Abstract:
Apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal ladder oriented vanes with pliable hinges and rotation limiting flexible webs that are attached between flexible support beams on swim fins. The fins can have a foot pocket for attaching to a swimmer or diver&#39;s foot. A pair of roughly parallel support beams can be secured to the foot and toe portion of the foot pocket and support a plurality of hydrofoil vanes therebetween in a resisted pivotal arrangement. Pivotal rotation of the hydrofoil vanes can be restricted by flexible membranes, between the hydrofoil vanes and the support beams, to provide an optimum angle of attack for the hydrofoil vanes during a swimming stroke. Methods for increasing lift and decreasing turbulence and drag on hydrofoils and swim fins part of the fins. The fins can have at least one pivoting vane region connected to the fin with a flexible hinge member made from reduced vane cross sectional area, and injection molding of the flexible material of the foot pocket. Methods are provided for limiting the rotation of at least one of the pivoting vanes using flexible web members between the vanes and the support beams. Methods for forming flexible hinges with pivotal resistance to encourage propulsion during small kick movements and at kick reversal points are included. Injection molding assembly methods with chemical bonds and mechanical bonds are provided. A novel method for manufacturing a swim fin having a complex articulated system with few injection molding steps is also included.

Description:
[0001]    This invention claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/280,375 filed Nov. 9, 2009. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates to swim fins, in particular to apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes with pliable hinge members and rotation limiting web members on swim fins. 
       BACKGROUND AND PRIOR ART 
       [0003]    Over the years swimmers have been attempting to improve moving through water. Originally boards were attached to one&#39;s hands or feet, and have been used for over a hundred years with literally hundreds of variations. However, their hydrodynamic efficiency has been relatively poor in view of the difficulty of dealing with two human legs and allowing the fins to pass one another without collision. Current swim fins have evolved to an elongated flexible propulsion surface where their proliferation is mainly attributed to the ease of manufacture. All of these swim fins have suffered from problems of a very low aspect ratio and poor angle of attack. Other types of efficient swim assistance aids exist but have complexity and manufacturing costs that keep these aids from being used. 
         [0004]    Earlier swim fin designs have problems with the aspect ratio and induced drag such as documented in U.S. Pat. No. 5,746,631 to McCarthy (1998) which is incorporated by reference. A substantial amount of induced drag is created by the transverse travel and vortex of fluid near the lateral edges of a lifting body (or foil) when that foil travels through a fluid. This induced drag reduces the effectiveness of the remainder of the foil. It has been established that a greater distance between the lateral edges improves the effective lift to drag ratio of the foil. The aspect ratio measures the separation of the lateral edges to the chord of the foil and is an indicator of the efficiency of the foil. 
         [0005]    Most modern fins have an aspect ratio between 0.3 and 0.5. It is well known that a higher aspect ratio produces higher hydrodynamic efficiency. Many examples of this can be found in nature. Fish tails have widely varying aspect ratios. The fast swimming amberjack has a tail fin with an aspect ratio of about 8 while the much slower swimming grouper has an aspect ratio of about 1.5. Whales and dolphins have aspect ratios in the 5 to 6 range. 
         [0006]    The angle of attack of a foil also affects the lift to drag characteristics of the foil. The angle of attack is the relative angle that exists between the actual alignment of the oncoming flow and the lengthwise alignment of the foil (or chord line). When this angle is small, the foil is at a low angle of attack. When this angle is high, the foil is at a high angle of attack. As the angle of attack increases, the flow collides with the foil&#39;s high pressure surface (also called the attacking surface) at a greater angle. This increases fluid pressure against this surface. While this occurs, the fluid curves around the opposite surface, and therefore must flow over an increased distance. As a result, the fluid flows at an increased rate over this opposite surface in order to keep pace with the fluid flowing across the attacking surface. This lowers the fluid pressure over this opposite surface while the fluid pressure along the attacking surface is comparatively higher. The pressure differential results in lift, or force causing it move in the direction of the low pressure. 
         [0007]    A foil has an optimum angle of attack where the lift to drag ratio is the highest. When the foil is at a lower angle of attack than the optimum the lift is reduced with relatively little change in drag. When the foil is a higher angle of attack the drag increases substantially while the lift increases at a lesser rate. The increased drag is due to flow separation and the creation of turbulence on the low pressure side of the foil which is known as stalling. A typical optimum angle of attack for a foil is between 4 to 10 degrees. The angle of attack for most swim fins is 90 degrees which is in the stalled range and results in the swimmer having undue ankle stress and leg fatigue. 
         [0008]    U.S. Pat. No. 2,729,832 to Schmitz described an improvement in efficiency by aligning the propulsion surface with the travel direction rather than the sole of the foot, but did not resolve low aspect ratio and extreme angle of attack having inefficiency created by vortices. 
         [0009]    U.S. Pat. No. 107,376 to Hunter described a method for propelling ships using an oscillating rudder with multiple rubber propulsion vanes for ships. 
         [0010]    U.S. Pat. No. 3,122,759 to Gongwer described improving performance with a very efficient high aspect ratio hydrofoil of about three feet laterally. The device resulted in propelling the swimmer in a straight line in open water but its size and complexity made it impractical for common sporting use. 
         [0011]    U.S. Pat. No. 4,767,368 to Ciccotelli had a simpler high aspect ratio swim fin which was impractical for maneuvering in restricted areas and can cause significant stress on the swimmer&#39;s ankles due to the long lever arm from the ankle to the lifting vane. Generally, these high aspect ratio swim fins had protrusions which could snag underwater obstacles. 
         [0012]    U.S. Pat. No. 4,781,637 to Caires described a high aspect ratio swim fin that required the swimmer to place both feet into the foot pocket requiring the swimmer to simultaneously kick both feet which was only useful in open water free of obstacles. 
         [0013]    U.S. Pat. No. 4,178,128 Gongwer described a multi-vane hydrofoil shape swim fin to improve efficiency but required springs, hinges, and thin rods resulting in being mechanically complex, difficult to manufacture, prone to snagging underwater flora, and subject to abrasive wear from suspended grit. 
         [0014]    U.S. Pat. No. 4,944,703 to Mosier showed a swim fin having multiple articulating hydrofoil vanes. However, the composite construction of internal rigid parts molded into less rigid parts resulted in expensive manufacturing costs. The 19 shown discrete parts in the figures indicate either manual assembly or a complex automated assembly line would be necessary resulting in expensive manufacturing costs. An implementation relied on pin and socket hinges and rubber inserts to control the articulation of the vanes which is subject to clogging and jamming by sand and other waterborne debris. The rigid side support beams would cause undue stress on the swimmer&#39;s ankles. The small gaps between the vanes and side beams and at the hinges are prone to trap stringy aquatic fauna and other stringy debris which may be encountered in the water creating a potential entrapment problem and a serious safety hazard. 
         [0015]    An alternate embodiment in FIG. 6 of the Mosier &#39;703 patent shows a resilient (rubber) hinge as the method of providing a rotational axis and self aligning of the vanes. However, this configuration would not work if physically constructed. Given the axial rotation desired of about 90 degrees as shown in FIG. 7 the axial length of the resilient hinge is too short to allow the rotation without overstressing the material and causing a shear failure. If the axial length were increased the narrow diameter would permit the vane to move out of alignment with the axis. The resilient hinge geometry has very high stress areas created at the interfaces between the softer and harder materials further increasing the likelihood of hinge failure. During operation, there would be no hard limit to the rotation of the vane. As more power is applied to the stroke, the vanes would rotate further reducing the effective lift of the vanes. Manufacturing would be difficult since five separately molded pieces would have to be hand placed in a second mold for the over molding process. Any manufacturing process which requires human interaction necessarily increases the cost. 
