Fin box assemblies for windsurfers

A windsurfer board is formed, towards the tail end thereof, with a slot in which a box is fitted. The box provides a mounting for a fin which is movable, while in use, relative to the board in such manner as to permit simultaneous adjustment of the inclination of the fin relative to the board and of the extent by which the fin projects downwardly beneath the board. The mounting for the fin includes a bracket pivotally connected to the box and to the fin.

FIELD OF THE INVENTION 
This invention relates to fin box assemblies for windsurfers. 
BACKGROUND OF THE INVENTION 
One form of windsurfer fin box is described in European Patent 
Specification No. 0 088 430 and includes a box which is located towards 
the rear of the board and provides a pivot mounting for a fin which 
projects downwardly below the board and can be fixed in any one of a 
plurality of selected angular positions. 
The degree of adjustability of the fin is, however, limited, the mechanism 
is complex and the commercial success of this fin box has accordingly been 
rather limited. 
Waterboards having pivotally mounted fins are known from International 
Patent Specifications Nos. WO 87/04399 and WO 8/09744. Sailboards having a 
centrally located pivotally mounted centreboard are also known from U.S. 
Pat. No. 4,667,615 and European Patent Specification No. 0 416 442. 
The present invention is, however, specifically concerned with fin box 
assemblies which are mounted towards the rear of a windsurfer board and to 
windsurfer boards provided with such fin box assemblies. 
It is an object of the present invention to provide an improved form of fin 
box assembly for a windsurfer which is compact, permits ready adjustment 
of the position of the fin and is more effective than previous fin box 
designs. 
A further object of the invention is to provide a windsurfer including a 
fin box assembly having an adjustably mounted fin, which windsurfer can be 
sailed more effectively in a variety of wind conditions than other 
windsurfers. 
SUMMARY OF THE INVENTION 
According to one aspect of the present invention there is provided a fin 
box assembly for mounting towards the rear of a windsurfer board, said fin 
box assembly comprising a box and a fin, the box including spaced side 
walls and end walls defining a chamber, and the fin being located within 
and depending downwardly from the chamber, said fin having a leading edge 
and a trailing edge, a link pivotally mounted on the box and a pivotal 
connection between the link and the fin, said fin, link and box being so 
designed that the link is movable between and locatable in first and 
second limiting positions, in the first of which the leading edge of the 
fin extends substantially vertically and in the second of which the 
leading edge of the fin is raked rearwardly, said fin being displaced 
bodily upwardly during movement of the link from its first into its second 
position. 
According to a second aspect of the present invention there is provided a 
fin box assembly for mounting towards the rear of a windsurfer board, said 
fin box assembly comprising: 
a) a box, 
b) a fin, 
c) a pair of spacers, 
d) a seal, and 
e) mounting means for the fin, 
the box including a pair of spaced side walls and a pair of spaced end 
walls defining a chamber, 
the fin being located within and depending downwardly from the chamber, 
said fin having a leading edge and a trailing edge, 
said spacers being formed of a low friction plastics material and located 
between the fin and each of the side walls of the box, 
the seal being formed of a resiliently deformable foamed plastics material 
which is fitted around the fin and acts between the fin and the walls of 
the box to prevent the flow of air through the box, and 
the mounting means for the fin permitting movement of the fin relative to 
the box between a first position in which the leading edge of the fin 
extends substantially vertically and a second position in which the 
leading edge of the fin is raked rearwardly, 
said fin being displaced bodily upwardly relative to the box during 
movement thereof from its first into its second position, 
said spacers acting to facilitate sliding of the fin relative to the box 
side walls and 
the seal flexing to maintain its sealing action during such movement of the 
fin. 
A loop which can be grasped manually is preferably attached to the fin 
adjacent the upper end thereof so that a user of the windsurfer board can 
grasp the loop during sailing to move the fin from its first position into 
its second position, such movement of the fin comprising a lifting 
component and a tilting or pivoting component. The upper surface of the 
fin is preferably so formed as to facilitate the application of foot 
pressure thereto so that, when it is desired to move the fin from its 
second position into its first position, such movement can be effected 
during sailing by the application of foot pressure to the upper surface of 
the fin. 
