Fins with improved fluid dynamic properties

Abstract

A fin for use on a surfboard, the fin comprising: a leading edge, a trailing edge, and a base, the base comprising at least one mount for mounting the fin onto a surfboard; a first and a second outer fin surface which meet along the leading edge and the trailing edge and abut the base; and a first ridge protruding laterally from the first outer fin surface, and/or a second ridge protruding laterally from the second outer fin surface; wherein the shape and configuration of the fin creates an area of lower water pressure around and in front of the fin, as well as disrupting and/or reducing the size of trailing vortices, resulting in additional forward thrust for the board on which the fin is mounted.

Claims

1. A fin for use on a propeller or impeller, the fin comprising: a leading edge, a trailing edge, and a base, the base comprising at least one mount for mounting the fin onto a propeller or impeller; a first and a second outer fin surface which meet along the leading edge and the trailing edge and abut the base; a first ridge protruding laterally from the first outer fin surface, and a second ridge protruding laterally from the second outer fin surface, a third ridge protruding laterally from the first outer fin surface, and a fourth ridge protruding laterally from the second outer fin surface; wherein the third ridge and the fourth ridge are smaller and located further from the base than the first ridge and the second ridge.

2. A fin according to claim 1, wherein the distance of the first ridgeline or the second ridgeline to the base is between approximately 4% and 8% of the distance of the base to the tip of the fin.

3. A fin according to claim 1 wherein the first ridge protrudes laterally from the first outer fin surface, or the second ridge protrudes laterally from the second outer fin surface, to a maximum distance from the centreplane of between 2 to 4.5 times greater than the maximum distance of the centreplane to a non-ridged portion of the first outer fin surface, wherein the centreplane passes through the leading edge and trailing edge of the fin.

4. A fin according to claim 1, wherein the first ridge and the second ridge are located equidistant from the base.

5. A fin according to claim 1, wherein the first ridge comprises a first ridgeline, and the second ridge comprises a second ridgeline, and the first and second ridgelines are on a plane substantially parallel to the base and/or on adjacent surface of the propeller or impeller to which the fin is mounted.

6. A fin according to claim 1, wherein the first ridge comprises first ridge sides, and the second ridge comprises second ridge sides, and the third ridge comprises third ridge sides, and the fourth ridge comprises fourth ridge sides, and at least a portion of the first ridge sides or second ridge sides or third ridge sides or fourth ridge sides comprise concave, convex, and/or flat portions.

7. A fin according to claim 5, wherein the first ridgeline or second ridgeline end at the leading edge.

8. A fin according to claim 1, wherein the third or fourth ridges are on a plane that is substantially parallel to the base, or a plane that is substantially parallel to an adjacent surface of the propeller or impeller.

9. A fin according to claim 1, wherein the third ridge protrudes laterally from the first outer fin surface, or the fourth ridge protrudes laterally from the second outer fin surface, to a maximum distance from the centreplane of between 1.5 to 6 times greater than the maximum distance of the centreplane to a non-ridged portion of the first outer fin surface, wherein the centreplane passes through the leading edge and trailing edge of the fin.

10. A fin according to claim 1, wherein the third ridge and the fourth ridge are located equidistant from the base.

11. A fin according to claim 1, wherein the fin is an adjustable fin comprising: a base comprising: a mount for attaching the fin to a propeller or impeller; and an insert member extending in a direction contrary to the mount; a fin section comprising: two outer fin surfaces which meet at a leading edge and a trailing edge comprising the first and the second outer fin surfaces; an underside surface comprising an opening to an internal cavity within the fin section, the internal cavity within the fin section configured to house the insert member of the base and enable slidable movement of the insert member in a direction towards the leading edge or the trailing edge; and a lock that is manipulable, wherein the lock can releasably couple to the insert member at one of two or more locking positions thereby preventing slidable movement of the insert member; wherein the fin section is configured to adjust relative to the base by manipulating the lock to uncouple the lock from the insert member at a first locking position, slidably moving the insert member through the internal cavity, and releasably coupling the lock to the insert member at a second locking position.

12. A fin according to claim 1, wherein the fin is a detachable fin comprising: a base comprising: a mount for attaching the fin to a propeller or impeller; and an insert member extending in a direction contrary to the mount; a fin section comprising: two outer fin surfaces which meet at a leading edge and a trailing edge comprising the first and the second outer fin surfaces; an underside surface comprising an opening to an internal cavity within the fin section, the internal cavity within the fin section configured to house the insert member of the base; and a lock that is manipulable, wherein the lock can releasably couple to the insert member thereby preventing movement of the fin section relative to the base; wherein the fin section is uncoupled and detached from the base by manipulating the lock to uncouple the lock from the insert member.

13. A fin according to claim 5, wherein the distance of the first ridgeline or the second ridgeline to the base is between approximately 1% and 15% of the distance of the base to the tip of the fin.

14. A fin according to claim 5, wherein the first ridgeline or second ridgeline end at the trailing edge.

15. A fin for use on a propeller or impeller, the fin comprising: a leading edge, a trailing edge, and a base, the base comprising at least one mount for mounting the fin onto a propeller or impeller; a first and a second outer fin surface which meet along the leading edge and the trailing edge and abut the base; a first ridge protruding laterally from the first outer fin surface, or a second ridge protruding laterally from the second outer fin surface, and a third ridge protruding laterally from the first outer fin surface, or a fourth ridge protruding laterally from the second outer fin surface; wherein the third ridge or the fourth ridge is smaller and located further from the base than the first ridge or the second ridge.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1. matching rendered and black and white illustrations showing (A) a port (left) side view, (B) a starboard (right) side view, (C) a front view, and (D) a rear view, of a preferred embodiment of a fixed (non-adjustable) centre fin according to the invention; the fins comprising mounting blocks which can be secured within FCS® fin plugs.

(3) FIG. 2. matching rendered and black and white illustrations showing (A) bottom perspective view, (B) top perspective view, (C) bottom view, and (D) top view, of the preferred embodiment of the non-adjustable centre fin shown in FIG. 1.