         [0016]    U.S. Pat. No. 5,536,190 to Althen shows a propulsion method with an appropriate angle of attack using vane rotation limiters, high aspect ratio and plural vanes, but is hindered by many hinges and small parts which cause expensive manufacturing costs with the product prone to breakage and wear from captured grit. This device is impractical in aquatic environments since its parts can become entangled with flora. 
         [0017]    U.S. Pat. No. 5,746,631 to McCarthy shows a fin with a longitudinal gap effectively creating a fin with propulsion surfaces which swing sideways during the power stroke. The apparatus reduces ankle stress but makes it difficult to attain higher rates of speed. 
         [0018]    U.S. Pat. No. 3,084,355 to Ciccotelli uses narrow vanes which rotate along a transverse axis and are mounted parallel to each other in a direction that is perpendicular to the direction of swimming with vanes that are not hydrodynamically streamlined to generate lift, and no system is used to control tip vortices. The vanes are arranged so they only provide resistance to the kick during a small portion of the kicking stroke. When they are providing resistance they are effectively joined resulting in a lower aspect ratio vane than they are individually. Only two of the four vanes are functioning at any one time which leads to a cumbersome arrangement reducing the ability of the swimmer to control his attitude in a non-mobile condition. The device is overly complex and contains many small parts which are prone to corrosion, grit accumulation and snags. 
         [0019]    U.S. Pat. No. 4,209,866 to Loeffler describes a thin pivotally mounted vane with reversibly effective streamline camber, but has a low aspect ratio which is known to have lower efficiency than higher aspect ratio vanes. The device was of complex construction with many wear points increasing the manufacturing and maintenance costs. 
         [0020]    U.S. Pat. No. 5,330,377 to Kernek shows a swim fin with multiple connected surfaces creating channelized flow between them. The large surface area of the propulsion surfaces created sufficient viscous drag to cancel any gained benefit and the complex molding indicate a high fabrication cost. 
         [0021]    U.S. Pat. No. 6,290,561 shows a swim fin with a propulsion surface supported by an elastic band and external beams. The elastic support restricts the maximum deflection of the propulsive surface but does nothing to control flow along the lateral surface edges. The edge vortices would create increased induced drag between the propulsion surface and support beams causing a reduction in efficiency compared to conventional swim fins. 
         [0022]    U.S. Pat. App. 2009/0088036 to Garofalo shows a swim fin with restrained trailing edge and loose sides. The lack of a gap between the foot pocket and the vane eliminates the small benefit of its improved angle of attack. It includes “deformable folding side pockets which will be able not only to ensure a good “channel effect” but also to operate as deformation limiters.” The long longitudinal length of the side pockets is sufficiently long that the vortex limiting capability is reduced. The volume of channelized flow is large enough that it creates a cushion effectively acting as a new hydraulic surface which forces the free flow to move laterally and create new edge vortices. 
         [0023]    U.S. Pat. No. 5,634,613 to McCarthy shows tip vortex canceling devices and U.S. Pat. No. 3,411,165 to Murdoch and U.S. Pat. No. 4,738,645 to Garofalo use pleats with composite construction to increase local deflection of the propulsion surface. However, these swim fins have low aspect ratios with the problems previously described. 
         [0024]    U.S. Pat. No. 4,981,454 to Klein and U.S. Pat. No. 7,462,085 to Moyal show swim fins with a hinge on the foot pocket allowing the propulsion surface to rotate upward against the swimmer&#39;s shin to facilitate simplified walking while wearing the device. However, these devices are limited in their efficiency since they use conventional flat low aspect ratio propulsion surfaces subject to all the problems previously described. 
         [0025]    Hinges using rubber like substances to provide torsional resistance are shown in U.S. Pat. No. 2,987,332 to Bonmartini and U.S. Pat. No. 4,097,958 to Van Dell that use composites of rubber and metal. The metal provides support for the hinge while the rubber provides the torsional resistance. However, the metal parts are not practical in a salt water environment, and their geometry requires a relatively large area for the installation of the hinge which would reduce the area allotted for the attached vanes. 
         [0026]    The ScubaPro Nova SeaWing swim fin uses a flexible support beam combined with a very flexible root section of the support beam which allows the entire support beam to rotate in excess of 30 degrees. Additional flexing of the support beam allows a total flex in excess of 40 degrees which is what is considered the optimum angle of attack. The SeaWing, while innovative, still suffers from adverse propulsion surface curvature, a low aspect ratio, the lack of a hydrodynamic lifting surface, and insufficient control of tip vortices. 
         [0027]    Thus, the need exists for solutions to the above problems with the prior art. 
       SUMMARY OF THE INVENTION 
       [0028]    A primary objective of the present invention is to provide apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes with pliable hinges and rotation limiters on swim fins used for swimmers or divers. 
         [0029]    A secondary objective of the present invention is to provide apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes having few parts that are easy and inexpensive to manufacture. 
         [0030]    A third objective of the present invention is to provide apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes which eliminates any snagging and abrasion in aquatic environments that were associated with closely associated moving parts used by fins in prior art aquatic environment. 
         [0031]    A fourth objective of the present invention is to provide apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes that are easy to operate by swimmers in both salt water and fresh water applications, and has mobility on land. 
         [0032]    A fifth objective of the present invention is to provide apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes that reduces stress on ankles and increases maneuverability of the swimmer, and increases efficiency of the effort of the swimmer, and increases foot angle efficiency. 
         [0033]    A sixth objective of the present invention is to provide apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes that reduces tip vortex losses and results in a narrowly directed thrust. 
         [0034]    A seventh objective of the present invention is to provide apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes that causes low environmental disturbances. 
         [0035]    An eighth objective of the present invention is to provide apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes that uses reversible flexible vanes. 
         [0036]    A ninth objective of the present invention is to provide apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes that can be manufactured by a one piece overmolding process. 
         [0037]    A tenth objective of the present invention is to provide apparatus, devices and methods of using and operating multiple high aspect ratio hydrodynamic horizontal vanes that can be injection molded in two steps. 
         [0038]    The invention improves the efficiency of a swimmer or diver in self propulsion through water by increasing the aspect ratio of the propulsion surfaces of swim fins while using a more hydrodynamic shape and maintaining a narrow mechanism width to allow normal swimming action and keeping the manufacturing cost and maintenance requirements low. The invention groups multiple high aspect ratio hydrodynamic vanes into a single fin, arranged in a ladder form between two side support beams. These vanes would be allowed to rotate on a lateral axis during the kicking stroke but the rotation would be resisted by a pliable rubber like hinge. The maximum rotation would be limited by a flexible rubber like web connected between the vanes&#39; lateral edges and the support beams. The limiting webs would also serve as winglets to cancel a significant amount of vortex creation at the vane ends. Ankle stress would be reduced through the use of flexible support beams which would flex as greater pressure is applied thus reducing the lever arm to the ankles without substantially reducing the effective thrust. 
         [0039]    The novel invention provides a controllable high efficiency swim fin which directs its thrust directly opposite the direction of travel without causing undue ankle stress or disturbance to the surrounding water. The pliable hinge eliminates the need for a conventional pin and hole type hinge which involves additional assembly steps during manufacture. The pliable hinge makes it possible to manufacture the entire mechanism through injection molding in two steps, a process known as overmolding. This results in a substantial reduction in production cost. The lack of closely associated moving parts eliminates snagging and abrasion associated with them in the aquatic environment. Unlike the prior art, this invention does have closely associated moving parts and instead uses connections of flexible materials so there is no possibility of things getting caught between connected parts. 
