AU2009214814A1 - Surfboard fin - Google Patents

Description

WO 2009/100479 PCT/AU2009/000147 -1 Surfboard Fin Field of the Invention This invention relates to a fin for a watercraft, particularly, although not exclusively, a surfboard. 5 Background Art The following discussion of the background to the invention is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge of the 10 person skilled in the art in any jurisdiction as at the priority date of the invention. Surfboards have been used as a recreational pastime and sport for some decades. Surfboards comprise an elongate deck made of materials such as polyurethane or polystyrene with a pointed or rounded front end or 'nose' and a back end or 'tail'. The edges of the surfboard are called the 'rail'. 15 The underside of the surfboard is called the bottom and this rests on the water when in use. Importantly, one or more fins are provided on the bottom of the surfboard towards the tail of the surfboard. Fins provide stability for the surfboard, reducing the tendency for the surfboard to slide sideways on the water. Single or multiple fin arrangements are known. 20 Fins extend substantially perpendicular to the bottom of the surfboard and are generally constructed to have a curved cross-sectional profile with at least one curved face. Surfers stand on the deck of the surfboard and ride breaking waves. Surfers are able to manoeuvre the surfboard by leaning their bodies at different angles. 25 Particularly, the surfer will lean so as to dip the left or right rails into the wave to enable the surfboard to turn when riding the wave. The rail can have a rounded WO 2009/100479 PCT/AU2009/000147 -2 or squared cross-section, and the shape will also have an effect upon the way in which the surfboard rides across the surface of the water, and the wave face. It is the combination of the hydrodynamic effects of the curvature of the rail, the orientation and construction of the fin(s) and any curvature of the bottom of the 5 surfboard that contribute to the dynamics and manoeuvrability of the surfboard. In particular, the effect of the curved surfaces on the velocity of water travelling over the surfaces of the rail and fin and velocity and pressure differentials arising therefrom, as well as the Coanda effect influence the manoeuvrability of the surfboard. 10 Disclosure of the Invention In accordance with a first aspect of the present invention, there is provided a watercraft fin comprising a leading foil, an inner foil and an outer foil, the leading foil, the inner foil and the outer foil having proximal ends for attachment to a watercraft and distal 'ends, the inner foil and the outer foil being integrally formed 15 at the distal ends to define a curved outer portion, and the leading foil being integrally formed with the curved outer portion at its distal end. Preferably, the inner foil and the outer foil have a curvi-linear cross-sectional profile. Alternatively, the inner foil and the outer foil have a cross-sectional profile in which both faces are curved. 20 Preferably, the leading foil has a cross-sectional profile in which both faces are curved, a first face being concave and a second face being convex. Alternatively, the leading foil has a cross-sectional profile in which first and second faces are convex. Preferably, the leading foil extends from the curved portion with a lateral curve 25 therein. Preferably, the leading foil is arranged forward of the inner foil and the outer foil. Preferably, the inner foil is mounted forward of the outer foil.

WO 2009/100479 PCT/AU2009/000147 -3 Preferably, the leading foil, inner foil and outer foil have splayed proximal ends. In accordance with a second aspect of the present invention, there is provided a watercraft comprising a board comprising a deck, a bottom, and at least two edges and at least one fin provided at the bottom, the at least one fin comprising a 5 leading foil, an inner foil and an outer foil, the leading foil, the inner foil and the outer foil having proximal ends for attachment to the bottom and distal ends, the inner foil and the outer foil being integrally formed at the distal ends to define a curved outer portion, and the leading foil being integrally formed with the curved outer portion at its distal end. 10 Preferably, the inner foil and the outer foil have a curvi-linear cross-sectional profile. Alternatively, the inner foil and the outer foil have a cross-sectional profile in which both faces are curved. Preferably, the leading foil has a cross-sectional profile in which both faces are curved, a first face being concave and a second face being convex. Alternatively, 15 the leading foil has a cross-sectional profile in which first and second faces are convex. Preferably, the leading foil extends from the curved portion with a lateral curve therein. Preferably, the watercraft comprises at least two fins, one fin adjacent each of the 20 edges of the watercraft. Preferably, the watercraft comprises a third fin located substantially centrally of the width of the watercraft. The present invention has the advantage that the cross-sectional profile and the arrangement of the leading, inner and outer foils may combine the Coanda effect with other hydrodynamic effects to generate improved stability and 25 manoeuvrability than known surfboards. The present invention may also be structurally stronger than traditional fins. The provision of the curved top surface of the fins may also provide a protective element as its curved profile may be blunt rather than sharp with traditional surfboard fins.

