US 3810269 A
A swimmer's foot fin is provided with a blade which slopes at an angle downwardly from a foot receiving portion. This blade includes sloping areas which form an inverse V-section to decrease the profile drag of the blade. Additionally, the lateral edges of the blade have ribs projecting above and below the blade and supplementary propulsive areas that are angled upwardly to form additional flow channels to direct the water during the kicking movement of the swimmer's foot to control turbulent flow and aid the propulsive effect of the kick.
Claims available in
Description (OCR text may contain errors)
nited States Patent [1 1 Tabata et a1.
1451 May 14,1974
1 1 SWIMMER'S FOOT FIN  Inventors: Kazuo Tabata, 1-3-17 Higashi-Komagata, Surnido-ku, Tokyo; Masanari Togasaka, 768 Kisone, Yashio-cho, Minami Saitama-gun Saitama. Japan  Filed: Sept. 14. 1972  Appl. No.: 289,076
 U.S. Cl. 9/309  Int. Cl A63b 31/10  Field of Search 9/309, 301
 References Cited UNITED STATES PATENTS I 2,889,563 6/1959 Lamb et a1 9/309 3,411,165 11/1968 Murdoch 9/309 3,019,458 2/1962 Barbieri et al. 9/309 FOREIGN PATENTS OR APPLICATIONS 1,419,398 10/1965 France 9/309 Primary Examiner-Duane A. Reger Assistant Examiner-Gregory W. OConnor Attorney, Agent, or Firm-Flam & Flam  ABSTRACT A swimmers foot fin is provided with a blade which slopes at an angle downwardly from a foot receiving portion. This blade includes sloping areas which form an inverse V-section to decrease the profile drag of the blade. Additionally, the lateral edges of the blade have ribs projecting above and below the blade and supplementary propulsive areas that are angled upwardly to form additional flow channels to direct the water during the kicking movement of the swimmers foot to control turbulent flow and aid the propulsive effect of the kick.
1 Claim, 6 Drawing Figures PATENTEWY 14 1914 381 0.269
sum 2 ur a The present invention relates to swimmers foot fins, such as are used for example when skin-diving" or carrying out underwater operations.
It is an object of the present invention to provide a swimmers foot-fin wherein axial configuration of a blade portion is modified so as to allow its smooth entering into the water and to give direction to and increase the water current in the area of surface which acts against the water whereby a turbulent flow is controlled and hence increasing of a propulsive effect is obtained.
Another object of the present invention is to provide a swimmers foot-fin wherein a blade portion thereof is build up thinly in a degree that such construction does not weaken the strength of the blade portion but lighten the total weight of the foot fin so that the swimmers weariness with propulsive movements may be lessened.
Further objects of the present invention and advantages thereof may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a perspective elevation of one embodiment of the foot fin according to the present invention, seen from one side and above;
FIG. 2 is a perspective underplan of the foot fin of FIG. 1;
FIG. 3 is a section on the line X-X of FIG. 1;
FIG. 4 is a section on the line Y-Y of FIG. 1;
FIG. 5 is a schematic diagram to illustrate the manner in which the foot fin operates; and
FIG. 6 is a perspective elevation of another embodiment of the foot fin according to the present invention, seen from one side and above.
Similar reference characters refer to similar parts throughout the several views of the drawings.
Referring now to FIGS. 1 to 5, the foot fin, designated generally by reference numeral 1], is made as a one-piece moulding of a resiliently flexible material such as rubber or plastics and comprises a shoe portion 12 adapted to receive the swimmers foot and a blade portion 13 which forms a forward extension of the shoe portion and which has the effect of obtaining a propulsive effect by the swimmers alternative kicking movements up and down with the foot. The blade portion 13 extends forwardly of the substantially flat plantar region of the shoe portion in such a manner that each of both sides of the blade portion with an axial center line therebetween bends at a suitable angle downwardly thereby to obtain an inverse V-section and to form propulsive slope-areas 13a and 13b. Each ends of these propulsive slope-areas 13a, 13b in the axial direction generally parallel to the axial center line of the blade portion 13 is provided with ribs 14 and 15 which are projecting symmetrically above and below with an acute angle. At a portion immediately below the axial center line of the blade portion 13, there is also provided a rib l6 projecting downwardly with similar acute angle to that of the ribs 14 and 15. Each ends of these propulsive slope-areas 13a, 13b in the axial direction generally parallel to the axial center line of the blade portion 13 and in the extreme lateral portions over the ribs 14, 15, there are provided supplementary propulsive narrow slope-areas 13c, 13d each extending obliquely and upwardly with a suitable angle contrary to as in the case of the propulsive slope-areas 13a, 13b, As will be obvious from FIG. 3, the lateral sides of the blade portion 13 in its axial direction are formed with water-flow channels, each of the channels being defined by the propulsive slope-areas 13a, 13b and the upper ribs l4, 15; by the supplementary propulsive slope-areas 13c, 13d and the upper ribs I4, 15; or by the propulsive slope-areas 13a, 13b and the supplementary propulsive slope-areas 13c, 13d.