         [0040]    An embodiment of a novel fin apparatus for increasing the efficiency of a swimmer or diver during self propulsion through water, can include a plurality of high aspect ratio dynamic vanes arranged in a ladder configuration, each vane having a left end and a right end, two side beams, each arranged to both side ends of the ladder configuration of vanes, a plurality of pliable hinges that attach the ends of the vanes to the side beams, the hinges allowing the vanes to rotate on a lateral axis during a kick stroke and be resisted by the pliable hinges, and a plurality of flexible webs that attach the ends of the vanes to the side beams, the flexible webs allowing for limiting a maximum rotation of the vanes, and serve as winglets to cancel a significant amount of vortex creation at the vane ends, wherein ankle stress is reduced through using the support beams which would flex as greater pressure is applied thus reducing the lever arm to the ankles without substantially reducing the effective thrust, resulting in a high aspect ratio, increasing the efficiency of the swimmer. 
         [0041]    The pliable hinges can be formed from the group selected from one of: rubber, silicone rubber, polyvinylchloride, Polyurethane, Polybutadiene, Chlorosulphonated Polyethylene, and neoprene. 
         [0042]    The flexible webs can be formed from the group selected from one of: rubber, silicone rubber, polyvinylchloride, Polyurethane, Polybutadiene, Chlorosulphonated polyethylene, and neoprene, and the like. 
         [0043]    The flexible side beams can be formed from the group selected from one of: Polyvinyl chloride, polypropylene, Acrylonitrile butadiene styrene, nylon, polyethylene, rubber and neoprene, and the like. 
         [0044]    Each of the vanes can be a laterally oriented vane, and each of the vanes can be formed from the group selected from one of: Polyvinyl chloride, polypropylene, Acrylonitrile butadiene styrene, nylon, polyethylene, rubber and neoprene, and the like. 
         [0045]    The pliable hinges can include a connection shaft attached at one end to one of the side beams and a second opposite end attached to one of the ends of the vane, and a pliable material overmolded over the connection shaft. Each of the pliable hinges can include a generally cylindrical or elliptical configuration with concave curved sidewalls. Each of the pliable hinges can have a generally cylindrical or elliptical configuration with concave curved sidewalls, and each of the flexible webs has a generally trapezoidal configuration. The pliable hinges can also formed without a connection shaft. 
         [0046]    The side beams can be flexible side beams as well as be rigid side beams, where flexible side beams can reduce stress and strain on the users&#39; ankles. 
         [0047]    The novel fin can include a foot pocket attached to one end of the side beams, and a pivoting portion for allowing the side beams with the vanes to flip up relative to the foot pocket, in order to allow the user to walk with the fins. 
         [0048]    A novel method of improving the efficiency of a swimmer or diver in self propulsion through water, can include the step of increasing aspect ratio of propulsion surfaces of a swim fin while using a more hydrodynamic shape and maintaining a narrow mechanism width to allow normal swimming action and keeping the manufacturing cost and maintenance requirements low. 
         [0049]    The step of increasing the aspect ratio can include the steps of grouping a plurality of high aspect ratio hydrodynamic vanes into a single fin, arranging the plurality of the vanes horizontally in a ladder configuration between side support beams, rotating the vanes along a lateral axis wherein rotation is limited by pliable hinges attached between each of the vanes and the side beams, and limiting maximum rotation of the vanes along the lateral axis by flexible webs that are attached between each of the vanes and the side beams. The limiting step can include the step of using the flexible webs as winglets to cancel significant amounts of vortex creation at the vane ends. 
         [0050]    The method can further include the steps of providing flexible side support beams as the side support beams, and reducing ankle stress through the use of flexible beams which flex as greater pressure is applied and reduce the lever arm to ankles without substantially reducing the effective thrust. 
         [0051]    The method can include the step of directing thrust with the fin opposite direction of travel without causing undue ankle stress or disturbance to surrounding water. 
         [0052]    The method can further include the steps of providing a foot pocket attached to one end of the side beams, providing a pivoting member between the foot pocket and the one end of the side beams, and flipping up the side beams with the vanes in order to allow the user to walk while wearing the fins. 
         [0053]    Further objects and advantages of this invention will be apparent from the following detailed description of the presently preferred embodiments which are illustrated schematically in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0054]      FIG. 1  is a perspective view of a first embodiment of the novel fin apparatus invention. 
           [0055]      FIG. 2A  is an isometric view of one vane-beam connection with the outer pliable hinge and web removed for visibility. 
           [0056]      FIG. 2B  is an isometric overhead view of the one vane-beam connection of  FIG. 2A . 
           [0057]      FIG. 2C  is a plan view of the one vane-beam connection of  FIG. 2A . 
           [0058]      FIG. 2D  is a rear view of the one vane-beam connection of  FIG. 2A . 
           [0059]      FIG. 2E  is an isometric view of the one vane-beam connection of  FIG. 2A  with an alternate web slot configuration. 
           [0060]      FIG. 3  is an isometric view of the novel hinge and web interconnection between the support beam and vane in a neutral position. 
           [0061]      FIGS. 4A ,  4 B and  4 C are plan profile and side views of the novel hinge and web interconnection and the support beam and vane of  FIG. 3  in its neutral position. 
           [0062]      FIGS. 5A-5B  are cross-sectional views of  FIG. 4A  showing the overmolding of the pliable material. 
           [0063]      FIG. 5C  is a cross-sectional view of  FIG. 4A  taken at  FIG. 5B  showing an alternate configuration for the overmolding of the web pliable material. 
           [0064]      FIGS. 6A ,  6 B,  6 C and  6 D are isometric, plan, profile and side views of the novel support beam and vane interconnection of the preceding figures in a rotated position. 
           [0065]      FIGS. 7A ,  7 B and  7 C show an operational sequence of the first embodiment of the preceding figures using symmetrical rigid vanes. 
           [0066]      FIGS. 8A ,  8 B, and  8 C show the flow around individual vanes from  FIGS. 7A-7C . 
           [0067]      FIGS. 9A ,  9 B and  9 C show the flow around individual vanes from  FIG. 10A-10C . 
           [0068]      FIGS. 10A ,  10 B and  10 C show the operational sequence of another embodiment of the invention using symmetrical flexible vanes. 
           [0069]      FIG. 11  is an isometric view of an alternate embodiment of the swim fin with pivotally attached support beams in the operating latched position. 
           [0070]      FIG. 12  is an isometric view of an alternate embodiment of the swim fin with pivotally attached support beams in the un-latched and rotated walking position. 
           [0071]      FIG. 13  is an isometric view of an alternate embodiment of the swim fin with flexible vanes. 
           [0072]      FIG. 14  is an isometric view of an alternate embodiment of the swim fin with flexible vanes and pivotally attached support beams in the operating latched position. 
           [0073]      FIG. 15  is an isometric view of a latching system for the pivotally attached support beam embodiment with the cam lever in the latched position. 
           [0074]      FIG. 16  is an exploded isometric view of a latching system for the pivotally attached support beam embodiment with the cam lever in the un-latched position. 
           [0075]      FIG. 17  is a plan view of a latching system for the pivotally attached support beam embodiment with the cam lever in the latched position. 
           [0076]      FIG. 18A  is a plan view of a latching system for the pivotally attached support beam embodiment with the cam lever in the un-latched position. 
           [0077]      FIG. 18B  is a detail of  FIG. 18A  showing the gap created when the cam lever is operated. 
           [0078]      FIG. 19A  is an end view of the latching system for the pivotally attached support beam embodiment shown in  FIG. 17  with the cam lever in the latched position. 