(4) FIG. 3. rendered illustrations showing (A) a perspective view, and (B) a front view, of a preferred embodiment of a three-fin thruster arrangement of non-adjustable fins according to the invention; and matching rendered and black and white illustrations showing (C) a starboard side view, and (D) a port side view of the starboard side fin of the thruster arrangement of (A) and (B), the fins comprising mounting blocks which can be secured within FCS® fin plugs.

(5) FIG. 4. illustrations of (A) a side view, (B) a front view, and (C) a side view, of preferred embodiments of a non-adjustable centre fin according to the invention with a mounting block which can be secured within a Futures® fin box.

(6) FIG. 5. matching rendered and black and white illustrations showing (A) front view, (B) top perspective view, (C) port side view, (D) top view, and (E) bottom view, of a preferred embodiment of a non-adjustable centre fin according to the invention with a base attachment surface for mounting the fin to the bottom surface of a surfboard.

(7) FIG. 6. illustrations showing a (A) front view, (B) a rear view, (C) top view, (D) bottom view, (E) starboard side view, and (F) port side view, of a non-adjustable port side fin (left side fin) according of the invention for use in a dual, thruster or quad arrangement, with mounting blocks that can be secured within FCS® fin plugs.

(8) FIG. 7. illustrations showing a (A) front view, (B) a rear view, (C) top view, (D) bottom view, (E) right or starboard side view, and (F) left or port side view, of a non-adjustable port side fin according to the invention for use in a dual, thruster or quad arrangement, with a mounting block that can be secured within a Futures® fin box.

(9) FIG. 8. illustrations showing a (A) front view, (B) a rear view, (C) top view, (D) bottom view, (E) right or starboard side view, and (F) left or port side view, of a non-adjustable port side fin according to the invention for use in a dual, thruster or quad arrangement, with mounting blocks that can be secured with a base attachment surface for mounting the fin to the bottom surface of a surfboard.

(10) FIG. 9. (A) Graphical representation of a sectional component of a conventional modern surfboard coupled with either the Inventive fins (fins according to the invention) or Standard fins, and showing the two geometries modelled; illustrations of: (B) the simulation domains at the Waterline 1 for the fins modelled, and (C) a front view of the geometry with inlet flow moving into the paper (as denoted by crosses).

(11) FIG. 10. Graphical representation of a mesh distribution on the rear Inventive fin (157 million faces, such as those appeared on the fin, are used in the simulation at Waterlevel 1). The overall mesh cell thickness on the board is 0.4 mm and on the fin is 0.06 mm, leading to y+ in the range of 30˜100-300 to allow wall function to be used.

(12) FIG. 11. Secondary velocity vectors (Ux, Uz) comparison between right (a) Inventive fins and (b) Standard fins (at 10 m/s). (c) shows the position of the cutting plane through the lateral fins.

(13) FIG. 12. Secondary velocity vectors (Ux, Uz) comparison between right (a) Inventive fins and (b) Standard fins (at 10 m/s). (c) shows the position of the cutting plane aft of the lateral fins.

(14) FIG. 13. Secondary velocity vectors (Ux, Uz) comparison between central Inventive fins and Standard fins (at 10 m/s). (c) shows the position of the cutting plane through the aft central fin.

(15) FIG. 14. Flow field comparison showing lateral velocity Ux [m/s] on a cut-plane located at the gap height under the lateral Inventive fin immediately adjacent to the board surface.

(16) FIG. 15. Streamlines generated besides the Inventive fins and Standard fins (at 10 m/s) showing the formation of a longitudinal wake vortex behind the ‘lower ridge’.

(17) FIG. 16. The comparison on the geometry of Inventive fin (inner side fins) and the Standard fin (outer side fins), with inlet flow moving out the paper (as denoted by dots), where ‘right’ fin is the starboard fin and ‘left’ fin is the port fin in the thruster arrangement.

(18) FIG. 17. illustrations showing (A) a port side view, (B) exploded port side view, (C) exploded front view, and (D) exploded top perspective view, of an adjustable version of a preferred embodiment of a fin according to the invention with a base attachment surface for mounting the fin to the bottom surface of a surfboard.

(19) FIG. 18. is an illustration showing (A) a side view, (B) a front view, (C) a perspective view, and (D) a bottom view, of a further adjustable version of a preferred embodiment of a fin according to the invention. Mount comprises mounting blocks which attach to FCS® fin plugs.

(20) FIG. 19. is an illustration showing (A) an exploded front view, and (B) an exploded perspective view, of the embodiment shown in FIG. 18.

(21) FIG. 20. is an illustration showing (A) a side view, (B) a front view, (C) a cross sectional front view, and (D) a bottom view, of a further adjustable version of a preferred embodiment of a fin according to the invention.

(22) FIG. 21. is an illustration showing (A) an exploded front view, (B) an exploded perspective view, and (C) an underside perspective view (of the base) of the fin shown in FIG. 20.

(23) FIG. 22. is an illustration showing (A) an exploded front view, (B) a front view, (C) a cross sectional front view, (D) a perspective view, and (E) an exploded perspective view, of a further adjustable version of a preferred embodiment of a fin according to the invention.

(24) FIG. 23. is an illustration showing (A) a perspective view (B) an exploded perspective view, and (C) a front view, of a further adjustable version of a preferred embodiment of a fin according to the invention; and (D) a front view, of a further adjustable version of a preferred embodiment of a fin according to the invention.

(25) FIG. 24. is an illustration showing (A) an exploded side perspective view, and (B) an exploded side perspective view, of the bottom portion of the fin section of the embodiment shown in FIGS. 18 to 23.

(26) FIG. 25. is an illustration showing (A) a front perspective view, (B) a side view, and (C) a rear perspective view from above, of a preferred embodiment of a propeller according to the invention.

(27) FIG. 26. is an illustration showing (A) a cross-sectional front view, (B) a cross-sectional side view, and (C) a rear perspective view from below, of a preferred embodiment of a propeller according to the invention.

(28) FIG. 27. is an illustration showing a portion of a front view cross-section, of a preferred embodiment of a propeller according to the invention.

(29) FIG. 28. is an illustration showing a partial front view of a boat comprising a keel according to a preferred embodiment of the invention.

(30) FIG. 29. is an illustration showing (A) a partial rear perspective view of a boat comprising a keel according to a preferred embodiment of the invention, and (B) a partial rear perspective view of the keel.

