Patent Grant
8944872
The invention relates generally to surfboards and more particularly to hydrodynamic fins mounted underneath a surfboard and methods of using the same to achieve surfboard lift.
Surfboards may generally be described as water planing devices used to ride waves. The term “surfboard” may include boogie boards, wind surfing boards, and other hulled craft which are maneuvered by shitting the weight borne by the craft relative to the craft's center of gravity. Surfboards may be constructed of various lengths, width, shapes and thicknesses. Initially, surfboards had a single vertical fin located along the centerline of the surfboard at the rear that provided directional stability. Later designs added additional smaller fins of various sizes and shapes along the sides of the surfboard to improve the stability and maneuverability of the surfboards.
In terms of its design, a surfboard fin is analogous to a “fixed wing.” The surface curvature of conventional fins reflects architecture similar to that of a “fixed wing” aircraft. When the physics are applied to an aqueous environment, the “fixed wing” is termed a “hydrofoil” or sometimes simply a “foil.”
Holding all other variables constant and for a constant hydrofoil speed, the velocity of water passing over the top surface of the hydrofoil wing is greater than that which passes below the flat bottom surface. With an increase in water velocity over the top of the hydrofoil wing, the pressure of the water over this surface is reduced when compared to the pressure below the hydrofoil wing. This difference in pressure tends to push the hydrofoil wing toward the side of lowest pressure of the pressure gradient. The velocity of the water over the top surface of the wing is forced to rise with increased velocity because (a) water is essentially incompressible and (b) the distance a water molecule must travel for a given linear distance is longer due to the curvature of the wing over the hydrofoil surface as compared to the straight line distance enjoyed by water molecules passing below the hydrofoil wing. The upward force generated through relative motion between the wing and the environment through which it travels, in this case water, is proportional to the velocity of the water over the wing surfaces and the surface area of the wing's bottom surface. The velocity of a surfboard is largely a function of wave height, wave velocity, and gravity.
A reduction in lift may be expected from “turbulence” or “cavitation” that could theoretically develop over the wing surface. For example, turbulence may be created by high surface friction coefficients and disrupt desired laminar flow. Cavitation is a phenomenon whereby gasses actually come out of solution in the surrounding water mass due to significant pressure reduction. Similar to opening a carbonated beverage, and under the appropriate temperature and pressure conditions, air bubbles may form in the low pressure zones over the wing's surface. Cavitation may disrupt laminar flow and will also produce aquatic sounds as the bubbles collapse and return to solution.
The single vertical fin is generally speaking, a type of hydrofoil, whose function is to provide lift or some other force to the surfboard in reaction to its motion through the water. The single vertical fin is usually a symmetrical foil (a “50/50” foil) with both sides convex, which provides for even water flow on both sides of the fin such that a single vertical fin promotes stability and control. If the hydrofoil has a convex, top surface and a flat bottom surface, the velocity of water flow over the top surface of the hydrofoil is increased, thus creating a water pressure differential between the bottom and top surfaces and producing Sift or thrust in the direction of the pressure differential toward the area of lowest pressure.
The performance of a surfboard is affected by the design, placement, and number of fins affixed to the surfboard. For example, a fin may be defined by its dimensions: its base, its depth, its sweep, its flex, and its cant, and changes in these dimensions affect the performance characteristics of the surfboard. As for the hydrofoil effects, the fin may be the aforementioned symmetrical foil or a flat foil having one flat side and one convex side, which promotes maneuverability and fast transitions between turns. Other fins may combine the characteristics of a symmetrical foil and a flat foil in various proportions dependent on the desired performance characteristics of the surfboard. For optimum foil performance, flexibility in design characteristics is necessary, as well as the ability to modify these design characteristics as surfing conditions change.
Therefore, as competitive surfers attempt more challenging maneuvers and ride bigger waves, there is need for improved fin designs that improve the lift, maneuverability, and other performance characteristics of the surfboards.
The present invention relates to a lifted fin apparatus comprising one or more lifted fin elements with foiled fin components for a reduction of pressure and drag and an increase in surfboard lift as well as a method of achieving surfboard lift through the use of said apparatus. In some embodiments, said individual lifted fin elements may be combined into a single unitary structure embodying the physical characteristics of a combination of two or more fin elements.
In some embodiments, the lifted fin apparatus of the present invention comprises two or more lifted fin elements. Lifted fin elements may further comprise at least two fins exhibiting a foil design on one or more of the fin surfaces. In some embodiments, the at least two fins may comprise a substantially vertical fin attached to a first edge of a base member and oriented at a substantially 90° angle in relation to the bottom surface of the surfboard or to the first edge of the base member. The at least two fins may further comprise an angular fin mounted to a second edge of the base member at one end and the lower portion of the first fin at the other end. In said embodiment, a bend or elbow is formed between a first fin component of angular fin and base member proximate the point of attachment at second edge of base member. Alternatively, the base member may not have a defined second edge representing the intersection between base member and a first fin component of angular fin, but rather the base member and the angular fin may be manufactured as a unitary structure with a bend or elbow between base member and a first fin component as described below.
