AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: PAUL HOLLIDAY Actual Inventor: PAUL HOLLIDAY Address for Service: Chrysiliou IP Patent and Trade Mark Attorneys 114-115/Biztek 20 Dale Street Brookvale, Sydney NSW 2100 Invention Title: A Fin The following statement is a full description of this invention, including the best method of performing it known to me/us: o:\patcnts\application\206R5.doctp 20685 A Fin Technical Field This invention relates to a fin suitable for use with watercraft. Although it will be convenient to describe the invention with reference to a surfboard, it is to be s understood that this is not to be a limitation of the scope of the invention. Background Watercraft often relies upon fins to provide stability in forward travel and to facilitate tight, smooth turns. These fins generally protrude from an underside of the craft so as to engage the water and obtain lift therefrom, as well as to change the io water direction as it flows past the fin. However, much is demanded from the fins by modern craft and by modem riders, particularly board riders, as the craft is quickly changing yaw, roll and pitch, and often the flow around the fin detaches quickly causing turbulence, cavitation or other unwanted eddies. In those situations, the fin's ability to grip and influence the water is greatly reduced, and manoeuvrability 1, suffers. It is also known that straight-line stability is difficult to achieve on certain surf craft, especially when learning the art of surfing. It is an object of the present invention to provide a fin which overcomes or at least ameliorates the foregoing disadvantages, or which at least provides a useful 20 alternative. Summary of the Invention According to one aspect of the present invention, there is provided a fin for use with a watercraft, the fin including front and rear edges, and a base edge having front and rear ends, the front end being joined to the front edge, the rear end being joined to 25 the rear edge, the rear edge defining first and second recesses; wherein at least part of the second recess extends past the rear end towards the front 2 20685 edge such that the part is in use located directly below at least a portion of the base edge. The watercraft may include a surfboard, a kiteboard, a kayak, a surf ski and the like. Preferably, the rear edge includes a first section defining the first recess and a second s section defining the second recess. The first recess is preferred to be substantially V or U-shaped. Preferably, the first recess is configured such that a swallowtail is created on the rear edge. The configuration of the swallowtail provides a generally lower aspect ratio than would otherwise be provided, reduces friction and increases lift. This offers the advantage of enabling the watercraft to travel at a relatively high 10 speed. More preferably, the second recess may be substantially arcuate in shape. In a preferred embodiment, the fin includes a flexing element. Preferably, the flexing element is made of a flexible material. It is preferred that the flexing element is defined by a combination of the first section, part of the second section and part of the front edge. The flexing element may also be defined by a line representing the 15 shortest distance between the second section of the rear edge and the front edge. It is preferred that the front edge has a first end joined to the front end of the base edge and a second end joined to a first end of the first section of the rear edge. The first section of the rear edge is preferred to have a second end joined to a first end of the second section. The second section of the rear edge is preferred to have a second 20 end being joined to a rear end of the base edge. Preferably, the second section of the rear edge follows a path that curves towards and then away from the front edge. More preferably, at least part of the path is in use located directly below at least part of the base edge. The fin may be connected to the surfboard by any suitable means, In a preferred 25 embodiment, the fin includes an upper end from which one or more tabs stem. The or each tab may be received into corresponding plugs provided in an underside of the surfboard and removably held therein by fastening means such as posts or screws, 3 20685 Alternatively, the fm is retained by attaching its upper end to the underside of the board by fibreglass and resin. According to another aspect of the present invention, there is provided a fin for use with a watercraft, the fin including: s a front edge; a rear edge having a first section defining a first recess and a second section defining a second recess; and a base edge joining the front edge and rear edge; wherein the second section of the rear edge follows a path which extends towards 1o the front edge such that when the fin is in use, at least part of the path is located directly below at least a portion of the base edge. Brief Description of the Drawings The invention may be better understood from the following non-limiting description of preferred embodiments, in which: 15 Figure 1 is a side view of a fin in accordance with one embodiment of the present invention; Figure 2 is a perspective view from above of the fin of Figure 1; Figure 3 is a plan view from bottom of the fm of Figure 1; Figure 4 is a plan view from above of the fin of Figure 1; 20 Figure 5 is an cnd view from behind of the fin of Figure 1; Figure 6 is an end view from the front of the fin of Figure 1; Figure 7 is a side view of a fin in accordance with another embodiment of the present invention; and Figure 8 is a side view of a fin in accordance with a further embodiment of 25 the present invention. 