(31) FIG. 30. is an illustration showing (A) a partial front view, and (B) a partial side view, of a boat comprising a keel according to a preferred embodiment of the invention.

(32) FIG. 31. is an illustration showing (A) a rear view, and (B) a partial side perspective view, of a catamaran comprising keels according to a preferred embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

(33) Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

(34) The present invention is not to be limited in scope by the specific embodiments described herein, which are intended for the purpose of exemplification only. Functionally equivalent products, compositions and methods are clearly within the scope of the invention as described herein.

(35) Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be 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.

(36) Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention belongs.

(37) Features of the invention will now be discussed with reference to the following preferred embodiments.

(38) Surfboard Fins

(39) A preferred embodiment of a fin according to the invention is shown in a variety of views in FIG. 1 and FIG. 2. The fin can be used as the centre fin of a three-fin thruster arrangement. This embodiment is a fixed, and non-adjustable form of the fin of the invention. The fin comprises a leading edge 602, a trailing edge 604, and a base 606, the base 606 comprising mounting blocks 608 which can be secured into FCS® plugs in a surfboard to mount the fin onto a surfboard. The mounting blocks 608 comprises the ‘mount’ 609 (or ‘mounting means’).

(40) The fin further comprises a first outer fin surface on the ‘port’ or ‘left’ side of the fin (the port side outer fin surface 610), and a second outer fin surface on the ‘starboard’ or ‘right’ side of the fin (the starboard side outer fin surface 612), when considered from the rear or trailing edge 604 of the fin looking towards the front or leading edge 602. The port side outer fin surface 610 meets the starboard side outer fin surface 612 along the leading edge 602 and the trailing edge 604. Both the port side outer fin surface 610 and the starboard side outer fin surface 612 abut the base 606 by meeting along separate edges of the base 606 as shown in FIG. 2C.

(41) Protruding laterally from the port side outer fin surface 610 adjacent the base 606 is a port side main ridge 614 (i.e. a “first ridge”) from leading edge 602 to trailing edge 604. This may also be considered a port side main protrusion. Protruding laterally from the starboard side outer fin surface 612 adjacent the base 606 is a starboard side main ridge 616 (i.e. a “second ridge”) from leading edge 602 to trailing edge 604. This may also be considered a starboard side main protrusion. The port side main ridge 614 and starboard side main ridge 616 lie substantially parallel to the base 606 and equidistant to the base 606. When the fin is mounted to a surfboard with mounting blocks 608 secured in FCS® plugs in the board, the port side main ridge 614 and starboard side main ridge 616 also lie substantially parallel to the bottom surface of the surfboard, at least at the location the fin is mounted.

(42) The port side main ridge 614 and starboard side main ridge 616 produce a kite or diamond shape when viewing the front of the fin or through a cross-sectional front view. The kite or diamond shape having a truncated base at the fin base 606, and an elongated port side main ridge upper side 618 and starboard side main ridge upper side 622.

(43) The main ridges in the fin of the invention do not comprise sections of a standard fin attached or protruding from either or both sides of the fin.

(44) In alternative embodiment, the kite or diamond shape is instead a bulbous shape, torpedo-like shape, or tear-drop shape, with a truncated base and an elongated top, when viewing the front of the fin or through a cross-sectional front view where the ridge sides comprise convex surfaces.

(45) In another means for describing the shape produced by the port side main ridge 614 and starboard side main ridge 616 of the fin of the invention, the front view or a cross-sectional front view shows the port side main ridge 614 and starboard side main ridge 616 protruding from the sides of the fin. The port side main ridgeline 615 and starboard side main ridgeline 617 at the crest of each ridge are at substantially right angles or at right angle planes to the centreplane 603 of the fin (shown with a symbol for a right angle superimposed over the illustration of the fin in FIG. 1C), the centreplane 603 on a plane that passes through the leading edge 602 and trailing edge 604 of the fin.

(46) The port side main ridgeline 615 and starboard side main ridgeline 617 meet at the leading edge 602 and at the trailing edge 604.

(47) The port side outer fin surface 610 either side of the port side main ridge 614 comprises a port side main ridge upper side 618 and a port side main ridge lower side 620.

(48) The starboard side outer fin surface 612 either side of the starboard side main ridge 616 comprises a starboard side main ridge upper side 622 and a starboard side main ridge lower side 624.

(49) In this embodiment, the port side main ridge lower side 620 and starboard side main ridge lower side 624 comprise a slight curve; however, they may also comprise more curvature, or less curvature, or comprise at least a portion that is flat.

(50) In this embodiment, the port side main ridge upper side 618 and starboard side main ridge upper side 622 comprise flat and curved portions; however, they may also comprise curved portions with no flat portions, and the curved portions may have more or less curvature.

(51) The ends of the port side main ridge 614 and starboard side main ridge 616 meet at the leading edge 602 and trailing edge 604.

(52) A port side minor ridge 626 (i.e. a “third ridge”) protrudes laterally from the port side outer fin surface 610 above the port side main ridge 614. The port side minor ridge 626 is smaller than the port side main ridge 614 and is positioned further from the base 606. The port side minor ridge 626 does not extend to the leading edge 602 or the trailing edge 604. In the embodiments of the fin that are adjustable and contain a knob, the port side minor ridge 626 can comprise the knob.

(53) A starboard side minor ridge 628 (i.e. a “fourth ridge”) protrudes laterally from the starboard side outer fin surface 612 above the starboard side main ridge 616. The starboard side minor ridge 628 is smaller than the starboard side main ridge 616 and is positioned further from the base 606. The starboard side minor ridge 628 does not extend to the leading edge 602 or the trailing edge 604 though may in other embodiments. In the embodiments of the fin that are adjustable and contain a knob, the starboard side minor ridge 628 can comprise the knob.

(54) The port side minor ridge 626 and starboard side minor ridge 628 may be parallel to the main ridges, but in this embodiment, the port side minor ridge 626 and starboard side minor ridge 628 have a slight angle of attack towards the base at the ends closest the leading edge 602 as shown in FIGS. 1A and 1B. The port side minor ridge 626 and starboard side minor ridge 628 may also be tapered in shape towards their ends or evenly shaped throughout their length. The ends of the port side minor ridge 626 and starboard side minor ridge 628 may be rounded as shown or end in a relatively sharp point, or even squared ends, for example, at the rear end of the minor ridges. Alternatively, the minor ridges may be the shape of inverted flat foils with the flat surface of the foil facing the direction of the base 606.

