US3510894A - Propulsion device for swimmers - Google Patents

Description

May 12, 1970 B. ERlKsEN 3,510,894

PROPULSION DEVICE FOR SWIMMERS Fla Filed Jan. 14. 1969 Q EL INVENTOR. BYRON ERIKSEN Attorneys United States Patent O ABSTRACT F THE DISCLOSURE A device for assisting a swimmer to travel through the water comprises a iioat and pair of paddles secured to the iioat and projecting in opposed relation therefrom. The device is manufactured from a foamed plastic material and has a high density outer skin and a low density inner structure.

This invention relates in general to water propulsion devices for aiding swimmers in traveling through water, and pertains more particularly to a combined oat and paddle device having an outer skin of relatively dense plastic material with an interior structure comprising a foam plastic of lesser density than the outer skin.

While devices of this general type have been known to the prior art for some time, the present invention provides for the iirst time in a unique and novel manner a float and paddle device which affords more strength, results in substantially greater safety in congested areas, and can be manufactured simply 'and inexpensively by molding techniques.

A typical device known to the prior art is shown in U.S. Pat. 1,509,551 issued Sept. 23, 1924 to Andrew Gibson. The device as shown in this prior art patent essentially comprises a shaft to the central portion of which is encompassingly attached a canvas bag having an inflatable bladder mounted therein. Paddle blades are attached to the end portions of the shaft by means of bolts. Obviously, the entire strength of this device is obtained from the central shaft while the canvas bag and bladder combination do not materially add to the strength of the paddle device. The construction is cumbersome, complicated and dangerous when used in crowded bathing areas.

It is accordingly yan object of the present invention to provide an improved water propulsion device for swimmers embodying apparatus for reducing and substantially eliminating safety hazards to swimmers and bathers in the immediate vicinity in which the device is employed.

Another object of the present invention is to provide a device which will 'assist in propelling the body of a swimmer through water at a greater rate of speed than can be obtained by a swimmer without the aid of the device.

Another object of this invention is to provide a device which will serve as a safety iioat as well `as a paddle apparatus for efliciently assisting a swimmer to traverse a considerable distance in water with ease. In this regard, it is an aim of the invention to provide a device of foamed plastic material in which the entire structure lends buoyancy to the swimmer.

A further object of the present invention is to provide a propulsion device for swimmers which has considerably more strength on a density basis than devices heretofore known to the prior art.

Yet another object is to provide a propulsion device of the foregoing character that will last indefinitely because the plastic material from which it is made does not deteriorate.

A still further object of the invention is to provide a water propulsion device for swimmers which can be 3,510,894 Patented May l2, 1970 manufactured in a single unit or economically from but a few parts.

Other advantages, features and objects of the invention will become more apparent with the teachings of the principles thereof in connection with the disclosure of the preferred embodiments thereof in the specification, claims and drawings.

Brief description of the drawings FIG. 1 is a front elevational view, shown partially in cross section, of the device constructed in accordance with the principles of the present invention;

FIG. 2 is a plan View of the device of the present invention;

FIG. 3 is a sectional view taken in the direction of line 3 3 of FIG. 2; and

FIG. 4 is a fragmentary sectional view of a modied arrangement of the structure shown in FIG. 1.

IDescription of the drawing Referring to the drawing, and particularly to FIGS. 1 and 2, the water propulsion device of my invention is comprised of a central tear-shaped portion 10 having a major axis 11 and a minor axis 12 passing at right angles through the sides of the central portion 10 and intersecting the major axis 11 at right angles as shown in FIG. 2. As viewed in FIG. l, the major axis 11 resides in a Vertical plane 11a and appears as a point where the minor axis intersects or passes through this -vertical plane. The central portion 10, when constructed in the tear-shape as shown, constitutes a streamlined float element which can be manipulated by a swimmer and yet will offer a minimum of resistance when caused to travel over the surface of water.

At locations 13 and 14, and in a vertical plane containing the minor axis 12, shaft portions 15 and 16 are connected to the central portion 10. As will be discussed in detail hereinbelow, the shaft portions 15 and 16 may be integral with the central portion 10 or suitably bonded thereto.

As shown in FIG. l and 2 the shaft portions 15 and 16 extend outwardly at each side from the central portion 10, the shaft portions inclining slightly upwardly as illustrated in FIG. 1. The outer ends 17 and 18 of the shaft portions 15 and 16 are equipped `with paddle blades 19 and 20. The paddles 19 and 20 are in the form of relatively thin iiat blades and lie somewhat to either side of a vertical plane 12a (FIG. 3) containing the minor axis 12 as mentioned above 'and thus reside in a plane transverse to the longitudinal axis 11 of the central portion 10 (which plane 12a is of course perpendicular to the plane 11a), being positioned equidistant from the central por tion, as shown. The shaft portions 15 and 16 are of such cross sectional dimension and length as will permit easy mnaual grasping so as to enable a swimmer to hold the shaft portions 15 and 16 in each hand respectively durmg use.

