JP2015517954A - Watercraft fins - Google Patents

Abstract

A drag generated by a fin can be reduced. In one aspect, the present invention is a watercraft fin comprising a first side and a second side, wherein a plurality of dimples are formed on at least one of the first side or the second side. Provide watercraft fins. [Selection] Figure 5

Description

  The present invention relates to a fin for a watercraft, particularly a fin for a surfboard.

  An important part of watercraft, especially surfboards, is one or more fins. The fins act as a stabilizer that allows the user or rider to ride, control and enjoy the board or watercraft. The latest serve board has 3 or 4 fins. Designs using these three or four fins, known as “Thruster” and “Quads”, can create propulsion while maintaining hold on the wavefront. Propulsion is generated from the outward force created by the side fins during the turn.

  Side fins (left and right) work on the same principle as aircraft wings. The fluid moves faster on the curved foil face than the fluid moves on the flat inside foil face of the fin as the fluid moves over the fin . As a result, the flat surface has a high pressure and the curved surface has a low pressure. The high pressure pushes the foil upward. This creates lift on the wings of the plane. For surfboard fins, high pressure pushes the foil / fin outward. The lift created outward on the fins is the “feel” felt by the surfer when making a turn, known as “drive”. This feel is based on the amount of control, speed, and maneuverability that the fins can provide. The drive is activated when the surfboard is turning and the angle of attack (flow) across the fin causes the fin to create lift. If this outward force (lift) can be increased, this force (lift) increases the size of the drive the fin has.

  This increase in lift remains a major goal for fin designers who attempt to minimize drag. It is desirable not to sacrifice control and maneuverability as speed increases. As an example, in the case of a surfboard, the smaller the surfers, the less lift is required, so smaller fins can be used when the rider is lighter. As the fins become smaller, the lift decreases due to the reduction in the surface area of the foil, but the drag also decreases. The shape of the foil is designed based on the trade-off between lift and drag.

  Various attempts have been made over the years to improve the fin design. Generally speaking, these attempts have failed and only serve to reinforce traditional design standards that are not significantly different from the original design. Such failures also make the industry extremely important to attempt to change the standard design.

  The fin design is still important, but the actual structure of the fin is also very important. For example, it will be appreciated that to minimize drag, it is important that the surface of the fin be as smooth as possible so as to reduce friction between the fin and water. It has been found that the friction needs to be reduced as much as possible to allow the fins to slide smoothly in the water.

  Despite these efforts, drag is a problem in fan design, and therefore the present invention seeks to reduce the drag caused by the fins.

  In a wide variety of forms, surfboards or other watercraft fins are provided on the surface of the fins with a plurality of dimples that improve the performance of the fins. The dimple is like a small concave or convex portion on the surface. In one aspect, the present invention is a watercraft fin having a first side and a second side, wherein a plurality of dimples are formed on at least one of the first side or the second side. Provide craft fins. Reference to “two sides” is understood to mean the two main sides of the fin. In the conventional fin, in the case of a side fin, one side surface is substantially flat and the other side surface is curved. These aspects can be compared to the upper and lower parts of an aircraft wing.

  In a preferred configuration, the dimples are substantially circular and have a diameter of 2.0 mm to 4.5 mm and a depth of 0.1 mm to 0.5 mm. Ideally, the diameter is between 3.8 mm and 4.3 mm and the depth is between 0.2 mm and 0.5 mm.

  The dimple spacing is also important for the present invention. The center points between adjacent dimples must be separated from each other by 3.7 mm to 4.5 mm, the center point is regarded as the center of the dimple, and the adjacent dimples are close to each other and between other dimples Means two dimples arranged in a state where they are not arranged.

  Ideally, a predetermined interval is provided between the dimples so as not to deform the shape of the foil or deteriorate the bending characteristics of the fin. The edges of the adjacent dimples may be arranged 0.2 mm to 0.5 mm apart from each other. In a preferred configuration, the distance between adjacent edges is 0.3 mm to 0.4 mm.

  The dimples may be arranged in a row. In some embodiments, these rows are substantially parallel to the base of the fin, i.e., the surface of the watercraft. The base of the fin is a part of the fin integrated with or attached to the watercraft, and the opposite end is the tip of the fin. In other embodiments, these rows are provided at an angle of 170-190 degrees with respect to the base of the fin, ie, an angle of ± 10 degrees from parallel.

