WO2004002582A1

WO2004002582A1 - Swim fin with energy storage and release system for improved angle of attack and water flow characteristics

Info

Publication number: WO2004002582A1
Application number: PCT/US2003/020393
Authority: WO
Inventors: Sergio A. Angelini
Original assignee: Johnson Outdoors Inc.
Priority date: 2002-06-28
Filing date: 2003-06-27
Publication date: 2004-01-08
Also published as: AU2003261098A1

Abstract

A fin for use by a swimmer is disclosed. The fin comprises a foot pocket adapted to receive a foot of the swimmer, a blade extending from the foot pocket, and a biasing system configured to control the bending of the blade to within a predefined range of angles during use. The biasing system includes at least one set of adjacent ribs extending along a longitudinal dimension of the blade. The at least one set of ribs includes a portion having a reciprocating configuration relative to a plane generally perpendicular to the blade. A fin having a foot pocket, a blade, and a pair of connector ribs is also disclosed. The blade is spaced apart from the foot pocket and connected to the foot pocket by the ribs so that water passes through the gap created therein.

Description

SWIM FIN WITH ENERGY STORAGE AND RELEASE SYSTEM FOR

IMPROVED ANGLE OF ATTACK AND WATER FLOW

CHARACTERISTICS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. Patent Application No. 10/184,231 , filed June 28, 2002, and U.S. Patent Application No. 10/274,283, filed October 18, 2002, hereby incorporated by reference.

[0002] U.S. Design Patent Application No. titled "FIN" filed October 18, 2002 (Attorney Docket No. 40022-130) is hereby incorporated herein by reference.

FIELD OF THE INVENTION

[0003] The present invention relates to a swim fin with improved angle of attack control and water flow characteristics. More particularly, the present invention relates to a swim fin with a biasing element configured to provide improved angle of attack at various kicking power levels, and to a swim fin with flow channels to provide improved water flow characteristics.

BACKGROUND OF THE INVENTION

[0004] Swim fins are generally known and typically include a foot pocket and a blade portion. A desirable feature of a swim fin is that the blade portion of the fin easily attains a correct "angle of attack" during use. The angle of attack is the relative angle that exists between the actual alignment of the oncoming flow (i.e., direction of motion of the swimmer) and the lengthwise alignment of the blade of the fin. A "correct" angle of attack optimizes the conversion of kicking energy of the swimmer to thrust or propulsion through the water. When this angle is small, the blade is at a low angle of attack. When this angle is high, the blade is at a high angle of attack. As the angle of attack increases, the flow collides with the fins attacking surface at a greater angle. This increases fluid pressure against this surface.

[0005] Conventional fins tend to assume different curvatures or attack angles according to the direction of movement and the magnitude of the forces applied during use (i.e., the kicking energy or power). Therefore, it is generally known to design a swim fin to provide a particular angle of attack for a particular kick power. For example, such known swim fins are typically designed for either light kicking, medium kicking, or hard kicking. One way to design a fin for one of these particular kicking powers is by the composition of the material (e.g., stiff material for hard kicking, flexible or soft material for light kicking, etc.). Changing the composition of the material, however, does not efficiently or adequately control the angle of attack, is difficult to match or "size" to the strength of the swimmer, and requires the swimmer to use the "prescribed" kicking power for that particular fin. Also, most existing fins can only reach a compromise in that they are either stiff, soft, or somewhere in between. When conventional fins are designed for hard kicking (e.g., made of stiff material), they reach the correct angle of attack when kicked very hard. On a normal, relaxed kick they don't bend far enough and this negatively affects the performance. Fins of this kind will be uncomfortable on the legs, strenuous and with poor performance on a relaxed dive. When conventional fins are designed for light kicking (e.g., made of soft material), they reach the correct angle of attack when kicked very gently. With a strong kick, such as when swimming in a current or needing to get up to speed, the blade is overpowered and there is little or no thrust available. Fins like this might be comfortable on a relaxed dive, but could become unsafe by not being able to provide the thrust to overcome a slight current. When conventional fins are somewhere in between, they can be overpowered when kicked real hard, are still uncomfortable when kicked gently, but cover a wider range of useful kicking power.

[0006] When such known fins are used outside their prescribed kicking power, the angle of attach tends to be too low or too high. When the fin blade is at excessively high or low angles of attack, the flow begins to separate, or detach itself from the low pressure surface of the fin. This tends to cause the fin to be less efficient. Another problem that occurs at higher angles of attack is the formation of vortices along the outer side edges of the fin. This tends to cause drag. Drag becomes greater as the angle of attack is increased. This reduces the ability of the fin to create a significant difference in pressure between its opposing surfaces for a given angle of attack, and therefore decreases the power delivered by the fin.