WO 2009/100479 PCT/AU2009/000147 -4 Brief Description of the Drawings The invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic, perspective drawing of a surfboard incorporating two fins 5 in accordance with an aspect of the present invention; Figure 2 is an underside view of the rear section of the surfboard of Figure 1, as viewed in the direction of arrow I in Figure 1; Figure 3 is a rear view of the tail of the surfboard of Figure 1, as viewed in the direction of arrow Ill in Figure 2; 10 Figure 4 is a side perspective view of a first outside fin for mounting on the surfboard of Figure 1; Figure 5 is a front perspective view of the first outside fin of Figure 4, as viewed in the direction of arrow V in Figure 4; Figure 6 is a plan view of a first outside fin for mounting on the surfboard of Figure 15 1; Figure 7A is a front view of the first outside fin of Figure 6, as viewed in the direction of arrow VII in Figure 6; Figure 7B is a front view of a second outside fin for mounting on the surfboard of Figure 1; 20 Figure 8A is a rear view of the first outside fin of Figure 6, as viewed in the direction of arrow VIII in Figure 6; Figure 8B is a front view of a second outside fin for mounting on the surfboard of Figure 1; WO 2009/100479 PCT/AU2009/000147 Figure 9 is a schematic cross section of the first outside fin of Figure 6, as viewed along the plane IX-IX' in Figure 4, illustrating water flow around the foils of the fin during travel of the fin through water; Figure 10 is a perspective view of an alternative embodiment of a central fin for 5 mounting on the surfboard of Figure 1; Figure 11 is a front view of the central fin of Figure 11, as viewed in the direction of arrow XI in Figure 10; Figure 12 is a schematic partial cross-section of the rail edge of the surfboard of Figure 1 illustrating the travel of the surfboard through a wave; 10 Figure 13 schematically illustrates how the fins and rail of the surfboard of Figure 1 assist the travel of the surfboard through a wave; Figure 14A is a schematic plan view of a surfboard with the central fin of Figure 10 mounted thereon; Figure 14B is a schematic side view along the direction of arrow XIV of the 15 surfboard illustrated in Figure 14A; Figure 15 illustrates the fluid flow around the central fin of Figure 10; Figure 16A is a schematic plan view of a surfboard With the central fin of Figure 10 mounted thereon with two conventional outer fins; and Figure 16B is a schematic side view along the direction of arrow XVI of the 20 surfboard illustrated in Figure 16A. Best Mode(s) for Carrying Out the Invention Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to WO 2009/100479 PCT/AU2009/000147 -6 imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Furthermore, throughout the specification, unless the context requires otherwise, the word "include" or variations such as "includes" or "including", will be 5 understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. A surfboard 1 has a deck 2, a bottom 3, a nose 4 and a tail 5. The rails 6a, 6b or edges of the surfboard 1 run from the nose 4 to the tail 5. In this embodiment, the rails 6a, 6b have a curved edge, although other constructions can be used. This 10 curved cross section is illustrated schematically in Figure 12. In use, the straight profile of the bottom 3 and the curved profile of the deck 2 provide for high pressure and low pressure areas adjacent the bottom 3 and deck 2 respectively. This, along with the downward force of the surfer standing on the surfboard 1 allows the surfboard 1 to ride the wave: the face 26 of the wave being illustrated in 15 Figure 12. Towards the tail 5 of the surfboard 1 and mounted on the bottom 3 of the surfboard 1 are three fins 7, 8a, 8b. The three fins 7, 8a, 8b extend substantially vertically from the bottom 3 of the surfboard 1 parallel to the longitudinal axis 9 of the surfboard 1. The central fin 7 is located substantially centrally of the bottom 3 20 of the surfboard 1 along the longitudinal axis 9 and adjacent the tail 5. The outer fins 8a, 8b are located towards the rail 6a, 6b, respectively, forward of the central fin 7 and substantially equal distances from the longitudinal axis 9. In a first embodiment, the central fin 7 is a conventional fin and need not be described in any further detail herein. 25 The outer fins 8a, 8b will now be described in further detail. The two outer fins 8a, 8b are substantially identical, except that one is a mirror image of the other.