According to a third aspect of the present invention there is provided a 
windsurfer board having upper and lower surfaces and provided, adjacent 
the rear thereof, with a fin box assembly, said fin box assembly 
comprising: 
a) a box mounted within the board so that it is substantially flush with 
the upper and lower surfaces of the board, 
b) a fin which extends a significant amount downwardly below the lower 
surface of the board and which extends to an appreciably lesser extent 
above the upper surface of the board, and 
c) mounting means for the fin, 
the box including spaced side walls and end walls defining a chamber, 
the fin being located within and depending downwardly from the chamber, 
the mounting means comprising a bracket having spaced pivotal connections 
to the box and to the fin, 
said fin, bracket and box being so designed that the bracket is movable 
into and locatable in first and second positions, 
the first position of the bracket being one in which the trailing edge of 
the fin extends substantially vertically and the second position of the 
bracket being one in which the trailing edge of the fin is raked 
rearwardly, 
the pivotal connections between the bracket, the box and the fin being such 
that the fin is displaced bodily upwardly during movement of the bracket 
from its first into its second position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The fin 10 shown in FIGS. 1 to 3 is of aerofoil configuration and is formed 
of a carbon fibre or mesh-reinforced polyester resin or other equally 
strong and durable semi-rigid plastics material. It is located within a 
rectangular box 11 fixed within an elongated slot formed in the windsurfer 
board 12 towards the rear or tail end 13 of the board 12. The box 11 has 
walls formed either of metal plate or of a glass-fibre-reinforced 
polyester resin and is bonded in position within the slot in the board 12 
so that the upper surface of the box 11 extends just above the upper 
surface of the board 12 and the lower surface of the box 11 is spaced 
upwardly a short distance from the lower surface of the board 12. 
The mounting for the fin 10 includes a U-shaped bracket 14 which has a pair 
of parallel arms 15 which fit one on each side of the fin 10 and are 
pivotally connected to the fin 10 by means of a pin 16 which passes 
through aligned apertures 17 formed in the arms 15 adjacent the ends 
thereof and an aperture 18 formed in the fin 10. The pin 16 has an 
enlarged head portion 19 to facilitate removal of the pin 16 if, for 
example, it is desired to replace the fin 10 by one of greater or lesser 
length or, as described below with reference to FIGS. 4 and 5, to replace 
the adjustable fin 10 by a fixed fin. 
In practice, the overall length of the fin 10 which is chosen will depend 
on the area of sail carried by the windsurfer board and this will depend 
not only on the wind conditions but also on the weight and sailing ability 
of the person using the windsurfer board. For a larger area of sail, a 
longer fin will be used As shown in the drawings, a small number of spaced 
apertures 18 may be formed in the fin 10 so that, by appropriate selection 
of the aperture 18 in which the pin 16 is to be fitted, a degree of 
adjustment of the effective fin area can be achieved. Such adjustment will 
be effected out of the water and will depend on the individual user and on 
the wind and wave conditions. 
The fin 10 has a leading edge 20 and a trailing edge 21 and, although the 
design of the fin 10 may be varied significantly, the leading edge 20 may 
comprise an upper straight portion followed by a relatively short lower 
curvate portion 22, whilst the trailing edge 21 again comprises an upper 
straight portion followed by a somewhat longer lower curvate portion 23. 
The fin 10 is formed, adjacent its upper edge, with a pair of transverse 
bores 24 and 25 in which stop plugs 26 and 27 respectively are fitted so 
as to project beyond the adjacent surfaces of the fin 10 and on each side 
of the fin 10. The plug 26 which is closer to the trailing edge 21 of the 
fin 10 is a simple cylindrical plug whereas the plug 27, which is closer 
to the leading edge 20 of the fin 10, is provided at each end with a 
raised projection 28 of square cross-section positioned so that, when the 
fin 10 is in its raised position as shown in FIG. 2, each projection 28 
engages the associated arm 15 of the bracket 14 to limit the extent of 
movement of the bracket 14 and hence of the fin 10. 
