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10/15/09 - USPTO Class 441 |  1 views | #20090258553 | Prev - Next | About this Page  441 rss/xml feed  monitor keywords

Thick, elliptical-planform fin for a water sports board

USPTO Application #: 20090258553
Title: Thick, elliptical-planform fin for a water sports board
Abstract: A thick, elliptical-planform fin for use on a water sport board such as a surfboard. One set of attributes of the fins according to the present invention is the use of a substantially thick cross-section which, at its maximum thickness, overhangs the receiver slot, typically a 12 to 15 percent thickness ratio, with a maximum thickness at 30 percent of chord length, a blunter leading edge, and a short elliptical planform of constant relative dimension cross-section along its length. (end of abstract)



Agent: Antony C. Edwards - Westbank, BC, CA
Inventor: Derek Robert Leek
USPTO Applicaton #: 20090258553 - Class: 441 79 (USPTO)

Thick, elliptical-planform fin for a water sports board description/claims


The Patent Description & Claims data below is from USPTO Patent Application 20090258553, Thick, elliptical-planform fin for a water sports board.

Brief Patent Description - Full Patent Description - Patent Application Claims
  monitor keywords CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Patent Application No. 61/071,152 filed Apr. 15, 2008 entitled A Thick, Elliptical-Planform Fin for a Water Sports Board.

FIELD OF THE INVENTION

This invention relates to the field of water sports boards such as surfboards and in particular to an improved design of fin for such boards.

BACKGROUND OF THE INVENTION

Surfing is a popular sport, enjoyed throughout many parts of the world today. Surfing generally involves a surfer riding a wave while upright on a surfboard. The surfer controls the surfboard by positioning himself at different locations on the surfboard and by varying his center of gravity. The surfboard (and other types of water sport boards) typically has one or more fins, located on the underside of the surfboard that help direct the flow of water and have a substantial effect on the stability and the maneuverability of the surfboard.

The initial goal was to make longboards, surfboards longer than 9 feet in length, more maneuverable and turn better. Due to their larger displacement, longboards paddle faster and are better able to catch smaller waves than shorter surfboards. However due to their longer lengths and heavier weight, longboards don\'t turn or manoeuvre as well as shorter surfboards. The intent was to improve the performance of surfboards, specifically long boards, by applying aerodynamic theory to increase the performance of the surfboard fins.

Surfboards originally did not have a fin. Originally surfboards were heavy long planks of wood that had no fin. A surfer dragged his foot in the water to turn the surfboard.

In the 1950\'s the construction of surfboards changed with the introduction of foam core construction and the incorporation of a large keel-like fin at the tail of the surfboard. The fin helped the board track straight. The intent to riding was to drop into a wave, control the stall rate to set up for the tube ride, and drive the board straight. There was no maneuvering such as seen today.

Modern surf fins have been patterned after the planform shape of fins found on fish. These fins allowed development of a new style of surfing that involved considerable maneuvering. These smaller fins, coupled with smaller boards gave birth to the style of surfing people are accustomed to today. The planform was cut to match a desired shape and the leading and trailing edges were ground by hand.

In the early 1970\'s multi fin arrangements started to emerge. Twin fin setups were the first to gain market dominance. The twin fin setup has removable fins that were spaced apart on opposite sides of the rear of the board and each fin could be adjusted in its receiver box that was mounted in the board. A male tang protruding from the base or root of the fin mated into a female slot in the receiver box. Because of variations found in the depth of the slots between different types of receiver boxes, and because fins were often fashioned from plate-like material, such as of fibreglass, having a thickness of less than or equal to ⅜ inch and then hand ground into the desired platform and thickness profile, the thickness of a fin was kept to no more than the width of the slot opening. This allowed the fin root to be pushed into the slot if the tang was otherwise too short to properly seat against the base, i.e. bottom, of the slot.

A three fin “thruster” setup emerged in the early 1980\'s and has been dominant in the short board market until today. Typically the outermost fins have flat inner surfaces with curved outer surfaces. Additionally the fins toe slightly inward pointing toward the nose of the board. During maneuvering, when the surfer shifts his weight toward the rear of the board, the flow off the tail of the surfboard tends to be more radial, meaning that the outermost fins are experiencing positive angles of attack. When the surfer shifts his weight forward so the surfboard rides flatter in the water for speed, the flow tends to come more straight off the tail of the board, meaning that the toed-in outer fins are experiencing negative angles of attack. The sharp leading edge and thin thickness ratio of conventional fins encourages flow separation around the fin and noticeable drag. A variation on the thruster setup is the 2+1 setup, with two smaller outer fins and a larger central fin, this arrangement is common on longboards. The fins typically still retain the rearwardly raked planform shape mimicking fish fins.

Typically the chord length of such conventional fins, where the fin rakes back, is longer that the chord length of the base of the fin. The fin is thinner at the tip than at the base. While the base is typically 8% thick, towards the tip of the fin where the chord is longer and the fin thinner, the fin may be only 5% thick. Most longboard fins start as a ⅜ inch thick piece of fibreglass that is cut to the desired planform profile and shaped by hand using a grinder.

The resulting cross section of popular longboard cutaway style fins are often unintentionally non-symmetrical about their center line, have a flat middle section that extends to roughly 60% of chord length, and have a sharp leading edge. Most fin manufacturers focus on the planform shape with almost no emphasis or analysis of the cross-sectional shape. This is especially the case with longboard fins.

The most common fin shape for outside fins for Thruster and 2+1 setups are flat on inside surface and have a large flat section through most of the middle of upper surface of the fin, and have a sharp leading edge. During aggressive maneuvering the fins are subject to alternating positive and negative angles of attack. The sharp leading edges and flat bottom surfaces of the fin encourage separation of low angles of attack and an increase in the resultant drag.

Surfboard fins with thin cross-sections (typically 6 to 8% in thickness), sharp leading edges, surfaces that have abrupt changes in the radius of curvature (referred to as curve incontinuity), and fins where the thickest part of the fin is located more rearward (40 to 50% of chord length), are common designs found throughout the surfing industry today.

It is an object of the present invention to provide fins for water sports boards which are more responsive, cause less drag, and enable the surfboard to run faster in the water than conventional fins.

SUMMARY OF THE INVENTION

The thick, elliptical-planform fin apparatus described herein is for use on a water sport board such as a surfboard. The fin provides for improved stability and maneuverability for the water sport board. The fin has a tang portion which attaches the base or root of the fin to the water sport board to transfer the forces of the fin to the board. The fin has a hydrodynamic portion that extends into the water that interacts and directs the flow of water to provide stability and steering for the water sport board. The tang attaches to a receiver mounted into the water sports board such that the fin is removable. Any of several different conventional styles of tang can be used which are compatible with receivers commonly found in water sports boards. One set of attributes of the fins according to the present invention is the use of a substantially thick cross-section which, at its maximum overhangs the receiver slot, typically 12 to 15 percent thickness ratio as seen in FIG. 1, with a maximum thickness at 30 percent of chord length, a blunter leading edge, and a short elliptical planform of constant relative dimension cross-section along its length. These attributes combine to provide substantial hydrodynamic benefit when compared with available surfboard fins on the market today.

The present invention may be characterized as a surfboard fin for mounting into a slot in a receiver box in the underside of a surfboard, where the fin includes:

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