WO 2009/100479 PCT/AU2009/000147 -7 Consider the first outer fin 8a which is designed to be located towards the first rail 6a. In this embodiment, this would be the left-hand rail 6a as determined by a surfer standing on the deck 2 of the surfboard 1. The first outer fin 8a comprises three separate foil sections 10, 11, 12 joined 5 together to form an integral unit, as will be described in more detail below. The first outer fin 8a is illustrated in more detail in Figures 4 to 6. The three foils are an inner foil 10, an outer foil 11, and a leading foil 12. Each foil 10, 11, 12 has a proximate end 10 a, 11 a, 12a for attaching to the bottom 3 of the surfboard 1, and distal ends 1Ob, 11b, 12b. The distal ends 1Ob, 11b, 12b 10 are joined together to form the integral fin unit. Specifically, the distal end 1Ob of the inner foil 10 and the distal end 11 b of the outer foil 11 are joined together in a curved configuration to define a substantially U-shaped curved outer portion or arch 14 of the first outer fin 8a. This can be seen clearly in Figure 4. The distal end 12b of the leading foil 12 is also joined to the curved outer portion 15 or arch 14 so as to be integrally formed with therewith. The leading foil 12 extends from the arch 14 at an angle to the vertical so that the proximate ends 10a, 11a, 12a of the respective foils 10, 11, 12 have a generally triangular configuration in relation to each other when mounted on the bottom 3 of the surfboard 1. 20 The leading foil 12, the inner foil 10, and the outer foil 11 extend from the arch 14 at an orientation so that when the first outside fin 8a is mounted on the surfboard 1, the leading foil 12 is mounted forward of both the inner foil 10, and the outer foil 11. The outer foil 11 and the inner foil 10 extend so that, when the first outer fin 8a is mounted on the surfboard 1, the outer foil 11 is located towards the first rail 25 6a (i.e. 'railside') of the surfboard 1 while the inner foil 10 is located towards the central longitudinal axis 9 of the surfboard 1. The inner foil 10 is mounted slightly forward of the outer foil 11. This can be seen in Figures 3 and 6. The staggered arrangement allows the water to move freely around the foils 10, 11, 12 during manoeuvres.

WO 2009/100479 PCT/AU2009/000147 -8 The leading foil 12 extends with a slight lateral curve so that, when it is mounted on the surfboard 1, the leading foil 12 curves towards the longitudinal axis 9 of the surfboard 1. This can be seen in Figures 3 and 6. This lateral curve is important as it enhances the Coanda effect - which is discussed in more detail below. The 5 curve assists the water flow to the inner foil 10 which increases the velocity of the water flow. However, in an alternative embodiment, there can be no curve. The arch 14 of the first outer fin 8a, defines a curved outer surface 17 which acts similar to the rails 6a, 6b - that is that water will tend to flow along the curved surface 17 in accordance with the Coanda effect, thus providing release and hold 10 in the same way as the rail 6a, 6b functions when the surfboard 1 travel across the water and in the face 26 of a wave. This is illustrated schematically in Figure 13, with high pressure developed under the surfboard 1 and the weight of the surfer acting downwards on the surfboard 1 as discussed above. The leading foil 12, the inner foil 10 and the outer foil 10 have specific horizontal 15 cross -sectional profiles to provide the required functionality and advantages over known surfboard fins. These are illustrated in Figure 9. The inner and outer foils 10, 11 have a horizontal cross-sectional profile in which each has a curved upper face 13 that faces the first rail 6a, while the opposing inner face 14 of each of the inner and outer foils 10, 11 is substantially planar with 20 a slightly foiled edge that allows for the Coanda effect to work - see Figure 9. That is the inner and outer foils 10, 11 have a curvi-linear cross-sectional profile. The leading foil 12 has both faces 15, 16 that are curved - again towards the first rail 6a. The leading foil upper face 15 is curved towards the first rail 6a in the same way as the curved upper faces 13 for the inner and outer foil 10, 11 i.e. a 25 convex curve. The lower curved face 16 is curved inwardly (or concave in profile). The inner foil 10, the outer foil 11, and the leading foil 12 have splayed proximate ends 1Oa, 11a, and 12a.