The provision of the propulsive slope-areas 13a. 13b will decrease the profile drag of the blade portion 13 and allow its smooth entering into the water, and the provision of the water-flow channels l7, 18 will cause the water-flow divided by the upper ribs 14, 15 during the kick movements of the swimmers foot to ejectively flow toward the direction parallel to the propulsive direction, whereby a turbulent flow of the water is controlled, a balanced swimming and propulsive effect is.
Such modification in the axial configuration of the blade portion 13 and the arrangements of the ribs 14, 15 and 16 as shown and described above in connection with FIG. 3, will allow the blade portion to be build up thinly without weakening the strength thereof, so that the total weight of the foot fin 11 is lightened and the swimmers weariness with propulsive movements may be lessened.
The forward end of the blade portion 13 is provided witha slope-area 13c bending slightly downwardly with a suitable angle. Provision of such slope-area 13a is intended to merely obtain a beautiful profile of the footfin 11 and produces no particular advantageous effects on the propulsive movement. In this connection, it will be appreciated that if the slope-area 13a does maintain its designed configuration during the swimmers driving stroke by moving his lower limb 19 upwardly (FIG. 5) without coincidentally and resiliently following the water influence acting thereagainst, the speed of propulsive movement will naturally be decreased by the resistance produced by the water acting against such slope area 132. The slope area 13c according to the present invention, however, is build up toreably thinly in a degree that during the swimmers alternate kicking movements up and down as in FIG. 5 it may conform to the water resistance acting thereagainst and present a generally flat configuration, as will be obvious from FIG. 3. Accordingly, no such drawbacks, as referred to above will not be produced by the provision of the slope-area 13:: at the forward end of the blade portion 13.
Referring now to FIG. 6 showing another embodiment according to the present invention, the foot fin is designated generally by the reference numeral 111. This foot fin 111 is almost identical in its design to the foot fin 11 according to the embodiment previously referred to, and is intended to offer certain advantageous effect. Specifically, each of the forward ends of the upper/lower ribs l4, 15 is provided with vertical blade portions 114 and 115 respectively, these blade portions 114, 115 being made integral with the ribs l4, 15. These vertical blade portions 114, 115 is designed to present a configuration as well as a function like the vertical tail of an airplane shows and offers so that the directional stability of the blade portion 13 in the propulsive movement may advantageously be maintained. In this connection, it is to be noted that the lower vertical blade portions 114, 115 will not be so important as the upper vertical blade portions 114, 115 to obtain the above-mentioned effect. In other words, provision of the lower vertical blade portions 114, 115 will not be a prerequisite.
While the particular embodiments of the present invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.
What we claim is:
1. In a swimmers foot fin of one-piece molded plastic wardly at an angle to the plane of said plantar region from a place located near the forward end of said plantar region; said blade portion having two side parts angled laterally from a center line of the fin to define an inverted V-shaped dihedral angle; said side parts having lateral boundaries there being ribs at the lateral boundaries of said side parts and extending from the sides of said plantar region on the outside of said shoe portion to a point located at the frontal portion of said blade portion; there being a central rib extending longitudinally on the under side of said blade portion and operative in conjunction with said ribs to maintain a cup configuration on the underside of said fin upon downward effort being imposed thereon by the user; said blade portion having at the outer sides of said ribs, supplementary propulsive flanges each extending 'obliquely and upwardly to form on the inside and outside of each rib, a pair of companion water flow channels to achieve a controlled turbulent flow and a balanced swimming and propulsive effect.