SURFBOARD FIN SYSTEM

FIELD OF THE INVENTION

[1] This invention is related to water planing hulls, such as surfboards, and the design of hydrodynamic fins to stabilize the performance of the planing hull as it moves through the water.

BACKGROUND OF THE INVENTION

[2] Surfboards may generally be described as water planing hulls and are constructed of various lengths, width, shapes and thicknesses. Surfboards have a forward tip which is connected by generally symmetrically shaped sides to the rearward tail. Surfboards currently available in the marketplace typically have a large vertical fin located underneath and near the tail of the surfboard. The large fin is usually located on the center line of the surfboard. Some surfboards have additional smaller fins, which are offset at equal distances from the center line. Current fin designs may result in undesirable horizontal or lateral stability of the entire surfboard. Moreover, fin designs typically do not affect the vertical or pitch stability of the surfboard. Thus, the desire for enhanced stability is an objective of surfboard designers.

SUMMARY OF THE INVENTION

[3] Briefly, the present invention relates to a fin which includes a generally horizontal hydrofoil intersecting or connecting with a typical vertical fin. The generally horizontal hydrofoil of the invention is designed using principles of hydrodynamics, that is, the forces generated by the flow of water over a hydrofoil or wing, to create a force that pulls downward on the fin system and, in turn, downward on the tail end of the water planing hull or surfboard. The effect of the downward force on the tail is counterbalanced by an upward force on the planing hull forward of the tail. The upward force acts to stabilize the planing hull by the effects of the positive upward force of the lifting or rising of the middle and forward section of the planing hull.

[4] The improved fin design results in a surfboard with a forward section that will rise higher out of the water due to the tail being pulled downwardly from the surface of the water by the negative force generated by hydrodynamic flow over the hydrofoil.

The negative force is generated by the generally inverted wing foil shape of the hydrofoil. Thus a generally vertical fin provides lateral stability and directional control, and generally horizontal sections or vector components thereof on fins or foils attached to the vertical section provide vertical stability and negative lift. For purpose of the invention "horizontal" describes the hydrofoil attached to the vertical section or fin, and does not require that the foil be limited to any particular angle as compared to the vertical section or fin. Thus, the foil may include or generate both horizontal as well as vertical vector forces on the generally horizontal board.

[5] Thus, it is an object of the invention to provide a surfboard construction having enhanced stability.

[6] Another object of the invention is to provide a surfboard construction which employs stabilizing fin elements or foils on the underside of the surfboard.

[7] A further feature of the invention is to provide a surfboard construction which employs a stabilizing fin construction which provides a downward vector force on the board.

[8] These and other objects, advantages and features will be set forth in the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[9] In the detailed description which follows, reference will be made to the drawing comprised of the following figures:

[10] Figure 1 is a side elevation view an embodiment of the fin system of the invention attached to the tail portion of a surfboard;

[11] Figure 2 is a side elevation view of the fin or foil construction of Figure 1 ;

[12] Figure 3 is a cross-section of the hydrofoil of the fin system of Figure 1;

[13] Figure 4 is a top plan view of the fin system of Figure 1 depicting a rectangular shaped hydrofoil;

[14] Figure 5 is a top plan view of a fin system having two vertical fins and a rectangular- shaped hydrofoil;

[15] Figure 6 is a top plan view of a fin system with two generally parallel vertical fins, a rectangular-shaped center hydrofoil section and two tapered rearward-swept hydrofoil sections;

[16] Figure 7 is a top plan view of a fin system with a tapered, rearward-swept hydrofoil;

[17] Figure 8 is a top view of a fin system, with a tapered, forward-swept hydrofoil;

[18] Figure 9 is a top plan view of a fin system with a rectangular-shaped, rearward- swept hydrofoil;

[19] Figure 10 is a front plan view of the fin system of Figure 1;

[20] Figure 11 is a front plan view of a fin system with the hydrofoil attached to the vertical fin with a dihedral angle;

[21] Figure 12 is a front plan view of a fin system with winglets;

[22] Figure 13 is a front view of a fin system with a hydrofoil attached to the vertical fin with an anhedral angle and with winglets on the ends of the hydrofoils;

[23] Figurel4 is a front plan view of a fin system with a hydrofoil attached to the vertical fin with a dihedral angle and with winglets on the ends of the hydrofoils;

[24] Figure 15 is a front plan view of a fin system with two vertical fins and a rectangular-shaped hydrofoil; and

[25] Figure 16 is an isometric view of the fin system of Figure 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[26] A surfboard with a fin system of the invention typically includes at least one vertical fin 21, to provide lateral stability and directional control, and a horizontal section or foil 22 attached to the vertical fin 21 to provided vertical stability and negative lift. Vertical stability and negative lift are generated by the inverted wing shape of the horizontal fin or hydrofoil. The term "horizontal" is intended to broadly describe a hydrofoil 22 attached to the vertical fin, and does not require that the foil be limited to any particular angle as compared to the vertical fin 21 or the plane of the surfboard. Moreover, the generally horizontal fin or fin construction which provides which provides negative lift, need not be attached to a vertical fin. For example, the

negative lift fin constructs described may be positioned on the underside of a surfboard by means of a rod or post independent from a vertical fin.

[27] The vertical fin 21 may be of any shape, and generally has a proximal end 24 attachable to a surfboard and a distal end 23 defining a vertical fin tip 23. In addition to the inverted wing shape, the hydrofoil typically has an arcuate leading edge 31, an upper or first surface 33 nearer to the proximal or surfboard attachment end 24 of the vertical fin 21, a lower or second surface 32 nearer to the distal end or vertical fin tip 23, and a trailing edge 34. The hydrofoil has a root end 41, which is the end that is attached to the vertical fin 21 , and a tip end 42 opposite the root end 41.