WO 2009/100479 PCT/AU2009/000147 -9 The profiles and curvature of the foils 10, 11, 12 may be altered to meet the requirements of the performance of the surfboard 1. For example, the arch 14 may be made tighter or larger in size for use in large waves, while the arch 14 can be wider or smaller for use in smaller waves or for other surf craft. Variations to 5 the size and relative dimensions and shape can be made, providing the dynamics of the water flow are maintained. The other second outer fin 8b is the same as the first outer fin 8a described above, except that it is a mirror image. In this way, the curved faces 13 of the inner and outer foils 10, 11 also face the rail 6b when the second outer fin 8b is 10 mounted on the bottom 3 of the surfboard 1. Figures 7A and 8A provide front and rear views of the second outer fin 8b - as compared to the front and rear view of the first outer fin 8a illustrated in Figures 7B and 8B. The sizes and dimensions of the outer fins 8a, 8b depend to some extent upon the performance required of the surfboard 1. As an example, the dimensions 15 described below are used. There are a number of different aspects to the shape and size of the outer fins 8a, 8b, as will be described in more detail below: Base: This is the length of the outer fin 8a, 8b where it meets the surfboard 1. The base primarily affects the amount of drive the surfboard 1 will have. Generally the more base the more area the outer fin 8a, 8b has to push against the water and 20 therefore the more drive. The less base the shorter the turning arc. In this embodiment, the base sizes for the outer fins 8a, 8b are as follows: leading foil 12 - 80-105mm, inner foil 10 - 80-95mm, and outer foil 11 - 70mm. The length from the tip of leading foil 12 to the back of the outer foil 11 is 220mm. Height (Depth): The height of the fin determines the distance/depth that the outer 25 fin 8a, 8b penetrates into the water. It affects the hold and control the outer fin 8a, 8b has in a turn. The shorter the fin, the less hold the surfboard 1 will have. The longer the fin, the more hold. Generally a larger heavier person will need a fin with more depth than smaller and lighter person. In this embodiment, the height (depth) of the outer fins 8a, 8b from base to highest point is between 112mm and 30 125mm.

WO 2009/100479 PCT/AU2009/000147 -10 Sweep: The sweep is the angle measured between the vertical line from the mid point of the base to the highest point on the fin. Put simply, this is the extent to which the outline shape is curved backwards. The more sweep, the longer the turning arc, whilst the less sweep, the tighter the tuning arc. In this embodiment, 5 the sweep of the leading foil 12 is 55 degrees. The inner and outer foils 10, 11 have a sweep of 100 degrees. Toe Angle: The toe angle is the angle the outer fin subtends to the centre line (sometimes called a 'stringer) of the surfboard 1. In the present embodiment, the optimum toe angle for the outer fins 8a, 8b is 5 to 6 degrees 10 Cant: The cant is the angle of the outer fin 8a, 8b leaning out from the bottom surface 3 of the surfboard 1. In this embodiment, the cant for the leading foil 12 is 84 to 94 degrees. Fin distance from tail of board: The placement of fins in relation to how far back towards the tail 5 of the surfboard 1 affects the looseness of the surfboard 1. The 15 further back the fin towards the tail 5 the stiffer the surfboard 1 feels during manoeuvres and the further forward to wards the nose 4 the looser the feel of the surfboard 1. In this embodiment, the distance of the outer foil 11 to the tail 5 is 254mm, and can be adjusted depending on desired performance. Generally, the inner and outer foils 10, 11 and the leading foill 2 generate more lift 20 for less drag - therefore are more efficient, faster, can push them harder, are smoother and offer more controlled maneuvers. The operation of the surfboard 1, and specifically the first and second outer fins 8a, 8b, will now be described with reference to Figure 9. When in the water, the surfboard 1 will be travelling in the direction of arrow A (as 25 shown in Figure 9). The flow of the water around the first outer fin 8a, and the inner foil 10, the outer foil 11 and the leading foil 12 can be seen.

