US3649979A

US3649979A - Swim fin

Info

Publication number: US3649979A
Application number: US46061A
Authority: US
Inventors: Douglas K Macniel
Original assignee: US Divers Co Inc
Current assignee: Aqua Lung America Inc
Priority date: 1970-06-15
Filing date: 1970-06-15
Publication date: 1972-03-21
Anticipated expiration: 1989-03-21
Also published as: GB1261168A; FR2095243A1; FR2095243B1; JPS4836519B1; DE2128725A1

Abstract

A foot-mounted fin for use by skin divers and other swimmers, and including means to mount the fin on the foot of the swimmer and blade means to propel the swimmer through the water in response to kicking movement of the leg and foot. Water-intake (scoop) or mouth openings are provided in the top of the fin and adjacent the foot pocket or other mounting means. Water-outlet or jet-exhaust openings are provided at the tip of the blade and are directed away from the foot pocket. Wall means are provided to define nozzle passages connecting the water-intake openings with the jet-exhaust openings to thereby cause high-velocity jets of water to emanate from the blade tip, particularly during each downstroke of the foot of a swimmer who is in a face-down position.

Description

I United States Patent MacNiel [451 Mar. 21, 1972 541 swI'M FIN [72] inventor: Douglas K. MacNiel, Costa Mesa, Calif.

{73] Assignee: U.S. Divers Co., Santa Ana, Calif.

[22] Filed: June 15, 1970 [21] Appl. No.: 46,061

[52] US. Cl ..9/309 [51] ..A63b 31/10 [58] Field of Search ..9/309. 301

[56] References Cited UNITED STATES PATENTS 3,183,529 5/1965 Beuchat ..9/309 3,055,025 9/1962 Ferraro et a1 ..9/309 3,032,787 5/1962 Mazzeila ..9/309 Primary Examiner-Milton Buchler Assistant Examiner-Gregory W. O'Connor Attorney-Gausewitz, Carr & Rothenberg [57] ABSTRACT A foot-mounted fin for use by skin divers and other swimmers, and including means to mount the fin on the foot of the swimmer and blade means to propel the swimmer through the water in response to kicking movement of the leg and foot.

Water-intake (scoop) or mouth openings are provided in the top of the tin and adjacent the foot pocket or other mounting means. Water-outlet or jet-exhaust openings are provided at the tip of the blade and are directed away from the foot pocket. Wall means are provided to define nozzle passages connecting the water-intake openings with the jet-exhaust openings to thereby cause high-velocity jets of water to emanate from the blade tip, particularly during each downstroke of the foot of a swimmer who is in a face-down position.

17 Claims, 5 Drawing Figures PATENTEDHARZI I972 3,649,979

SHEET 1 [1F 2 I'I'I'IIII IIIIII'IIII? IIAIIIII/II 'I'II'II" ("III'IIII II'III'III INVENTOR. lira, 4 500414.; A/ M46N/EL 4 ORA/[VS PATENTED MAR 21 I972 SHEET 2 [1F 2 swnvr FIN BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of foot-mounted swim fins used by sport swimmers, skin divers, professional divers, and others, in order to increase the speed and efficiency of propulsion through the water.

2. Description of Prior Art It has previously been proposed to provide ports, openings or passages through the blade of a swim fin, in attempts to achieve advantages including increased propulsion, reduced turbulence, and reduced drag. Patents of this general type include US. Pat. Nos. 3,032,787, 3,055,025, and 3,183,529.

In no instance known to applicant, however, has it been proposed to create jets of water which pass outwardly from the tip region of the blade and in directions away from the foot pocket. More specifically, in no instance known to applicant has it been proposed to transmit water from the top of the blade, adjacent the foot pocket, through passage means to water-outlet or jet-exhaust openings formed in the blade tip and directed away from the foot pocket. Such location of the jet-exhaust openings produces major advantages described hereinafter.