[0007] Accordingly, it would be advantageous to provide a swim fin that provides a desired or optimum angle of attack for a variety or range of kicking strengths or powers. It would further be desirable to provide a swim fin in which the angle of attack is accurately controlled both for the upstroke and for the downstroke so that the ratio of power to fin area is markedly increased (which makes it possible to reduce the overall size of the swim fin without sacrificing total power) for various kicking efforts. It would further be advantageous to control the angle of attack by structural characteristics of bending, not merely by characteristics of materials. It would further be desirable to provide a swim fin with biasing members such as integrally molded, sinusoidal shaped ribs that increase the performance by controlling the angle of attack and converting a higher percentage of the kick energy into thrust. It would further be advantageous to provide a swim fin with flow channels that reduce spillover and provides improved water flow characters. It would further be desirable to provide for a swim fin having one or more of these or other advantageous features.

[0008] To provide an inexpensive, reliable, and widely adaptable swim fin with improved angle of attack and water flow characteristics that avoids the above-referenced and other problems would represent a significant advance in the art.

SUMMARY OF THE INVENTION

[0009] For a fin to move a diver efficiently through the water, it preferably achieves an optimum angle of attack under all workloads. The latter range from a very relaxed kick on a leisure dive to a powerful and hard kick if the diver finds himself or herself in a strong current or for a commercial diver performing underwater work.

[0010] Typically, full blade fins are able to achieve an optimum angle of attack for a limited range of workload only: a fin that achieves an optimum angle of attack on a light kick is too soft on a hard kick (it is easily overpowered and looses its performance); analogously, a fin that achieves an optimum angle of attack on a hard kick will be stiff and uncomfortable on a light and relaxed dive. Consequently, the diver that has the advantage of being able to kick the fin comfortably on a relaxed dive will be in trouble if he or she has to swim against a current; similarly, the diver with performance on a hard kick will be uncomfortable when swimming leisurely.

[0011] The present inventions are configured to provide a progressively-increasing resistance to the bending of the blade, allowing the fin to get to a near optimum angle of attack on a light kick, and progress to an only slightly higher angle on a hard kick. According to a preferred embodiment, inner ribs comprise reciprocating shaped elements (e.g., zigzag, sinusoidal, arcuate, etc.). In addition to the natural deformation of the material (which is roughly linear over a wide range of deformation) that known ribs provide, there is a geometric deformation that initially provides a minor role but, as the bending progresses, reaches a point where it inhibits (e.g., practically stops) the blade from bending any further.

[0012] According to a preferred embodiment, these zigzag portions are placed along the length of the fin, towards the center, connecting the foot pocket portion to the blade. The blade is preferably dimensioned to provide a hinging effect near or adjacent the foot pocket. The blade portion beyond this non-discrete hinge is preferably stiff efficiently pushing against water and providing optimum propulsion. As the diver or swimmer begins the kick, the blade bends downwards around the hinge. The zigzag portions on the front side of the fin (the side pushing against the water) will be stretching, whereas the zigzag portions at the back side will be contracting. The geometrical deformation initially opposes little, if any, resistance, but this increases as the bending progresses. Beyond a certain point, the consecutive crests in the zigzag on the compressed part will touch, thereby inhibiting the blade from moving further.

[0013] According to a particularly preferred embodiment, the inner ribs are include a first rib portion comprised of a soft and elastic material such as thermo plastic rubber (TPR) and a more rigid portion made of polypropylene. By combining materials of different properties and characteristics, one can achieve a desirable blend of strength and elastic behavior, both fundamental aspects of the energy storage and non-linear spring effects. [0014] Aside from the advantage of allowing the fin to reach optimum angles of attack regardless of kick strength, the inner ribs have the additional advantage of being energy storage devices. Both the geometrical and the elastic deformation occur due to energy transfer from the diver's legs to the fins. This energy is stored during the kick, as the deformation takes place, only to be subsequently released when the diver inverts the kick sequence. The blade returns forcefully to the neutral position providing additional thrust while doing so. This energy release also helps in achieving a quicker kicking cycle.

[0015] In addition, the absence of side ribs connecting the foot pocket with the blade allows the water to flow undisturbed over the blade, thereby minimizing turbulence. Side "winglets" on the blade itself contain the water once it has reached this point, avoiding energy dissipating spill-over and maximizing the available thrust.

[0016] How these and other advantages and features of the present invention are accomplished (individually, collectively, or in various subcombinations) will be described in the following detailed description of the preferred and other exemplary embodiments, taken in conjunction with the FIGURES. Generally, however, they are accomplished in a fin for use by a swimmer comprising a foot pocket adapted to receive a foot of the swimmer, a blade extending from the foot pocket, and a biasing system configured to control the bending of the blade to within a predefined range of angles during use. The biasing system includes at least one set of adjacent ribs extending along a longitudinal dimension of the blade. The at least one set of ribs includes a portion having a reciprocating shape relative to a plane generally perpendicular to the blade. Preferably, the set of ribs comprises a first rib and a second rib adjacent to the first rib. [0017] These and other advantages and features of the present invention may also be accomplished in a fin for use by a swimmer comprising a foot pocket adapted to receive a foot of the swimmer, a blade extending from the foot pocket and configured to flex about an axis, and a biasing system configured to control the angle of attack of the blade. The biasing system comprises one or more sets of ribs that extend generally perpendicular from the blade and include a portion having a sinusoidal shape relative to a plane generally perpendicular to the blade.