  In some embodiments, dimples are formed substantially across the sides of the fin. In another configuration, the dimples are arranged from the widest part of the fin to the rear edge of the fin.

  The dimples may be arranged on both sides of the fin according to required performance, or may be arranged only on one side.

  In the case of a fin having only one side surface with dimples, it is necessary to form dimples on the lift generation side.

  Depending on the implementation, the dimple shape may be hexagonal, triangular, rectangular, elliptical, or square rather than circular. Further, in some configurations, one may choose to have different dimple sizes, i.e., the dimple size increases in a row starting from the leading edge and extending to the trailing edge of the fin.

  The present invention is a significant development from the conventional idea employed in current fin designs. Forming dimples leads to a significant improvement in fin performance, thereby leading to a significant improvement in the watercraft on which the fin is mounted.

(A) is a figure which illustrates the flow of the water around a smooth surface, (b) is a figure which illustrates the flow of the water around the surface with a dimple. (A) is a figure which shows the flow of the water on the surface of a smooth foil, (b) is a figure which shows the flow of the water on the surface of the foil with a dimple. (A) is a figure which shows the production | generation of the vortex around the front-end | tip part of a fin, (b) is a figure which shows the reduction | decrease of a tip vortex by use of a dimple. (A) is a figure which shows the preferable position of the dimple which concerns on a modification, (b) is a figure which shows the preferable position of the dimple which concerns on another modification, (c) is the arrangement | positioning which concerns on another modification. It is a figure which shows the preferable position of the dimple. It is a figure which shows the foil which concerns on one Embodiment of this invention. FIG. 6 is a representative cross-sectional view of the foil of FIG. 5 (ie, the dimples are not drawn to scale). It is a figure which shows the foil which concerns on another embodiment of this invention. It is a figure which shows the shape variation in which a dimple is realizable. It is a figure which shows arrangement | positioning of the possible dimple on the curved outer surface of a fin. FIG. 5 shows possible dimple placement on the “flat” inner surface of the fin. (A)-(c) is a figure which shows the foil shape which can be implemented. It is a figure which shows the foil which concerns on another embodiment of this invention. It is a figure which shows the foil which concerns on another embodiment of this invention. It is a figure which shows the foil which concerns on another embodiment of this invention. FIG. 6 is a diagram showing possible dimple arrangements on the applicant's conventional fin design. FIG. 3 is a diagram showing an arrangement of a preferred embodiment of the present invention. FIG. 4 is a diagram illustrating a preferred depth and arrangement of an embodiment of the present invention. (A)-(d) is a figure which shows another embodiment of this invention. It is a figure which shows the number of the dimples on the curved outer surface of the small symmetric fin in one Embodiment of this invention. It is a figure which shows the number of the dimples of the single side | surface of the small symmetric fin in one Embodiment of this invention. It is a figure which shows the number of the dimples on the curved outer surface of the medium type symmetry fin in one Embodiment of this invention. It is a figure which shows the number of the dimples of the single side | surface of the medium symmetric fin in one Embodiment of this invention. It is a figure which shows the number of the dimples on the curved outer surface of the large symmetric fin in one Embodiment of this invention. It is a figure which shows the number of the dimples of the single side | surface of the large symmetric fin in one Embodiment of this invention. It is a figure which shows the space | interval of the dimple from the edge of the fin in one Embodiment of this invention. FIG. 26 is a diagram showing another method of measuring the dimple spacing of FIG. 25. FIG. 6 is a diagram showing a preferred setback of a specific fin dimple in one embodiment of the present invention. (A) is a figure which shows the simulation streamline on the conventional fin, (b) is a figure which shows the simulation streamline on the fin with a dimple. It is the graph and table | surface which compared the lift (N) of the fin with a dimple and the lift (N) of the conventional fin without a dimple.

  Exemplary embodiments of the present invention will be described with reference to the accompanying drawings. Other features and advantages of the invention will be apparent from the accompanying description.

  The following description is presented to enable one of ordinary skill in the art to make and use the invention, and the art is presented for a particular application and what is required for that application. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be used in other embodiments and without departing from the spirit and scope of the invention. You may apply to an application example. The present invention is not limited to the embodiments shown, but is to be construed in the widest scope consistent with the principles and features disclosed herein.

  In order to optimally control a watercraft such as a surfboard, it is desirable for the water flow to remain in contact with a control surface such as a fin. As the water stream leaves the foil surface, the water stream begins to form exfoliation bubbles. This usually occurs when the angle of attack is high or during a sudden turn, and the Coanda effect (the tendency of the running water to adhere to the curved surface) does not occur, generating pressure drag and reducing lift. Is undesirable because the fin will stall. That is, the speed and controllability of the watercraft are reduced.