           [0079]      FIG. 19B  is a section view as shown in  FIG. 17  of a latching system for the pivotally attached support beam embodiment with the cam lever in the latched position. 
           [0080]      FIG. 20A  is an end view of the latching system for the pivotally attached support beam embodiment shown in  FIGS. 18A-18B  with the cam lever in the un-latched position. 
           [0081]      FIG. 20B  is a cross-section view as shown in  FIGS. 18A-18B  of a latching system for the pivotally attached support beam embodiment with the cam lever in the un-latched position. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0082]    Before explaining the disclosed embodiments of the present invention in detail it is to be understood that the invention is not limited in its applications to the details of the particular arrangements shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. 
         [0083]    This invention claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/280,375 filed Nov. 9, 2009, which is incorporated by reference. 
         [0084]    A list of the components will now be described.
     50  symmetric vane fixed support beam swim fin     52  foot pocket     53  foot strap     54  toe portion     56  foot strap peg     58  left side     60  right side     62  support beam L     64  support beam R     66  end portion L     68  end portion R     70  flow guide L     72  flow guide R     74  vane  1       76  vane  2       78  vane  3       80  vane  4       82  vane  5       84  hinge  1  L     86  hinge  1  R     88  hinge  2  L     90  hinge  2  R     92  hinge  3  L     94  hinge  3  R     96  hinge  4  L     98  hinge  4  R     100  hinge  5  L     102  hinge  5  R     104  web  1  L     106  web  1  R     108  web  2  L     110  web  2  R     112  web  3  L     114  web  3  R     116  web  4  L     118  web  4  R     120  web  5  L     122  web  5  R     124  leading edge     126  trailing edge     128  connection shaft     130  beam hinge base     132  vane hinge base     134  vane hinge hole     136  web connection slot     138  web connection rail     140  beam hub     142  beam hub wing     144  beam hub wing hole     146  hinge axis point     148  oblong hole     150  front of web     152  rear of web     154  connection bump     156  flow     158  user&#39;s leg     160  heel     162  foot     164  maximum flexure     166  direction of foot motion     168  support beam deflection     170  lift     171  flexible vane fixed support beam swim fin     172  flexible connector     174  rigid leading edge     176  rigid trailing edge     178  rail system     180  flexible vane     182  latch ledge     184  cam lever     186  lock clip     188  replacement foot strap peg     190  cam lever rotation     192  beam rotation     194  latch slot     196  foot strap peg receptacle     198  keyway     200  tab     202  cam lever post     204  shoulder     206  cam pivot hole     207  broad upper surface     208  gap     209  receptacle back opening     210  symmetric vane pivotally attached support beam swim fin     212  left latch assembly     214  right latch assembly     216  flexible vane pivotally attached support beam swim fin   
 
       First Embodiment 
       [0173]      FIG. 1  is a perspective view of a first embodiment of the novel fin apparatus invention showing a fixed rail swim fin  50 . A foot pocket  52  can include a common usage foot strap  53 . Foot pocket  52  can include a toe portion  54  and one of a pair of outwardly extending lateral foot strap peg  56 . Foot pocket  52  further defines a left side  58  and right side  60 . Fixedly attached to the left side  58  and right side  60  of the foot pocket  52  can be a pair of elongated support beams  62  and  64  which extend toward the toe portion  54  of the foot pocket  52  and terminate in rounded end portions  66  and  68  respectively. A pair of flow guides  70  and  72  can extend laterally between the foot pocket  52  and support beams  62  and  64  respectively. 
         [0174]    The support beams  62  and  64  are generally parallel and define therebetween a uniform space. A plurality of hydrofoil vanes  74 ,  76 ,  78 ,  80  and  82  can be pivotally secured between support beams  62  and  64  by a plurality of pliable hinges  84 ,  86 ,  88 ,  90 ,  92 ,  94 ,  96 ,  98 ,  100  and  102 . The first embodiment can have five vanes  74 - 82  that are each pivotally supported by pairs of pliable hinges  84 - 102 . The hydrofoil vane  74  nearest the toe portion  54  is secured by a hinge  84  to support beam  62  and by a hinge  86  to support beam  64 . Similarly, vane  76  is secured by hinges  88  and  90  to support beams  62  and  64  respectively and vanes  78 ,  80 , and  82  are secured to support beam  62  by hinges  92 ,  96 , and  100  respectively and to support beam  64  by hinges  94 ,  98 , and  102  respectively. Each hydrofoil vane  74  through  82  can also be flexibly attached to support beams  62  and  64  by a plurality of pliable webs  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118 ,  120  and  122  which are described in greater detail below. The hydrofoil vane  74  nearest the toe portion  54  is secured by a web  104  to support beam  62  and by a web  106  to support beam  64 . Similarly, vane  76  is secured by webs  108  and  110  to support beams  62  and  64  respectively and vanes  78 ,  80 , and  82  are secured to support beam  62  by webs  112 ,  116 , and  120  respectively and to support beam  64  by webs  114 ,  118 , and  122  respectively. In accordance with an important aspect of the present invention and as is described below in greater detail, hydrofoil vanes  74  through  82  define high aspect ratio hydrofoils in which their individual transverse or lateral dimensions are substantially greater than their widths in the flow direction. 
         [0175]    The cross section of the five shown hydrofoil vanes  74  through  82  generally conform to airfoil shapes NACA (National Advisory Committee of Aeronautics) 0009 to NACA 0012, alternative airfoil shapes having high aspect ratios could also be used. Support beams  62  and  64  defines a plurality of molding connection points which are hidden from view under the hinges  84 - 102  and webs  104 - 122  in  FIG. 1  and are shown and described in subsequent figures. The lateral ends of the vanes also contain a plurality of molding connection points which are hidden from view under hinges  84 - 102  and webs  104 - 122  in  FIG. 1 , and are also shown and described in subsequent figures. 
         [0176]    A preferred embodiment of the novel swim fin  50  can be fabricated from a resilient semi-rigid molded plastic or rubber material and a more pliable plastic or rubber for the hinges  84 - 102  and webs  104 - 122 . Alternatively, other materials resulting in similar results can be used. 
         [0177]    The foot pocket  52  can receive the swimmer&#39;s foot such that the swimmer&#39;s foot  162  extends into interior cavity with the swimmer&#39;s toes situated within toe portion  54  after which it is secured by a strap system  53  to foot strap peg  56  that is known in the field. In accordance with conventional swim fin fabrication techniques, the strap system  53  can include an adjustment to accommodate foot size variations. Furthermore, the axes of support beams  62  and  64  in their elongated direction can be angularly displaced with respect to foot pocket  52  in a downward direction. This angular displacement can be seen in  FIGS. 6A-10C  and is to compensate for the typical angular relationship between a swimmer&#39;s leg and foot due to the restriction of ankle movement. As a result, support beams  62  and  64  are generally aligned with the swimmer&#39;s leg for more efficient stroking action. 
         [0178]    The novel hydrofoil vanes  74 - 82  can be secured with hinges  84  through  102  in a limited travel pivotal attachment in which hydrofoil vanes  74 - 82  are pivotally movable about their respective hinges within a limited angular motion which is restricted by their respective webs  104 - 122 . The vanes  74 - 82  are torsionally biased to assume the position shown in  FIG. 1  in which the vanes  74 - 82  are substantially aligned with the major axis of support beams  62  and  64 . In the absence of a stroking motion, this torsionally biasing force operative upon vanes  74 - 82  urges the vanes to the aligned position shown in  FIG. 1 . 
