WO1991017080A1

WO1991017080A1 - Variable angle fin

Info

Publication number: WO1991017080A1
Application number: PCT/AU1991/000174
Authority: WO
Inventors: Robert James Cross; William Charles Barber
Original assignee: Robert James Cross; William Charles Barber
Priority date: 1990-04-30
Filing date: 1991-04-30
Publication date: 1991-11-14

Abstract

A fin (1), used on water craft (25) such as surfboards, giving an adjustable angle (A) to the transverse axis of the water craft (25). The fin (1) is frictionally or mechanically locked in a selected one of a number of possible angular positions. One form includes a box (22), placed in the water craft (25), having a circular sectioned groove (9) which closely houses a cylindrical intermediate section (21), the fin closely sits in a slot within the section (21) and the assembly is clamped tight by screws (19) which force the root (2) of the fin (1) against the bottom of the groove (9).

Description

VARIABLE ANGLE FIN Background Art This invention relates to fins used on surf boards and similar craft. Many recreational water craft such as surf boards and sail boards are required to be manoeuvrable to varying responsive degrees according to water, wave and wind conditions and the desires of the moment of the user. To this degree, surf boards for instance include multiple fins arranged to the rear of the board symmetrically about its centre line and movably adjustable for and aft of the board. They are always set at some predetermined fin inclination angle, typically at an acute outward angle relative to the board undersurf ce. Disclosure of Invention

The present invention sets out to provide a fin which can be set at adjustable fin inclination angles.

Accordingly, in one broad form, the present invention may be said to consist in a fin and attachment assembly wherein the attachment is rigidly fixable to an underside of a water craft and includes a receiving section and the fin includes a root section shaped correspondingly to the receiving section so that it can be releasably, rigidly fixed to the attachment at selectable fin inclination angles.

Preferably the fin is fixedly movable in the attachment in a line within a plane of the fin. Normally the attachment is fixed to an underside of the water craft so that the plane of the fin is aligned approximately longitudinally of the water craft centre line, in some cases the attachment might be fixed to the water craft to provide a small toe in angle of the fin.

Preferably the root is of a generally circular cross-section constant along its length and the attachment includes a correspondingly sized cylindrical hollow defined in part between two sections relatively movable by clamping means so as to releasably clamp the root section within the hollow. In this arrangement the fin root is preferably expandable and retractable so as to effect the releasable clamping action.

An alternative arrangement provides a splined root and correspondingly cross-sectioned receiving section such that the fin may be inserted into the attachment in a selected any one of a plurality of orientations to effect a selected any one of a corresponding number of fin inclination angles.

The fin and attachment assembly are well adapted for use as a steering or stabilising fin of a surf board, sail board or similar. Brief Description of Drawings

By way of example only, two embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Fig. 1 is a cross-sectional sketch of a fin in two possible positions within a fin box, in accordance with the invention;

Fig. 2 is a cross-sectional sketch view of the fin box of Fig. 1;

Fig. 3 is a side sketch view of an alternative, partially disassembled, embodiment of the invention;

Fig. 4 illustrates two portions of the embodiment of Fig. 3 in more detail;

Fig. 5 shows in cross-section a modified fin similar in part to the fin shown in Fig. 1; and Fig. 6 shows in a partially disassembled state an alternative embodiment of the -invention.

Best Mode of Carrying out Invention Fig. 1 shows a surf board fin 1 which has a generally cylindrical sectioned root portion 2 and a hydrodynamic foil section 3. The fin 1 engages by way of the root portion 2 a hollow section of a two-part fin box 4. The two parts of the fin box 4 include a major body section 5, adapted to be fixed within a correspondingly sized hollow portion of the surf board underside in the conventional manner. Further, there is a clamp section 6 connected to the body portion 5 in a manner allowing the fin box to clamp against the root portion of the fin 1 in a releasable manner. Thus the fin 1, while released, may be rotated to any inclination angle A up to that shown at position 3a (in dotted outline).

Further detail of the fin box 4 is shown in Fig. 2. Sections 5 and 6 of the fin box are secured together by a clamp device 7 actuable by a recessed lever device 8. The free end of the attachment 7 is fixed within section 5 while the lever device 8 has a cam action on attachment device 7 so as to draw sections 6 and 5 together in a manner which closes down the cross-sectional size of the generally cylindrical hollow section 9. It is within this hollow section 9 that the root portion 2 of the fin 1 normally resides and the contraction of the cross-sectional width thereby provides the required clamping action.

Fig. 3 shows an alternative embodiment in which the root section 2 of the fin 1 is of a splined cross-section and slides into a mating intermediate section 12, which in turn is attached within a conventional fin box 11. The intermediate section 12 and fin root portion 2 include respective lands 13 and 14, each with a through hole which are aligned once installation is complete and which accept a screw device 15 which threadably engages a conventional clamping plate 16. The clamping plate 16 fits within the conventional side grooves of the fin box 11.

Fig. 4 shows the respective cross-sections of the root portion 2 and intermediate portion 12 of the Fig. 3 embodiment of the device. The non-circular but still rotationally symmetrical cross-section allows rotational free mounting of the two components in a number of selectable, finitely angled apart, orientations.