[0018] These and other advantages and features of the present invention may also be accomplished in a fin for use by a swimmer comprising a foot pocket adapted to receive a foot of the swimmer, a blade extending from the foot pocket, and a biasing system configured to control the bending of the blade to within a predefined range of angles during use. The blade is spaced apart from the foot pocket and connected to the foot pocket by the at least one set of ribs so that water passes through the gap created therein.

[0019] The present invention also relates to a swim fin for use by a swimmer. The fin comprises a foot pocket adapted to receive a foot of the swimmer, a blade extending from the foot pocket, and a biasing system configured to allow the blade to bend within a narrow range of angles of attack under a wide range of loads.

[0020] The present invention further relates to a swim fin for use by a swimmer. The fin comprises a foot pocket adapted to receive a foot of the swimmer, a blade extending from the foot pocket, a biasing system configured to control the angle of attack of the blade. The biasing system comprises one or more biasing members such as a sinusoidal shaped rib.

[0021] The present invention further relates to a swim fin for use by a swimmer. The fin comprises a foot pocket adapted to receive a foot of the swimmer, a blade extending from the foot pocket, and means for controlling flexing of the blade.

[0022] The present invention further relates to a method of providing thrust from a kick by a swimmer. The method comprises providing a swim fin comprising a foot pocket, a blade, and one or more reciprocating ribs that extends generally perpendicular to the blade. The method also comprises bending the blade relative to the foot pocket about an axis and controlling the bending of the blade by providing varying resistance by the reciprocating ribs.

[0023] The present invention further relates to various features and combinations of features shown and described in the disclosed embodiments. Other ways in which the objects and features of the disclosed embodiments are accomplished will be described in the following specification or will become apparent to those skilled in the art after they have read this specification. Such other ways are deemed to fall within the scope of the disclosed embodiments if they fall within the scope of the claims that follow.

DESCRIPTION OF THE FIGURES

[0024] FIGURE 1 is a top perspective view of a swim fin according to a preferred embodiment.

[0025] FIGURE 2 is a top perspective view of the swim fin of FIGURE 1 with the blade flexed downward.

[0026] FIGURE 3 is a bottom perspective view of the swim fin of FIGURE 2.

[0027] FIGURE 4 is a top perspective view of the swim fin of FIGURE 1 with the blade flexed upward. [0028] FIGURE 5 is a top perspective view of a swim fin according to an exemplary alternative embodiment.

[0029] FIGURE 6 is a perspective view of a fin according to a preferred embodiment.

[0030] FIGURE 7 is a top plan view of the fin of FIGURE 6.

[0031] FIGURE 8 is a sectional view of FIGURE 7 taken along the line 8-8.

[0032] FIGURE 9 is a bottom view of the fin of FIGURE 6.

[0033] FIGURE 10 is a side elevation view of the fin of FIGURE 6.

[0034] FIGURE 11 is a top plan view of a fin according to an alternative embodiment.

[0035] FIGURE 12 is a perspective view of a fin according to an alternative embodiment.

[0036] FIGURE 13 is a top plan view of the fin of FIGURE 12.

[0037] Before explaining a number of preferred, exemplary, and alternative embodiments of the invention in detail it is to be understood that the invention is not limited to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or being practiced or carried out in various ways. It is also to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. DETAILED DESCRIPTION OF PREFERRED AND OTHER EXEMPLARY EMBODIMENTS

[0038] For a fin to move a diver efficiently through the water, it preferably achieves an optimum angle of attack under all workloads. The latter range from a very relaxed kick on a leisure dive to a powerful and hard kick if the diver finds himself or herself in a strong current or for a commercial diver performing underwater work. Typically, full blade fins are able to achieve an optimum angle of attack for a limited range of workload only: a fin that achieves an optimum angle of attack on a light kick is too soft on a hard kick (it is easily overpowered and looses its performance); analogously, a fin that achieves an optimum angle of attack on a hard kick will be stiff and uncomfortable on a light and relaxed dive. Consequently, the diver that has the advantage of being able to kick the fin comfortably on a relaxed dive will be in trouble if he or she has to swim against a current; similarly, the diver with performance on a hard kick will be uncomfortable when swimming leisurely.

[0039] Referring to FIGURE 1 , a pair of swim fins 10 are shown according to a preferred embodiment. Each fin 10 comprises a foot pocket 12, a blade 14, and an energy accumulation and biasing system 16 configured to maintain blade 14 in the desired angle of attack for a variety or range of kicking strengths or powers.

