U.S. patent application number 13/740260 was filed with the patent office on 2014-07-17 for swim devices.
The applicant listed for this patent is George Dan Suciu. Invention is credited to George Dan Suciu.
Application Number | 20140199902 13/740260 |
Document ID | / |
Family ID | 51165496 |
Filed Date | 2014-07-17 |
United States Patent
Application |
20140199902 |
Kind Code |
A1 |
Suciu; George Dan |
July 17, 2014 |
Swim Devices
Abstract
A swim device comprising elongated foot pockets which surround
each of the feet of the swimmer, continued distally with tapers
ending in neckings connected in a functional manner to blades for
each foot. The neckings of the tapers of both feet may be connected
to one blade (monofin). A swim device comprising a cowling of
generally elongated shape which surrounds both feet of the swimmer,
continued distally with a taper, ending in a necking to which one
blade (monofin) is connected in a functional manner. The tapers and
the hydrodynamic cross-sections of the foot pockets and of the
cowling, result in stronger thrust and lower drag than in the
designs of prior art.
Inventors: |
Suciu; George Dan; (Edmonds,
WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Suciu; George Dan |
Edmonds |
WA |
US |
|
|
Family ID: |
51165496 |
Appl. No.: |
13/740260 |
Filed: |
January 14, 2013 |
Current U.S.
Class: |
441/64 |
Current CPC
Class: |
A63B 2031/115 20130101;
A63B 31/11 20130101 |
Class at
Publication: |
441/64 |
International
Class: |
A63B 31/11 20060101
A63B031/11 |
Claims
1. A swim device worn on the feet of a swimmer, for producing
thrust by a flapping motion of the feet, comprising: (a) a foot
pocket of elongated shape and hydrodynamic cross-section,
surrounding each foot of the swimmer, (b) a taper of the distal end
section of said foot pocket, extending distally beyond the sole of
the feet of the swimmer and ending as a necking of substantially
smaller width than the maximum width, of said foot pocket, normal
to the plane of the flapping movement, (c) a blade of predetermined
size, shape and profile, connected to said taper in a functional
relationship, whereby during each half-stroke of the flapping feet,
water from the higher dynamic pressure area, in front and upstream
of the foot pocket is made to move across the necking of the taper,
into the area of lower dynamic pressure, behind the flapping blade,
thereby a more efficient conversion of the power expended by the
swimmer into thrust is achieved and less power is wasted as drag,
than in absence of these components.
2. The swim device of claim 1, wherein said foot pocket has
transversal cross-sections of hydrodynamic shape, such as an
ellipse, with the long axis parallel to the plane of the flapping
movement.
3. The swim device of claim 1, wherein a frontal cross-section of
said taper in said distal end section of said foot pocket encloses
an angle of less than 90 degrees, preferably between 35 and 50
degrees.
4. The swim device of claim 1, wherein said necking of said taper
has a transversal cross-section the width of which is not more than
25%, preferably not more than 15% of the largest width of the foot
pocket in a direction normal to the plane of the flapping
movement.
5. The swim device of claim 1, wherein each said foot pocket on the
two feet of the swimmer is connected by the respective said necking
to one blade, in a functional relationship.
6. A swim device, comprising: (a) a cowling of generally prolate
shape, surrounding both feet of the user, (b) a taper of the distal
end of said cowling, extending distally beyond the soles of the
swimmer and ending as a necking of substantially smaller width than
the maximum width of the cowling, in a direction normal to the
plane of the flapping movement, (c) a blade of predetermined size,
shape and profile, connected to said taper in a functional
relationship, whereby during each half-stroke of the flapping feet,
water from the area of higher dynamic pressure, in front and
upstream of the cowling is made to move across the necking of the
taper, into the area of lower dynamic pressure, behind the flapping
blade, thereby a more efficient conversion of the power expended by
the swimmer into thrust is achieved and less power is wasted as
drag, than in absence of these components.
7. The swim device of claim 6, wherein said cowling extends
proximally a certain length above the ankles of said swimmer,
whereby a further reduction of the drag encountered by the flapping
feet is achieved.