Spacers 29 and 30 are fitted within the box 11, one adjacent each of the 
side walls 31, 32 of the box. The spacers 29 and 30 are formed of a 
material having a low coefficient of sliding friction with the fin 10, the 
preferred material being ultra high molecular weight polyethylene, though 
other low friction materials, for example polytetrafluoroethylene, could 
also be used. Each of the spacers 29, 30 is in the form of a generally 
flat plate of the configuration shown in FIG. 3. 
The upper edge of each spacer 29, 30 is thus provided with a pair of spaced 
rebates 33, 34 which are aligned with corresponding rebates 33, 34 formed 
in the side walls 31 and 32 of the box 11. The spacings between the 
rebates 33, 34 correspond to the spacing between the plugs 26 and 27. 
Thus, when the fin is in its lowermost position as shown in FIG. 1, the 
plugs 26 and 27 sit in the rebates 33, 34 in the spacers 29 and 30 and in 
the aligned rebates 33, 34 in the box side walls 31 and 32, which rebates 
act as locating elements for the fin 10. Each spacer 29, 30 and each box 
side wall 31, 32 is also formed with a cut-out 35 which acts (as described 
below) as a locating formation when a fixed fin is used (as shown in FIGS. 
4 and 5) in place of the fin 10 of FIGS. 1 to 3. 
In production, there will inevitably be variations in the transverse 
spacings of the side walls 31 and 32 of the box 11 and in the thickness of 
the fin 10. The spacers 29 and 30 may thus additionally act as shims and, 
as appropriate, two or more spacers will be used to ensure that the fin 10 
is a close sliding fit between the walls 31 and 32 of the box 11. As an 
alternative to using different numbers of spacers 29, 30, it is also 
possible to provide spacers of different thicknesses or to provide 
separate shims. This will be of advantage if, for example, a fin box 
assembly is provided which includes a plurality of alternatively usable 
fins which are of different lengths and of different thicknesses. 
One of the arms 15 of the bracket 14 is formed with a seating 36 in line 
with the through aperture 17 which receives the pin 16. The pin 16 can be 
a drop-nose pin and the seating 36 will then receive the drop-nose 
formation of the pin 16 to receive and locate it in position. 
The upper surface 39 of the fin 10 is formed with a pair of spaced recesses 
each of which receives a tag 37 attached to a lifting loop 38 which 
projects above the fin 10. The tags 37 are fixed in position by suitable 
pins (not shown). The lifting loop 38 may comprise a tube of polyvinyl 
chloride with a fabric covering of, for example, polyethylene 
terephthalate. 
The upper surface 39 of the fin 10 is of a non-slip nature and this may be 
afforded by, for example, bonding a layer of non-slip material to the 
upper edge of the fin 10. The upper surface 39 is proud of the box 11 when 
the fin 10 is in its raised position as shown in FIG. 2. 
When the windsurfer is being sailed up-wind, the fin 10 will be in its 
lowermost position as shown in FIG. 1. The fin 10 will project downwardly 
a substantial distance below the board 12 and will accordingly provide 
substantial transverse reaction in respect of the transverse forces to 
which the sail and board are subjected while sailing up-wind. The area of 
the fin 10 which is in the water and the depth of downward projection of 
the fin 10 provide additional lift and enhance the pointing ability of the 
board 12 to enable the board to be sailed up-wind more efficiently than 
would otherwise be the case. 
At the end of the up-wind leg, the windsurfer will bear off slightly to 
reduce the pressure on the fin 10 and bend down to grasp the lifting loop 
38. An upward lifting action will then serve to move the fin from its 
lowermost position as shown in FIG. 1 into its raised position as shown in 
FIG. 2 in readiness for sailing the board along the down-wind leg. As 
shown in FIG. 2, the fin 10 is not only displaced bodily upwardly but is 
also raked rearwardly as compared to its FIG. 1 position thereby effecting 
a very substantial reduction in the extent by which the fin 10 projects 
downwardly below the board 12 and in the degree of lift arising from the 
presence of the fin. 