WO 2009/100479 PCT/AU2009/000147 The Venturi effect provides pressure variations (due to velocity variations in the fluid flow) with low pressure regions within the central region 19 of the first outer fin 8a, while the two curved faces of the leading foil 12 result in the Coanda effect providing improved water flow around the leading foil 12. It is the applicant's 5 understanding that the synergistic effects of the three foils 10, 11, 12 and in particular the Coanda effect of the leading foil 12, and the Venturi effect providing low and high pressure regions around the three foils 10, 11, 12 provide for reduced drag and turbulence in the water flow in and around the fin 8a and thus enhanced stability and manoeuvrability of the surfboard 1. In addition, the joining 10 of the three foils 10, 11, 12 and the resultant curved outer surface 17 of the arch 14 increase cohesion of the surfboard 1 to the wave face when turning while reducing drag. This also helps water flow around the inner foil 10, and the outer foil 11. However, it should be understood that the physics of hydrodynamics is complex 15 and the advantages displayed by the present invention may be due to additional or different effects or combinations of these. Prototype experiments with these fins have demonstrated significant advantages over known fins and surfboards. The construction of these fins and the fact that there is a plurality of foils also provides for increased sturdiness and strength. In particular, the three points of 20 attachment create a sturdier arrangement than a single foil fin. In another embodiment of the invention, the central fin 20 can also have a three foil construction. This is illustrated schematically in Figures 10 and 11. The central fin 20 in this embodiment comprises first and second rear foils 21, 22, and a central forward foil 23 joined together to form an integral unit. As with the 25 first and second outer fins 8a, 8b, this central fin 20 forms a central fin arch 24 or outer curved portion provided by the joining of distal ends 21 a, 21 b of the first and second rear foils 21, 22. The central forward foil 23 also extends from the central fin arch 24. In this embodiment, all first and second rear foils 21, 22 and the central forward foil 23 have curved faces 25, rather than one curved face and one WO 2009/100479 PCT/AU2009/000147 - 12 planar face. Figures 14A and 14B are partial plan and side views of a surfboard 1 with a central fin 20 fixed thereon. The dimensions for the central fin are - in this embodiment - as follows: Base: central forward foil 23 - 80mm, first and second rear foils 21, 22 - 75 mm. 5 The length from tip of central forward foil 23 to the back of the rear foils 21, 22 111mm. Height: 125mm 10 Sweep: 50 degrees Toe angle: none as it is centred. Cant: none as it is vertical 15 Fin distance from tail 5 of surfboard 1: 100m to 140mm depending on desired performance The fluid flow around this central fin 20 is illustrated schematically in Figure 15. The surfboard 1 can be any suitable surfboard and, as such, need not be 20 described in any further detail herein. The fin is manufactured from resin or any other suitable material such as fibre glass, plastic, epoxy, wood, aluminium or other strong lightweight material. Any suitable manufacturing technique can be used. The foils can be permanently and integrally formed with the bottom 3 of the 25 surfboard 1. Alternatively, the fins 7, 8a, 8b can be detachably mounted on to the bottom 3 of the surfboard 1 using any suitable fixing, for example using available fin attachment systems, bolts or screws. The use of three foils in particular provides extra contact points with the bottom 3 of the surfboard 1. This provides the more robust attachment to the surfboard 1 30 referred to above, and also makes the surfboard 1 go faster in powerful sections of waves and provides increased 'hold' of the waves.