  Referring to FIG. 1a, a laminar flow of water around a smooth object is shown. Laminar flow, also known as streamlined flow, is a parallel laminar fluid flow. The fluid continues to flow linearly without the layers mixing. As shown in FIG. 1a, when a smooth-shaped object is inserted into the flow, the parallel layers continue to flow in generally the same direction (from left to right in the figure), but each layer is greatly separated. To do.

  In contrast, when a dimpled surface is inserted into the flow as shown in FIG. 1b, the dimple effect reduces this separation. The dimples on the surface create turbulence that pulls the flow back over the foil / fin and prevents backflow (also called flow separation) from the rear high pressure region. The turbulent boundary layer contains more energy, and therefore the turbulent boundary layer delays separation until the magnitude of the negative pressure gradient is increased, thereby effectively moving the separation point to the rear on the foil In some cases, peeling is completely eliminated.

  This effect can also be seen in FIG. 2, which illustrates the water flow on the surface of the fin. Similar to the smooth object in FIG. 1a, the smooth surface of the fin in FIG. 2a does not provide any attraction and can cause significant separation between the water and the surface of the fin. As a result, the flow scrapes off the foil to create cavitation, which causes the fins to stall during maneuvering or high angles of attack. FIG. 2b shows the effect of dimples on the surface of the fin. In this case, the turbulence generated by the dimples flows back over the curved foil surface, allowing the foil to function at a higher angle of attack.

  Similarly, FIG. 3a shows the known problem that a vortex is created around the tip of the fin. These fin tip vortices are associated with induced drag, and lift is generated by inevitable side effects on the fins. The tip vortex of the fin forms the main component of wake turbulence. As shown in FIG. 3a, by creating a low pressure region in front of the fin, the fin generates aerodynamic lift. The fluid flows from high pressure to low pressure, and the fluid at the rear of the fin tends to move through the fin tip toward the top of the fin. The fluid can flow around the tip without escaping around the front edge of the fin due to its velocity. As a result, the fluid flows from the rear of the fin to the periphery of the tip and flows in an annular fashion to the front of the fin. This leakage increases the pressure at the front of the fin and reduces the lift that the fin can generate.

  The problem of the tip vortex can be reduced by using dimples around the tip of the fin. This is illustrated in FIG. 3b. In this case, the dimples reduce flow leakage at the tip. By creating a turbulent flow along the tip, the turbulent flow pulls the separating flow back to the tip surface.

  All solid objects moving through the fluid have a fluid boundary layer around them. In the boundary layer, a viscous force is generated in the fluid layer near the solid surface (in this case, the outer edge of the fin). The boundary layer can be either laminar or turbulent.

  Conventional fins have a smooth surface that provides a laminar flow of water over the fins. The realization of this laminar flow has been an issue in the industry, and is still an issue today. However, if the angle of attack received by the fin is high, laminar flow actually increases drag and reduces fin performance in contrast to the present invention. In the present invention, by introducing dimples on the fin, turbulent water flow is brought about on the surface of the fin.

  This reduces the separation of water flowing over the fin by attracting water molecules to the surface of the fin, thereby delaying the separation that takes away the energy of the water stream.

  This is due to reducing laminar separation of the flowing water on the surface of the fin.

  Flow separation occurs when the boundary layer moves far enough against the reverse pressure gradient and the velocity of the boundary layer relative to the fin drops to approximately zero. If the boundary layer peels, resulting in a decrease in lift and speed, and the fin stalls, the efficiency of the fin is compromised.

  Boundary layer delamination occurs when the flow in the portion of the boundary layer closest to the fin surface or leading edge is reversed. As a result, the entire boundary layer is first suddenly thickened and then separated from the surface by backflow at the bottom of the boundary layer.

  The fluid flow leaves the surface of the fin with a smooth surface and takes the form of vortices and vortices (as shown in FIG. 2a). In flow mechanics, drag increases due to flow separation.

  When the laminar boundary layer around the fin surface peels off very rapidly, it creates a very large fin wake, resulting in cavitation.

  The present invention creates a dimpled surface on the fin, thereby creating a turbulent flow of water on the surface of the fin.