At the end of the down-wind leg, the person sailing the board will apply 
foot pressure to the non-slip upper surface 39 and, by pressing 
downwardly, will move the fin 10 from its raised position back into its 
lowermost position. The increase in the effective area of the fin 10 which 
is then achieved by pivoting the fin 10 back into a substantially vertical 
position as well as displacing the fin 10 bodily downwardly is 
considerably greater than would be the case if the fin 10 were merely 
pivoted forwardly into a generally vertical position. 
As shown in the drawings, the fin box assembly is located centrally of the 
board 12 just to the rear of the foot straps 40. The upper edges of the 
walls of the box 11 will be sanded or ground away so that they lie either 
flush with the upper surface of the board 12 or project just above the 
upper surface of the board 12. In this respect, a small degree of 
projection above the upper surface of the board 12 is to be regarded as 
"substantially flush" with said upper surface. 
The box 11 includes a boss 41 which fits between forwardly extending stubs 
42 and 43 of the bracket 14 with a pin 44 extending through aligned bores 
in the boss 41 and the stubs 42 and 43 to provide for the pivotal mounting 
of the bracket 14. In a typical construction, the axis of the pin 44 is 
located approximately 0.3 inches above the upper surface of the board 12. 
The front and rear walls 45 and 46 of the box 11 can be inclined rearwardly 
so that, when the fin 10 is moved into its rearwardly raked position as 
shown in FIG. 2, the leading and trailing edges 20 and 21 of the fin 10 
will lie in substantial contact with the walls 45 and 46. The walls 45 and 
46 will thus act as stops. In addition, the close spacing between the 
leading and trailing edges 20 and 21 of the fin 10 and the walls 45 and 46 
will reduce the tendency for the generation of a downward flow of air 
through the box 11 during the high-speed down-wind leg. 
This downward flow of air is further prevented by means of a sealing gasket 
47 which is bonded to the downwardly facing surfaces of the walls of the 
box 11 and is formed of a resiliently deformable foamed plastics material, 
such as a foamed polyurethane or a foamed silicone rubber. The sealing 
gasket 47 is shaped so that it is a close fit around the fin 10 whilst the 
resilient nature of the gasket material enables the gasket 47 to flex and 
maintain its sealing action during movement of the fin 10 between its 
lowermost position as shown in FIG. 1 and its raised position as shown in 
FIG. 2. 
The walls of the box 11 and the spacers 29 and 30 have a height which is 
slightly less than the thickness of the board 12. The lower surfaces of 
the walls of the box 11 are spaced upwardly from the lower surface of the 
board 12 by a distance corresponding to the thickness of the gasket 47 and 
a flush-fitting arrangement is thus provided. 
Turning next to FIGS. 4 and 5, these show the provision of an additional 
fixed fin 50 which can be installed in place of the adjustable fin 10. The 
fin 10 can be removed, as explained above, by withdrawing the pin 16 from 
apertures 17 and 18. The fixed fin 50, which can be fitted in position in 
place of fin 10, includes an upper portion 51 which is of increased 
thickness as compared to the remainder 52 of the fin 50 which, as shown, 
is of an appropriate streamlined configuration. 
The upper portion 51 of the fin 50 is formed with a transverse slot within 
which is mounted a clamping plate 53 which is rotatable between a 
projecting locking position (as shown) and a release position. Such 
rotation of the clamping plate 53 is effected by means of a locking screw 
54 which can be tightened by means of a screwdriver or similar tool so 
that the ends of the plate engage within the cut-outs or locating 
formations 35 in the spacers and box side walls 31, 32. 
The upper portion 51 of the fin 50 is formed with spaced transverse bores 
in which depth stop plugs 55 and 56 are fitted. These plugs 55 and 56 
engage in the rebates 33 and 34 in the spacers and in the aligned rebates 
in the box side walls 31 and 32. A sealing gasket (not shown) 
corresponding to sealing gasket 47 is again fitted around the fin 50 to 
prevent the down-flow of air through the box. The length of the fin 50 
will be chosen so as to obtain an acceptable compromise performance, 
providing substantial lateral restraint during the up-wind leg without 
excessive drag and lift during the downwind leg.