Technical Field

This disclosure relates to a fin for a water sport board system and particularly, but by no means exclusively, to a fin for a surfboard.

Background

Fins are provided on surfboards and other such watercraft to facilitate turning and provide general board stability. Without fins the rear end of the board would slide over the surface of the water with little control, particularly during a turning manoeuver. Surfboards commonly use anywhere between one and four fins (located toward the rear end of the board on its bottom surface). For a three finned configuration, there is typically provided a centre fin centrally located between a pair of side fins.

Surfboard fins typically employ a convex or "foiled" surface, enabling them to operate as a type of hydrofoil wing, which can generate lift as the board travels through the water. As persons skilled in the art will appreciate, the ability to generate lift may improve the turning capability of the board to which the fin is attached. However, it is also known that trailing vortices created by the fin as it moves through the water can result in a reduction in lift as well as to create drag.

Summary

In a first aspect there is provided a fin for a surfboard, comprising: a body having a leading edge and a trailing edge; at least one channel defined on a first side face of the body, the at least one channel beginning at, or substantially at, the leading edge and extending at least partially toward the trailing edge and wherein the at least one channel widens as it extends toward the trailing edge.

In an embodiment the channel widens substantially towards the trailing edge.

In an embodiment the depth of the at least one channel decreases towards the trailing edge.

In an embodiment the at least one channel extends substantially from the leading edge of the first side face to the trailing edge thereof. In an embodiment the at least one channel is longitudinally aligned with a surfboard abutment edge of the body.

In an embodiment a plurality of channels are defined on the first side face of the body and wherein the channels are substantially evenly spaced along its length.

In an embodiment the side face has a generally convex profile.

In an embodiment the body has a second side face opposite the first side face and wherein the second side face is substantially planar or concave.

In an embodiment the body has a second side face opposite the first side face and wherein the second side face also has a convex profile.

In an embodiment at least one further channel is defined on the second side face of the body, the at least one further channel beginning at the leading edge and extending at least partially toward the trailing edge and wherein the at least one further channel widens as it extends toward the trailing edge.

In accordance with a second aspect there is provided a fin for a surfboard, comprising: a body having a leading edge and a trailing edge; at least one channel defined on a first side face of the body, the at least one channel beginning substantially at the leading edge and arcing downwardly toward a tip portion of the body.

In accordance with a third aspect there is provided a surfboard fitted with a fin as described in accordance with either of the above aspects.

Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of the inventions disclosed. Description of the Figures

The accompanying drawings facilitate an understanding of the various embodiments:

Figure 1 shows various elevation views of a centre fin in accordance with an embodiment;

Figures 2a and 2b are diagrams shown fluid flow results for a conventional fin and the fin of Fig. 1, respectively;

Figure 3 is a side view of a side fin, in accordance with an embodiment;

Figure 4 is a partial view of a surfboard incorporating centre and side fins, in accordance with an embodiment; and

Figure 5 is a side view of a fin in accordance with an alternative embodiment;

Detailed Description

With reference to Figure 1, there are shown various elevation views of a fin 10 in accordance with one embodiment. According to this particular embodiment, the fin is designed for use with a surfboard and takes on a typical shark fin edge profile. More particularly, the fin 10 illustrated in Figure 1 is suitable for use as a stand-alone centre fin, or as a centre fin in a multi fin configuration.

The fin 10 comprises a fin body 12 which has a leading edge 14 and a trailing edge 16. In use, a board abutment edge 13 of the fin body 12 abuts a bottom surface of a board to which the fin 10 is attached. The fin body 12 comprises a first face 18 and an opposite second face 20. According to the illustrated embodiment, both faces 18, 20 of the fin body 12 have a convex profile. In this manner, the fin body 12 acts as a form of hydrofoil which functions to provide lift, in turn promoting stability and

manoeuvrability during turning manoeuvers. Due to the symmetrical nature of the hydrofoil, such a vertical fin is typically referred to as a "50/50" foil fin.

A plurality of channels 22 are defined on both faces 18, 20 of the fin body 12. The channels 22, which are equally spaced along each face 18, 20, begin adjacent the leading edge 14 and extend toward the trailing edge 16. According to the embodiment shown in Figure 1, the channels 22 are longitudinally aligned with the abutment edge 13. At a mid-point between the leading edge 14 and trailing edge 16 the channels 22 begin to gradually widen. The channels 22 also become shallower as they extend, such that they have all but tapered out by the time they reach the trailing edge 16. In a particular embodiment, the channel width at the leading edge 14 is about lmm and widens to about 5mm near the trailing edge 16. It will be appreciated that the actual widths may vary depending on the size of the fin and the desired flow dynamics.