8. The swim device of claim 6, wherein a frontal cross-section of
said taper in said distal end section of said cowling encloses an
angle of less than 90 degrees, most preferably between 35-50
degrees.
9. The swim fin of claim 6, wherein said necking of said taper of
said cowling has a transversal cross-section the width of which is
not more than 25%, preferably not more than 15% of the largest
width of said cowling, in a direction normal to the plane of the
flapping movement.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] This invention refers to devices which increase the swimming
speed when attached to the feet or legs, flapping in tandem (fins)
or in unison (monofins), of swimmers.
[0003] 2. Prior Art
[0004] Swim devices, whether fins or monofins, are fastened to the
feet of the swimmer, who imposes on them an oscillating motion
(flapping), usually in the sagittal plane. In general terms, the
swim device consists of a "blade" which is fastened to the feet of
the swimmer and may be provided with "pockets", "shoes" or similar
devices which accommodate the feet of the swimmer, to which it is
attached. The blade and the feet are fastened to each-other in a
variety of ways, sometimes in a fixed relationship, other times in
a manner which allows a relative movement or re-orientation. The
strength of the thrust produced is function of the speed and
amplitude of the oscillatory movement of the legs and size, shape
and orientation of the swim device.
[0005] The shapes of most of the blades vary between two extremes.
On one side, the shape of the blade is modeled after the flukes of
cetaceans, mainly dolphins, in terms of shape, size, cross section,
elasticity. A few typical devices, out of the numerous patents
belonging to this class are: U.S. Pat. No. 5,429,536 (Evans), U.S.
Pat. No. 6,086,440 (Fechtner), U.S. Pat. No. 6,183,327 (Meyer),
U.S. Pat. No. 7,510,453 (Nguyen). One of the advanced designs of
this group of swim devices is the Lunocet [Adventure, September
2008, p. 21]. The design was based on detailed measurements of the
shape, profile, texture, of the cetacean flukes as well as of
advanced methods of mathematical modeling. The result is a swim
monofin having a span of approx. 1 m, provided with the means to be
fastened to the feet of the swimmer. The legs of the swimmer are
close and parallel to each-other. Swimmers using the Lunocet claim
that they can achieve a speed by 50% higher than when using regular
(one on each foot) fins. On the other extreme, the blade is shaped
as a hydrofoil, with a more or less straight (un-swept) leading
edge, incorporating the features which will confer to it high lift
and low drag. The blade has hydrodynamic cross section (hydrofoil)
and high aspect ratio, such as in U.S. Pat. No. 4,781,637 (Caires),
U.S. Pat. No. 6,881,113 (2005) to Smith, U.S. Pat. No. 7,988,508
(2011) to Langenfeld et al. Such monofins are attached to the feet
of the swimmer, by means of a pair of shoes, foot pockets, provided
with straps, buckles or similar devices. Hundreds of patents for
fins and monofins have been issued over the years, by the US Patent
Office. Only a few typical patents which are somewhat relevant to
the present invention, will be reviewed.
[0006] U.S. Pat. No. 4,689,029 (1987), U.S. Pat. No. 4,767,368
(1988), U.S. Pat. No. 4,869,696 (1989), all to Ciccotelli, refer to
swim fins which basically consist of a foot pocket to which a rigid
blade is pivotally attached by means of beams, such that a free
space is provided between the foot pocket and the blade.
[0007] The exterior of the foot pocket has basically a rectangular
plane form. The slim beams connecting the foot pocket to the blade
will reduce somewhat the resistance to movement through the water.
Still, the shape of the foot pocket will produce a high drag.
[0008] U.S. Pat. No. 3,665,535 (1972) and U.S. Pat. No. 4,934,971
(1990) both to Picken, refer to swim fins in which a web, acting as
the blade is attached to the shoe assembly by means of a rigid
supporting frame, provided with means for limiting the amplitude of
the pivotal movement of the web.