In some embodiments, the second angular fin comprises at least two fin components, a first fin component and a second fin component, with a bend or elbow between first fin component and second fin component and a bend between first fin component and base member (as described above) wherein the first tin component extends downward from the second edge of the base at an angle of 17.99° from the substantially vertical, fin for a specified length and the second fin component extends downward at an angle of 72.10° until the second angular fin reaches and is attached to the substantially vertical fin. The angular design of the second angular fin and engagement to a second edge of base member and lower portion of the substantially vertical fin yields a box design in some embodiments. In some embodiments, the lead opening of the box is larger than the rear opening resulting in a Venturi effect.
In some embodiments, the second angular fin may be attached to the first substantially vertical fin at an angle to redirect water downward through the box design—thereby generating lift. To achieve this effect, in some embodiments, the second fin is attached at a 5° declined plane in relation to the plane of the water surface on which the surfboard rides.
In some embodiments, at least one surface of the first (“substantially vertical”) and second (“angular”) fins is foiled. For example, in one embodiment the exterior surface of first fin or the surface facing the outside (lateral) edges of the surfboard is convex, in another embodiment, the upper or interior face of the lower portion, of said second fin is convex. And in yet another embodiment, both interior faces of said second fin. (e.g., interior faces of the first fin component and the second fin component) are hydrofoils (e.g. convex). In some embodiments, the length between the leading edge of the first and second fins to the nearest point of maximum thickness is a predetermined length, for example, about 0.25″ and the length between the rear edge of the first, and second fins and the thickest part of the fin is also a predetermined Length, for example, about 1.5″.
The foregoing and other features, objects, and advantages of the invention will become more apparent from a reading of the following detailed description in connection with the accompanying drawings.
Certain embodiments of the present invention can be better understood with reference to the following figures. Like reference numerals designate corresponding parts throughout the different views.
Further scope of applicability of the present invention will become apparent from the description of representative embodiments given herein. However, it should be understood that the description and specific examples, while indicating embodiments of the invention, are given by way of illustration only since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.
Lifted fin elements 102, 103 are mounted to the surfboard 101 by means of a plug system 105. Plug 105 may be a long, thin piece of high-density plastic or aluminum with a plurality of threaded mounting holes on its bottom surface, which accept machine screws attaching the lifted tin elements 102, 103. The plug may be may be built, into the surfboard as is the case today with most major surfboard manufacturers and held in place either with an angled grub screw, or other methods. Other lifted fin attachment mechanisms are equally suitable for the purposes of this invention which will be readily recognized by one of ordinary skill in the art. For example,
With continued reference to
Referring to
Second fin 114 is also a foil and is comprised, of a first fin component and a second fin component (represented by reference numerals 116 and 117 respectively in
Both fin components of second fin 114 may be foils and provide additional lift vectors depending on their configuration. In the embodiment shown in
By employing a foil design to one or more of the fin components of the second fin 110 and orienting the foiled fin component such that convex surface interfaces with the interior physical space of the “box frame” of the lifted fin, further pressure reduction is experienced for water passing over these surfaces. Once again, an element of design is employed to provide further pressure reduction of the water mass traveling in the vicinity of the top surface of the horizontal hydrofoil wing. With additional pressure reduction, the net result is greater effective lift.
It should be recognized that while the first and second tins shown in the figures exhibit so-called “flat” foil design, other conventional foil designs are equally applicable for the purposes of the present invention, including for example “inside” foils, 50/50 foils, 80/20 foils, and the like.
The foiled fins of the present invention have one or more convex surfaces depending on the type of foil utilized, e.g. a flat foil or 50/50 foil, etc. In the embodiment depicted in
Turning to
Additional lift vectors may be designed into the lifted fin elements 102, 103. For example, the first fin 113 may be attached to the second fin 114 at a specific angle to the horizontal wherein the edge of second fin 114 is slightly pitched downward from front to rear. In the embodiment shown in
While the specific angles described in the preceding paragraphs were found to exhibit the best performance, it should be recognized by one of ordinary skill in the art that through experimentation other angles and dimensions were determined to yield positive result as well. For example, it was determined that the declined angle 123 shown in
A lifted fin element may also be designed to create a “Venturi” effect by using a box frame opening or mouth that has a larger cross sectional area at points of water entry when compared to a cross sectional area at points of water discharge. For a constant mass flow rate of water passing through the box frame, the reduction in the Sifted fin interior cross sectional area forces water to travel a longer distance through the interior physical space. Given water's incompressible characteristic, and in consideration of the need for additional water velocity to keep up with the speed of the fins for a constant velocity, water pressure is reduced inside the box frame, i.e., the interior physical space. The reduction of water pressure by the Venturi effect produced within the box frame interior space tends to further reduce the water pressure over the top surface of the horizontal hydrofoil fin. With further reduction in water pressure over the hydrofoil fin's top “curved” surface, the upward force applied to the bottom of the hydrofoil fin is greater. The net effect is the production of additional lift for a constant fin velocity.