  By placing the dimples on the fins in the region where the flow delaminates, the flow separation is delayed and the flow remains attached to the surface longer. This improves fin performance at high angles of attack (such as important surfboard maneuvers).

  By adding dimples to the curved surface of the foil, the transition of the boundary layer from laminar to turbulent flow along the length of the foil is facilitated (as compared to the standard design). The turbulent boundary layer can remain attached to the surface of the foil much longer than the laminar boundary layer, thereby reducing the overall pressure drag. The disadvantage of this is that the viscous drag of the turbulent boundary layer is slightly increased compared to the laminar boundary layer. However, testing of dimpled fins has shown that the pressure on the curved surface of the fin decreases, resulting in an increase in lift at an angle of attack of 7.5-15 degrees (9-12%).

  The placement of dimples can be affected by the intended use of the fins or the desired effect. Referring to FIG. 4, the preferred position of the dimple based on the expected angle of attack is shown. The angle of attack is the direction of water flow when the water flow contacts the fins. In FIG. 4a, when the fins are moving on a straight line, forming a dimple at the rear of the widest section of the foil can provide a clean transition without laminar separation bubbles. This clean transition reduces the pressure drag caused by the foil and thus improves performance. The transition is where the flow begins to change from laminar to turbulent. When the pressure changes from high pressure to low pressure, the flow leaves the foil.

  As the fluid flows over the fins (foils), there is a fluid layer called a boundary layer between the fin surface and where the fluid is not disturbed. Depending on the fin profile, water often flows smoothly through a thin boundary layer across most of the fin surface. The boundary layer is laminar near the leading edge, and becomes turbulent at a certain distance (depending on surface roughness and Reynolds number (velocity)) from the leading edge. However, due to the magnitude of the positive pressure gradient, the boundary layer reaches the point where it departs from the surface of the fin, that is, the separation point. As the pressure of the wake behind the peel point drops, under the peel layer, stagnant water form bubbles are created creating additional drag.

  These bubbles can be reduced and possibly eliminated by adding dimples that turbulent the boundary layer. The turbulent boundary layer contains more energy, so the turbulent boundary layer delays separation until a larger negative pressure gradient is reached, effectively moving the separation point further back on the foil In some cases, peeling is completely eliminated. As a result of the turbulent boundary layer, surface friction against the laminar boundary layer is increased, which is very small compared to the increase in drag associated with separation.

  When the board rider attempts a sharp turn, the angle of attack is considered quite large. This case is illustrated in FIGS. 4b and 4c. Surfboards typically turn 0-35 degrees and 0-360 degrees in an arc or S-turn. With a large angle of attack, it will exceed 35 degrees for a straight path.

  In some embodiments, the dimples are located only on one side of the fin, as shown in FIG. 4b. In general, this is the lift generation side of the fin. However, in other arrangements, the dimples are placed on both sides of the fin, as shown in FIG. 4c. This is especially the case for asymmetric fins.

  This also reduces peeling from the inside of the foil. Surfboards typically have two or more fins, each side contacting the flow at a different angle. In order to maximize foil performance, it is desirable to reduce delamination on both sides of the foil. Delamination occurs in various regions on the flat inner surface opposite the curved outer surface of the fin.

  The dimpled surface moves quickly to the turbulent region. This has the advantage of controlling the separation of water from the surface.

  Depending on the desired performance, the dimples may be placed in a smaller or larger area on the surface of the fin, or may be placed in multiple portions of the fin. Referring to FIG. 9, various embodiments are shown with the dimpled portions of the fins each shaded.

  Each of the various variations provides a different feel and different performance. There are also various situations when surfing, and the arrangement of various dimples may be preferred according to different circumstances. That is, increasing the dimple coverage will give a gripper feel and less feel the fin will slide out, so this arrangement will be better on steep and larger waves .

  Generally speaking, the fin has an active curved surface and a flat surface. A common exception is center fins with single fin and trifin arrangements. In this case, the center fin is usually symmetrical and is curved on both sides. These common foil shapes can be seen in FIG. FIG. 11b shows a curved upper surface and a flat inner surface. FIG. 11a shows a curved upper surface and a slightly curved inner surface, for the sake of simplicity, consider the inner surface as flat as the foil of FIG. 11b. FIG. 11c shows a symmetrical foil shape, with the upper and inner surfaces both curved. This is a foil commonly used as a center fin and a single fin.