In the use of the water propulsion device of my invention the central portion 10 is placed upon the water and the shaft portions 15 and 16 are permitted to lie above the surface of the water with the paddle blades 19 and 20 presenting a vertical surface adapted to be alternately dipped into the water for propulsion 0f the swimmers body. The central portion 10 is caused to rock about the longitudinal axis 11 (that is the plane 11a shifts angularly to either side of the vertical position that has been illustrated in FIG. l) and also to be oscillated forwardly and rearwardly in a generally horizontally plane as the swimmer manually actuates the paddle members 19 and 20.

Thus, one hand of the swimmer causes the shaft 16 to be dipped into the surface of the water and to be pulled rearwardly to advance the swimmer and the central portion and automatically causing the other shaft portion to raise the opposed paddle blade 19 and to move it forwardly with respect to the central portion 10. After the second named paddle blade 19 has been moved to its forwardmost position, it is then lowered so as to lie beneath the surface of the water and is subsequently drawn rearwardly to cause forward propulsion of the central portion 10 and the swimmers body.

It will be noted that the generally tear-shaped character of the central portion 10 is such as to present a streamlined surface to the water irrespective of the rocking movement and to offer a minimum of resistance to the water as the swimmer and the apparatus progress therethrough.

If the swimmer becomes tired and desires to rest before continuing, he may pull the central portion 10 beneath his torso and hold the apparatus in position so as to support his body until he is again ready to proceed.

The apparatus of the present invention eiciently simulates a pair of paddles or oars which are alternately dipped and pulled through the water with similar motion to that required when rowing a boat. However, since the resistance of a boat hull is not present and since the central portion 10 has a streamlined configuration as previously noted, a minimum of resistance is offered by the apparatus. For this reason, a swimmer utilizing this apparatus can easily propel himself through the water more rapidly and efficiently than with a rowboat utilizing oars of comparable structure.

As previously indicated, the apparatus of the present invention is constructed in a unique and novel manner affording additional strength while maintaining a high degree of buoyance and providing for more safety in congested areas. Essentially, the apparatus is constructed of a molded plastic having an outer skin of relatively dense material and a relatively low density inner structure. Characteristically, therefore, the structure of the present invention comprises a cellular core and an integral solid skin which structure may be obtained by one of several methods which will be described in detail hereinbelow.

It can be shown that a foamed or cellular structure is at least four times as rigid as its solid counterpart of the same weight.

By way of demonstration, it will be appreciated that the deflection formula for a cantilever beam states that the deection y, is equal to PL3/3EI where P is the load;

L is the beam length;

E is the modulus of elasticity of the material and I is the cross-sectional moment of inertia, which is equal to where b and lz are the width and thickness of the beam, respectively.

If the load, length and width are kept constant, the deection formula simplifies to K/Eh3 (1) If the material is now foamed to one-half its original specific gravity and the weight held constant, the thickness will double and the modulus, being approximately linear with density, will increase by one-half.

Substituting then in Equation 1 Ef=1/2Es hf=2hs where the subscripts f and s refer to foam and solid,

yields:

yf: YS/f It will thus be seen that a foamed structure will be four times as rigid as its solid counterpart of the same weight.

The manufacture of foamed structures yields another advantage which adds to the strength to the'ultimate product in that a solid skin formed during the molding process which encloses the molded material and which skin is typically 0.040 inch thick in a one quarter inch section.

An extruder, and accumulator, a hydraulic press, and a mold are the equipment needed to mold structural foam products. The extruder feeds and melts the plastic raw material. A blowing agent is introduced into the plastic melt while it is still in the extruder, at about the midway point.

The accumulator is divided into two chambers by a piston, the topside of which is pressurized to two thousand to three thousand p.s.i. The plastic-gas mixture pumped by the extruder works against this pressure and therefore remains in a compressed and unfoamed state. When the accumulator has been filled with the desired amount of material, a valve closing off access to the mold is opened and the plastic-gas mixture is rapidly forced out of the accumulator and into the mold. The valve then closes and the filling cycle repeats. The two forces involved in filling the mold with plastic are the direct pressure exerted by the accumulator and the expansion of the gas as it leaves the high pressure accumulator and enters the low pressure mold. The force required to keep the mold closed is supplied by the hydraulic press and is in the range of 200-300 p.s.i. times the projected area of the part to be molded. The characteristic structure of a cellular core and integral solid skin is formed during the mold fill. As the material ows through the mold, the surface cells are ruptured by the shearing action of the material flowing against the mold surface. This produces a solid skin, as mentioned above, that is typically 0.040 inch thick in a one-quarter inch thick section. After the mold has been filled, the part is cooled sufficiently and then ejected.

