Low-drag fin and foil system for surfboards

Abstract

The present invention is a Low-Drag Fin and Foil System for Surfboards (10), particularly including cambered fin foils (40; 42). The invention (10) also discloses low-drag, directionally unstable fin positions wherein the lesser of negative angle of attack of a trailing fin (50), versus the higher or positive angle of attack of a forward fin (48), makes the board (12) highly maneuverable by creating a yawing moment that aids the rotation of the board (12) as it is turned. The system particularly utilizes fins (40) having foil (42) shapes in which either the cambered side (74) or the non-cambered side (76) is provided with a combination of a convex curvature (68) and a concave curvature (70) to result in an oscillating curvature (72) which has a positive effect on control and acceleration.

Claims

1. A surfboard comprising: a board having a nose region, a center, a tail region, and a longitudinal centerline passing from the nose region to the tail region, wherein the nose and tail regions comprise a nose edge and a tail edge delimiting a front edge and a rear edge at a very extremity of the board, and the center is a point equidistant from the very extremity of the board at either end, further wherein the board comprises a plurality of independent side-fins on a bottom surface of the board, and the independent side-fins are positioned in a multi-fin arrangement, and the multi-fin arrangement comprises: an independent rearward side-fin extending from the bottom surface of the board; and an independent forward side-fin extending from the bottom surface of the board and positioned forward of the rearward side-fin, wherein the rearward side-fin is set at a lesser angle of attack with respect to the longitudinal centerline and the forward side-fin is set at a positive angle of attack with respect to the longitudinal centerline, and further wherein the independent side-fins in the multi-fin arrangement are located forward of the rear edge at the every extremity of the tail, behind the center of the board, offset from the longitudinal centerline, and further wherein the juxtaposition of the side-fins is such that it creates a yawing moment that aids the rotation of the board in a turn.

2. The surfboard of claim 1 wherein the forward side-fin has a first side surface, a leading edge, a second side surface opposite the first side surface, and a trailing edge opposite the leading edge, and further wherein the forward side-fin has a virtual chord in the form of a vertical plane passing through a respective center point of the leading edge and the trailing edge of the fin, and further wherein the virtual chord of the forward side-fin is set to be at a positive angle of attack greater than one degree measured against the longitudinal centerline of the board.

3. The surfboard of claim 1, wherein at least one of the side-fins is a cambered foil, and further wherein the at least one side-fin has a first side surface, a leading edge, a second side surface opposite the first side surface, and a trailing edge opposite the leading edge, wherein the first and second side surfaces have a horizontal curvature through a vertical extent of the side-fin, and the horizontal curvature of the second side surface is continuously convex through the vertical extent of the side-fin, and further wherein the horizontal curvature of the first side surface has a first convex curvature in one direction, and a second concave curvature in an opposite direction, such that the first side surface has an oscillating curvature through the vertical extent of the side-fin similar to a shallow sine wave.

4. The surfboard of claim 1 further including fin attachment points adapted to secure the side-fins to the bottom of the board body.

5. A surfboard comprising: a board having a nose region, a center, and a tail region with a longitudinal centerline passing from the nose region to the tail region, wherein the nose and tail regions comprise a nose edge and a tail edge delimiting a front edge and a tail edge at a very extremity of the board, and the center is a point equidistant from the very extremity of the board at either end, wherein the board comprises a plurality of independent side-fins on a bottom surface of the board body, and the independent side-fins are hydrofoils positioned in a multi-fin arrangement, wherein the multi-fin arrangement comprises: an independent rearward side-fin that extends from the bottom surface of the board that is set at a negative angle of attack with respect to the longitudinal centerline of the board, and an independent side-fin that extends from the bottom surface of the board that is set forward of the rearward side-fin, and further wherein the rearward side-fin is set behind the forward side-fin, and the forward side-fin is set at an angle of attack that is substantially parallel to the longitudinal centerline of the board, and further wherein both the forward side-fin and rearward side-fin are located forward of the tail and behind the center of the board, and offset from the longitudinal centerline, and further wherein the juxtaposition of the side-fins is such that in a fluid flow of water the rearward side-fins and the independent side-fin are hydrofoils that redirect a flow of water and create a yawing moment that aids the rotation of the surfboard in a turn.