[0040] According to a preferred embodiment, foot pocket 12 and blade 14 are fused together to form an integral structure. Alternatively, foot pocket 12 and blade 14 are integrally molded (e.g., in a single molding operation). Foot pocket 12 is shown with an open heel and buckles 17 for attachment of conventional heel straps (shown in FIGURE 3). Alternatively, foot pocket 12 includes a closed heel instead or any of a variety of conventional designs. Foot pocket 12 is preferably formed of a material having a different stiffness than blade 14. For example, if the preferred material for blade 14 is stiff, the material for foot pocket 12 may be softer for increased comfort of the diver.

[0041] Blade 14 comprises a composite ribbed framework. The ribbed framework is configured to provide stiffness to blade 14 and channel water flow across fin 10. The framework includes a plurality of segments shown in the FIGURES as a central or main segment 18 and two projecting lateral segments 20, 22 defined by a plurality of longitudinally extending ribs (shown as inner ribs 24 and outer ribs 26) that extend generally along the longitudinal axis of fin 10. Lateral segments 20, 22 of the blade 14 have leading edges 28 that slant rearwardly, and configured to smoothly divide the on-flowing water. Inner ribs 24 extend along the sides of foot pocket 12 rearwardly to the end of blade 14, and are configured to provide structure and rigidity to fin 10.

[0042] Outer ribs 26 extend along a portion of the outer sides of lateral segments 20, 22 of blade 14. Outer ribs 26 are configured to minimize the obstruction to water by being parallel to the direction of flow with minimal cross section to the flow itself, to prevent energy loss by reducing spill-over effect, and to increase performance by stiffening blade 14 itself. Whereas a conventional fin design allows for a progressive bending of the entire blade to somewhat accommodate a wider range of kicking powers, a preferred embodiment of the present invention focuses the bending action around the biased elements 16, thus maintaining the blade as a rigid and substantially "straight" structure, the consequence of a conventional progressively bending blade is also that the angle of attack progressively varies, whereas a straight blade (as used in the preferred embodiment) maintains a more constant angle of attack. (The outer ribs on conventional fins connect to the foot pocket to provide stiffness to the fin). According to a particularly preferred embodiment, the rearward portions of inner ribs 24 are tapered and (to a slight degree) downwardly angled, and frontal edges of the outer ribs 26 are curved to reduce flow resistance.

[0043] An inner flow channel 30 is defined by inner ribs 24 and the surface of foot pocket 12 and blade 14. Outer flow channels 32 are defined by inner ribs 24, outer ribs 26, and the surface of foot pocket 12 and/or blade 14. The parallel disposition of inner and outer ribs 24, 26 provides inner and outer flow channels 30, 32 that are generally uniform along the length of fin 10. Alternatively, inner and outer flow channels 30, 32 are non-uniform along their length (e.g., narrows, broadens, varying, etc.). As the swimmer (or snorkeler or diver) propels her/himself, water passes along the sides, top and bottom of foot pocket 12. The flowing water need not traverse ribs interposed in its path as it flows along blade 14. As such, fin 10 is configured to minimize the resistance to flow and the dissipation of swimmer's energy due to turbulence.

[0044] According to a preferred embodiment, blade 14 is relatively rigid or stiff so that flexing substantially occurs about an axis 34 at a particular region of fin 10. As such, blade 14 remains essentially flat during use and provides a regular planar surface to interact with the water flow. Preferably, inner and/or outer ribs 24, 26 are configured to provide additional support and rigidity to blade 14. By maintaining a substantially flat blade 14, the angle of attack is optimized along substantially the entire length of blade 14 (e.g., providing substantially a single angle of attack), and not merely at one location (as may be the case with a relatively flexible blade which tends to have a continuously varying angle of attack). The increased efficiency derived from the use of a rigid fin and from the use of flow channels of uniform area permits the design of a more "powerful" fin having a relatively short fin part.

[0045] According to a preferred embodiment, biasing system 16 is configured to provide an optimum angle of attack for a variety or range of kicking powers. By controlling the angle of attack, biasing system 16 is configured to increase performance and efficiency of fin 10 by converting a higher percentage of the kick energy into thrust.

[0046] According to an exemplary embodiment, biasing system 16 gradually increase the resistance to flexing or bending of fin 10 as a function of the degree of bending itself. The difference between a soft kick and a hard kick is the amount of effort provided by the swimmer and the energy transferred from the leg to the fin and from there to the water. Typically the harder the kick, the more energy transferred to fin 10, and the more fin 10 wants to bend. Biasing system 16 will bend fin 10 within a narrow range of angles of attack under a wide range of loads (i.e., kick strengths or powers). As such, the angle of attack is configured to not significantly vary under differing load conditions (e.g., between a soft kick and a hard kick). Such control of the angle of attack also provides for the concentration and storage of the difference in energy between a soft and a hard kick in the biasing element 16 of fin 10. These particular sections will at first accumulate the excess energy and later on release it and transfer it to the water for a high efficiency forward thrust. This energy accumulation is achieved with a small change in degree of bending of blade 14 so when fin 10 is kicked gently, it approaches the optimal angle of attack, and when kicked harder, the angle of attack is increased only slightly (but remains near the optimum angle of attack) as biasing system 16 absorbs and/or stores the additional energy. [0047] According to a preferred embodiment, biasing system 16 includes one or more sinusoidal-shaped ribs proximate flexing axis 34. As shown in FIGURES 2-4, flexing axis 34 is located in the portion of fin 10 that connects foot pocket 12 with the blade 14 (e.g., upper ribs 38 on top portion of fin 10, and lower ribs 40 on bottom portion of fin 10). According to an alternative embodiment shown in FIGURE 5, upper ribs 44 and lower ribs (not shown) comprise alternating, traversing linear segments (e.g., non-arcuate). According to yet other alternative embodiments, upper and lower ribs 38, 40 are any of a variety of biasing designs (e.g., springs), dimensions, configurations, and orientations.