         [0179]    The pivotal attachments of vanes  74 - 82  to support beams  62  and  64  can be positioned forward of the center lines of the hydrofoil vanes  74 - 82  at approximately 15% of the chord distance from the leading edge  124  toward the trailing edge  126  of each vane. Accordingly, substantial motion of the present invention swim fin in either direction causes vanes  74 - 82  to be pivoted to a desired angular position with respect to support beams  62  and  64 . While the pivotal action of vanes  74  through  82  described in detail, the hydrofoil vanes  74 - 82  align with the appropriate angle of attack in response to the hydrodynamic pressure created during the movement of the fin through the water. The pivotal motion of the hydrofoil vanes  74 - 82  to the desired angle of attack simultaneously reduces the resistance of the water against fin motion thereby making the stroke easier for the swimmer and concurrently develops a localized area of higher flow velocity and reduced pressure along the front sides of each of the hydrofoil vanes. The reduced pressure on the front sides of the hydrofoil vanes  74 - 82  then produces a forward thrust component for increased efficiency of the swim fin. 
         [0180]    During each stroke of swim fin the motion of the swim fin through the water aligns vanes  74 - 82  at the appropriate angle and the stroke action causes a flow of water across the angled vanes  74 - 82  producing a forward thrust carrying the swimmer forward. In the event of a small motion of the swim fin in either direction the torsional resistance of the pliable hinges  84 - 102  allows the vanes  74 - 82  to rotate partially toward the desired angular position and, in doing so, allows flow between the vanes  74 - 82  creating a smaller amount of forward thrust through the hydraulic mechanics previously described. 
         [0181]      FIGS. 2A ,  2 B,  2 C,  2 D and  2 E show a representative portion of support beam  62  and vane  82  showing the attachment surfaces for the pliable hinges and pliable webs that are not shown. These figures show the connection at hinge  100  and web  120  as shown in  FIG. 1 . The vane  80  nearer the foot pocket in  FIG. 1  is not shown for clarity. All of the other attachment hinge and web locations are similar. 
         [0182]    A hinge base  130  can be centered at the location on the support beam  62  which would be laterally aligned with the hinge axis point  146  (shown in  FIG. 2B ) of the vane  82 . The hinge base  130  can include a beam hub  140  with two hub wings  142  with holes  144  through each as described below. The rail hub  140  can have a tapered cylindrical shape with a height equivalent to approximately ¼ of the gap between the support beam  62  and the vane  82  with a diameter such as to provide sufficient coverage by the hinge pliable material (not shown) to prevent tearing under stress. The covering thickness can depend on the specific material used and expected rotation of the hinge. 
         [0183]    Connected to the rail hub  140  and in line with the longitudinal axis of the support beam  62  can be a pair of hub wings  142  on opposing sides of the rail hub  140 . Their thickness is about half of their height and their height can be equivalent to that of the rail hub  140 . The hub wings  142  can be rounded on their free corner with a radius equivalent to the height of the rail hub  140 . Each hub wing  142  can be pierced perpendicular to its major plane by a hole  144  with a diameter equivalent to half of the height of the huh wing  140 . The holes  144  can provide for a mechanical connection of the pliable material of the hinge. The hinge base  130  can be connected to the vane hinge base  132  by an elongated connection shaft  128  extending laterally from the top of the rail hub  140 . On both sides of the vane hinge base  132  can be vane hinge holes  134 . 
         [0184]    The diameter of the connection shaft  128  can be the minimum sufficient to allow plastic material to flow through the mold tool. The connection shaft  128  serves the purpose of holding the parts together during the molding process and it should be sufficiently small in diameter to allow it to twist through a rotation of about 90 degrees repeatedly without breaking. Alternatively, the shaft  128  can be allowed to break after a number of articulations but the shaft  128  is at the center of rotation of the hinge so it will have no effect on the effectiveness of the pliable hinge. 
         [0185]    All the edges can be rounded to reduce stress concentration in the pliable hinge material. While this description covers a configuration of the hinge bases,  130 ,  132  other geometries can be used to accomplish a similar function and this invention is not dependant on this particular configuration. 
         [0186]    This first embodiment illustrates the substructure necessary in the event a simple fusion bond between the firm and pliable materials is not sufficiently strong by itself to prevent separation of the materials when under stress. An alternate configuration is described in  FIG. 5C  where the fusion bond alone is sufficiently resilient. A key element in reduction of the manufacturing cost is minimizing the handling of individual pieces of the unfinished product. To this end all of the firm parts are intended to be injection molded at one time and are connected to each other. The connection is clearly shown as the connection shaft  128 . 
         [0187]    Laterally piercing the support beam  62  between the hinge base  130  and end portion  66  are web connection slots  136  with a thickness approximately equivalent to the thickness of the web  120 . Opposite the slots  136  can be a web connection rail  138  on the vane  82 . The slots  136  a length of about 1.5 times the spacing between the slots  136  to assure sufficient material remains in the support beam  62  to minimize structural degradation of the support beam  62 . 
         [0188]    A preferred version shown in  FIG. 2E  would be enhanced by having one slot  136  piercing the end portion  66  to provide better support for the pliable web material. 
         [0189]      FIG. 2B  shows  FIG. 2A  from another overhead vantage point which makes the edge of the vane  82  more visible. Centered on the hinge axis point  146  at approximately 15% of the chord length of the vane  82  from the leading edge  124  is the vane hinge base  132  which is described below in greater detail. The vane hinge base  132  is a part of the vane  82  on the lateral edge which is a protrusion with a height of approximately ¼ of the lateral width of the hinge and with a thickness which is similar to the thickness of the vane  82  at the hinge axis point  146  less the required thickness of the pliable hinge material overlay as described and shown in  FIG. 2A . The longitudinal length of the vane hinge base  132  is approximately three to four times its height and it is rounded on the free corners. A plurality of holes  134  can pierce the vane hinge base  32  to create additional mechanical connection between the vane  82  and pliable hinge material. 
         [0190]    A web connection rail  138  runs along the centerline of the lateral edge of the vane  82  the height of which is approximately two times the thickness of the web  120  and is perforated with oblong holes  148  half of the connection rail height. The connection rail  138  tapers to no height near the trailing edge  126 . Since the connection rail  138  provides additional stiffness to the web  120  the connection rail  138  is on a base which is offset from the support beam  62  an additional distance approximately equivalent to the height of the rail  138 . 
         [0191]    The first embodiment of the swim fin  50  as shown in  FIG. 1  improves human in water self propulsion by utilizing the benefits of high aspect ratio vanes while maintaining a relatively narrow overall width. Initially the swim fin operates similar to many swim fins already available in the marketplace. It has a foot pocket  52  for attachment to the user&#39;s foot with a foot strap  53  to keep it attached during use. This feature is common to most swim fins and is not considered unique in this invention but a base on which the other features are built. Beams  62 ,  64  attached to the left side  58  and right side  60  of the foot pocket  52  serve as support frame for the hydrodynamic vanes  74 - 82 . In this embodiment the beams  62 ,  64  are essentially parallel to allow all the vanes  74 - 82  to be equal in width but that feature is not necessary for the overall function of the invention. Some variation in the width between the beams  62 ,  64  for aesthetic purposes would not substantially degrade the performance of the invention. 
         [0192]    Because the user&#39;s foot  162  is not normally in line with the direction of travel of the user, the support beams  62 ,  64  deflect downward about 30 degrees such that they are substantially aligned with the axis of the user&#39;s leg  158  ( FIG. 7B  or  10 B) when in a neutral position such as when coasting as shown in  FIGS. 7B and 10B . 