6. The surfboard of claim 5 wherein the forward side-fin and the rearward side-fin have a first side surface, a leading edge, a second side surface opposite the first side surface, and a trailing edge opposite the leading edge, and a base where the side-fins meet the board, wherein the leading edge of the rearward side-fin at the base is behind the trailing edge of the forward side-fin at the base, and further wherein the side-fins have a virtual chord in the form of a vertical plane passing through a respective center point of the leading edge and the trailing edge of the side-fins, and further wherein the virtual chord of the forward side-fin is set to be substantially parallel to the longitudinal centerline of the board, and the virtual chord of the rearward side-fin is set at a negative angle of attack with respect to the longitudinal centerline of the board.

7. The surfboard of claim 5, wherein at least one of the side-fins is a cambered foil, and further wherein the at least one side-fin has a first side surface, a leading edge, a second side surface opposite the first side surface, and a trailing edge opposite the leading edge, wherein the first and second side surfaces have a horizontal curvature through a vertical extent of the side-fin, and the horizontal curvature of the second side surface is continuously convex through the vertical extent of the side-fin, and further wherein the horizontal curvature of the first side surface has a first convex curvature in one direction, and a second concave curvature in an opposite direction, such that the first side surface has an oscillating curvature through the vertical extent of the side-fin similar to a shallow sine wave.

8. The surfboard of claim 5 further including fin attachment points adapted to secure the side-fins to the bottom of the board.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The first several figures of the drawing (FIGS. 1-3) depict prior art and are discussed above.

(2) FIG. 1A (Prior Art) is a cross-section view of a fin foil according to the prior art that depicts the pressure field assumed to develop around the foil of a fin when it is positioned at a low incidence or angle of attack relative to a water flow;

(3) FIG. 1B (Prior Art) is cross-section view of a fin foil according to the prior art that depicts the pressure field assumed to develop around the foil of a fin as a result of a very high incidence or angle of attack.

(4) FIG. 2 (Prior Art) is view of the bottom of a surfboard depicting a conventional tri-fin arrangement according to the prior art, and the low-pressure area or turbulence that develops on the lee or inside surface of the side-fins due to the negatively angled toe-in of the side-fins;

(5) FIG. 2A (Prior Art) is a closer, longitudinal cross-sectional view of the flat-sided foil of a side-fin according to the prior art;

(6) FIG. 2B (Prior Art) is a cross-sectional view of a prior art side-fin foil having a slightly concave inside surface; both views show the high drag, which is depicted as turbulent water flow, that develops on the lee or inside surface due to the side-fin's negative angle of attack or toe-in towards the longitudinal centerline at the nose.

(7) FIG. 3A (Prior Art) is a view of the bottom of a prior art tri-fin board in a turn that shows how the rotation of the board in a turn changes the direction of water-flow striking the fin(s), and thereby alters the fins' angle of attack.

(8) FIG. 3B (Prior Art) depicts the bottom of a prior art fish style board with the largely unsuccessful parallel side-fin setting, and shows how the wide split tail and parallel side-fin setting will cause the side-fins to be placed at a much higher angle of attack due to the rotation of the board in a turn.

(9) The purposes and advantages of the present invention will be apparent from the following detailed description in conjunction with the appended drawings in which:

(10) FIG. 4 is a bottom plan view of a typical surfboard with the system of the present invention being installed thereupon and also showing, in phantom, a turn having been made;

(11) FIG. 5 is a perspective view of an inventive fin member according to the present invention, shown disassembled from the board;

(12) FIG. 5A is a cross-section view of the fin foil of FIG. 5 taken along line A-A, showing how an oscillating curvature on the inside surface of the fin, opposite the cambered side, can be used to reduce turbulence and drag when the fin is at a negative angle of attack.