Fig. 5 shows a fin 1 that can be considered to be a modification of the fin 1 of Fig. 1. It. includes a generally circular cross-section root 2 but in this case the root 2 comprise half sections 17 and 18 which can be forcibly screwed apart by screw 19 engaged in plate 20. Plate 20 is fixed to, or at least held in place below the surface of half section 18.

With the half sections 17 and 18 closely positioned the root 2 is placed in the hollow 9 of the fin box 4 (Fig 2). The root 2 is captured in the hollow cavity 9 by tightening the attachment devices 7 but is still free to move until the securing screw 19 is turned down firmly. This forces apart the halves 17 and 18 and effects the clamping action between the root 2 and fin box 4, thus fixing the fin in position.

Fig. 6 shows another example of the invention. A fin 1 has a root section 2 shaped in. cross section to provide a segment of a circle, the complimentary segment shape being provided by a wedge collar or sleeve 21 slidable down over the fin 1. The root section 2 fits up within a recess of the collar 21. Longitudinally the root section 2 is "T" shaped to provide overhanging ends 26 which stop the collar 21.

Clamping screws 19 and co-operative nuts 20 are used to force apart the root section 2 and collar wedge 21 once they have been slid into a mating box adapter 22. Forcing section 2 and wedge 21 apart wedges the fin 1 into the set position within the circular groove of the adaptor box 22. A coffin 23 is attached in and sealed to a corresponding cavity in the bottom of the board 25, in the same way as a conventional fin box, and, typically by screws 24, the adaptor 22 is fixed within the coffin 23. Thus by loosening screw 19 the fin 1 can be tilted and/or moved longitudinally in adaptor box 22 for performance adjustment purposes or removed completely by removing screws 24 and the adaptor box 22 as a whole.

Claims

CLAIMS: -

1. A water craft fin and attachment assembly comprising: a clamp box fixable rigidly within a water-craft underside and having an exposed generally constant cross-sectional hollow along the substantial length of the box; and a hydrodynamic foil section and a root section, the root section being shaped in cross-section to be releasably rotatably locked in said hollow of said clamp box in a selectable one of a plurality of angular positions, the cross-sectional shape of the root section being generally corresponding to the cross-sectional shape of said hollow.

2. A fin and attachment assembly as defined in claim 1 wherein the root section comprises: a sleeve section of constant part circular cross-section along at least a substantial part of its length and the foil section residing closely within a slot of the sleeve section; and a clamp section integral with the foil section and being shaped so as to compliment the sleeve section cross-section so as to combine and provide a generally constant circular cross-sectioned root assembly.

3. A fin and attachment assembly as defined in claim 2 wherein the sleeve section further includes screw devices being threadably drivable relative to the sleeve section and bearing against respective portions of the clamp section so as to forceably expand the root section in a manner to lock the root section relative to the clamp box in a said selectable angular position.

4. A fin and attachment assembly as defined in claim 1 wherein the clamp box is fixable within a coffin structure, the coffin structure being permanently and rigidly fixable within the water craft body and provides, at least when so fixed, rigidity to the clamp box.

5. A fin and attachment assembly as defined in claim 1 wherein the clamp box is substantially a long rectangular prism including a circular sectioned groove along its length and being exposed through one side of the box.

6. A fin and attachment assembly as defined in claim 5 wherein the clamp box includes clamping devices which when actuated reduce the cross-section of the groove so as to rigidly hold fixed in a selected angular position a fin root within the hollow.

7. A fin and attachment assembly as defined in claim 1 wherein the hollow of the clamp box and the root of the fin are correspondingly splined.

8. A water craft fin and attachment assembly comprising: a clamp box with attaching means to removably fix the box to permanent structure of a water craft underside; a cylindrical hollow along the length of the clamp box being exposed through one side of the clamp box; a fin with a hydrodynamic foil and integral "T" section at a root end of the fin; a sleeve forming part of the fin root end, the foil closely slidingly extending through a slot in the sleeve, the slot being a length shorter than the "T" section so as to provide two overhanging sections at opposite ends of the "T" section; and clamping means threadedly drivable relative to the sleeve and bearing against respective said overhangs so as to screw apart the "T" section and the sleeve, and the sleeve and "T" section combine to define an expandable substantially constant circular cross-sectioned fin root which, when not expanded, fits snugly and rotatably within the hollow, and when expanded fits tightly and non-rotatably within the hollow.

9. A fin having a hydrodynamic foil and an integral "T" section at a root end of the fin, the length of the "T" section being greater than the length of the foil proximate the "T" section so as to provide two overhangings at opposite ends of the fin.

10. A water craft fin comprising: a hydrodynamic foil section and a root section, the root section being shaped in cross-section so as to be releasably rotatably locked in a correspondingly shaped hollow of a clamp box in any one of a plurality of selectable angular positions.

11. A novel fin sized and shaped so as to function in combination with a fin attachment assembly fixed to a water craft underside, such that the combination includes a locking means locking the fin rigidly to the attachment assembly at a selectable one of a plurality of transverse angles to the water craft underside.