[0048] Upper and lower ribs 38, 40 provide a spring constant, which is defined by the period, amplitude, material, wall thickness, and the like of upper and lower ribs 38, 40. Preferably, this spring constant is constant and "tuned" to provide a particular desired performance. According to a particularly preferred embodiment, the period or wavelength of upper and lower ribs 38, 40, is about one inch and has a wall thickness of about 0.3 inches at its base and tapers to about 0.15 inches at its top. According to an alternative embodiment, biasing system 16 is configured to provide a variable spring constant (e.g., by varying the period, frequency, or the like at various portions of biasing system 16).

[0049] Referring to FIGURE 1 in a non-stressed configuration, upper and lower ribs 38, 40 are "neutral" (i.e., unstressed, not biased, unstrained, etc.). A downward kick (a horizontally swimming diver that kicks downwards) bends blade 14 upwards. Referring to FIGURE 2 when fin 10 bends under the action of the kick, upper ribs 38 on the top of foot pocket 12 tend to stretch due to the bending action. Similarly, lower ribs 40 on the bottom tend to compress, as shown in FIGURE 3. When the kick is reversed (as shown in FIGURE 4), the upper ribs 38 reverse the role with the lower ribs 40 and the whole process repeats symmetrically. According to an alternative embodiment, sinusoidal-shaped upper and lower ribs 38, 40 are located on only one side of the fin (e.g., the side that typically provides the most thrust).

[0050] According to a preferred embodiment, upper and lower ribs 38, 40 are made from an elastic material such that the more it stretches, the more resistance it will give. As such, the more blade 14 of fin 10 wants to bend, the higher the resistance given by the stretching upper ribs 38. Similarly, as bending of blade 14 increases, lower ribs 40 tend to compress more and will increasingly resist this compression. By deforming upper and lower ribs 38, 40 the energy is being spent to deform these sections of fin 10 rather than flexing fin 10 past its optimum angle of attack. This energy is stored within the fin structure itself (elastic deformation of upper and lower ribs 38, 40). By adjusting the size, shape and material used for upper and lower ribs 38, 40, the amount of energy stored in these upper and lower ribs 38, 40 and the angle of attack attained under soft and hard kicks can be controlled. In addition to controlling the angle of attack (which in itself increases efficiency), the stored energy in upper and lower ribs 38, 40 is returned at the end of the kick in the form of snapping back of blade 14. This snap has been observed as playing a significant role in increasing the efficiency of a diving fin. According to a preferred embodiment, upper and lower ribs 38, 40 are located at top and bottom of fin 10.

[0051] Ribs 38, 40 are configured to allow fin 10 to efficiently attain an initial angle of attack with minimal effort. In contrast, in conventional designs, these ribs are straight such that upon first bending the stretched fibers would immediately commence to pull hard, whereas the compressed fibers would tend to buckle because of excess material not knowing where to flow. By incorporating biasing system 16, material of blade 14 is preferably stiff, yet still reaches a good angle of attack under various loads.

[0052] One source of energy loss in kicking a fin is the amount of water that (during the movement of fin 10 through the water) instead of being pushed back by blade 14, "spills over" the sides of blade 14. Such "spillover" is typically caused by high pressure fluid on one side of blade 14 spilling over the side of blade 14 to the low pressure side. The difference in pressure multiplied by the cross- sectional area of blade 14 provides the thrust that pushes the swimmer forward. As such, spillover reduces the amount of thrust generated by fin 10. According to a preferred embodiment, spillover is reduced by having a stiffer blade, controlling flexing of blade 14 by biasing system 16, providing inner and outer flow channels 30, 32 for improved water flow, and providing outer ribs 22 with a profile better designed to retain water in inner and outer flow channels 30, 32.