(13) FIG. 6 is a perspective view of another inventive fin member according to the present invention, shown disassembled from the board;

(14) FIG. 6A is a cross-section view of the fin foil of FIG. 6 taken along line A-A, showing how an oscillating curvature on the cambered side of the fin.

(15) FIG. 7 is a perspective view of still another inventive fin member according to the present invention, shown disassembled from the board;

(16) FIG. 7A is a cross-section view of the fin foil of FIG. 7 taken along line A-A, showing how an oscillating curvature on the inside surface of the fin, opposite the cambered side, can be used to reduce turbulence and drag when the fin is at a negative angle of attack.

(17) FIG. 8 is a bottom plan view of a multi-fin configuration according to the present invention showing how the higher angle of attack of a forward fin versus the lesser angle of attack of a rearward fin will create a yawing moment that aids the rotation of the board in a turn.

(18) FIG. 9 is a close up view of a portion of the tail section of the board according to the configuration of FIG. 8.

(19) FIG. 10 is a view of a multi-fin configuration according to the present invention illustrating how the negative angle of the trailing side-fin acts as a deflected rudder and creates a yawing moment that aids the rotation of the board in a turn.

(20) FIG. 11 is a close up view of a portion of the tail section of the board according to the configuration of FIG. 10.

BEST MODE FOR CARRYING OUT THE INVENTION

(21) The preferred embodiment of the present invention is a system for providing a surfboard with improved fins, arranged in an improved pattern, with said pattern being customizable to the specific characteristics of the user. As illustrated in the various illustrations of the drawing herein, this preferred embodiment of the inventive surfboard system is depicted and referred to by the general reference character 10. The system 10 is adapted to optimize the characteristics of a multi-fin form of surfboard 12 for use by proficient surfers.

(22) FIG. 4 illustrates, in a bottom plan view, a typical surfboard 12, with a turn being shown in phantom. As the present invention is adaptable for use with surfboards of a wide variety of configurations, the particular shape of the surfboard 12 illustrated in this figure is selected for purposes of illustration only.

(23) The typical surfboard 12 includes an under surface 14 which is shown. This is the portion which faces downward into the water during use. It also has an upper side (not shown) upon which the surfer rides and stands. An edge, also known as a perimeter rail 16, extends around the periphery of the board 12. A longitudinal center line 18 (often a structural feature of the board) divides and bisects the board 12 longitudinally. The center line 18, when a physical part of the board 12, is also known as a stringer 18. The board 12 is also characterized by having a front 20 (bow) and a rear 22 (tail). Although not an apparent physical characteristic, each board also has a vertical rotation axis 24 which defines the center point about which the board 12 effectively rotates during turns see phantom representation of pre-turn position).

(24) For the purposes of discussion, various external physical factors and forces are relevant. These are somewhat discussed above in connection with the prior art. These include a heading 28 which is the direction of absolute travel of the board, and a water flow direction 30 of the wave which will normally coincide with the heading 28, but in the opposite direction. A rotation force 32 is applied by the user in order to achieve a turn. Various force vectors 34 are created by the interaction of the medium (water or air) with the components of the board and a yaw moment 36 may be envisioned to reflect the twisting forces involved. A drag force 38 also exists and is characterized and the force acting against the forward movement of the board along the heading 28.

(25) The principal aspects of the present invention are embodied in a plurality of fins 40 which are situated on the board 12. These fins 40 come in various sizes and placement positions and significantly affect the board in use. Each fin has a portion which acts as a foil 42, similar to an airplane wing.

(26) Among the types of fins 40 which appear in the present invention are center fins 44, situated along the center line 18 (see FIG. 3A), side fins 46 situated between the center line 18 and the rail 16, and forward fins 48 and rearward (tail) fins 50 which are defined by their relative positions. A given fin 40 may be characterized by more than one of these descriptors. For an example, a given fin 40 may be both a side fin 46 and a tail fin 48.