I SUMMARY OF THE INVENTION The swim fin comprises a blade adapted to be employed in propelling the swimmer through the water, means to secure the blade to the foot of a swimmer, and passage and orifice means responsive to the downward movement of the foot of a downwardly facing swimmer to cause jets of water to emanate from the tip of the blade and in directions away from the foot. Stated more specifically, relatively large-area water-scoop or mouth openings are formed in the top of the blade adjacent the inner end of the foot pocket, and relatively small-area water-outlet or jet-exhaust openings are formed in the tip of the blade. Nozzle passage means are formed through the blade from such mouth openings to such jet-exhaust openings, and are of decreasing cross-sectional area in directions toward the jet-exhaust openings in order to effect high-velocity jet exhaust therethrough.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a view, partially in side elevation and partially in longitudinal section, showing the swim fin as mounted on the downwardly moving foot of a swimmer who is swimming in a face-down position;

FIG. 2 is a top plan view of the fin;

FIG. 3 is a longitudinal central section taken along line 3-3 of FIG. 2; and

FIGS. 4 and 5 are, respectively, transverse sectional views taken along lines 4-4 and 5-5 ofFIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Throughout this specification and claims, such expressions as top of the blade" denote that portion of the fin blade which is uppermost when the wearer is standing on the ground. Conversely, the bottom of the blade is that portion which is lowermost when the wearer is in standing position. Only one swim fin is described herein, it being understood that the swim fin for the other foot is identical or is substantially identical to the one illustrated and described. All of the figures, excepting FIG. 1, show the swim fin in its natural (unstressed and undeflected) condition.

Referring first to FIGS. 2 and 3, the'swim fin is illustrated to comprise a blade adapted to be secured by mounting means I] to one foot 12 (FIG. I) of the swimmer. The mounting means 11 is so constructed that the blade 10 is generally in a plane perpendicular to the leg of the wearer when the wearer is in standing position on the ground or other supporting surface. The blade then extends away from the ankle of the wearer, in line with (and outwardly of) the instep and toes thereof.

Very desirably, the mounting means I1 comprises wall means 13 to define a foot pocket or chamber 14 adapted to receive the toes and the instep of the foot 12. It is to be understood that additional wall means, not shown, may be provided to enclose the ankle and/or heel.

In the illustrated embodiment, a heel strap 15 (FIG. 1) extends around the heel of the wearer and is connected at its ends, through adjustable connections, to lugs or ears 16 formed integrally on the sides of wall means 13.

Side ribs 17 are provided along the side edge portions of the blade 10 and of wall means 13. The end regions of the side ribs 17 may be generally parallel to each other, as shown in FIG. 2, but the central regions thereof diverge substantially and in a direction away from the ankle of the wearer. Thus, the blade 10 is caused to be substantially wider than is the mounting meansll.

Mounted in equally spaced relationship intermediate the forward portions of side ribs 17 are intermediate ribs 18. Such ribs are parallel to each other and extend forwardly from the wall means 13 which defines the foot pocket 14. Stated more definitely, the intermediate ribs 18 extend forwardly from the toereceiving portions of wall means 13. In the illustrated embodiment, there are two such intermediate ribs 18, and the spacing between such ribs is approximately equal to the spacing between either of such ribs and the adjacent side rib 17.

The blade 10 comprises, in addition to the various ribs, a bottom wall 20 which covers the entire bottom and forward portion of the swim fin. Such wall 20 merges at a thickened portion 21 (FIG. 3) with the bottom portion of the wall means 13. The bottom wall 20 thus extends to the wall means for defining the foot pocket.

A top wall 22 is provided in spaced relationship from bottom wall 20, and covers the entire region of the fin blade 10 forwardly of the top-wall edges 23 illustrated in FIGS. 2 and 3. Such edges 23 are spaced a substantial distance forwardly from the wall means 13.

Referring particularly to FIGS. 4 and 5, each of the top and

bottom walls

22 and 20 is integral with all of the

ribs

17 and 18, such ribs serving to maintain the

walls

20 and 22 spaced from each other as illustrated. The

ribs

17 and 18 not only extend between the walls but also extend above and below the walls in order to increase the strength of the ribs and also to provide deflector or baffle means for guiding the water as it flows along the exterior surfaces of

walls

20 and 22.