(55) In another preferred embodiment, the fin according to the invention may not comprise one or more port side minor ridge and/or starboard side minor ridge. Alternatively, the fin according to the invention may comprise additional minor or major ridges on one or both sides of the fin, similar or different to the ridges shown in these preferred embodiments.

(56) This embodiment of the non-adjustable fin is made in a mould constructed in one part, though could be constructed from more than one part.

(57) FIG. 3 shows in 3A and 3B a three fin ‘thruster’ arrangement similar to how the fins would be positioned once mounted to a surfboard. The centre fin 630 is set back from the side fins, and the side fins positioned with a slight inwards toe towards the centre of the arrangement and on a slight outward cant. The right or ‘starboard’ fin 632 of the thruster arrangement and left or ‘port’ fin 634 of the arrangement may be identical to the centre fin 630 or may comprise differences. FIG. 3C shows the right side of the starboard fin 632, and FIG. 3D shows the left side of the starboard fin 632.

(58) FIG. 4 shows a fin according to the same embodiment except the mount at the base comprises a single mounting block 636 which can mount the fin into a Futures® finbox in a surfboard. FIG. 4A shows a mounting block 636 with one shape of mounting block holes 638. However, other mounting block hole shapes or cutouts, including triangles, ovals, or circles, amongst others, are also within the scope of the invention. Alternatively, there may be no cutouts, or holes in the mounting block 636 though the benefit of such holes is to reduce weight and the amount of material required to manufacture the fin which can be a cost saving.

(59) FIGS. 4B and 4C show a front and side view, respectively, of a further embodiment of the fin with dimensions in mm shown. As is shown from the dimensions in FIG. 4B of the front view of the fin according to a preferred embodiment of the invention, the thickness of the fin between the first main ridgeline and second main ridgeline (i.e. at its widest point of the major ridges) is 21.28 mm. The thickness of the fin between first outer fin surface and second outer fin surface above the main ridges and ridge sides at its widest point is 6.38 mm. Thus, the maximum width of the main ridges when compared to the maximum thickness of the (non-ridged portion of the) fin above the ridges equals a factor of approximately 3.33 (i.e. 21.28/6.38=3.33). The factor would be approximately the same if there was only a main ridge on one side, for example, for a flat foil version of the fin according to the invention.

(60) The distance between the main ridgeline and base (where the fin meets the mount) is approximately 7 mm. Thus, the distance of the main ridgeline to the base is approximately 6% of the distance of the base to the tip of the fin.

(61) The maximum thickness of the minor ridges at 19.29 mm, when compared to the maximum thickness of the (non-ridged portion of the) fin at 6.38 mm, equals a factor of approximately 3 (i.e. 19.29/6.38=3.33). The distance between the minor ridge and base (where the fin meets the mount) is approximately 18.31 mm. Thus, the distance of the minor ridge to the base is approximately 16% of the distance of the base to the tip of the fin.

(62) The distance between the front of the fin where the leading edge meets the base and mount, and the front end of the minor ridge is 31.74 mm. Thus, the minor ridge starts approximately one third of the distance of the total fin behind the front of the fin. The distance between the rear of the fin where the trailing edge meets the base and mount, and the rear end of the minor ridge is 40.12 mm. Thus, the minor ridge ends approximately one third (approximately 36%) of the distance of the total fin from the end of the fin.

(63) The shape of the minor ridge is of FIG. 4C is substantially a flat foil with a flat upper surface facing away from the base. The maximum height of the minor ridge is approximately 5 mm. The ‘angle of attack’ of the minor ridge towards the base is 2.61°.

(64) The distance from the base to where the upper ridge sides merge into, meet, or become, the outer fin surface is approximately 30 mm. Thus, the portion of the height of the outer fin surfaces of the fin comprising ridges is approximately one quarter (approximately 26.5%) of the height of the fin from base to tip.

(65) FIG. 5 shows a fin according to the same embodiment except the mount at the base comprises a base attachment plate 640 as a further means for mounting the fin to a surfboard, as already described herein. The base attachment plate comprises a substantially flat base attachment surface 642 for contacting to the external bottom surface of a surfboard to which it is to be mounted (FIG. 5E). Cavities 644 (which could also be referred to as indents) which are oval-shaped in this embodiment but may comprise a variety of different shapes, are locations for adhesive which will be one means by which the fin can be attached to the external bottom surface of a surfboard. Preferably, the adhesive is injected into each cavity 644 through an injection conduit in the form of a tunnel or injection hole through the base attachment plate 640 (not shown) once the base attachment plate 640 is placed in the desired position on the surfboard to which it is to be mounted. A second injection conduit (not shown) in each cavity 644 would enable air to be released from the cavity 644 as the adhesive is injected into a first injection conduit and spreads throughout the cavity 644. Thus, the formation of air bubbles and therefore weaknesses in the adhesive attachment can be avoided. Once the cavity 644 is full of adhesive, excess adhesive will exit the second injection conduit indicating that the cavity 644 is full, and the excess adhesive can be wiped away before it dries. Preferably, screws are driven through injection conduits and into the surfboard prior to, or after the adhesive has dried, to provide additional strength in the attachment of fin to the surfboard to which it is mounted.

(66) The portion of the fin relative to the base attachment surface 642 may be created at a specific cant for use as side fins in a thruster set up.

(67) FIG. 6 shows a left or port side fin 634 as shown in the thruster arrangement of FIG. 3 with mounting blocks which can be secured into FCS® plugs in a surfboard in the port side position of a thruster or quad arrangement. Front the front view, the port side fin 634 is asymmetric as opposed to the centre fin of FIG. 1 and FIG. 2. This asymmetric configuration aims to benefit from both: (i) the effect of having both the main ridges and minor ridges on both sides of the fin to reduce the size of trailing vortices to reduce drag; and (ii) a substantially flat portion on the starboard side outer fin surface 612 of the port side fin 634 (that is, facing towards the centre line or stringer of the surfboard) and a curved port side outer fin surface, which can generate the known thrust experienced with flat foil side fins in a thruster arrangement on a surfboard as already described herein.