[28] The inverted wing shape is most easily determined by examining the cross- sectional profile of the hydrofoil such as depicted in Figure 3. A chord line 35 of the inverted wing or foil 22 is the straight line between the leading edge 31 and the trailing edge 34 of the foil 22. The mean camber line 36 is the mid-point of the thickness 37 of the hydrofoil 22 at an infinite number of points moving across the foil 22 from the leading edge 31 to the trailing edge 34, parallel to the root end of the foil 22. The camber 38 of the foil 22 is greatest distance between the chord line and the mean camber line. In the inverted foil 22 in cross-section, the distance from the lower surface 32 to the mean camber line 36 is predominately less than the distance from the lower surface 32 to the chord line 35. At some points in the cross-section of the inverted foil 22, the distance from the lower surface to the mean camber line may be equal to, or in some designs, greater than the distance from the lower surface to the chord line 35. However, overall, the distance from the lower surface 32 to the mean camber line 36 is less than the distance from the lower surface 32 to the chord line 35 in order to provide negative lift.

[29] The foil 22 typically is characterized by an overall distance from the lower surface 32 to the mean camber line 36, which is less than the overall distance from the lower surface 32 to the chord line 35, and thus will have a lower surface area that is greater than the upper surface area. As the foil 22 is passed through the water, there is typically laminar flow over the lower 32 and upper 33 surfaces of the hydrofoil. The longer path of water traveling over the lower surface 32, as compared to the upper surface 33, creates what can be described as "negative lift." The negative lift pulls the hydrofoil 22 and thus the surfboard 12 downward, toward the tip of the vertical fin 21.

Because the hydrofoil 22 is attached to the vertical fin 21 at the root end 41 of the hydrofoil 22, the downward force is transferred through the vertical fin 21 to the surfboard 12. The transfer of the downward force through the vertical fin 21 causes the tail of the surfboard 12 to be pulled downward as the surfboard 12 moves forward in the water.

[30] The inverted wing shape of the hydrofoil 22 generates downward force as the hydrofoil 22 is moved through the water at an angle of attack that is generally parallel to the forward movement of the surfboard. That is, because of the shape of the hydrofoil 22, the foil 22 need not be angled upward, from leading edge 31 to trailing edge 34, to generate the downward force. Although not required to generate the downward force, the angle of attack of the hydrofoil 22 may be adjusted to supplement or negate in part the downward force generated by the shape of the hydrofoil 22 itself.

[31] Utilizing the inverted wing cross-sectional profile, the hydrofoil 22 may be formed in many different shapes. The hydrofoil 22 may have a relatively constant chord length 35 from the root end 41 to the tip end 42, forming a rectangular shape when viewed from above [Figure 4]. In such an embodiment, there may be slight variations at the root end 41, as the hydrofoil 22 is flared for attachment to the vertical fin 21, and at the tip end 42, as the corners are rounded. However, over the majority of the foil, the chord length 35 remains the same. Alternatively, the foil 22 may be tapered from root end 41 to tip end 42 [Figure 7]. That is, the chord length 35 is reduced or increased or varied in whole or in part from root end 41 to tip end 42. Other configurations may have the foil swept forward in relation to the forward movement of the fin through the water [Figure 8]. In the embodiment of Figure 8, the leading edge 31 of the foil 22 at the tip end 42 is forward of the leading edge 31 of the foil 22 at the root end 41. Conversely, the foil 22 may be swept rearward, with the leading edge 31 of the foil 22 at the root edge 41 forward of the leading edge 31 of the foil 22 at the tip 42, as the fin system moves through the water [Figures 7 and 9]. In either forward- swept or rearward swept embodiment, the foil 22 may be tapered or have a constant chord length.

[32] In addition to the being swept forward and rearward, tapered or rectangular, the sections of the hydrofoil 22 on each side of the vertical fin 21 may be angled. If the hydrofoils 22 are angled upward from root end 41 to tip end 42 symmetrically on either

side of the vertical fin 21, they are configured with a dihedral angle 61 [Figures 11 and 14]. Conversely, if the hydrofoils 22 are angled downward from root end 41 to tip end 42 symmetrically on either side of the vertical fin 21, they are configured with an anhedral angle 62 [Figure 13]. The hydrofoils 22 may be attached to the vertical fin 21 at any point along the entire length and depth of the vertical fin 21 or independently of the fin 21. Embodiments within the scope of the invention may have many of these combined attributes, such as a tapered, rearward-swept hydrofoil with a dihedral angle. Winglets 51 may also be used at the tip end 42 of the hydrofoil 22 to improve the lift characteristics of the foil 22 and to reduce drag [Figures 12, 13 14].

[33] In another embodiment, two vertical fins 21 are employed, with a hydrofoil 23 section between the two vertical fins 21, as well as hydrofoils 22 extending outwardly from each vertical fin 21. The center hydrofoil 23 is generally rectangular in shape, while the outward-extending foils 22 may be rectangular or tapered, unswept, swept forward or swept rearward. The described fin construction or system is typically positioned at or near the tail of a surfboard. However, it may be positioned at other places along the median longitudinal axis of the board. It may be placed on the axis or parallel thereto and spaced therefrom.

[34] Variations and modifications of the foregoing are within the scope of the present invention. It should be understood that the invention disclosed and defined herein extends to the individual features and all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein comprise modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art. The invention is therefore limited only by the following claims and equivalents thereof.