As shown in FIG. 4, the

ribs

17 and 18 are relatively large and thick at regions adjacent the wall means 13. From such thick portions, the ribs taper progressively in a forward direction and become smaller as illustrated in FIG. 5. Thus, the

walls

20 and 22 come progressively closer to each other and, additionally, the blade portions remote from the foot pocket are more flexible than are the blade portions adjacent thereto.

Walls 20 and 22, and theribs l7 and 18, cooperate with each other to define three

nozzle passages

24, 25 and 26 (FIGS. 3-5). Passage 24 is generally rectangular in section and is defined between a side rib 17 and the adjacent intermediate rib 18, and also between the portions of top and

bottom walls

22 and 20 extending between such ribs. Correspondingly, passage 26 is defined between the remaining side rib l7 and the adjacent intermediate rib 18, as well as between the wall portions 22 and '20 extending between such ribs. The central passage 25 is formed between the two intermediate ribs 18 and between the top and

bottom wall portions

22 and 20 extending between such ribs.

Since the

walls

22 and 20 are spaced far from each other relatively adjacent the wall means 13, the noulepassages 24-26 have relatively large cross-sectional areas adjacent such wall means. The cross-sectional areas of the passages 24-26 progressively diminish in a direction away from the wall means 13, becoming minimum adjacent the tip regions of the blade (namely, those regions farthest from the ankle of the wearer). Thus, in FIG. 5 each of the passages 24-26 is illustrated as being relatively wide but thin (that is to say, there is only a short distance between the opposed portions of walls 20 and 22).

The ends of passages 24-26 remote from wall means 13 constitute water-outlet or jet-exhaust openings or orifices 27 (FIG. 3) which are directed forwardly and directly away from the wall means 13. Stated otherwise, such jet-exhaust openings or orifices 27 direct water generally in the plane of the tip region of the blade 10, and away from the foot and ankle of the wearer.

The other ends of the nozzle passages 24-26, those closest to the wall means 13, constitute water-intake or mouth openings 28. The water-intake or mouth openings 28 face generally upwardly, when the wearer is in standing position on a supporting surface, that is to say such openings face up and approximately 90 away from the direction of facing of jet-exhaust openings 27 when the wearer is standing on such surface. When the wearer is swimming through the water, in downwardly facing position, the downstroke of the leg and foot causes water to enter the mouth openings 28 and then pass around a gentle curve (formed by wall portions 29 and 30 shown in FIG. 3) to the tip regions of the blade for exhaust through jet-exhaust openings 27. The water not only passes around the gentle curve but also rapidly accelerates due to the progressively decreasing cross-sectional areas of the passages 24-26, the result being the efficient creation of three highvelocity jet exhausts from the tip of the blade and away from the ankle of the wearer.

The entire swim fin, excepting the heel strap and associated fastener means, is molded integrally from an elastomeric material such as natural or synthetic rubber. The elastomeric material should be sufficiently hard to prevent excessive deformation. For example, the shore hardness may be about 70. The present swim fin is characterized by the advantage that, despite the presence of passages 24-26, molding may be readily effected.

OPERATION The operation of the present swim fin may best be understood with reference to FIG. 1, which shows the fin mounted on the foot l2ofa wearer who is swimming in a facedown position. FIG. 1 illustrates the condition which occurs when the wearer is moving forwardly through the water and is simultaneously kicking downwardly the foot and leg portion illustrated in the drawing, the direction of kicking being indicated by the arrow C. ,y j

The illustrated downstroke creates thrust, and also generates relatively high pressure regions H.P.l and H.P.2

along the downwardly facing surface of the blade 10, namely along and adjacent the top wall 22. The downstroke also causes a certain amount of upward flexing of the blade, espedaily at portions thereof relatively adjacent the tip (namely, portions remote from wall means vl3). h