(27) Each fin 40 has various components, as particularly illustrated in FIGS. 5, and 5A, 6 and 6A, and 7 and 7A. Each has a leading edge 52, and outside surface 54 (closer to the rail 16), an inside (lee) surface 56 (closer to the center line 18) and a trailing edge 58. Each fin 40 also includes a mounting protrusion 60 by which it is mounted on the board 12. A virtual portion of each fin 40 is a chord 62 which is a vertical plane passing through the center point of the leading edge 52 and the trailing edge 58 of the fin 40 and extending outward therefrom. The chord 62 is useful in understanding the effect of the foil 42 on the flow medium and the handling of the board 12.

(28) The selection and placement of fins 40 is the object of the system 10 of the invention. The present invention therefore discloses a number of multi-fin configurations designed with the problems of reverse yawthe source of the original multi-fin control problemsfully taken into account. Some of these settings are shown in FIGS. 8-11 and are discussed in connection therewith. According to the present invention, when properly designed, a multi-fin configuration can be successfully based a parallel side fin 46 setting (see example in FIG. 3B); the parallel side fin setting not only reduces drag when the rider's weight is neutrally centered on the board, but in a turn the side fin 46 is placed at a significantly higher angle of attackthis dramatically improving the acceleration of the board since it allows the fin to more closely approximate the function of a sail. The problems of reverse yaw are prevented by additional fins 40 or fin-foils 42 set at a specific angle so as to dampen or counter the adverse effects of the fin foil 42 at the higher angle of attack. This greatly enhances speed and control through the arc of the turn; moreover, the additional foils 42 may be deployed so as to function as permanently deflected control surfaces that provide the yawing moment 36 and aid the rotation 32 of the board in the direction of the turn. According to actual embodiments, this can dramatically improve the looseness and subjective feel of the board while enhancing its overall maneuverability as well.

(29) As described in more detail below, the present invention discloses a number of fin-foils that reduce drag at the conventional negative angle of attack, and perform exceptionally well when the fin is set substantially parallel to the longitudinal center line 18 or stringer of the board 12. FIG. 5, FIG. 6, and FIG. 7 are perspective views of such fins, while FIG. 5A, FIG. 6A and FIG. 7A are cross-section views, taken along the respective lines A-A of the associated figure, depicting the foil 42 of a first configuration fin 64 (FIG. 5), a second configuration fin 65 (FIG. 6) and a third configuration fin 66 (FIG. 7) according to the present invention. As shown in FIGS. 5 and 7, the inside surface 56 of the configured fins 64 and 66 (assuming mounting on the right rear portion of the board 12) has a first side with a convex curvature 68 from the leading edge 52 that curves first in one direction, followed by a second, concave curvature 70 in the opposite direction, such that a portion of the lee side 56 of the fin has an oscillating curvature 72 similar in shape a to a shallow sine wave. The fin 64 also has an upper end 55 which is independent from other fins and is unencumbered (as shown in FIGS. 8-11), i.e., not connected to other fins, and a bottom end 53 which delimits the lower extremity of the foil 42 where it meets the board 12. The illustrations of FIGS. 5 and 7 show the oscillating curvature 72 on the non-cambered side 76 while FIG. 6 illustrates a configuration where the oscillating curvature 72 is on the cambered side 74, which is the outside surface 54 in FIG. 6.

(30) Each fin 40 acts as the foil 42 with respect to the fluid through which the fin is traveling. To operate as an effective foil, each fin 40 has a cambered side 74 and a non-cambered side 76. A virtual camber line 78 is used to define the degree of horizontal curvature and cambering of the foil 42 against the plane of the virtual chord 62, which intersects the bottom 14 of the board 12 at the chord line 62. The plane includes the chord line 62, which is a straight, horizontal line passing from a center point on the fin's very leading edge 52 to a center point at the very trailing edge 58; the chord line 62 also extends outward from the very leading edge 52 and the very trailing edge 58the virtual chord 62 allows the angle of the fin 40 to be accurately set against the centerline 18, and is useful in understanding the fluid flow patterns around the fin 40. The cambered side 74 may be the outside surface 54 or the inside (lee) surface 56 of the fin 40, depending on the configuration and mounting of the particular fin 40.