The differences in the surface area of the box design entry and exit openings may be modified to change overall pressure reduction experience inside the fin's zones of influence. Current design utilizes the Venturi effect through its lateral cross section normal to the direction of travel. An example of an implementation of a design of differences in a cross sectional area at points of water entry and a cross sectional area at points of water discharge is shown in
Additionally, the lifted fin elements 102, 103 may be configured to produce hydrodynamic effects in conjunction, with each other when affixed to a surfboard as mirror images of one another on opposing sides of the bottom surface of the surfboard relative to the surfboard's longitudinal centerline. When compared to a single surfboard fin design, the symmetrical placement of two lifted fin elements, left and right, provides performance balance across the tail of the surfboard in addition to theoretically doubling the available lift force over a single element lifted fin design. Beyond lift force multiplication, the left and right lifted fin elements may also be designed to provide surfboard lift and speed enhancements through a combined and symbiotic effect.
For example, desired laminar flow characteristics may be enhanced for water volumes passing through the space between the left and right element interior feces. This is accomplished by the physical boundaries presented by the interior faces of each lifted fin element. The interior faces of the lifted fin elements and the bottom surface of the surfboard provide boundaries for a passage way that serves as a directional “aqueduct” as water passes through the system. Rotational adjustment of the left and the right elements provides opportunity for “tuning” “aqueduct” performance. For a particular direction of travel the Sifted fin elements may be adjusted such that theoretical “aqueduct” boundaries are “toed” to the right, or “toed” to the left, providing opposition to the tendency for gravity to drive the surfboard to the trough of a wave. The lifted fin elements may be adjusted such that they are “toed in,” “toed out,” or are in “parallel alignment.” When “toed in,” the lifted fin elements increase drag. When “toed out,” the Venturi effect raises water velocity between the lifted fin elements increasing surfboard speed. When in “parallel alignment,” the lifted fin elements help preserve laminar flow in the “aqueduct” and enhance the performance of the left and the right vertical wing and hydrofoil performance by mitigating turbulence.
Although the lifted fins elements 102, 103 are described in terms of separate components, one skilled in the art will, appreciate that a lifted fin elements may be manufactured as a single integrated component. Additionally, the lifted fin elements 102, 103 may be constructed utilizing a composite plastic selected to provide a balance between rigidity and flexibility. The selected material, and its design, is intended to provide structural rigidity under load while remaining flexible enough to enhance performance and sustain mechanical shock. The flexibility of the material enhances performance as velocity increases. The pressure inside the box frame is reduced with increased surfboard speeds. The net effect is that water pressure outside the box frame increases.
In general, lifted fin design considers all of the ultimate forces that are developed, particularly those that tend to “push” against relatively “flat” exterior faces of the vertical stabilizing elements. Vertical element design parameters include the integration, of “balanced surface areas” to minimize lateral differential pressure across the entire box frame that in turn mitigate lateral distortion under load. Also, the flexible properties of the composite plastic tend to absorb oscillation and flex slightly “inward” with the goal of enhancing the Venturi effect and providing an additional measure of lift.
As the “low point” of the vertical fin sections are pushed inward under load, the horizontal hydrofoil fin provides resistance to this “force of compression.” Force of compression applied through vertical fin “low points” is opposed by the structural rigidity of the horizontal fin; the system tends to remain rigid when “squeezed” or “pushed” from both ends.
Conventional “inverted shark fin” designs, for surfboard “rudders” and “stabilizers.” experience “flutter” as pressure conditions oscillate between their vertical faces under load. The box frame design of the lifted fins underneath a surfboard includes dimensional consideration aimed at an equitable distribution of pressure across the vertical members. When equitable pressure distribution is coupled with the inclusion of “low point” vertical wing stabilization offered by the connecting horizontal hydrofoil, fin “flutter” is nominal, producing smooth surfboard control as the rider provides input.
Virtually all performance gear experiences physical punishment when utilized under extreme conditions, The plastics selected for use in presenting the lifted fin physical form are chosen for their ability to remain rigid under load, yield predictable performance characteristics, and remain flexible enough to absorb mechanical shock during transport and use over a wide range of temperatures. Whether surfing a bulge in Arctic water originating from glacial collapse or a wave over a Hawaiian Island lava flow, the plastics chosen are designed to mitigate brittle fracture and heat deformation.
The foregoing description of an implementation has been presented for purposes of illustration and description. It is not exhaustive and does not limit the claimed inventions to the precise form disclosed. Modifications and variations are possible in Sight of the above description or may be acquired from, practicing the invention.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/701,715 filed Sep. 16, 2012. The disclosure of U.S. Provisional Patent Application 61/701,715 is incorporated by reference herein in its entirety.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6739925 | Burns et al. | May 2004 | B2 |
| 20140080371 | Hill et al. | Mar 2014 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20140080371 A1 | Mar 2014 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61701715 | Sep 2012 | US |