  In the present invention, the main dimples are placed on the curved surfaces of the fins. These arrangements are described above and illustrated in FIG. However, it is also beneficial to form dimples on the “flat” surface of the fin. FIG. 10 shows the preferred position of the dimples on the flat surface of the fin. These are areas where delamination is expected.

  In a preferred arrangement, the dimples are circular. A combination of wave and surfer maneuvering is preferred because the flow is constantly changing and there is no steady flow from one direction. The circular dimples are uniform so that the circular dimples deal with various flow angles. In modern surfing, surfers can turn 360 degrees and ride surfboards backwards. In such a situation, the round circular dimple can give a uniform result in whatever direction the surfer is moving. However, a variety of different shapes can be used. A preferred shape of the dimple is shown in FIG. The dimple shape may be selected according to the purpose of use. Different performance may be required for different crafts. For example, a wake board is towed to the rear of a boat and generally travels in a straight line and does not receive as much angle of attack as a surfboard. Thus, the wakeboard can benefit from non-circular dimples, such as hexagonal dimples, but it will be appreciated that circular dimples still improve performance.

  In most embodiments, the dimples have a common size and shape. However, in some cases, dimples having different sizes may be used. These different sized dimples can be made smaller at the tighter rounded part of the front edge, just in front of the widest part of the fin (depth 0.1 mm x width 2.0 mm), The dimple increases by about 1.0 mm as it crosses the curved surface of the foil until it reaches the maximum size, ie 0.325 mm depth x 4.0 mm width, and decreases by 1.0 mm as the dimple approaches the trailing edge. The depth is 0.1 mm and the width is 2.0 mm.

  Current testing has shown that preferred dimples have a diameter of 2.0 mm to 4.5 mm and a depth of 0.1 mm to 0.5 mm. If the diameter is too small, for example less than 2.0 mm, it will increase the drag without decreasing the pressure drag or increase the lift to counter the increase, and similarly the diameter will be too large, for example 5 mm. Beyond that, it has been found that the surface area increases excessively and drag is still created.

  In a preferred embodiment, the dimple has a diameter of 2.0 mm to 4.5 mm and an optimum diameter of 3.8 mm to 4.3 mm. Further, the depth range of the dimple is 0.2 mm to 0.5 mm, and the ideal range is 0.28 mm to 0.325 mm.

  In a preferred configuration, as illustrated in FIGS. 16 and 17, the dimples have a diameter of 4.036 mm and a depth of 0.325 mm. Preferably, the centers of the dimples are spaced 4.378 mm apart from each other to provide a 0.367 mm spacing between the dimples.

  Another configuration is illustrated in FIG. 18 showing various diameters, depths, and spaces of other preferred embodiments of the present invention.

  Ideally, the dimples are arranged such that the distance between the dimple edges is 0.2 mm to 5 mm. The ideal distance between the edges of each dimple is 0.3 mm to 0.4 mm.

  In examining the distance between the centers of each dimple, the preferred range is 3.70 mm to 4.5 mm. In the above configuration, the number of dimples on one side of the fin is preferably 350 to 900. The range of the number of dimples on one side depends on the size of the fin. For example, the small fin, the medium fin, and the large fin may have the following dimensions and dimples.

a) Small left and right side fins, symmetrical foil:
Base: 101.0 mm (3.98 inches)
Depth: 105.0mm
Area: 8964.0 mm ²
As shown in FIG. 19, there are 382 dimples with a diameter of 3.76 mm on the curved outer surface.

b) Small center fin, symmetrical foil:
Base: 100.0 mm (3.98 inches)
Depth: 105.0mm
Area: 8964.0 mm ²
FIG. 20 shows one outer surface, the opposite side having a similar inverted shape, with 764 dimples with a diameter of 3.76 mm on both curved outer surfaces.

c) Medium left and right side fins, symmetrical foil:
Base: 110.0 mm (4.37 inches)
Depth: 115.0 mm (4.55 inches)
Area: 9608.0 mm ²
FIG. 21 shows 418 4.15 mm diameter dimples on the curved outer surface.

d) Medium center fin, symmetric foil:
Base: 110.0 mm (4.37 inches)
Depth: 115.0 mm (4.55 inches)
Area: 9608.0 mm ²
FIG. 22 shows one outer surface, with the opposite side having a similar inverted shape, with 836 diameter 4.15 mm dimples on both curved outer surfaces.

e) Large left and right side fins, symmetrical foil:
Base: 116.0 mm (4.55 inches)
Depth: 115.0mm
Area: 9608.0 mm ²
FIG. 23 shows 456 dimples having a diameter of 4.036 mm on the curved outer surface.

f) Large center fin, symmetrical foil:
Base: 116.0 mm (4.55 inches)
Depth: 115.0mm
Area: 9608.0 mm ²

  FIG. 24 shows one outer surface, the opposite side having a similar inverted shape, with 910 dimples with a diameter of 4.036 mm on both curved outer surfaces.