         [0193]    It is well known that an improperly sized swim fin will not perform well regardless of how efficient it is. Testing has revealed a total projected propulsive surface area of approximately 90 to approximately 100 square inches provides a comfortable balance between propulsive effort and actual forward speed. It is also known the width of a swim fin assembly should not exceed approximately 9.5 inches for widths in excess of this often collide during use. Consequently, the composite length of the vane array is the desired propulsive area divided by the available width between the support beams  62 ,  64 . 
         [0194]    The number of vanes  74 - 82  can be determined by the strength of the materials selected for their construction and the vane thickness to chord ratio. Stronger materials will allow thinner vanes. Computational fluid dynamics computer modeling of various vane shapes has revealed lift to drag ratios improve as the thickness to chord ratio decreases. 
         [0195]    Given the limitations of unreinforced plastic like materials it was found that NACA (National Advisory Committee of Aeronautics) 0009 to NACA 0012 airfoils work well. The NACA airfoil 4 digit designation describes the shape of an airfoil based on its camber as a percentage of the chord (first 2 digits) and the maximum thickness (occurring at 30% of the chord) as a percentage of the chord length (last 2 digits). Thus a NACA 0009 airfoil is symmetrical (00) with a maximum thickness of 9% of the chord length (09). NACA is not the only designation for airfoil shapes and not all airfoil shapes have been tested so there can be other airfoil shapes which could also be applied to this invention. Division of the actual vane thickness required given the materials selected by the vane thickness to chord ratio of the airfoil shape will then yield the physical chord of the vane. Dividing the length of the propulsive area by the airfoil chord length will reveal the number of vanes which can be installed. 
         [0196]    A major problem with previous swim fin designs is the angle of attack of the propulsive surface which is resolved with this invention by separating the propulsive surface or vanes  74 - 82  from the foot pocket  52  and allowing them to rotate toward the direction of foot motion  166  ( FIGS. 7A ,  7 C,  10 A,  10 C). This is accomplished by pivotally connecting the vanes  74 - 82  to the support beams  62 ,  64 . The problem of limiting the vane rotation to the optimum angle of attack is resolved by connecting the rearward portion of the lateral edges of the vanes  74 - 82  to the support beams  62 ,  64  with the pliable limiting webs  104 - 122  shown in  FIG. 1 . 
         [0197]    In the past post and hole type hinges were used to allow rotation of the vanes but these were subject to problems of grit inclusion and snagging of waterborne debris. Additionally, a free swinging hinge would necessarily allow portions of the swimming stroke where no propulsive force would be generated. That portion is mostly during the transition in direction of the stroke where the vane pivots between the optimal angle of attack in one direction to the optimum angle of attack in the opposite direction. Videos of testing has revealed this transition portion to include as much as 30% of the stroke. All three of these issues were resolved through the use of the novel pliable hinges  84 - 102  shown in  FIG. 1 . 
         [0198]    The novel pliable hinges  84 - 102  have no sliding interface to get clogged with grit, no gaps to allow snagging of waterborne debris, and the vanes  74 - 82  are always torsionally biased to the neutral position providing some lift component even during the transitional stages of the swimming stroke. The torsional bias to the neutral position provides another benefit of encouraging some propulsive lift with small foot movements. Small foot movements are often used by swimmers while remaining stationary to maintain one&#39;s attitude in the water or for maneuvering. 
         [0199]      FIGS. 2A-6D  show the construction of the hinge and web. Previously, all multivane swim fin devices have relied on many discrete parts and often small parts. The interfaces between these parts have often involved relative motion in contact resulting in wearing surfaces and subsequent part failure. Few of the previous multivane swim fin devices have made it to commercial production due to the high production cost involved with assembly of multiple parts. The subject invention uses a common two step overmolding process to fabricate the entire swim fin as a single part thus eliminating much of the previously required fabrication costs. 
         [0200]    One of the key elements to inexpensive overmolding is maintaining the alignment of the parts as they are transferred from one mold tool to the next. This is accomplished with the connection shaft  128  between the support beam  62  and vane  82  as shown in  FIGS. 2A-2D . This shaft  128  can be sized as small as possible to allow support of the parts during handling, allow repeated pivot about its axis up to 90 degrees, and allow molding material to flow through without creating a cold joint. Due to the torsional resistance created by the pliable hinge it is necessary to assure a good bond between the hinge  100  and the support beam  62  and vane  82 . To this end the beam hinge base  130  is formed on the support beam  62  and the vane hinge base  132  is formed on the lateral edge of the vane  82 . These bases  130 ,  132  serve to increase the surface area for bonding contact and holes  134 ,  144  through the bases provide additional mechanical bonding. The bases  130 ,  132  shown here are only one example of a method to improve bonding between two materials, there are others methods which will also work and this invention is not limited to this single example. The web  120  is subject to substantial tension and flexural stresses where they bond to the support beam  62  and vane  82 . To accommodate these stresses web connection slots  136  are incorporated in the support beam  62  and a web connection rail  138  is incorporated into the vane(s)  82 . These provide increased surface area for bonding contact. Holes  148  through the web connection rail  138  provide additional mechanical bonding to the web. The spacing of the web connection slots  136  is such as to cause little decrease in the flexural properties in the support beam  62 . 
         [0201]      FIG. 3  shows the neutral position of the pliable hinge  100  and pliable web  120  installed over the features in  FIG. 2  attached to the support beam  62  and vane  82 . The nominal thickness of the material for the web  120  can vary depending on the particular substance from which it is fabricated. If it were made out of neoprene the thickness of the web would be approximately 0.07 inches. Other materials or even fabric could be used for this feature and would have a substantial effect on the necessary thickness and attachment method. 
         [0202]    The web(s)  120  can have a generally trapezoidal sheet configuration in its rotated position with its lateral edges attached to the vane(s)  82  and support beam  62 . The web(s) in its neutral position can have a generally gently folded sheet form with a small drape at its front of web  150  and a large drape at its rear of web  152 . 
         [0203]    The hinge(s)  100  can have a generally cylindrical or elliptical configuration with concave curved sidewalls. 
         [0204]      FIG. 4  shows the plan profile and rear views of the hinge  100  and web  120  in a neutral position. The amount of drape of the web  120  can be determined by the amount of pivot to be allowed between the longitudinal axis of the support beam and the longitudinal axis of the vane and its derivation will be described later. 
         [0205]      FIG. 5A  is a cross-sectional view through the centerline of the hinge  100  and showing how the pliable hinge material  100  is overmolded on the beam hinge base  130  and vane hinge base  132  between the beam  62  and the vane  82 . The large amount of hinge material  100  over the connection shaft  128  is what allows the vane  82  to pivot while remaining torsionally biased to the neutral position. 
         [0206]      FIG. 5B  shows a cross-sectional view through the web  120  according to the first embodiment. It can be seen that the pliable web material  120  extends through the support beam  62  in the web connection slot  136  and the web  120  is thickened where it covers the web connection rail  138  on the vane  82 .  FIG. 5C  illustrates an additional embodiment of the web connection using only a bump  154  on the vane  82  and support beam  62 . This approach is used in the situation where there is sufficient fusion bonding between the pliable and rigid materials that no additional mechanical bonding is necessary. While the embodiments shown herein use separate hinge  100  and web  120  structures this does not preclude the use of a system in which both are merged together as a single unit. 
         [0207]      FIGS. 6A ,  6 B,  6 C, and  6 D show the pliable hinge  100  and pliable web  120  with the vane  82  pivoted to an optimum angle of attack. It can be seen the web  120  is stretched out essentially flat with allowance for the bends along the fused edges. When the vane  82  is pivoting from its neutral position and has not yet reached the optimum angle of attack the pivoting is resisted only by the pliable hinge  100  but once the optimum angle of attack is reached the web  120  starts to resist the pivoting action and effectively stops it. Testing has revealed the total lifting force on an individual vane is between 4 and 5 pounds. 