At the same time that downward kicking is occurring, as indicated by the arrow C, the swimmer is moving forwardly through the water, with consequent flow of water rearwardly along the blade walls 22 and and as indicated, respectively, by arrows 31 and 32. Such forward movement of the swimmer is the result of the indicated kicking action which kicking generates two important effects as described in the following paragraphs. 7 v I The first effect is direct thrust of the blade wall 22 against the water. Such thrust, when the fin is in the position shown in FIG. 1, has vertical and horizontal components, and only the latter is operative to produce forward propulsion of the swimmer through the water. It is emphasized that the horizontal component of direct thrust is greatest adjacent the highpressure region H.P.l, since the portion of wall 22 adjacent such region is inclined sharply upwardly. Conversely, there is very little horizontal component of direct thrust adjacent highpressure region H.P.2, since the fin is, when in the FIG. 1 position, only very slightly inclined adjacent such region.

After the fin has moved downwardly (from the FIG. 1 position) until all portions thereof are generally horizontal, there is very little or no horizontal component of direct thrust.

The second effect is different from the direct-thrust effect described above, and instead is jet thrust. The jet thrust effect results from converting the relatively no-work" region adjacent area H.P.2 into a useful jet pump. Such pumpf' causes flow of water through passages 24-26, as shown by arrows 33, with consequent jet thrust action at the blade tip. In addition, such pump" augments the flow along the blade surfaces and as indicated by arrows 31 and 32.

The water scoop (mouth or intake) openings 28 at the forward ends of nozzle passages 24-26 face in the general direction of blade movement in response to the downward blade-kicking indicated by arrow C. This is because the waterscoop openings 28 are directed transversely to the plane of blade 10 (FIG. 3). Therefore, the high pressure at region H.P.2 is very effective in causing flow (arrows 33) into and through nozzle passages 24-26. The water entering such passages passes around a gentle corner (surfaces 29 and 30) and then accelerates efficiently (along paths generally in the plane of blade 10) until it discharges at high speed through jet-exhaust openings 27. Such acceleration results from the progressively decreasing cross-sectional areas of the passages 24-26 as the exhaust openings or orifices 27 are approached. The direction of jet exhaust is away from the foot and ankle of the wearer, namely, away from mounting means 1 1.

The water jetting through exhaust openings 27 creates substantial thrust having a major horizontal component, with consequent increased propulsion of the swimmer in a forward direction. It is emphasized that such jet thrust is still present when the swim fin is generally horizontal, at which time there is, as stated above, little or no direct thrust.

Because the jet-exhaust openings are at the tip of blade 10, an entrainment or drag effect is generated whereby blade surface flow (shown by arrows 31 and 32) is augmented. The water jetting from orifices 27 (upper arrow 33, FIG. 1) entrains or drags the water passing rearwardly off

blade walls

22 and 20 and as shown by upper arrows31 and 32. Such entrainment or dragging generates a relatively low-pressure region v adjacent the blade tip, and such low-pressure region makes it easier for water to flow rearwardly off the blade walls. It follows that there are three layers of jets off the blade tip, as shown by the upper arrows 31-33, and these three jet layers augment the propulsive action: which moves the swimmer.

In addition to the above, the tip-located jets from passages 24-26 serve to'minimize the turbulence and vortexing which is inherently present at the blade tip due to the kicking action. The result is greater efficiency of propulsion.

Because the jets are through the tip-located orifices 27, instead of through the bottom wall 20, there is a relatively greater thrust in the horizontal (useful) direction. For example, and referring to FIG. 1, the uppermost arrow 33 is much closer to the horizontal than would be any corresponding arrow representing flow through bottom wall 20. On the other hand, the jet exhaust representedby the uppermost arrow 33 in FIG. 1 is not to a high pressure region, as would be the case if discharge were through top wall 22 adjacent region H.Pl. However, this does not imply that the tip-located orifices 27 may not be inclined away from the plane of the tip region of blade 10. They may, for example, be inclined in a direction somewhat counterclockwise from that shown in FIG. 1, with consequent reduction of the angle between uppermost arrow 33 and the horizontal.