  19 to 24 show a preferable number of dimples in each “row”. In a preferred configuration, each row of dimples is substantially parallel to the surface of the surfboard or watercraft to which the fins are attached. This is the same as each row of dimples being substantially parallel to the fin base, which is connected to the surfboard or watercraft. In a preferred configuration, the rows of dimples are substantially parallel, i.e., 180 degrees, but in other embodiments, the dimples may be arranged between 170 degrees and 190 degrees. That is, the preferred angle of the dimple row is parallel to the base of the fin, but a variation of up to 10 ° is acceptable.

  Various embodiments of fins having dimples may be provided. In one embodiment, as shown in FIG. 5, dimples are formed on substantially the entire outer surface of the fin, but the dimples are placed back from the edge. Ideally, the leading edge of the fin should not form dimples so as to maintain the foil curve and not interfere with the Coanda effect. Similarly, in the preferred arrangement, the trailing edge of the fin is not dimpled to reduce vibration in the thinned portion of the foil. Ideally, the dimple should be at least 5 mm away from the trailing edge.

  Figures 25 and 26 show a preferred setback from the edge of the fin. From FIG. 25, it can be seen that the setback from the edge of the fin in the line parallel to the row of dimples is 5.0 mm to 60.0 mm. Alternatively, referring to FIG. 26, the center of each dimple that is closest to the edge of the fin is positioned 8.0 mm to 60.0 mm vertically from the edge of the fin.

  A preferred setback for the dimensions of one embodiment of the present invention is also shown in FIG.

  In another embodiment, the fin has a dimpled surface disposed at a set distance from the leading edge of the foil. This offset distance can be determined such that the dimples begin behind this widest point, relative to the location where the foil has the widest point. Behind the widest part of the foil is a place where the flow tends to peel off. Dimples placed behind the widest point reduce separation by creating a turbulent layer that draws backflow.

  In another embodiment, the dimples are placed on the fins in a region where the computational flow dynamics have determined that the greatest flow separation (and cavitation) occurs. However, the boundary layer reaches the point where it departs from the surface of the fin due to the magnitude of the positive pressure gradient, that is, the separation point. Under the release layer, the pressure drops in the wake behind the release point, resulting in stagnant air form bubbles creating additional drag.

  These bubbles can be reduced and possibly eliminated by shaping the fins to move the separation point further, or by adding dimples that turbulent the boundary layer. Can do. The turbulent boundary layer contains more energy, so the turbulent boundary layer delays separation until a larger negative pressure gradient is reached, effectively moving the separation point further back on the foil In some cases, peeling is completely eliminated. This peeling point differs depending on the fins of various shapes, and the best region for arranging the dimples can be determined by computational fluid dynamics.

  Previous fin designs define a smooth surface. Contrary to conventional belief, the present invention introduces a dimpled surface for better control of the surfboard, thereby providing watercraft fins, such as surfboard fins in modern surfing To improve the performance). Conventional fin designs with smooth and flat surfaces cannot continue to hold the fins in highly diverging waves due to cavitation caused by flow separation on the foil surface of the fin.

  The dimple design utilizes turbulence to delay flow separation and reduce cavitation and drag. The turbulent boundary layer helps the flow overcome the counter pressure gradient and continue to adhere to the surface longer than without the turbulent boundary layer.

  Surfers in the process of “capturing waves” and propelling the board into the water have a so-called “adhered laminar fluid flow” around either side of each fin, following the Coanda effect during this linear motion. Feel the effects of physical phenomena of fluid dynamics that regulate