Through extensive testing, the present inventor has found that such a channel design promotes laminar fluid flow past the fin. More particularly, the present inventor has found that such a design can minimise the turbulence or cavitation that can develop over the hydrofoil body 12 and which can disrupt laminar flow causing drag. Indeed, with reference to the test fluid flow diagram of Figures 2a and 2b, there are shown two fins that have been subjected to a flow of water. The fin in Figure 2a does not include any channels, whereas the fin in Figure 2b includes four channels as described herein. Turning to Fig. 2a, the water approaches the fin at a speed of 3ms then splits around the fin to reforms at the trailing edge of the fin. Here it can be seen that the water speed slows and becomes turbulent, extending well behind the fin. With regards Fig. 2b, the incident water speed is the same (3ms) as for the fin of Fig. 2a, but it can be observed that the area of turbulence (in light grey) is greatly reduced. This turbulent area causes a reduction in speed/drag of up to 0.4ms (for both fins), but for the channelled fin of Fig. 2b quickly returns to normal flow in as little as one fin length.

With reference to Fig. 3, there is shown a fin 10' which is particularly configured for use as a side fin, in accordance with an embodiment. A first 'inner' face is configured for face toward a centre line of the board while the other 'outer' face 54 will face away. According to such an embodiment, the outer face 54 has a convex profile while the inner face has a generally planar profile, as is typical for such side fins. This type of fin design is typically referred to as a "flat foil" fin. The side fin advantageously employs the same spaced apart channels 22 as previously described for the centre fin 10, on only the foiled outer face. Such a channelled side fin design may provide improved turning manoeuvrability, in addition to promoting laminar flow across the fin (i.e. as previously outlined for the centre fin 10).

With reference to Figure 4 there is shown a partial view of a surfboard 70 incorporating a centre fin 10 and a pair of side fins 10', in accordance with an embodiment. The fins 10, 10' secure to the board 70 via one or more board attachment projections (not shown) which extend from the board abutment edge 13 of the respective fin bodies. The projection(s) may be adapted to be removably secured to a mating structure on the bottom surface of the board, or alternatively may be

permanently secured to the board using techniques which are well understood in the art (e.g. as part of the fibre glassing of a fibre glass surfboard, etc.).

With reference to Figure 5 there is shown a fin 10" incorporating a slightly different channel design which still serves to promote flow.

In an alternative embodiment to that described above, the fins may include channels that divert upward or downward as they extend toward the trailing edge.

According to such an embodiment, the channels are not designed to promote laminar flow, but instead to induce spray during sharp turning manoeuvres. In order to achieve this function, the channels (which may be mirrored on each face) may curve

downwardly toward a tip portion of the fin so as to redirect the water away from the board. In further contrast to the channel design of Figs. 1 to 5, the channels may have a constant width and depth. In alternative embodiment, the channels may actually narrow as they extend toward the tip portion to further promote inducing of spray.

According to the illustrated embodiments of Figures 1 to 5, the channels 22 begin to both widen and shallow out approximately half way between the leading edge 14 and trailing edge 16. It will be understood that this may not always be the case. Depending on the desired flow characteristics, the widening/shallowing can commence either closer to the leading edge 14 or closer to the trailing edge 16. Furthermore, it will be understood that the widening may occur before the channels 22 start to shallow and vice versa.

It will also be understood that the number and spacing of channels 22 defined on the fin should not be seen as being limited to that shown in the figures. For example, a smaller sized fin may carry fewer channels that a larger sized fin. Equally, the number of channels and corresponding spacing may be chosen to suit the desired flow characteristics for the fin.

It will be understood that the fins 10, 10' and 10" as described herein can be formed of any suitable material including, fibreglass, glass, carbon fibre, aluminium, nylon, plastic or hard rubber. Further, it should be understood that the general shape of the fins should not be seen as being limited to that particular shape illustrated shown in the Figures. For example, the depth, area, sweep (i.e. the angle measuring how far the outline of the fin is curved backward) and foil can vary depending on waters port application, experience of rider, etc.

In the foregoing description of certain embodiments, specific terminology has been resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "upper" and "lower", "above" and "below" and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

In this specification, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

The preceding description is provided in relation to several embodiments which may share common characteristics and features. It is to be understood that one or more features of any one embodiment may be combinable with one or more features of the other embodiments. In addition, any single feature or combination of features in any of the embodiments may constitute additional embodiments.

In addition, the foregoing describes only some embodiments of the inventions, and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

Furthermore, the inventions have described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the inventions. Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.