(31) Referring now to FIGS. 5, 6 and 7, the present invention 10 discloses a series of cambered fin foils 42 that exhibit greatly reduced drag at the conventional negative angle of attack due to the oscillating curvature 72 on the non-cambered surface 76 of the fin 40 (and opposite the cambered side 74), and also performs exceptionally well when the fin is set substantially parallel to the longitudinal centerline or stringer 18 of the board. As shown, this is advantageous in that the oscillating curvature 72 on one side of a forward fin foil 40 can be used to create a sidewash, similar to the downwash known to exist behind an airplane wing, that changes the direction of the water flow F striking a trailing fin foil, thereby altering the effective incidence or angle of attack of a trailing fin 50, which in this view has a reflexed foil, as the oscillating curvature 72 is on the cambered side 74; combined, these effects can be effective in reducing drag and increase the yawing moment of the board in a turn (as described in greater detail below).

(32) FIG. 5 is a perspective view of a fin 40 illustrating a configuration where the oscillating curvature 72 is on the non-cambered surface 76 of the fin. The cross sectional view of FIG. 5A illustrates how the oscillating curvature 72 comprises a forward (toward the fin's leading edge) convex curvature 68 followed by trailing concave curvature 70. The view also depicts the chord line 62, an imaginary straight line drawn through the leading 52 and trailing edges 58 of the fin 64, which is used to measure the angle of attack of the particular fin 40.

(33) FIG. 5A, a cross-section view taken along lines A-A of FIG. 5, provides a view of the foil section 42 of the fin 40; the fin foil is cambered, as represented by the camber line 78 which shows that the fin 40 has an average curvature greater on the cambered side 74, than the non-cambered side 76. The cross-section view shows that the foil of the fin 40 according to the present invention exhibits the oscillating curvature 72. This involves a convex curvature 68 that curves first in one direction, followed by a second, concave curvature 70 in the opposite direction. Thus a portion of one side of the fin has an oscillating curvature 72 similar in shape to a shallow sine wave. As shown, the oscillating curvature 72 allows the forward portion of the fin 40 (e.g., from approximately mid-chord 62 forward to the leading edge 52) to have a curvature approaching a symmetrical foil, giving it a low-drag, streamlined shape. However, in the trailing portion both sides of the fin 40 curve in the same direction, to make the overall foil section of the fin cambered. The fin foil shown has been found to reduce drag when used at the conventional negatively angled side-fin setting, and it appears to reduce the required toe-in to an angle of less than 3.degree.; in addition, it performs very well when placed substantially parallel to the stringer (when the fin is set approximately .+0.2.degree. to the centerline or stringer 18).

(34) Arrangements are feasible (see FIGS. 7 and 6A) where the oscillating curvature 72 is on the cambered side 74 of the narrow fin 65, and the trailing edge 58 curves in a direction opposite the forward part. This curvature would create a reflexed foil that has a slight yawing moment 36 in the direction of the cambered side 74 due to the high pressure area and pressure differential resulting from the reflexed curvature near the trailing edge 58. When the fin 40 is set substantially parallel to the centerline 18, the yawing moment 36 can be used to aid the rotation of the board in a turn. (Note: when the oscillating curvature 72 occupies one entire side of the fin, the curvature 72 will be understood to be distinct from the severe curvature present at the leading edge 52, although a precise demarcation is not shown. In addition, the curvature may occupy only a portion of one side of the fin, e.g., from approximately mid-chord to the trailing edge 58.)

(35) In particularly advantageous embodiments of the present invention 10, the juxtaposition of fin foils 42 is such that the lesser or negative angle of attack of a rearward fin 50 foil, versus the higher or positive angle of attack of a forward fin 48 foil, creates a yawing moment 36 that aids the rotation of the board in a turn; as noted above, this can dramatically improve the looseness and subjective feel of the board, while enhancing overall maneuverability as well. Equally important, however, the yawing moment 36 and the resulting rotation of the board causes at least one forward fin 48 to come at a progressively higher angle of attack; from the preceding discussion, it can be seen that the pressure differential (see FIG. 1A and FIG. 1B above) around the forward fin 48 will enhance both the rotation and the acceleration of the board through the arc of a turn, while the lesser angle of attack of the rearward fin 50 can be used to counter the reverse yaw of the forward fin 48, so that the rider can maintain complete directional control.