It is emphasizedthat the jets from orifices 27 are directed into the main body of water and not against or adjacent any portion of the fin itself. In the prior art, on the other hand, any jets were substantially forward of the tip region of the fin, which diminished the propulsive action created by the jets.

During the upstroke --(not shown) of the foot of the swimmer, relatively little propulsive force is created, and relatively little effective work is done. It is to be noted, however, that the entire upper surface of the blade (as shown in FIG. 1

namely the bottom wall 20, is smooth and is not provided with orifices or ports which tend to create drag.

The foregoing detailed description is to be clearly understood as given by way of illustration and example only, the spirit and scope of this invention being limited solely by the appended claims.

I claim:

1. A swim fin, which comprises:

wall means to define a foot pocket,

first and second side ribs extending forwardly from said foot pocket wall means,

at least portions of said side ribs diverging relative to each other in a direction away from said foot pocket wall means, and

wall means extending between said side ribs and forming the blade of the swim fin, at least part of said blade wall means being a top wall,

said top wall terminating, at the inner end portion thereof relatively adjacent said foot pocket wall means, at an inner edge which is spaced from said foot pocket wall means, said top wall terminating, at the outer end portion thereof remote from said foot pocket wall means, in a region which is adjacent the tip of said blade, at least part of said blade wall means being a bottom wall which is spaced from said top wall, said bottom wall terminating, at the outer end portion thereof remote from said foot pocket wall means, in a region which is adjacent the tip of said blade, said top and bottom walls cooperating with each other in defining at least one water passage, said water passage terminating at its inner end in a water-scoop opening which is defined in part by said inner edge of said top wall, said water passage terminating at its outer end in a jetexhaust orifice which is defined between said outer end portions of said top and bottom walls, said orifice being directed away from said foot pocket walls means.

2. A swim fin, which comprises:

a blade adapted to be employed in propelling a swimmer through the water,

means provided at one end of said blade to mount the same to the foot ofa swimmer,

water-scoop means provided on the top of said blade and directed to receive water in response to downward movement of the foot of said swimmer when said swimmer is in a face-down position,

said water-scoop means being disposed relatively adjacent said mounting means,

jet-exhaust means provided at the other end of said blade remote from said mounting means, said jet-exhaust means being directed to discharge water in a direction away from said mounting means, said jet-exhaust means comprising orifice means disposed at the extreme tip of said other end of said blade, said tip being the portion of said blade most remote from said mounting means, and passage means to conduct water from said water-scoop means to said jet-exhaust means for discharge through the latter, said passage means comprising at least one nozzle passage through said blade, the walls of said nozzle passage being shaped to effect acceleration of water passing from said water-scoop means to said jet-exhaust means, said shaping being such that said nozzle passage has a cross-sectional area which decreases progressively in a direction toward said jet-exhaust means, and throughout substantially the entire distance from said water-scoop means to said jet-exhaust means.

3. A swim fin, which comprises:

a blade adapted to be employed in propelling a swimmer through the water,

means provided at one end of said blade to mount the same to the foot of a swimmer,

said water-scoop means being disposed relatively adjacent said mounting means,

jet-exhaust means provided at the other end of said blade remote from said mounting means,

said jet-exhaust means being directed to discharge water in a direction away from said mounting means, and

passage means to conduct water from said water-scoop means to said jet-exhaust means for discharge through the latter,

said passage means being defined in part by upper and lower walls which extend from said water-scoop means to said other end of said blade and substantially separate the water flowing through said passage means from the water passing along the exterior of said blade.

4. The invention as claimed in claim 1, in which said jet-exhaust means comprises orifice means disposed at the extreme tip of said other end of said blade, said tip being the portion of said blade most remote from said mounting means.

5. The invention as claimed in claim 1, in which said passage means comprises at least one nozzle passage through said blade, the walls of said nozzle passage being shaped to effect acceleration of water passing from said water-scoop means to said jet-exhaust means.

