Swim fin

Details Swim fin Swim fin

1994-04-26

1995-10-24

Basinger, Sherman

Buoys, rafts, and aquatic devices

Swimming aid to increase stroke efficiency

Foot attached

A63B 3111

Patent

active

054605571

DESCRIPTION:

BRIEF SUMMARY
The invention is based on a swim fin for divers or swimmers, as defined hereinafter. Swim fins of this kind are intended to increase the forward speed of a diver or swimmer in that as a result of the up-and-down motion of the swim fin in the water, buoyancy acting on the fin is produced, whose component in the forward motion direction exerts forward thrust upon the diver or swimmer.


SUMMARY AND OBJECTS OF THE INVENTION

In contrast to conventional swim fins, which are embodied in the shape of the tail fin of a fish, generic swim fins have a freely leading profile as a fin blade that on both the upwardly and the downwardly oriented stroke of the fin is kept at a positive angle of attack with respect to the oncoming flow direction of the water, which is a product of the forward motion and the stroke of the fin. Similarly to what happens with an airplane wing, this oncoming flow to the profile at a positive attack angle produces a circulation around the profile, which is superimposed on the water flowing toward it. This builds up a pressure system that causes overpressure on one side of the profile, and negative pressure on the other.
By varying the attack angle, depending on the direction of the stroke of the fin, it is attained that the buoyancy always has a component in the forward motion direction, which acts as a forward thrust upon the swimmer or diver. With such swim fins, a much higher forward motion speed is achieved than with conventional swim fins lacking a freely leading profile.
It is known for a swim fin of this generic type to be embodied like the tail fin of a dolphin (Published German Patent Application DE-OS 34 38 808). Such swim fins have the form of an airfoil of great length, and each fin of a pair of fins is provided with an airfoil that points laterally outward from the leg of the swimmer or diver.
Because of this unilateral disposition of the airfoil on the swim fin, the result when the fin strokes through the water is a torsional effect on the leg of the diver or swimmer. Hence such swim fins are either embodied as a monofin, with two receptacles for both feet of the diver or swimmer and two airfoils each pointing outward, or else a second airfoil of slight length must be produced on the side opposite the airfoil of great length, i.e., between the legs or feet of the diver or swimmer, in order to compensate for the torsional effect. Both versions have the disadvantage of drastically impeding the freedom of motion of the diver or swimmer both on land and in the water.
The object of the invention is therefore to create a swim fin that on the one hand enables high forward motion speeds and on the other limits the freedom of motion of the diver or swimmer only a little or not at all.
This object is attained by the swim fin of the invention, having the characteristics set forth hereinafter.
Because the profile is disposed downstream, in the swimming direction, of the foot of the diver or swimmer and is always located in the undertow of the foot of the swimmer, whether the stroke of the fin is oriented upward or downward, optimal flow conditions are attained, which among other consequences lead to a later separation of the eddy arising at the top of the flow over the profile, and hence to less flow resistance. In other words, this maintains a laminar flow on the negative-pressure side of the profile for a longer time. As a result of these provisions, on the one hand, the buoyancy of the swim fin is increased, and on the other, its flow resistance is reduced.
In an advantageous feature of the invention, the profile has a slight length and in outline is embodied symmetrically with respect to the longitudinal axis of the leg, extending through the knee of the swimmer or diver. This averts a torsional affect on the swimmer's or diver's leg. The resultant reduced width of the profile is compensated for by the optimal streamlining.
In an advantageous feature of the invention, lateral struts are disposed on both longitudinal sides of the profile, which on the other side are joined to a cuff that

REFERENCES:
patent: 3239857 (1966-03-01), Gwynne
patent: 3665535 (1972-05-01), Picken

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