  The dimple size, depth, and distance between the dimples of the present invention are important and greatly affect the overall performance and manufacturing of the fins. If the dimples are too large with respect to depth and width, the surface area of the dimples will be excessive and drag will increase. Furthermore, the lift is reduced and therefore the increased drag cannot be offset. In addition, as the dimples grow larger and deeper, the bending properties of the material used to make the fins begin to change, and the material in that region becomes too thin, too flexible or friable, thereby reducing performance. Making fins difficult to manufacture. Conversely, dimples that are too small or too shallow do not provide improved performance, but rather increase the drag of the fins. The distance between the dimples also affects the performance of the fins. If the dimples are too close or in contact with each other, the dimples have the effect of deforming the shape of the foil curved surface, thereby reducing the lift generated by the fin and coanda effects. The fact that the dimples are too close to each other also affects the bending properties of the material used to make the fins, making the material in that region thinner and more flexible, thereby reducing performance and reducing the fins. Making it difficult to manufacture. Conversely, if the dimples are too far away from each other, the amount of lift generated by the dimples can be reduced and therefore the drag cannot be offset. Thus, the present invention provides dimple parameters that provide improved performance contrary to conventional thinking within the industry.

  The fins of the present invention are believed to be produced using known plastic injection molding techniques. Injection molding is a manufacturing process for making parts from both thermoplastic and thermoset plastic materials. The material is fed into a heated barrel, mixed, and placed in a mold cavity where the material is cooled and hardened into a cavity structure.

  Injection molding can be a preferred option, but other techniques such as CNC cutting, vacuum forming, casting, etc. may be used. The choice of material will also depend on the manufacturing technique used and the desired effect. Suitable materials include fiberglass, polyester, polycarbonate, polycarbonate with glass fiber, nylon, nylon with glass fiber, aluminum, epoxy, wood, rubber, and other thermoplastic materials. In the case of plastic injection, a preferred material that mimics the bending properties of fiberglass is nylon containing 30-50% glass fiber, or alternatively, nylon containing 30-50% carbon fiber, or KEVLAR®. While it is not important that the bending properties of the fiberglass be maintained, current surfers are satisfied with the feel of existing fiberglass and therefore prefer to provide similar bending properties.

  In general, nylon KEVLAR® is considered a less expensive material that is less worn by work with tools, but less used.

  Ensinger Industries Inc.'s Hydlar ™ has been found to be a suitable material. An alternative is Nylon 6 ™ from IG Farben.

  When nylon is filled with KEVLAR® aramid fibers, it is stronger and more wear resistant than nylon alone. Such thermoplastic composites generally outperform other reinforced plastics, and in particular have increased tensile strength and bending strength.

  The advantages of the present invention can be seen in FIG. 29 where the lift (N) of the dimpled fin according to the present invention is compared to a conventional fin without dimples.

  The graph of FIG. 29 shows the resulting lift provided by each fin at various flow angles (attack angles). This graph shows two important points. First, in the dimple design of the present invention, the lift is significantly increased in the range of 7.5 degrees to 15 degrees. An increase in lift at this point is important because the surfer can push the board more strongly and increase the speed on the turn.

  The second point is that the conventional fin design cannot reduce the large stall effect after the lift reaches 25 degrees. The dimpled fin also stalls past the 25 degree point, but this stall is not as great as with the conventional fin, so the surfer can maintain the hold necessary to finish the turn.

  This test is based on Applicants' claims that a dimpled fin having the parameters described herein increases lift, reduces pressure drag, and improves fin fin performance compared to conventional fins. Support.

  The advantages of the present invention can also be seen in FIGS. 28a and 28b, which show simulated streamlines as the flow streamlines approach the fins and go over the fins. FIG. 28a shows the flow over a standard or conventional fin, and FIG. 28b shows the flow over a fin similarly designed and with dimples added. FIG. 28a shows in particular the fin tip vortex. The fin tip vortex is an annular pattern of rotating fluid that is left behind the fin when the fin generates lift. When the fins generate hydrodynamic lift, the pressure of the fluid on the top surface is low compared to the bottom surface. The fluid flows annularly from below the fin and around the tip to the top of the fin. A sudden annular flow pattern called a vortex is observed and is characterized by a low pressure core.

  In considering these tip vortices, the simulation diagrams of FIGS. 28a and 28b again illustrate two aspects of the present invention. First, the tip of the standard fin has a turbulent flow that draws a spiral in the wake of the tip. This is known as the tip vortex. The tip vortex results in fin drag, stall, and performance degradation. Forming dimples on the fins removes most of the tip vortex and, as a result, reduces drag, reduces stall, and improves overall performance compared to conventional fins.

  The second aspect seen in the figure is that the wake created by the standard fin is significantly larger than the wake created by the dimpled fin. This indicates that the flow separation or cavitation that occurs when the dimples pass through the water is smaller than that of the standard fins, and the dimples pass through the water more efficiently.