(68) FIG. 6 shows the port side minor ridge 626 and starboard side minor ridge 628 are of a similar size and equidistant to the base. However, the starboard side main ridge 616 and starboard side main ridge upper side 622 and starboard side main ridge lower side 624 are all smaller than the port side main ridge 614 and port side main ridge upper side 618 and port side main ridge lower side 620, respectively. The starboard side main ridge upper side 622 merges into the substantially flat starboard outer fin surface 612.

(69) Support plates 645 have been attached in this embodiment to the port side main ridge lower side 620 and starboard side main ridge lower side 624 to provide additional strength to this portion of the fin. Such support plates 645 may, or may not be part of the fins of the invention. Support plates 645 may be a metal or metal alloy including those already described herein. In a preferred embodiment, the support plates are made from titanium alloy.

(70) Gaps are produced between the support plate 645 and the surfboard onto which the fin in this embodiment is mounted, between the mounting blocks 608 and the front and rear of the fin where the leading edge 602 and the trailing edge 604 meet the bottom surface of the surfboard. These gaps assist to provide additional beneficial effects on the vortices created as water passes the fin according to the invention during use on a wave as shown in the modelling and analysis below.

(71) In this respect, the fin according to the invention can comprise one or more gaps between the base of the fin and the surfboard onto which it is mounted. These gaps may vary in shape, size, and height between surfboard and base, according to the desired vortices to be created around the fin as water passes the fin according to the invention.

(72) Without wanting to be limited by any one theory, a benefit of elevating a fin section from the outer surface of a surfboard on which it is mounted is to allow creation of additional vortices, when compared to a fin section which abuts or aligns flush with the outer surface of a surfboard.

(73) A starboard side fin (not shown in FIG. 6) will be the mirror image of the fin shown in FIG. 6.

(74) FIG. 7 is the same as the port side fin of FIG. 6 but with a mounting block which can be secured into a Futures® fin box in a surfboard in the port side position of a thruster or quad arrangement. A starboard side fin (not shown in FIG. 7) will be the mirror image of the fin shown in FIG. 7.

(75) FIG. 8 is the same as the port side fin of FIG. 6 but with a base attachment surface for mounting the fin to a surfboard as described herein in the port side position of a thruster or quad arrangement. A starboard side fin (not shown in FIG. 8) will be the mirror image of the fin shown in FIG. 8.

(76) Initially, the inventor introduced the main ridges either side of the fin of the invention to increase the width of the fin to accommodate an internal mechanism for adjusting a fin section relative to a base. The minor ridge was formed to accommodate the locking mechanism in order to reduce drag created by the protruding locking knob. However, during testing of the fins by expert surfers, surfing waves on surfboards to which fins according to these embodiments of the invention were mounted, additional velocity was experienced by the surfers on waves, particularly during turns, when compared to standard flat fins. Upon further analysis, it was considered that the shape of the fins was causing the increase of speed due to reduction of drag forces. This was predicted to be taking place through affecting vortices adjacent where the fin is mounted onto the board. It is understood that where large vortices are created behind an object moving through water, or air, these large vortices create drag or a ‘sucking’ effect, therein reducing velocity. Disruption of the formation of large vortices by instead creating smaller vortices around the base of the fin either sides of the main ridges, resulting in a reduction of drag forces behind the fins was predicted to be causing the observed effect. Thus, computational fluid dynamics modelling and analysis was performed to confirm the benefits provided by these fin configurations when compared to standard flat fins.

(77) Computational Fluid Dynamics Modelling and Analysis

(78) Background

(79) Comparative computational fluid dynamics (CFD) modelling of a three-fin ‘thruster’ arrangement of: fins of the invention (the “Inventive fins” or “INV”), compared to standard, commercially available flat fins (the “Standard fins” or “STD”) as shown in FIG. 9, was conducted by Aurora Offshore Engineering (Aurora). The modelling software used was the widely documented, validated and accepted open-source numerical modelling tool OpenFOAM®, which is a general-purpose CFD modelling code for solving the Reynolds Averaged Navier-Stokes equations for fluid flow.

(80) The geometries modelled are shown graphically in FIG. 9A featuring a sectional component of a conventional modern shortboard surfboard coupled with either the inventive fins or Standard fins. Two waterlines have been considered as shown in the FIG. 9A. The flow velocity combinations are given in Table 1. The flow direction is always parallel to the waterlines as given in FIG. 9A.

(81) TABLE-US-00001 TABLE 1 Flow velocity combinations modelled. INV Fins STD Fins Waterline 1 10 m/s 10 m/s Waterline 2  7 m/s  7 m/s  4 m/s  4 m/s

(82) The numerical model of the fluid flow was constructed using a rectangular domain containing the relevant board and fin sections as shown in FIG. 9B. The position and orientation of each fin system is shown in FIG. 9C and a view of the surface mesh on the base of the board, the main ridge (comprising the first and second ridges), and the minor ridge (comprising the third and fourth ridges) shown in FIG. 10.

(83) Results

(84) The analysis of the results focuses on investigation and identification of the flow fields around the different fin systems and differentiation of their resulting performance. FIG. 11 gives the velocity vector field normal to the board velocity and located on a cut-plane down through the side fins as shown in FIG. 11c. The secondary velocity field as generated by (Ux, Uz) shown in this figure demonstrates how the influences of the Inventive fin features on the local flow field compared to the Standard fins, showing (1) that both fins generate a similar trailing wake vortex around the fin tip, while (2) the Inventive fin main ridge and minor ridge also generate division of the longitudinal flow near the base of the fin. These rotational flows appear to be more apparent at the locations of geometry change along the Inventive fin, as shown in (3).

(85) FIG. 12 gives the velocity vector field normal to the board velocity and located on a cut-plane down just aft of the side fins as shown in FIG. 12c. The secondary velocity field as generated by (Ux, Uz) shown in this figure demonstrates how the influences of the Inventive fin features on the local flow field compare to the Standard fins, showing (1) that both fins generate a trailing wake vortex around the fin tip, while (2) the Inventive fin main ridge and minor ridge also generate a significant change in the flow behaviour against the board surface adjacent to and inboard of the fin. Comparing the flow at (3) in FIG. 12(iii), the Inventive fins cause changes in not only the direction of the flow, but also in the magnitude of the velocity.