6. The invention as claimed in claim 5, in which said nozzle passage has a cross-sectional area which decreases progressively in a direction toward said jet-exhaust means, and throughout substantially the entire distance from said waterscoop means to said jet-exhaust means.

7. The invention as claimed in claim 1, in which the mouth of said water-scoop means is directed transversely to the plane of said blade.

8. The invention as claimed in claim 7, in which the walls of said passage means include smoothly-curving portions adapted to change the direction of flow of water from said direction transverse to the plane of said blade to a direction in the plane of said blade.

9. A swim fin, which comprises:

wall means to define a foot pocket,

at least portions of said side ribs diverging relative to each other in a direction away from said foot pocket wall means,

intermediate rib means located between said first and second side ribs and extending forwardly from said foot pocket wall means,

a top wall connected to said side ribs and to said intermediate rib means,

said top wall extending to the tip of said blade,

said top wall forming the top surface of the blade of said fin,

said top wall terminating, at the inner portion thereof relatively adjacent said foot pocket wall means, in inner edges which are spaced forwardly from said foot pocket wall means, and

a bottom wall connected to said side ribs and to said intermediate rib means, said bottom wall extending to the tip of said blade, said bottom wall forming the bottom surface of the blade of said fin, said bottom wall being spaced from said top wall, at least portions of said bottom wall extending to said foot pocket wall means, said top and bottom walls cooperating with said side ribs and with said intermediate rib means in defining a plurality of water passages, each of said water passages terminating at its inner end in a water-scoop opening which is defined in part by one of said inner edges of said top wall,

each of said water passages terminating at its outer end in a jet-exhaust orifice which is defined at the tip of said blade between the extreme outer edges of said top and bottom walls, said orifice being directed away from said foot pocket wall means.

10. The invention as claimed in claim 9, in which said top and bottom walls converge toward each other in a direction away from said foot pocket wall means, whereby to effect progressive acceleration of water passed therethrough from said water-scoop opening to said jet-exhaust orifice.

11. The invention as claimed in claim 10, in which said first and second side ribs, and said intermediate rib means, taper convergently and progressively in a direction away from said foot pocket wall means.

12. The invention as claimed in claim 10, in which the portion of said bottom wall which is closer to said foot pocket wall means than are said inner edges of said top wall is curved in a concave manner to deflect water around a corner from said water-scoop openings to said jet-exhaust orifices.

13. The invention as claimed in claim 9, in which foot pocket wall means, said side ribs, said rib means, and said top and bottom walls are formed integrally of a single mass of elastomeric material.

14. The invention as claimed in claim 9, in which said first and second ribs and said intermediate rib means include portions which extend, respectively, above and below said top and bottom walls, such extension portions serving to direct water along the exterior surfaces of said top and bottom walls.

15. The invention as claimed in claim 9, in which said intermediate rib means comprises two parallel ribs spaced from each other.

16. The invention as claimed in claim 9, in which the crosssectional shape of each of said water passages is rectangular.

17. The invention as claimed in claim 16, in which said cross-sectional shape, at blade regions remote from said foot pocket wall means, is wide in the dimension between said ribs and thin in the dimension between said top and bottom walls.

Disclaimer 3,649,979.D0uglas K. MapNeil, Costa Mesa, Calif. SWIM FIN. Patent dated Mar. 21, 1972. Dlsclaimer filed Oct. 11, 1974, by the assignee, US.

Divers 0o. Hereby enters this disclaimer to claims 1, 3, 4, 7 8, 9, 13, 16 and 17 of said patent.

[Ojfioz'al Gazette November 26, 1974.]