WO 2009/100479 PCT/AU2009/000147 -13 While the embodiment described herein describes the use of two outer fins 8a, 8b used with either a conventional central fin 3 or a three-foiled central fin 20. The surfboard 1 could be used without a central fin, or could be used with a three foiled central fin 20 but without the two first and second outer fins 8a, 8b - as 5 illustrated in Figures 14A and 14B. In an alternative, the central fin 20 could be used with conventional fins on the outside - see Figures 16A and 16B. The three foiled fin can be used in any known surfboard configuration. Additionally, embodiments of the fin according to the invention may be used with watercraft other than surfboards that would benefit from their use including, for 10 example, body-boards and sail boards. It should be appreciated by the person skilled in the art that variations and combinations of features described above, not being alternatives or substitutes, can be combined to form yet further embodiments falling within the intended scope of the invention. 15 Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims (22)

1. A watercraft fin comprising a leading foil, an inner foil and an outer foil, the leading foil, the inner foil and the outer foil having proximal ends for attachment to a watercraft and distal ends, the inner foil and the outer foil being integrally 5 formed at the distal ends to define a curved outer portion, and the leading foil being integrally formed with the curved outer portion at its distal end.

2. A watercraft fin according to claim 1, wherein the inner foil and the outer foil have a curvi-linear cross-sectional profile.

3. A watercraft fin according to claim 1, wherein the inner foil and the outer foil 10 have a cross-sectional profile in which both faces are curved.

4. A watercraft fin according to any one of claims 1 to 3, wherein the leading foil has a cross-sectional profile in which both faces are curved, a first face being concave and a second face being convex.

5. A watercraft fin according to any one of claims 1 to 3, wherein the leading foil 15 has a cross-sectional profile in which first and second faces are convex.

6. A watercraft fin according to any preceding claim, wherein the leading foil extends from the curved outer portion with a lateral curve therein.

7. A watercraft fin according to any preceding claim, wherein the leading foil is arranged forward of the inner foil and the outer foil. 20

8. A watercraft fin according to any preceding claim, wherein the inner foil is mounted forward of the outer foil.

9. A watercraft fin according to any preceding claim, wherein the leading foil, the inner foil and the outer foil have splayed proximal ends.

WO 2009/100479 PCT/AU2009/000147 -15 1O.A watercraft comprising a board comprising a deck, a bottom, and at least two edges and at least one fin provided at the bottom, the at least one fin comprising a leading foil, an inner foil and an outer foil, the leading foil, the inner foil and the outer foil having proximal ends for attachment to the bottom 5 and distal ends, the inner foil and the outer foil being integrally formed at the distal ends to define a curved outer portion, and the leading foil being integrally formed with the curved outer portion at its distal end.

11.A watercraft according to claim 10, wherein the inner foil and the outer foil have a curvi-linear cross-sectional profile. 10

12.A watercraft according to claim 10, wherein the inner foil and the outer foil have a cross-sectional profile in which both faces are curved.

13.A watercraft according to any one of claims 10 to 12, wherein the leading foil has a cross-sectional profile in which both faces are curved, a first face being concave and a second face being convex. 15

14.A watercraft according to any one of claims 10 to 12, wherein the leading foil has a cross-sectional profile in which first and second faces are convex.

15.A watercraft according to any one of claims 10 to 14, wherein the leading foil extends from the curved portion with a lateral curve therein.

16.A watercraft according to any one of claims 10 to 15, wherein the leading foil is 20 arranged forward of the inner foil and the outer foil.

17.A watercraft according to any one of claims 10 to 16, wherein the inner foil is mounted forward of the outer foil.

18.A watercraft according to any one of claims 10 to 17, wherein the leading foil, the inner foil and the outer foil have splayed proximal ends. 25

19.A watercraft according to any one of claims 10 to 18, comprising at least two fins, one fin adjacent each of the edges of the watercraft. WO 2009/100479 PCT/AU2009/000147 - 16

20.A watercraft according to any one of claims 10 to 19, comprising a third fin located substantially centrally of the width of the watercraft.

21.A watercraft fin substantially as hereinbefore described with reference to the accompanying drawings. 5

22.A watercraft substantially as hereinbefore described with reference to the accompanying drawings.