(86) The effect of flow past the rear central fin is shown in FIG. 13 which gives the velocity vector field normal to the board velocity and located on a cut-plane through the aft fin as shown in FIG. 13c. The secondary velocity field as generated by (Ux, Uz) shown in this figure demonstrates how the influences of the Inventive fin features on the local flow field compare to the Standard fins, showing (1) that the prevailing flow at this location is upwards towards the free water surface and board, while (2) the Inventive fin main ridge and minor ridge also generate division of the longitudinal flow near the base of the fin, which are similar to those features in FIG. 11.

(87) Differentiation of the flow behaviour between the inventive and Standard fins is also investigated by considering a cut-plane parallel to and slightly below the board surface as shown in FIG. 14c at the elevation of the gap between the Inventive main ridge and the board. As can be seen by comparison of the lateral velocity (Ux) between figures (a) and (b), the flow immediately adjacent to the board differs significantly between the Inventive and Standard fins, with (1) the Inventive fin frontal gap under the main ridge enabling significant inboard flow, followed by (2) the rear gap enabling significant outboard flow which is not possible with the Standard fin which has continuous contact with the board surface. The downstream wake behind the fins (3) shows significant continuation of the wake from the Inventive fin which is much stronger than for the Standard fin.

(88) To further assist in understanding the response of the flow to the presence of the key design elements of the Inventive fin, streamlines are generated down either side of each fin system as illustrated in FIG. 15, looking forwards from behind the lateral fin. The streamlines demonstrate the formation (1) of a persistent downstream longitudinal wake vortex with its axis of vorticity centred around the longitudinal axis of the main ridge (which is predicted by the inventor to act in a manner similar to a caudal keel of some fast fish). This wake vortex is located adjacent to the board surface and is therefore anticipated to have a significant influence on the flow past the board downstream of the

(89) Forces in Tables

(90) The hydrodynamic forces extracted from the CFD model for each of the fins are presented in Table 2.

(91) TABLE-US-00002 TABLE 2 The ratios of change in lateral forces of inventive fins compared to Standard fins. Note: The sign convention is that the forces are the water force on the fin, which is oriented so that (for 4 and 7 m/s) the forces are towards the inner side of the board as shown in Figure 16. Board Lateral Force on Fin Speed Waterline f(x) [N] [m/s] (Figure 9A) Fin INV STD Δf(x) 4 2 Port −2.71 −3.98  −32% Centre 0.09 0.18  −50% Starboard 2.63 4.55  −42% 7 2 Port −17.86 −12.03    48% Centre 0.24 0.52  −54% Starboard 17.87 13.72    30% 10 1 Port −11.84 6.72 −276% Centre −0.54 1.65 −133% Starboard 13.27 −3.76 −453%

(92) The key observations from this are that: The lateral fin forces are considered as giving the best indication of how much of an effect the fins are having on the flow over the board; The centre fins have very low forces and therefore are expected to have very little effect since they are aligned with the flow; The lateral fins (both types and at all speeds) produce roughly equal and opposite forces—this is expected since the board is travelling straight ahead. There are subtle differences in the geometries which can be seen in the differences between left and right forces; and The lateral forces increase as speed increases for waterline 2, but the change in waterline and velocity results in a change in the direction of the forces on the Standard fins.

(93) In general, lateral forces increase greatly on the Inventive fins, compared to the Standard fins, which is anticipated to be important in the observed speed increase with Inventive fins. It will also be very important in the performance and stability of the board during turning manoeuvres, one of the most frequent actions needed to be taken during surfing.

(94) Conclusions

(95) The results of the CFD modelling show a significant change in the flow of water immediately adjacent to the board and downstream of the fins of the invention when compared to the standard fins in a thruster arrangement. These flow changes are potential causes for the observed speed and stability increases observed for boards using the fins of the invention.

(96) Prior to the modelling, the additional thrust was predicted to be due to the disruption of the formation of large vortices by instead creating smaller vortices around the base of the fin either sides of the main ridges, resulting in a reduction of drag forces behind the fins. However, the results of the modelling showed that while part of the additional forward thrust experienced was due to the effect of disruption or reduction of trailing vortices which reduced the negative ‘sucking’ effects (but maintained the area of high pressure), the main effect was that the ridges created a vortex as a result of the combination of the surfaces of (i) the lower surface of the surfboard adjacent to the fin, (ii) the lower main ridge surface adjacent the board, and (iii) the minor ridge. This vortex created a measurable area of lower pressure surrounding the lower portion of the fin and in front of the fin when compared to surrounding water and the high pressure measured behind the fin. Incredibly, an area of low pressure created in front of the fin was shown (video not able to be included) to be up to 500 mm long beneath the surfboard. This effect is believed to be the cause of the additional thrust (towards the area of lower pressure) experienced by surfers using fins according to the invention when compared to standard fins without the major or minor ridges.

(97) Detachable and Adjustable Fin

(98) FIG. 17 shows a detachable and adjustable version of the fin of FIG. 5. The fin comprises a base portion 646 engaging a fin section 648 to form the detachable and adjustable fin, wherein a planar member 650 attached to the base attachment plate 640 to form the base portion 646 is located within an internal cavity within the fin section 648. The planar member 650 is secured to the fin section 648 within the internal cavity by screws 652 that are accessible from the outer fin surfaces and pass through the fin section 648 into the internal cavity and can engage with the planar member 650 at locking cavities 654. To adjust the position of the fin section 648 relative to the base portion 646, screws 652 are unscrewed out of a set of locking cavities 654 at a first locking position, thereby un-securing the fin section 648 from the base portion 646, the fin section 648 is slidably moved toward the leading edge or trailing edge, and the screws 652 are screwed into locking cavities 654 at a second locking position, thereby re-securing the fin section 648 to the base portion 646 at the second position. The more locking cavities 654 on the planar member 650, the more locking positions are available for adjusting the fin section 648 relative to the base portion 646.