[0053] According to an exemplary embodiment, outer channels 32 are configured to channel water across blade 14 and reduce spillover. According to a preferred embodiment, the surface on either side of foot pocket 12 presents a reduced or minimal cross section to the water so a reduced minimal resistance to its flow over it. As shown in FIGURE 1 , outer ribs 22 do not directly join to the foot pocket 12, thereby an "inlet" 42 is formed at the upstream end of outer channel 32 to allow water to flow into channels 32. By providing inlet 42 with reduced cross- section, destruction and disruption to the water flowing into and through outer channels 32 are reduced, turbulence and spillover are reduced, and laminar flow is increased. [0054] Also, outer ribs 26 project from blade 14 further than conventional designs. Preferably, outer ribs 26 extend from blade 14 at least about 1/4 inches. According to a particularly preferred embodiment, outer ribs 26 extend from blade 14 between about V₂ inch and about 1 inch. Alternatively, the ribs extend from blade by an amount appropriate to reduce spill over effects for the swimming style. As such, outer ribs 26 have the function of limiting the "escape" of high- pressure flow (under the fin 10) around the sides of blade 14 to the area of low pressure (over the fin 10).

[0055] Referring to FIGURES 6-11 , a fin 50 is shown according to a preferred embodiment, fin 50 includes a foot pocket 52, a blade 54, and four sets of ribs 56 (two sets are shown on the top surface of fin 50 and two sets are shown on the bottom surface of fin 50).

[0056] Each rib 58, 60 includes a biasing system with a reciprocating portion 61 (e.g., zigzag, sinusoidal, arcuate, etc.). According to a preferred embodiment, reciprocating portion 61 of the biasing system is configured to provide a progressively-increasing resistance to the bending of blade 54 (e.g., a non-linear response), allowing fin 50 to get to a near optimum angle of attack on a light kick, and progress to an only slightly higher angle on a hard kick. In addition to the natural deformation of the material (which is roughly linear over a wide range of deformation) that known ribs provide, there is a geometric deformation that initially provides a minor role but, as the bending progresses, reaches a point where it inhibits (e.g., practically stops) blade 54 from bending further. According to an alternative embodiment, reciprocating portion 61 is configured to provide a linear response as blade 54 is flexed or bends during use. [0057] Aside from the advantage of allowing fin 50 to reach preferred angles of attack regardless of kick strength, the biasing system has the additional advantage of being an energy storage device. Both the geometrical and the elastic deformation occur due to energy transfer from the diver's legs to fins 50. This energy is stored during the kick, as the deformation takes place, only to be subsequently released when the diver inverts the kick sequence. Blade 54 returns forcefully to the neutral position providing additional thrust while doing so. This energy release also is intended to help achieve a quicker kicking cycle.

[0058] According to a preferred embodiment, reciprocating portions 61 are placed along the length of fin 50, towards the center, connecting foot pocket 52. Blade 54 is preferably dimensioned to provide a hinging effect near or adjacent the foot pocket. The portion of blade 54 beyond this non-discrete hinge is preferably stiff for efficiently pushing against water and providing optimum propulsion. As the diver or swimmer begins the kick, blade 54 bends downwards around the hinge. Reciprocating portions 61 on the front side of fin 50 (the side pushing against the water) will be stretching, whereas reciprocating portions 61 on the back side of fin 50 will be contracting. The geometrical deformation provided by reciprocating portions 61 initially opposes little, if any, resistance, but this increases as the bending progresses. Beyond a certain point, the consecutive crests in reciprocating portions 61 (e.g., the zigzag) on the compressed part will touch, thereby inhibiting blade 54 from moving further.

[0059] According to a particularly preferred embodiment, reciprocating portion 61 is formed by alternating triangular-shaped ribs extending from blade 54. Alternatively, reciprocating portion may be formed by any of a variety of alternative rib shapes (e.g., zigzag, sinusoidal, arcuate, or any of a variety of configurations) configured to provide linear or non-linear response to progressive bending of blade 54.

[0060] According to an exemplary embodiment, the fin comprises a plurality of materials selected and located to provide desired performance characteristics. By combining materials of different properties and characteristics, one can achieve a desirable blend of strength and elastic behavior, both fundamental aspects of the energy storage and non-linear spring effects. Referring to the FIGURES, The components of the fin (e.g., the foot pocket, blade, ribs) are composed of one or more of any of a variety of elastomers, thermoplastics, thermosets, filled or unfilled, or combinations thereof. According to a particularly preferred embodiment, most of foot pocket 52 is preferably made from rubber material (e.g., thermo plastic elastomer ("TPE") or thermo plastic rubber ("TPR")) and a portion of foot pocket 52 is preferably made from polypropylene (e.g., the "sole" or base 62) to provide desired comfort, rigidity and strength. Preferably, one or more projections (shown as grips 63) are molded into foot pocket 52 to provide traction in sand/gravel/rocky terrain and/or slippery surfaces (e.g., rocks, boat decks, etc.).

[0061] According to a particularly preferred embodiment, blade 54 includes a first portion 64, a second portion 66, and a third portion 68 that correspond to materials selected and located to provide desired performance characteristics. First portion 64 of blade 54 preferably comprises a mostly rubber material (e.g., TPE or TPR) and is included for cosmetic and manufacturing advantages, and to allow some flexibility in the foot pocket where the diver's toes are located. Second portion 66 comprises a rubber and polypropylene mixture and is configured to provide a desired level of performance to the main portion of blade 54. Third portion 68 comprises polypropylene and is configured to provide a desired strength and stiffness to blade 54 and a transition between first portion 64 and the second portion 66 (and the ribs 56, foot pocket 52, and blade 54).