  Prior to this application, it was desirable and common for fins to be a smooth surface over the entire area of the fin. On the contrary, the present invention discloses that the dimpled surface area on the fin surprisingly increases the lift generated by the fin and reduces the effects of pressure drag and tip vortex.

  Contrary to conventional thinking, the dimpled fin of the present invention provides better drive and maneuverability while maintaining hold and grip in water. This hold and grip in the water was usually sacrificed when using smooth fins for critical maneuvers.

  Prior to this application, the addition of dimples was thought to result in defects that increase the surface area, drag of the fins, thereby reducing performance.

  By adding dimples on the surface of the fin as described herein, the turbulence created is used to make the connection between the water flow and the surface of the fin large when subjected to a high angle of attack. Keep longer when turning. This maintains the speed and hold capability of the fins during maneuvering, thereby improving the performance of the surfboard.

  Although the present invention has been described with reference to fins for surfboards, it will be understood that the fins can be used in other watercrafts. For example, body boards, kite boards, stand-up paddle boards, wake boards, and the like.

  Throughout this specification, reference to “one, an” embodiment includes that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Means. Thus, the phrases “in one embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

  Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner to form one or more combinations. Those skilled in the art will appreciate that the present invention may be implemented in a manner different from that described above, and that alternative embodiments may be reduced without departing from the spirit and scope of the present invention.

  Discussion or literature, apparatus, acts, or knowledge in this specification is presented to illustrate the context of the invention. Prior to the date of the filing of a patent application herein, materials that form part of the common general knowledge in the basics of the prior art or related technical fields in any country should not be considered omitted.

Claims (19)

  A watercraft fin comprising a first side surface and a second side surface, wherein a plurality of dimples are formed on at least one of the first side surface or the second side surface.   The watercraft fin according to claim 1, wherein the dimple is substantially circular and has a diameter of 2.0 mm to 4.5 mm.   The fin according to claim 2, wherein the dimple has a diameter of 3.8 mm to 4.3 mm.   The fin according to claim 1, wherein the dimple has a depth of 0.1 mm to 0.5 mm.   The fin according to claim 4, wherein the dimple has a depth of 0.2 mm to 0.5 mm.   The fin according to claim 1, wherein the dimple has a diameter of about 4.036 mm and the dimple has a depth of about 0.325 mm.   The fin according to claim 1, wherein the center points between adjacent dimples are separated from each other by 3.7 mm to 4.5 mm.   The fin according to claim 1, wherein edges of adjacent dimples are separated from each other by 0.2 mm to 0.5 mm.   The fin according to claim 8, wherein the edges of adjacent dimples are separated from each other by 0.3 mm to 0.4 mm.   The fin according to any one of claims 1 to 9, wherein 300 to 900 dimples are formed on at least one of the first side surface and the second side surface.   The fin includes a base for joining the fin to the watercraft when in use, the dimples are arranged in a row, and the row is provided at an angle of 170 degrees to 190 degrees with respect to the base. The fin according to claim 1, wherein the fin is provided.   The fin according to claim 11, wherein the row is provided to be substantially parallel to the base.   The fin according to any of claims 1 to 12, wherein the fin comprises a leading edge and a trailing edge, and the size of the dimples increases from the leading edge to the trailing edge.   14. The fin of claim 13, wherein the size of the dimple increases by about 1 mm and the diameter of the dimple ranges from about 2 mm near the leading edge to about 4 mm near the trailing edge.   The fin includes a front edge and a rear edge, and the dimple is disposed at a rear portion of the widest portion of the fin, and the widest portion is determined from a cross-sectional area of the fin between the front edge and the rear edge The fin according to any one of claims 1 to 12.   The fin according to claim 1, wherein the dimple is a hexagon, a triangle, a rectangle, an ellipse, or a square.   The fin according to claim 1, wherein the fin includes a tip portion, and the dimple is disposed near the tip portion.   The fin according to claim 1, wherein the dimple is disposed in a region where laminar flow separation of water from the fin occurs.   A watercraft fin having a first side surface for generating lift and a second side surface, wherein a plurality of dimples are formed on at least one of the first side surface and the second side surface, It is substantially circular, has a diameter of 3.8 mm to 4.3 mm and a depth of 0.2 mm to 0.5 mm, and the dimples have center points between adjacent dimples of 3.7 mm to 4. mm. Watercraft fins arranged 5 mm apart and / or such that the edges of adjacent dimples are 0.3 mm to 0.4 mm apart from each other.

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