(99) Removing the screws 652 also enables the fin section 648 to be removed and separated from the base portion 646. This can be beneficial for transporting a surfboard to which the base portion 646 is permanently attached so that the fin section 648 is not damaged or in the way when stacking boards or other equipment on top of the surfboard. It also allows a fin section 648 to be replaced by a fin section of, for example, a different shape, size, colour, material, amongst others as the user requires or if the fin section 648 on the board becomes damaged.

(100) A detachable fin according to the invention may or may not also be adjustable in a direction towards the leading edge or trailing edge of the fin. Likewise, an adjustable fin according to the invention may or may not be detachable in the fin section being separable from the base.

(101) FIG. 18 shows collapsed views and FIG. 19 shows exploded views of a further detachable and adjustable version of an embodiment of the fin of the invention, wherein the base comprises mounting blocks 202 that can attach to FCS® fin plugs for mounting the fin onto a surfboard. In this embodiment, the knob 300 comprises the minor ridge. The outer fin surface 106 adjacent to the base of the fin forms main ridge on either side 107 as in the non-adjustable version of the fin of the invention.

(102) This embodiment further comprises an upper fin section attached to the bottom portion of the fin section, the upper fin section comprising a titanium alloy (comprising approximately 4% vanadium and approximately 6% aluminium) upper fin 500 covered with an overmolding 510 of protective safety polymer. The titanium alloy upper fin section is up to approximately 2 mm to 2.5 mm thick in the widest section 505.

(103) The upper fin 500 shown in FIG. 19B comprises upper fin attachment members 520 which are received and restrained in cavities 525 to attach the upper fin 500 to the bottom portion of the detachable and adjustable fin. Adhesive may be used to restrain the upper fin attachment members 520 in the cavities 525. The embodiment shown in FIG. 14B comprises 5 upper fin attachment members 520 and 5 matching cavities 525. However, more or less than 5 upper fin attachment members may be used, and they may comprise a variety of different shapes and sizes with matching cavities that can receive and restrain the members.

(104) The upper fin 500 shown in FIG. 18A also comprises circular holes 515 or cut outs of various sizes. These cut outs reduce the weight of the upper fin 500 further and assist in providing the beneficial flex characteristics for the detachable and adjustable fin of the invention. While the cut outs are circular in this embodiment, they may comprise a variety of different shapes.

(105) Across the profile of the upper fin section is varying thickness to create a single or double sided fin foil as is known in the art and common to the shapes of surfboard fins, with a thicker section 505 toward the leading edge of the fin section which decreases in thickness with closer proximity to the trailing edge.

(106) In the embodiment of the detachable and adjustable fin shown in FIGS. 15 and 16 and as shown in FIG. 19A, the base 400 and mounting blocks 202 form one piece and do not comprise separate components that have been attached. Thus, the base can be separated from the fin section with the base left attached to a surfboard or removed from the surfboard.

(107) A further detachable and adjustable version on an embodiment of a fin according to the invention is shown in a collapsed form in FIG. 20, and an exploded form in FIG. 21. This embodiment is similar to the embodiment of the detachable and adjustable fin in FIGS. 18 and 19 with the exception that instead of mounting blocks attached to the base, the base 400 is attached to a base attachment plate 420 for mounting onto the external bottom surface of a surfboard with adhesive and/or rovings, screws or other mechanical attachment means. Thus, similar to the fin of FIG. 17, the fin section can be removed from the base for storage, transport, or replacement of the fin section with a new fin section of the same or different template, shape, size, and/or material.

(108) The underside of the base plate is shown in FIG. 21C showing the base attachment surface 424 and large recesses or cavities 426 for accommodating adhesive.

(109) When mounted to a surfboard, the base of the embodiment of the detachable and adjustable fin of FIGS. 20 and 21 points away from the surfboard at an angle of approximately 90 degrees when measured from the external bottom surface of the surfboard on to which it is mounted. While being otherwise the same as the embodiment of FIGS. 20 and 21, the base of the embodiment of FIG. 22 points away from the surfboard at an angle of approximately 86.5 degrees (or approximately 3.5 degrees off ‘centre’ or 90 degrees) when measured from the external bottom surface of the surfboard on to which it is mounted, i.e. at a different cant. That is, the base 400 is 3.5 degrees off pointing in a direction perpendicular to the base attachment surface 424.

(110) A further detachable and adjustable version of a preferred embodiment of a fin according to the invention is shown in FIG. 23. This embodiment is similar to the embodiment shown in FIGS. 20 to 22 with a key difference that side shut-off cavities have been replaced with front and rear facing shut-off cavities 160. Another key difference is the presence of injection conduits 428 for injecting adhesive into the cavities or releasing air from the cavities as the adhesive fills the cavities 428, and/or for use as screw holes for attaching the detachable and adjustable fin to a surfboard with screw-type fasteners such as screws.

(111) An exploded view of the parts of the lock used in some adjustable versions of preferred embodiments described herein is shown in FIG. 24. The lock, which may also be referred to as a “locking means”, comprises a cam 304.

(112) Propeller for Watercraft Propulsion

(113) A preferred embodiment of a propeller 700 for providing propulsion through water is shown in FIG. 25 and FIG. 26. The propeller 700 combines features and benefits of a propeller and an impeller. In this respect, a propeller assists a vessel to move through water by providing a thrust force. The propeller 700 comprises a revolving hub 702 with rotating propeller blades 704 that convert rotational motion into forward thrust. This is due to the pressure differential that is created between the front and rear surfaces of the propeller blades 704. This pressure differential pushes water behind the propeller blade 704 in accordance with Newton's laws of motion and Bernoulli's theorem.

(114) An aperture 706 through the hub 702 comprises impeller blades 708 that rotate with the revolving of the hub 702 to create a sucking force to draw water through the aperture therein increasing the pressure of the fluid and thus its flow through the aperture 706.

(115) The combined forward thrust provided by the rotating propeller blades 704 and impeller blades 708 forces the propeller 700 of the invention through the water and the vessel to which it is attached.

(116) The rotational force applied to the propeller 700 of this preferred embodiment is via a motor which turns a sprocket 710 interlocking with a first end of a loop of roller chain 712. At a second end, the loop of roller chain 712 interlocks with teeth 714 on the hub 702, and the turning of the sprocket 710 by the motor therein rotates the loop of roller chain causing the propeller 700 to also rotate.