The above-described device used for the manufacture of my paddle device is well known to those skilled in the art and need therefore not be described herein with additional particularity.

In FIG. 3, the high density skin has been designated by the numeral 21 at one side and by the numeral 22 at the other. It will be appreciated that the skin 21, 22 becomes increasingly important where the thickness is less. Hence, the presence of a strengthening skin covering the central portion is not nearly as important as in the region represented in FIG. 3.

In accordance with the principles of my invention, other methods of manufacture may be employed. For example, the device may be molded in two halves represented by portions lying on either side of the minor axis 12 denoted in FIG. 2 or 3. In such a situation, two hollow shells would be molded, the shells corresponding to the skin portions 21 and 22, having a typical wall-thickness of 1/s or so. The hollow shells would then be joined at the plane 12a, which contains the minor axis 12, by means of a suitable glue or bonding agent and the interior of the device then filled with a self-foaming plastic such as polystyrene beads or other suitable plastic foam material. The self-foaming plastic thus injected into the hollow paddle device, when expanded by heat, results in positional oatation under all circumstances. For example, a puncture in the outer shell would not be harmful since the interior is filled entirely with the self-foaming plastic providing for positional oatation. The same holds true when the high density skin condition represented by the numeral 21, 22 in FIG. 3 prevails, because the expanded cellular interior does not permit the water to enter due to the blockage by the cell walls.

It will, therefore, be appreciated that with the foregoing methods of manufacture the structural advantages of a foamed or cellular structure will be maintained.

It may also be desirable to manufacture the device of the present invention in several constituent parts. For example, as illustrated in FIG. 4, it is feasible to manufacture the central portion as a separate unit, which has been designated 110, and to also manufacture the shaft portions and 16 with the paddle blades 19, 20 thereon as separate units. In this particular instance the central portion 110 is provided with a recess 125 of suitable diameter and shape while the depicted shaft portion 115 is provided with a suitable stub portion 126 which will fit into the recess 125. The shaft portion 115 may then be suitably bonded to the central portion 110.

The procedure pictorially outlined in FIG. 4 may have certain advantages in that it reduces the size of the required molds and the same mold may be used for each of the shaft portions, thus reducing the total capital investment. Stated somewhat differently, one mold would be made for the central portion 110 and a second mold for the shaft portion 115 and the blade (not shown in FIG. 4) which would be integral therewith. lSince the shaft portion 115 (and its blade) would be duplicated for the left Side in FIG. 4, just one mold would be required for the combined shaft and blade and one mold for the central portion 110. Such molds, quite obviously, would be simpler than the single mold required for making the one-piece device of FIGS. 1 and 2. Furthermore, should breakage necessitate, a shaft and blade could be replaced When utilizing the arrangement of FIG. 4.

It will, of course, be appreciated that in the latter described method of manufacture I may employ either of the above described molding techniques, that is, each of the parts may be molded integrally or in halves where the shells are joined and lled with a self-foaming plastic.

I claim:

1. A device for assisting a swimmer to travel through the Water which includes an elongated central portion having major and minor axes, a pair of shaft portions projecting in generally opposite directions from said central portion, said shaft portions projecting at right angles to said major axis and in a plane containing said minor axis, said plane being perpendicular to said major axis, and a blade portion integrally supported at the free end of each of said shaft portions, all of said portions being comprised of a foamed plastic material consisting substantially the entire device.

2. A device for assisting a swimmer to travel through the water which includes a central tear-shaped portion having major and minor axes, a pair of shaft portions projecting in generally opposite directions from said central tear-shaped portion at right angles to said major axis and angularly in a plane containing said minor axis, said plane being perpendicular to said major axis, and a blade portion supported at the free end of each of said shaft portions, said portions being comprised of a foamed plastic material.

References Cited UNITED STATES PATENTS 3,186,011 6/1965 Decker 9-24 1,509,551 9/1924 Gibson 9-24 1,894,874 1/1933 Kask 9-24 2,941,219 6/1960 Irving 9-313 3,052,897 9/ 1962 Martin 9-311 3,337,886 8/1967 Ekstrom 9-310 MILTON BUCHLER, Primary Examiner J. E. PITTENGER, Assistant Examiner

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