[0062] Each set of ribs 56 includes a pair of adjacent (or co- extending) ribs shown as an inner rib 58 and an outer rib 60. According to a preferred embodiment, inner rib 58 and outer rib 60 are composed of different materials. For example, inner rib 58 is preferably composed of mostly rubber material (e.g., TPE or TPR) and extends toward the end of blade 54. Outer rib 60 extends to approximately the mid-point of blade 54 and is composed of polypropylene. According to alternative embodiments, ribs 58, 60 can extend any of a variety of distances from foot pocket 52 towards the distal end of blade 54. As shown in FIGURES 2 and 3, the rib made of polypropylene is located nearer the outside of blade 54, and the rib made of mostly rubber is located on the inside of blade 54. Alternatively, the rubber rib is located nearer the outside of blade 54, and the polypropylene rib is located on the inside of blade 54. Alternatively, inner rib 58 and outer rib 60 may be composed of the same material. Also, additional ribs may be provided (e.g., co-extending along ribs 56). For example, a third rib may be provided on the inside of ribs 58, 60 and made from polypropylene. Alternatively, this third rib may be made from any of a variety of materials. By providing adjacent, reciprocating, co-extending ribs made from various materials, it is intended to "tune" the fin to a desired performance.

[0063] According to a particularly preferred embodiment, where fin 50 is molded (or co-molded) from three materials (e.g., rubber, polypropylene, and rubber/polypropylene mix), a pair of molding machines are used in two molding operations. For example, the portions of fin 50 that are molded from polypropylene are molded first (e.g., a portion of foot pocket 52, a portion of blade 54, and outer rib 60). Then, this portion is moved to another molding machine (e.g., manually or by a robotic device). The portions of fin 50 that are molded from the rubber/polypropylene (e.g., part of blade 54 and inner rib 58) are then molded, and the portions that are molded from the rubber (e.g., most of foot pocket 52 and first portion 64) are molded simultaneously (whereby the polypropylene portion acts as a physical separator between the rubber and the rubber/polypropylene portions). Alternatively, fin 50 may be molded or fabricated by any of a variety of operations and machines, typically depending on the number of materials used.

[0064] FIGURES 7 and 11 show exemplary embodiments of the selection and location of materials for a fin. According to a preferred embodiment shown in FIGURE 7, third portion 68 (rubber/polypropylene mix) of fin 50 is disposed along outer edges of blade 54 and extends between inner ribs 56 toward foot pocket 52 so that second portion 66 (i.e., the polypropylene portion) is primarily adjacent to inner ribs 56. According to an alternative embodiment shown in FIGURE 11 , a fin 70 includes a foot pocket 72, a blade 74, inner ribs 76. The portion of blade 74 between inner ribs 76 comprises polypropylene (i.e., there is no rubber/polypropylene portion disposed between inner ribs 76). By eliminating the rubber/polypropylene mix between inner ribs 76, it is intended to improve manufacturability (moldability) and provide desirable performance characteristics.

[0065] It is known that the part of a conventional fin closest to the foot pocket provides little, if any, propulsion and actually generates resistance as water is moved up and down during the kicking cycle and across blade. Due to the position and movement of the foot during a kick, the portion of the blade near or adjacent to the foot pocket tends to move in an up-and-down direction, whereas the remaining portion (i.e., most) of the blade becomes angled with respect to the foot pocket as the blade flexes during use. This angle is the angle of attack of the blade with respect to the water. When this angle is optimized, the blade generates the optimized propulsion. By removing the material between the foot pocket and the actual "working" portion of the blade itself (e.g., the portion that becomes angled with respect to the foot pocket), leaving only the two sets of ribs to connect the blade to the foot pocket, the portion of the blade that is considered to be inefficient and causes loss of energy is reduced or removed. Preferably, these "connector" ribs include reciprocating portions. Also, the behavior of the flexing elements (i.e., the sinusoidal non-linear springs) may also be further optimized as described herein. Further, spacing the blade apart from the foot pocket increases the lever arm and thus the amount of torque one can obtain from the same amount of effort applied into the kick. Referring to FIGURES 12 and 13, a fin 80 according to an alternative embodiment is shown. Fin 80 includes a foot pocket 82, a blade 84, and two sets of ribs 86 that connect blade 84 to foot pocket 82. As shown, blade 84 is not directly connected to foot pocket 82 as shown in fins 10, 50, 70 in FIGURES 1 , 7, 11. Rather, blade 84 is spaced apart from foot pocket 82 so that water passes through the gaps between blade 84 and foot pocket 86. Each set of inner ribs 86 includes an inner rib 88, a middle rib 90, and an outer rib 92. According to a preferred embodiment, inner rib 88 and outer rib 92 are comprised of polypropylene, and middle rib 90 is comprised of rubber (e.g., TPE, TPR). According to an alternative embodiment, each set of inner ribs 86 is comprised of any of a number of co- extending ribs (e.g., a pair of ribs or more than three) depending on the desired performance and the materials selected. [0066] It is also important to note that the construction and arrangement of the elements of the swim fin with improved angle of attack and water flow characteristics as shown in the preferred and other exemplary embodiments are illustrative only. Although only a few embodiments of the present invention have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, the energy accumulations may have any of a variety of shapes or configuration. Also, blade 14 may be made of a flexible material (rather than the preferred stiff material) and still incorporate the advantages of the biasing system. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the appended claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and/or omissions may be made in the design, operating conditions and arrangement of the preferred and other exemplary embodiments without departing from the spirit of the present invention as expressed in the appended claims.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A fin for use by a swimmer comprising: a foot pocket adapted to receive a foot of the swimmer; a blade extending from the foot pocket; a biasing system configured to control the bending of the blade to within a predefined range of angles during use, the biasing system including at least one set of adjacent ribs extending along a longitudinal dimension of the blade, a portion of the at least one set of ribs being of a reciprocating configuration relative to a plane generally perpendicular to the blade.