Claims

1. A swim fin, which comprises: wall means to define a foot pocket, first and second side ribs extending forwardly from said foot pocket wall means, at least portions of said side ribs diverging relative to each other in a direction away from said foot pocket wall means, and wall means extending between said side ribs and forming the blade of the swim fin, at least part of said blade wall means being a top wall, said top wall terminating, at the inner end portion thereof relatively adjacent said foot pocket wall means, at an inner edge which is spaced from said foot pocket wall means, said top wall terminating, at the outer end portion thereof remote from said foot pocket wall means, in a region which is adjacent the tip of said blade, at least part of said blade wall means being a bottom wall which is spaced from said top wall, said bottom wall terminating, at the outer end portion thereof remote from said foot pocket wall means, in a region which is adjacent the tip of said blade, said top and bottom walls cooperating with each other in defining at least one water passage, said water passage terminating at its inner end in a waterscoop opening which is defined in part by said inner edge of said top wall, said water passage terminating at its outer end in a jetexhaust orifice which is defined between said outer end portions of said top and bottom walls, said orifice being directed away from said foot pocket walls means.

2. A swim fin, which comprises: a blade adapted to be employed in propelling a swimmer through the water, means provided at one end of said blade to mount the same to the foot of a swimmer, water-scoop means provided on the top of said blade and directed to receive water in response to downward movement of the foot of said swimmer when said swimmer is in a face-down position, said water-scoop means being disposed relatively adjacent said mounting means, jet-exhaust means provided at the other end of said blade remote from said mounting means, said jet-exhaust means being directed to discharge wateR in a direction away from said mounting means, said jet-exhaust means comprising orifice means disposed at the extreme tip of said other end of said blade, said tip being the portion of said blade most remote from said mounting means, and passage means to conduct water from said water-scoop means to said jet-exhaust means for discharge through the latter, said passage means comprising at least one nozzle passage through said blade, the walls of said nozzle passage being shaped to effect acceleration of water passing from said water-scoop means to said jet-exhaust means, said shaping being such that said nozzle passage has a cross-sectional area which decreases progressively in a direction toward said jet-exhaust means, and throughout substantially the entire distance from said water-scoop means to said jet-exhaust means.

3. A swim fin, which comprises: a blade adapted to be employed in propelling a swimmer through the water, means provided at one end of said blade to mount the same to the foot of a swimmer, water-scoop means provided on the top of said blade and directed to receive water in response to downward movement of the foot of said swimmer when said swimmer is in a face-down position, said water-scoop means being disposed relatively adjacent said mounting means, jet-exhaust means provided at the other end of said blade remote from said mounting means, said jet-exhaust means being directed to discharge water in a direction away from said mounting means, and passage means to conduct water from said water-scoop means to said jet-exhaust means for discharge through the latter, said passage means being defined in part by upper and lower walls which extend from said water-scoop means to said other end of said blade and substantially separate the water flowing through said passage means from the water passing along the exterior of said blade.

6. The invention as claimed in claim 5, in which said nozzle passage has a cross-sectional area which decreases progressively in a direction toward said jet-exhaust means, and throughout substantially the entire distance from said water-scoop means to said jet-exhaust means.

9. A swim fin, which comprises: wall means to define a foot pocket, first and second side ribs extending forwardly from said foot pocket wall means, at least portions of said side ribs diverging relative to each other in a direction away from said foot pocket wall means, intermediate rib means located between said first and second side ribs and extending forwardly from said foot pocket wall means, a top wall connected to said side ribs and to said intermediate rib means, said top wall extending to the tip of said blade, said top wall forming the top surface of the blade of said fin, said top wall terminating, at the inner portion thereof relatively adjacent said foot pocket wall means, in inner edges which are spaced forwardly from said foot pocket wall means, and a bottom wall connected to said side ribs and to said intermedIate rib means, said bottom wall extending to the tip of said blade, said bottom wall forming the bottom surface of the blade of said fin, said bottom wall being spaced from said top wall, at least portions of said bottom wall extending to said foot pocket wall means, said top and bottom walls cooperating with said side ribs and with said intermediate rib means in defining a plurality of water passages, each of said water passages terminating at its inner end in a water-scoop opening which is defined in part by one of said inner edges of said top wall, each of said water passages terminating at its outer end in a jet-exhaust orifice which is defined at the tip of said blade between the extreme outer edges of said top and bottom walls, said orifice being directed away from said foot pocket wall means.

16. The invention as claimed in claim 9, in which the cross-sectional shape of each of said water passages is rectangular.