         [0208]    At the point of optimum angle of attack about half of the lifting force is carried by the hinge  100  and the remainder by the web  120 . Since there are two hinges  84 ,  86  and webs  120 ,  122  per vane  82  the resultant load to be resisted by the web  120  is about 1 pound along its entire connection bond. As it is not possible for a swimmer to kick more than twice as hard as was determined by testing it is clear there are many pliable materials which can handle the stresses applied in this application without undue distortion. When in the flexed position the web portion  120  serves to reduce the tip vortices in addition to holding the vane  82  at the correct angle of attack. The reduction of tip vortices effectively increases the aspect ratio over the physical aspect ratio. A side benefit of this is the channelizing of the thrust which reduces the turbulence behind the swimmer thus reducing the stirring up of silt when near a silty surface. Any underwater photographer can explain the importance of keeping the water as free of silt as possible. Stirred up silt reduces visibility in the water, sometimes to the point of totally obscuring one&#39;s path. Stirred up silt has been the root cause of the death of many scuba divers. 
         [0209]      FIGS. 7A ,  7 B and  7 C show the combined function of the support beams  62 ,  64  and vanes during a typical swimming stroke for the first embodiment of the novel fin  50  used with the leg  158 , heel, and foot  162  and the direction of foot motion  166 . For the purposes of this discussion up will be taken as toward the top of the page or toward the heel  160  of the swimmer since most swimming occurs with the swimmer&#39;s face down.  FIG. 7A  shows a typical up stroke using the invention,  FIG. 7B  shows a neutral or coasting position where no upward or downward force is being applied yet the swimmer is still moving forward, and  FIG. 7C  shows a typical downward stroke. 
         [0210]    In the neutral position shown in  FIG. 7B  all of the vanes are aligned with the support beam thus minimizing the overall drag created by the swim fin  50 . There is virtually no interaction between the flow  156  and the vanes  74 - 82  as shown in  FIG. 8B . During the upstroke in  FIG. 7A  the foot travels in an upward and forward direction  166  relative to the water. The vanes deflect to an optimum angle of attack with the flow 
         [0211]    It has been found that this optimum angle of attack to the flow for a NACA 0009 airfoil is approximately 4 degrees. To account for the dynamics of swimming it was necessary to determine the optimum angle of attack relative to the longitudinal axis of the support beams by physical testing which resulted in an angle of about 40 degrees on a swim fin with a fixed downward support beam deflection  168  of 30 degrees. 
         [0212]    Support beam flexibility is an important consideration in this invention. If the beam supports  62 ,  64  are too stiff there is undue ankle stress. If the beam supports  62 ,  64  are too flexible the vanes  74 - 82  when aligned at optimum angle of attack will not have sufficient offset to be efficient. It is known that as airfoils get closer together the efficiency of the pair decreases. Also it is known that staggering the upper airfoil forward of the lower one improves the efficiency of the pair. This invention provides for a substantial forward stagger of the vanes  74 - 82  and, with rigid support beams, has a reasonable vertical spacing of vanes  74 - 82 . Rigid support beams contribute to ankle stress so it is necessary to use semi-flexible support beams  62 ,  64  with a maximum flexure  164  of no more than 30 degrees. For the purpose of the illustrations the first embodiment shows a beam maximum flexure  164  of 30 degrees which is greater than should be used in practice. 
         [0213]    Given the flexing of the support beam, it is necessary to set the optimum angle of attack for each vane  74 - 82  so it will be proper with the support beam  62  is in the flexed position as shown in  FIG. 7A  or  FIG. 7C . It can be seen that while each vane  74 - 82  is set at a different angle to the support beam  62  they all are parallel to each other. This is accomplished by setting the drape of the web for each vane using common geometrical relationships as follows. First the optimum angle of attack is determined by experimental processes. Then the normal flexure of the support beam  62  is determined. Next, based on the location of each vane along the support beam determine the local support beam  62  flexure angle at each vane  74 - 82  location. The optimum angle of attack less the local support beam flexure angle is the individual vane rotation angle to be set as shown in  FIG. 6C . The length of the web from the longitudinal axis of the support beam to the center plane of the rotated vane is then determined for the front of the web and the rear of the web accounting for the limits of curvature of the pliable material along the edges. Next calculate the amount of drape required to fit the pivoted web distance into the non pivoted geometry as illustrated in  FIGS. 4C and 5B . 
         [0214]      FIG. 7A  shows that all vanes  74 - 82  are optimally aligned with the flow  156  since they are each aligned appropriately to the support beam  62  in the flexed position. Because there is a small angle of attack between the flow  156  and the vanes  74 - 82  then hydrodynamic lift  170  is generated generally in the direction of travel of the swimmer as shown in  FIGS. 8A , and  8 C.  FIG. 7C  shows the flow  156  for the downstroke, and it can be seen that the beam deflection angle  168  combined with the support beam flexure angle  164  and properly proportioned webs  104 ,  108 ,  112 ,  116 ,  120  serves to allow the optimum angle of attack on the downstroke also. 
       Second Embodiment 
       [0215]      FIGS. 10A ,  10 B and  10 C show the operational sequence of another embodiment of the invention using symmetrical flexible vanes in the fixed support beam fin  171  used with the leg  158 , heel, and foot  162  and the direction of foot motion  166 .  FIGS. 9A ,  9 B and  9 C show the flow  156  around individual vanes from  FIG. 10A-10C . The second embodiment is similar to the first except the vanes  180  are flexible along their lateral axes at about the 40% chord distance. The flexible connector  172  is a pliable material overmolded onto a rigid leading edge  174  and rigid trailing edge  176  as illustrated in  FIG. 9B . To facilitate a stronger bond between the two materials a rail system  178  similar to the web connection rail  138  of  FIG. 2C . The function of the swim fin in this embodiment is substantially similar to the function of the first embodiment except the flexure of the vanes  180  effectively creates a reversibly asymmetric hydrofoil with a higher lift to drag ratio than in the first embodiment. 
         [0216]      FIGS. 10A ,  10 B,  10 C illustrate the stroke dynamics which is similar to that of the first embodiment with the exception of the additional curvature of the flexible vane  180  which according to computational fluid dynamic calculations improves the lift to drag ratio by 290% over that of the symmetrical rigid vane. 
         [0217]      FIG. 13  shows an isometric view of the second embodiment of the invention in a neutral state. This is similar to the first embodiment except for the flexible vanes  180  which improve the overall lift drag ratio. The flexible vane operation is shown and described in reference to  FIGS. 9A-10C . 
       Third Embodiment 
       [0218]      FIG. 11  shows a third embodiment  210  which is similar to the first embodiment with the entire support beam and vane structure being pivotally attached to the foot pocket  52  and secured by dual latch assemblies  212 ,  214  on the sides of the foot pocket  52 . The latch assemblies  212 ,  214  are detailed in  FIGS. 16-20B . 
         [0219]      FIG. 12  shows the third embodiment in its pivoted up position. In this position it is possible for the swimmer to walk on land or a boat without stumbling over the large propulsion surface in front of him. Pivotally attached propulsion surfaces for swim fins exist in the public domain. U.S. Pat. No. 4,981,454 by Klein, which is incorporated by reference is an example which uses a toe located latch. 
         [0220]    The latching mechanism of the third embodiment operates through a captive ledge system much like the dead bolt on a door. The difference is that in this case the deadbolt is fixed and the pocket it slides into is movable. The support beams  62 ′,  64 ′ are pivotally attached to the foot strap pegs  56  ( FIG. 1 ) on the foot pocket  52 . 