(117) The propeller blades 704 comprise outer blade surfaces 716. A ridge 718 protrudes generally laterally from each outer blade surface 716 as shown in the cross-sections of FIG. 26A. At the crest of each ridge 718 is a ridgeline 720 which comprises a relatively sharp edge. Each side of the ridge 718 between the ridgeline 720 and where the ridge 718 protrudes from the outer blade surface 716 is a curved sloped inner ridge surface 722 adjacent and facing the hub 702, and a curved sloped outer ridge surface 724. These sloped inner ridge surfaces 722 and outer ridge surfaces 724 comprise curved portions, substantially flat portions, and comprise steeper curves where ridge 718 meets outer blade surface 716.

(118) The inner surfaces 722 of the lateral ridges 716, and the ridgeline 720 comprise a similar curve to the curved shape of the hub 702. The end of the ridgelines 720 meet at the blade edge 726. The blade edges 726 and ridgelines 720 are relatively sharp edges which assist in cutting through the water.

(119) The impeller blades 708 are relatively short blades compared to the propeller blades 704. The impeller blades 708 on the inner aperture surface 728 of the hub 702 are curved (spirally similarly to rifling in a barrel) assists to cause water passing through the aperture 706 and the impeller blades 708 to spiral in the direction of the revolving hub 702. A cross-section of the impeller blades 708 as shown in FIG. 26 and FIG. 27 shows an almost diamond-shape with concave impeller blade surfaces 730 and a wide impeller base 732 where the impeller blade 708 meets the inner aperture surface 728. This cross-section of the impeller blade 708 may also be considered as also showing two lateral impeller ridges 734 protruding from the sides of the impeller blade 708 with concave sloped impeller blade surfaces 730 either side of the impeller ridgelines 736. The impeller ridgelines 736 are at substantially right angles or at right angle planes to the centreplane of the impeller blade 708, the centreplane from between the middle of the impeller base 732 where it meets the inner aperture surface 728, to the impeller blade tip 738.

(120) Keels

(121) A preferred embodiment of a keel of a boat (or yacht) according to the invention is shown in FIG. 28 and FIG. 29. The keel 800 of this embodiment is located in the common location for a fin keel on a boat, projecting below the centreplane 802 of the vessel hull 804, the centreplane 802 between bow 806 and stern 807 of the boat.

(122) The keel 800 comprises two main ridges 808 protruding laterally from the sides of the keel 800 adjacent where the keel 800 meets the vessel hull 804. An upper minor ridge 810 protrudes laterally from each side of the keel 800 just above the main ridges 808. A lower minor ridge 810 protrudes laterally from each side of the keel 800 just below the main ridges 808.

(123) The rear 818 of the keel in FIG. 29B shows the diamond-like shape with elongated top and bottom ends produced by the main ridges 808 in the keel 800. At the crest of each main ridge 808 is a ridgeline 814. As is shown in FIG. 29, the main ridges 808 and the ridgelines 814 extend from the front 816 of the keel where they meet, to the rear 818 of the keel where they end at the flat surface of the rear 818 of the keel 800. In other embodiments, the ridgelines 814 may meet at the rear 818 of the keel 800 where the rear 818 of the keel 800 ends along an edge similar to the front 816 of the keel 800.

(124) Each side of the ridge 808 between the ridgeline 814 and where the ridge 808 protrudes from the outer keel surface 820 is a curved sloped ridge surface 822. These sloped ridge surfaces 822 may comprise curved portions, substantially flat portions, and steeper curves near the ridgelines 814 and/or where main ridge 808 meets the outer keel surfaces 820.

(125) The ridgelines 814 of the main ridges 808 are at substantially right angles or at right angle planes to the centreplane 826 of the keel 800 (see, for example, FIG. 30), the centreplane comprising a plane from between the middle of the keel 800 where it meets the vessel hull 804, to the keel tip 824.

(126) The upper minor ridge as shown in FIG. 29B comprises a configuration similar to a flat foil protruding from each side of the outer keel surface 820 adjacent where the outer keel surface 820 meets the sloped ridge surfaces 822 above the main ridges 808 (see for example, FIG. 30B). The flat side of the flat foil configuration for the upper minor ridge faces up whilst the more curved side of the upper minor ridge faces down.

(127) The lower minor ridge 812, is a similar shape and configuration to the upper minor ridge 810 except the flat foil shape of the lower minor ridge has the flat side facing down away from the vessel hull 804.

(128) The upper minor ridge 810 and lower minor ridge 812 extend only part way between front 816 and rear 818 of the keel 800.

(129) While these upper minor ridges 810 and lower minor ridges 812 of the preferred embodiment comprise a configuration of a flat foil, the upper and lower minor ridges may be differently shaped or not even present in other embodiments of the keel of the invention. For example, the upper and lower ridges may not be present; or one or both of the upper or lower ridges may be present; the upper and/or lower ridges may extend from the front 816 of the keel 800 to the rear 818; or the upper and/or lower ridges may comprise more evenly shaped ridges similar to, though smaller, than the main ridges 808. The upper minor ridges and/or lower minor ridges may comprise relatively sharp ridgelines at their crest, or they may comprise rounded, or even squared edges, or a combination of both or other shapes at their ridgelines. The upper minor ridges and/or lower minor ridges may also not comprise flat foil shapes, but comprise more even configurations with similar or the same sloped sides either side of straight or (curved) ridgelines on the upper minor ridges and/or lower minor ridges. The upper minor ridges and/or lower minor ridges may be similarly shaped or may comprise different shapes.

(130) While a fin keel according to the invention is shown in FIG. 28 and FIG. 29, the keel according to the invention may be another type of keel, for example, a full keel or ballast keel, a skeg, bilge keel, deep keel, dagger board, lee board, centre board, pivot board, winged keel, twin canting keel, folding keel, or lifting keel, amongst others. In this respect, the keel according to the invention shown in FIG. 30 is a full or ballast keel. A keel according to the invention may have one or more ridges only on one side surface, for example if it used on one side of the boat.

(131) A catamaran or trimaran may use the keel according to the invention on the bottom of one or more hulls as shown in FIG. 31.