       6 . Fin unit according to  claim 1 , characterised in that the fin ( 2 ), in the case of extreme motion or important variations of speed ΔV at great incidence i, swirl or gust, induce strong variation of lift ΔP, is self adjustable in incidence by the fact that the tenon ( 3 )/insert ( 5 ) linkage is elastic and that inertial forces, applied at the centre of gravity G and that the hydrodynamic forces applied to the action centre O′, depending on the swirling effect from induced drag t m  and root turbulence t e , induce yawning moments Mz and rolling moments Mx which reduce the gust effect by the angular variations Ai and Aj. 
   
   
       7 . Fin unit according to  claim 3 , characterised in that the tenon ( 3 ) is of circular section or rectangular or more or less elliptic, it can contain at its end a notch or a throttling ( 10 ) as to self position it in its sleeve ( 27 ) during its insertion and to be locked in at its end of travel on an elastic strip ( 28 ) or a spring ring of circlips type ( 20 ). 
   
   
       8 . Fin unit according to  claim 7 , characterised in that the fin ( 2 ) is locked in position by a cord ( 11 ) fixed at the tenon end or on the root ( 9 ) of the fin, which cord crosses through the thickness of the board in order to be fixed and tended by a rubber band ( 12 ) located and fixed ( 13 ) in a slot ( 14 ) practised in the deck of the board. 
   
   
       9 . Fin unit according to  claim 7 , characterised in that the fin ( 2 ) is attached to the careen ( 1 ) by two tenons ( 3   a - 3   b ) inserted in two mortises ( 19   a - 19   b ) of a non elastic material, each mortise include inside one or more elastic matter rings ( 18   a - 18   b ) in such a way that the tenons once introduced are maintained by radial pressure, at the level of the throttling ( 10 ), which allow however a light elastic displacement of the fin (around axes OX and OZ) in the gap left between the diameter of the tenons and that of the mortises. 
   
   
       10 . Fin unit according to  claim 9 , characterised in that the ring ( 18   a ) and the ring ( 18   b ) present different elastic deformations under the same effort, due to the difference of modulus of elasticity of chosen elastomer and/or with the difference of the shape of the ring as to position the OZ axis as closer to the front tenon axis. 
   
   
       11 . Fin unit according to  claim 9 , characterised in that the tenon ( 3   a - 3   b ) is a part brought back during the manufacture of the fin ( 2 ) whose material used is either metal stainless or titanium, or a composite, this same tenon includes outside a smooth or ridged or knurled surface to strengthen the behaviour of the assembly with the rings ( 18   a - 18   b ) and inside a tubular cavity ( 22 ) where there is a flexible bond ( 23 ) of safety connecting one and the other of the two ends ( 24 - 25 ) of the tenon which in the event of rupture makes it possible not to lose the fin in the fluid environment. 
   
   
       12 . Fin unit according to  claim 3 , characterised in that the insert ( 5 ) is a kind of very hard composite material cage including outside the protruding parts ( 26 ) for the mooring and the bonding in the careen ( 1 ) and inside other protruding parts ( 29 ) to receive equipments allowing the coupling with at least a tenon ( 3 ), the said insert ( 5 ) as to facilitate its installation in the board includes an angular positioning jig ( 30 ) composed of three arms ( 31 - 32   a - 32   b ) each one provided with pin ( 33 ), the said arm ( 31 ) of length greater than that of arms ( 32   a - 32   b ) is provided with at least a detachable pin ( 34 ) dimensioned and specified with the angle (ψ) required. 
   
   
       13 . Fin unit according to  claim 2 , characterised in that the fin includes at its root ( 9 ) an elastic joint ( 21 ) filling the clearances or the gaps between fin and careen.