         [0221]    Referring to  FIGS. 11-16  duplicate replacement foot strap pegs  188  are attached to the outside of the support beams  62 ′,  64 ′ to replace the foot strap pegs  56  ( FIG. 1 ) used by attaching the support beams  62 ′,  64 ′. When rotated to the closed position as in  FIG. 11  the support beams  62 ′,  64 ′ being elliptical in cross section collide with the latch ledge  182  which forces the support beams  62 ′,  64 ′ to separate sufficiently to slide over the latch ledges  182  until the latch slot  194  (shown in  FIGS. 12 and 16 ) in the support beams  62 ′,  64 ′ align with the latch ledges  182 . At this point the support beams  62 ′,  64 ′ snap back into their original alignment captivating the latch ledge  182  and preventing the support beams  62 ′,  64 ′ from further movement. At this point the cam lever  184  is secured by slipping the cam lock clip  186  over the latch ledge  182 . The support rails are then held in position by the stiffness of the support beams  62 ′,  64 ′ which are held in position by the foot strap pegs  56  and vanes  74 - 82  which are fused to the support beams  62 ′,  64 ′ through the pliable hinges  84 - 102 . The process for unlatching the latch ledge  182  is described in reference to  FIGS. 18A-20B . 
         [0222]    The cam lever  184  rotation is shown by arrow  190 , and the support beam(s)  62 ′,  64 ′ rotation  192  is shown in  FIG. 12 . 
       Fourth Embodiment 
       [0223]      FIG. 14  illustrates isometric view of the fourth embodiment  216  of my invention in its neutral state. This is similar to the third embodiment except for the flexible vanes  180  which improve the overall lift drag ratio. The flexible vane operation is described in reference to  FIGS. 9A-10C . 
         [0224]      FIG. 15  shows the latched position of one latching application for embodiments three and four. The support beam  62 ′ can be pivotally attached at the receptacle  196  for the foot strap peg  56  to the foot pocket  52  at the foot strap peg  56 . The geometry of the foot strap receptacle  196  is shown more clearly in  FIG. 16 . Since the foot strap peg  56  on the foot pocket is covered by the support beam  62 ′ the support beam  62 ′ has a replacement foot strap peg  188  to serve the purpose of the original foot strap peg  56 . The support beam  62 ′ can be attached to the foot pocket  52  by aligning the tab  200  on the foot strap receptacle  196  with the keyway  198  of the foot strap peg  56  and sliding it on. Once the foot strap peg  56  is inserted into the foot strap receptacle  196  on the support beam  62 ′ the support beam  62 ′ is slid laterally on the foot strap peg  56  until the foot strap peg  56  is aligned with the replacement foot strap peg  188  at which point the support beam is in its operating position and may be rotated to a horizontal latched position as described with  FIG. 12 . 
         [0000]    The cam lever  184  is a beveled rotating cam which in the latched position lies between the support beam  62 ′ and the foot pocket  52  without exerting any influence on either. 
         [0225]      FIG. 16  is a view of the support beam  62 ′ and cam lever  184  separated to show the underlying cam lever post  202  and a clearer view of the latch ledge slot  194  and foot strap peg receptacle  196 . The latch ledge slot  194  in the support beam  62 ′ which accepts the latch ledge  182  on the foot pocket  52  is shaped to match the shape of the latch ledge  182 . The particular shape of the slot  194  and the latching ledge  182  in this embodiment is based on an existing foot pocket  52  with a latch ledge  182  of this geometry. Other shapes of the latching ledge  182  would also suit this purpose and can have additional benefits. Of key importance to this invention is the top and bottom surfaces of both the latch ledge  182  and slot  194  need to be nearly parallel and near perpendicular to the axis of the shear force created at the interface of the two features when the swim fin is in active use. The latch ledge  182  must be sufficiently strong to resist the shear forces created. This is estimated at about 40 pounds per support beam  62 ′ perpendicular to the longitudinal axis of the support beam  62 ′. Depending on the spacing between the latch ledge  182  and the foot strap peg  56  the actual shear force can vary substantially. 
         [0226]    The cam lever  184  has three primary design features which will be described more thoroughly in reference to  FIGS. 17-20B . In embodiments three and four the cam lever  184  can be pivotally attached to the support beam  62 ′ by a press fit over a cam lever post  202  which is molded into the support beam  62 ′. Since this is a plastic material the lever post  202  is somewhat flexible so press fitting the cam lever  184  over the lever post  202  will cause the pegs to deflect somewhat then snap back to their original shape after the shoulder  204  in the cam pivot hole  206  has been reached.  FIG. 18A  shows the cam lever  184  in its installed condition. This example of cam lever  184  connection does not preclude other attachment methods such as a simple screw and washer. 
         [0227]    The foot strap peg receptacle  196  is also shown in  FIG. 16  showing the tab  200  to be aligned with the keyway  198  on the foot strap peg  56  before the foot strap peg  56  is inserted into the receptacle  196  and slid forward to its operational position. The opening  209  in the back of the support beam  62 ′ at the receptacle  194  is simply for the purpose of making the device injection moldable. 
         [0228]      FIG. 17  shows the cam lever  184  in a locked position as viewed from directly above. The broad upper surface  207  of the cam lever serves to channelize or normalize the flow between the foot pocket  52  and support beam  62 ′. The locking clip  186  is shown engaged over the edge of the latch ledge  182  to prevent the cam lever  184  from moving when the swim fin is in use. It can be seen the latch ledge  182  is well seated in the latch ledge slot  194  in this configuration preventing the support beam from rotating out of this position. 
         [0229]      FIG. 19A  is a view of  FIG. 17  from the front showing the cam lever  184  in the locked position. Notice the lock clip  186  has captured the edge of the latch ledge  182  and the latch ledge  182  is securely seated in the latch slot  194 .  FIG. 19B  is a cross-sectional view of  FIG. 17  through the axis of the cam latch post  202  clearly showing the tapered nature of the cam and how it fits between the support beam  62 ′ and foot pocket  52  without exerting any force on either. Also shown in  FIG. 17  is the foot strap peg  56  seated in the foot strap peg strap receptacle  196  pivotally fixing the end of the support beam  62 ′. Molded to the side of the support beam  62 ′ is the replacement foot strap peg  188  which is used to fasten the commonly available foot strap  53 . 
         [0230]      FIGS. 18A and 18B  show a view from above illustrating the effect of rotating the cam lever  184  up. This upward rotation pushes the support beam  62 ′ away from the foot pocket  52  releasing the latch ledge  182  from the ledge slot creating a gap  208  as shown in  FIG. 18B , thus allowing the support beam  62 ′ to rotate freely upward as illustrated in  FIG. 12 . 
         [0231]      FIG. 20A  shows how the thicker portion of the cam  184  is pressed against the side of the foot pocket  52  increasing the gap  208  between foot pocket  52  and the support beam  62 ′.  FIG. 20B  is a cross-sectional view through the axis of the cam latch  184  clearly showing the thicker portion of the cam and how it presses against the foot pocket  52  forcing the support beam  62  and foot pocket  52  apart and consequently removing the latch ledge  182  from the latch slot. 
         [0232]    While the invention describes a two step over molding process, the invention can be practiced with a three step process where the foot pocket is molded of a material other than the material used in the vanes, hinges and webs. 
         [0233]    Although the embodiments describe the invention for use with swim or sport fins, the invention can use the hydrofoil vanes in other water applications, such as but not limited to boats, paddles, and the like. 
         [0234]    While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.