4 20685 Detailed Description of the Drawings It will be appreciated that although a fin is used herein with a surfboard as an example, the fin may equally be used or adapted to use with other watercraft such as kite boards, kayaks, surf skis, stand up paddle boards and the like. s Referring to Figures 1 to 6, a fin 10 includes a front edge 12, a rear edge 14 and a base edge 16. The base edge 16 has a front end 18 and a rear end 20. The front end 18 is joined to the front edge 12, The rear end 20 is joined to the rear edge 14. As best shown in Figure 1, the rear edge 14 has a first section 22 and a second section 24. The first section 22 defines the first recess 26 and the second section 24 10 defines the second recess 28. The front edge 12 has a first end 30 joined to the front end 18 of the base edge 16. The front edge 12 also has a second end 32 joined to a first end 34 of the first section 22 of the rear edge 14. The first section 22 of the rear edge 14 has a second end 36 joined to a first end 38 of the second section 24. The second section 24 of the rear edge 14 has a second end 40 which is joined to the rear 15 end 20 of the base edge 16. As shown in Figures 1 and 2, the first recess 26 is substantially V-shaped rendering the creation of a swallowtail 42 on the rear edge 14. The swallowtail 42 acts to vary the aspect ratio of the end portion 37 (see Figure 1) of the fin along its height, The aspect ratio may be varied in other places along the height in order to gain differing 20 performance benefits, for example, a large bulb at a lower region 35, or a bulb at the upper region 33. The swallowtail 42 is associated with straight line speed as well as through turns, and with increased lift without drag. The second recess 28 is substantially arcuate in shapc. The second section 24 of the rear edge 14 follows a path 44 that curves towards and then away from the front edge 12. A part 46 of the 2s path 44 is in use located directly below a portion 48 of the base edge 16. The contour of the path 44 also means that a part indicated A defined by an imaginary line 50 in Figure 1 of the second recess 28 extends past the rear end 20 towards the front edge 5 20685 12 such that the part A is in use located directly below the portion 48 of the base edge 16. As best shown in Figures 1 and 2, the fin 10 has a flexing element 39 which is made of a flexible material. It should be noted that the entire fin 10 may b made of the 5 same flexible material or alternatively, the remainder of the body of the fin 10 may be made of a different material. The flexing element 39 is defined by a combination of the first section 22, part 4lof the second section 24 and part 43 of the front edge 12. The flexing element 39 is designed such that it is capable of flexing about a straight imaginary line 45 or a curved imaginary line 47. The imaginary line 45 in follows a path having terminal points 49 (on the second section 24 of the rear edge 14) and 51 (on the front edge 12). In other words, the path which the imaginary line 45 follows has the shortest distance between the second section 24 of the rear edge and the front edge 12. The curved imaginary line 47 however is an alternative which is more streamlined and hence may maximise the benefit offered by the flexing 1s motions of the flexing clement 39. It is believed that the flexing element 39 offers the advantage of providing a forward thrust during turns of the watercraft thereby enabling the watercraft to travel at a relatively higher speed. Referring to Figures 1, 2 and 4, the fin 10 has an upper end 52 from which two tabs 54 stem. The tabs 54 are received into corresponding plugs (not shown) provided in 20 an underside of the surfboard and removably held herein by fastening means such as posts or screws. Turning to Figure 7, fin 10A is another embodiment of the present invention having a substantially U-shaped first recess 26A defined by the first section 22A of the rear edge 14. 25 Referring to Figure 8, fin 10B is yet another embodiment of the present invention having an irregular V-shaped first recess 26B defined by the first section 22B of the rear edge 14. In this embodiment, the swallowtail 42A has two limbs 43 and 45. 6 20685 Unlike the embodiment 10 and 1 OB shown in Figures 1 and 7, the limbs 43 and 45 are asymmetrical with limb 43 extending further than limb 45. Now that preferred embodiments have been described, it will be appreciated that the fin of the present invention at least in some embodiments offers at least one or more s of the following advantages: 1. it enables a surfer to grip and influence the water; 2. it enhances manoeuvrability; 3. it facilitates achievement of straight-line stability on the surf craft; and 4. it generates a forward thrust during turns through the flexing element thereby 10 enabling the watercraft to travel at a higher speed Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. All such variations and modifications are to be considered within the scope and spirit of the present invention the nature of which is to be determined from the foregoing 15 description. 7