(36) FIG. 8 provides a first example and shows a board 12 with an inventive arrangement of fins 40 at the tail 22. Companion FIG. 9 shows a close up view of the tail 22 section, illustrating the same configuration as FIG. 8. In each of these views the fins are arranged so that a forward fin 48 is in a low-drag position which, as shown, is substantially parallel to but at a slightly positive angle of attack to the centerline 18, while the position of the trailing fin 50, in relation to the forward fin 48, is set at a negative angle of attack. In the example shown, the rider's weight is assumed to be neutrally centered on the board. This causes the water-flow 30 to roughly parallel to the centerline 18 of the board as shown, and creates a pressure field around the fins (48, 50) depicted here by the small vector arrows 34 shown. The pressure field creates a pressure differential, the direction of which is represented by the two larger vector arrows V that are shown pointing in opposite directions on the two sides of either fin (48, 50). As depicted, the negative angle of attack of the trailing fin 50 versus the positively angled forward fin 48 creates the yawing moment 36 and a side fin 42 setting that is directionally unstable, in that as soon as the rider leans to turn the board (not depicted) and lifts the opposing side-fins (not shown) free of the water, the yawing moment 36 of the fins (48, 50) will cause the board 12 to rotate. This allows the forward fin 48 to lead the rotation of the board through the arc of the turn while the rearward fin 50, which is set fairly close to the centerline 18 and almost directly under the rider's feet, allows the rider to maintain directional control.

(37) In a second example, FIG. 10 shows a board 12 with another inventive arrangement of fins 40 at the tail 22. Companion FIG. 11 shows a close up view of the tail 22 section, illustrating the same configuration as FIG. 10. FIG. 11, provides a partial view of the tail 22 section in which the fins 40, depicted here in cross-section, are in an especially advantageous configuration. In the embodiment shown, the rearward trailing fin 50 is positioned to function as a permanently deflected rudder that aids the rotation of the board through the turn, while the forward fin 48 is in a low drag position paralleling the stringer 18. In the example shown, the rider's weight is again neutrally centered on the board. This causes the water-flow 30 to roughly parallel the longitudinal centerline 18 of the board 12, which creates a pressure field/pressure differential around the forward fin 48 in the direction of the vector arrow V that is opposite the direction of the pressure differential and vector V of the rearward trailing fin 50. In the embodiment shown, the placement of the trailing fin 50 is further behind the axis of rotation 24 when compared to the negatively angled side-fin setting of the prior art (as shown in FIG. 2), and the increased leverage greatly increases the maneuverability of the board. When the rider leans to initiate a turn (not depicted; the rotation of a prior art tri-fin is shown in FIG. 3A), the added leverage of the trailing fin 50 creates a yawing moment 36 that aids the rotation of the board which also causes the forward fin to be immediately placed at a higher angle of attack (again, vs. the negatively angled side-fin setting of the prior art). From the discussion of the pressure differential provided above (see, e.g., FIG. 1A and FIG. 1B), it can be seen that this will enhance both the rotation and the acceleration of the boardas the board is rotated, it increases the pressure differential around the forward fin 48 which further enhances the rotation of the board in a turnat the same time, the rotation of the board causes the water-flow 30 striking the forward fin 48 to come at a progressively higher angle of attack (vs., e.g., the rotation of the prior art tri-fin depicted in FIG. 3A), thereby considerably enhancing the board's drive and acceleration as it is maneuvered on the wave; while the trailing fin 50 counters the reverse yaw of the forward fin 48 and allows the rider to maintain control.