2. The fin of Claim 1 wherein the at least one set of ribs comprises a first rib and a second rib adjacent to the first rib.

3. The fin of Claim 2 wherein the first rib is composed of an elastomer material.

4. The fin of Claim 3 wherein the second rib is composed of polypropylene.

5. The fin of Claim 2 wherein the biasing system is configured to provide a non-linear response to progressively-increasing bending of the blade.

6. The fin of Claim 1 wherein the biasing system is configured to provide a linear response to progressively-increasing bending of the blade.

7. The fin of Claim 1 wherein the blade comprises a first portion composed of a first material, and a second portion composed of a second material, wherein the configuration of the first and second portions and the properties of first and second materials are configured to provide a predefined performance.

8. The fin of Claim 1 wherein the blade is spaced apart from the foot pocket and connected to the foot pocket by the at least one set of ribs.

9. The fin of Claim 8 wherein the at least one set of ribs comprises a first rib, a second rib, and a third rib, the first, second, and third ribs adjacent each other.

10. The fin of Claim 9 wherein the second rib is located between the first rib and the third rib.

11. The fin of Claim 10 wherein the at least one set of ribs comprises a first set of ribs and a second set of ribs and wherein the first and second set of ribs each have first, second, and third ribs.

12. The fin of Claim 1 wherein the reciprocating configuration comprises at least one of a sinusoidal, zigzag, or arcuate shape.

13. A fin for use by a swimmer comprising: a foot pocket adapted to receive a foot of the swimmer; a blade extending from the foot pocket and configured to flex about an axis; a biasing system configured to control the angle of attack of the blade, the biasing system comprising one or more sets of ribs that extend generally perpendicular from the blade and include a reciprocating portion relative to a plane generally perpendicular to the blade;

wherein the biasing system is configured to provide a non-linear response to progressively-increasing bending of the blade.

14. The fin of Claim 13 wherein the reciprocating portion has a period of about one inch.

15. The fin of Claim 13 wherein the reciprocating portion has a spring constant.

16. The fin of Claim 13 wherein the non-linear response is increased resistance to further bending of the blade.

17. The fin of Claim 13 wherein the at least one set of ribs comprises a first rib and a second rib adjacent to the first rib.

18. The fin of Claim 13 wherein the at least one set of ribs comprise two sets of ribs, each including a pair of ribs.

19. The fin of Claim 13 wherein the blade comprises a first portion composed of a first material, and a second portion composed of a second material, wherein the configuration of the first and second portions and the properties of first and second materials are configured to provide a predefined performance.

20. The fin of Claim 19 wherein the blade is spaced apart from the foot pocket and connected to the foot pocket by the at least one set of ribs.

21. A fin for use by a swimmer, the fin comprising: a foot pocket adapted to receive a foot of the swimmer; a blade extending from the foot pocket; means for controlling flexing of the blade during use.

22. The fin of Claim 21 wherein the means for controlling flexing of the blade includes one or more sets of ribs extending along the length of the blade, each of the ribs having a reciprocating portion relative to a plane generally perpendicular to the blade.

23. The fin of Claim 22 wherein each set of ribs include a first rib and a second rib adjacent to the first rib.

24. The fin of Claim 23 wherein each set of ribs further comprises a third rib adjacent the second rib.

25. The fin of Claim 24 wherein the second rib is composed of an elastomer material and the first and third ribs are composed of a more rigid plastic material.

26. The fin of Claim 21 wherein the blade is spaced apart from the foot pocket and connected to the foot pocket by the one or more sets of ribs

27. The fin of Claim 21 wherein the means for controlling the flexing of the blade comprises providing the blade with a first portion composed of a first material, and a second portion composed of a second material different than the first material.

28. The fin of Claim 22 wherein the reciprocating portion provides a non-linear response to progressively-increasing bending of the blade.