(38) Persons knowledgeable in the art will recognize that the principles described hereinabove may be applied to other board types such as hybrids, eggs, modern longboards, etc., by reversing the prior art tri-fin setting: that is, the center stabilizing fin may be placed on the longitudinal centerline or stringer of the board and forward of the negatively angled, trailing side-fins on either perimeter rail. In addition, the oscillating curvature of either fin may be reflexed, or conventionally cambered; and the multi-fin configurations disclosed are not limited in terms of the foil of the fin, but may use any of fin foils known in the art. In addition, the size and planshape of the fin may be selected according to the specific performance characteristics soughti.e., the forward fin 48 may be considerably larger than the trailing fin and vice-versa.

(39) The present invention also discloses that the control problems associated with very early double-finned surfboards, which were poorly understood but had long been attributed to the parallel side-fin setting used on the original fish style boards, were actually caused by a side-fin setting that placed the side-fins too close to the tail 22 and to the perimeter edge or rail 16. It has been discovered that a side-fin setting that is substantially parallel to the centerline 18 may be successfully used if the side fins 46 are moved further forward on the board, so the setting is closer to the board's axis of rotation 24 and further away from the board's perimeter edge or rail 16. Specifically, it was found that if the setting of the side fin 46 is such that the leading edge 52 of the side fin 46 as measured at its base is at least twenty percent of the total distance forward of the tail 22 (or, alternatively, if the mean hydrodynamic chord of the side fin 46 is set at least fifteen percent of the total length of the board forward of the tail 22), and if the side fins 46 are placed so that the distance between centerline 18 and the mid-chord 62 of the side fin 46 as measured at its base is no greater than one-third the total width of the board 12 at that point, the control problems resulting from a substantially parallel side-fin setting largely disappear.

(40) In working embodiments, when the above side-fin setting was compared to a modern twin fin type board of the prior art, it was found to dramatically increase speed and responded immediately to very small weight shifts by the rider. Although problems of reverse yaw still existed, they were greatly reduced with a fairly low aspect ratio fin with symmetrical or reflexed foil. In preferred embodiments, additional fins or fin foils were used that successfully dampened, counteracted or eliminated the problem of the reverse yawing moment of the side-fins in a turn. The group of placements found to be successful in countering the reverse yaw comprised: forward and outboard of the mid-chord of the side-fin and fixed at a negative angle of attack (wherein outboard is defined as the side of the side-fin facing the perimeter edge or rail), rearward and outboard of the mid-chord of the side-fin and fixed at a negative angle of attack, and inboard and to one side of the mid-chord of the side-fin, and parallel to the longitudinal centerline or stringer.

(41) In the prior art, the multi-fin configurations that have been successful were arrived at through trial and error, with a poor or very limited understanding of the lift and pressure differential characteristics of the fin, and in particular without knowledge of the heretofore unidentified but entirely predictable problems associated and the reverse yaw of the fin-foil at high angles of attack. This has had the effect of discouraging or greatly limiting innovation in multi-fin design.

(42) Persons skilled in the art will therefore recognize that the multi-fin configurations disclosed herein may be adapted or modified according to individual performance preferences, skill levels or technique. In addition, it will be understood that in the preceding discussion, the various references and descriptions that have been made have included simplifications, exaggerations for purposes of clarity, and subjective interpretations of what may be a fairly complex interplay of a number of different phenomena. These descriptions have been presented in order to better illustrate the invention; the spirit and scope of the present invention, however, is not limited to the specific embodiments described above, but includes the various modifications and functional equivalents that a person skilled in the art of surfboard design might make using the principles disclosed herein. While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation.

INDUSTRIAL APPLICABILITY

(43) By incorporating the principles and teachings of the present invention, surfboards of improved acceleration and handling may be fabricated. Utilization of fins 40 having foils 42 with the oscillating curvature 72 described above will dramatically alter the handling characteristics of a multi-fin surfboard and will result in smoother handling and control. Incorporating the inventive fin configurations can also increase acceleration and control characteristics. Selection and placement of the fins 40 in accordance with the parameters of the rider can result in optimal performance, particularly in turns.

(44) For the above, and other, reasons, it is expected that the surfboard fin system 10 of the present invention will have widespread industrial applicability. Therefore, it is expected that the commercial utility of the present invention will be extensive and long lasting.