[0009] The design addresses only the shape pf the blade. No
attention is given to the drag and power loss caused by the shape
of the shoe assembly.
[0010] In U.S. Pat. No. 5,421,758 (1995) to Watson and Sigler, a
scuba fin is described which consists of a foot pocket and a fin
section, connected by a shaft of minimal thickness, so that it
encounters a minimal resistance when moving through water. The
cross-section of the shaft is rhombic in shape, with straight or
rounded sides. However, no attempt is made to reduce the drag
encountered by the foot pocket when moving through water. Also, the
blade of the fin is tilted relative to the bottom surface of the
foot plate, by an angle of less than 45 degrees, which is claimed
to be beneficial for walking with the fins on.
[0011] The imposing of such an angle is not conducive to good
swimming power efficiency. Although the shaft is intended to reduce
drag, no other component of the swim fin is suitable to this
objective. The drag generated due to the not hydrodynamic shapes of
the foot pocket and of the swimmer's foot will result in wasting a
significant fraction of the energy spent for flapping.
[0012] U.S. Pat. No. 5,460,557 (1995) to Arnold, has a fin blade
positioned so that it "always has a positive angle of attack" which
is connected by means of two struts having a flattened profile, to
the shoe on the foot of the swimmer and to a cuff placed above and
including the ankle. The blade may oscillate so that it is always
positioned in the "undertow" of the flapping foot. The shoe has a
"form of low flow resistance" in order to improve the "flow
conditions" around the swimmer's foot. This is important "because
the profile is in the undertow of the foot". A second profile, may
be placed downstream of the first profile, to which it is
"elastically" connected.
[0013] The approach taken in this patent for reducing the drag
encountered during flapping is to allow the blade to swing between
two extreme positions, at the beginning of the up- or
down-movements of the feet. The presence of the lateral struts will
disturb the flow up-stream of the blade and lower the power
efficiency of the device. Significant drag will result due to the
position, of the feet which interferes with the water flow produced
by the fin.
[0014] In U.S. Pat. No. 5,906,525 (1999) to Melius et al.,
describes a swim fin of modular constructions, inspired after
aquatic mammals or fishes, consisting of a "heel", a "boot" and a
"wing-like" blade, mimicking the head, body and tail respectively,
of a fish. The boot and the blade are connected to each-other by a
"flexible caudal shaft" and extend in the plane of the swimmer's
foot sole beyond the toes. The device is claimed to produce
propulsion by using only "power strokes" which generate "lift" and
produce a deformation of the blade and shaft, while releasing
vortices from the tips of the fin. The "recoil" to the original
shape is claimed to provide additional thrust.
[0015] The swim fin mimics the contour of a flattened the body of a
fish, the axis of which forms a large angle with the sheens of the
swimmer. This will reduce the efficiency of thrust generation.
[0016] In U.S. Pat. No. 6,183,327 (2001) to Meyer, the swim fin is
made of an "attachment portion" "removably secured" to a swimmer's
foot and consists of a two symmetrical halves, which basically
define the blade, shaped like a dolphin fluke, which has its
leading edge right at the tip of the swimmer's toes. In this design
no attempt is made to reduce the drag produced by the foot
attachment portion of the fin. In U.S. Pat. No. 6,375,531 (2002) to
Melius, a "flat blade" attached with its narrow end to the foot of
the swimmer is continued, with a "dolphin tail" connected at the
center of the wider end of the flat blade. When a "proper angle of
attack" is achieved, the water displaced by the flat blade is
claimed to be interacting with the dolphin-tail, to produce lift
and additional thrust. The subject device is claimed to efficiently
generate thrust by moving water, by means of a tail shaped after
the flukes of dolphins. Only a small amount of the water moved by
the flat blade will follow the shown paths needed for generating
thrust. Most of the moved water will not produce thrust, but will
generate eddies and drag. According to the same patent, blades
mimicking the shape of dolphin tails may be attached to the hands
of the swimmer and used for increasing the propulsion through
water.
[0017] U.S. Pat. No. 6,893,307 (2005) to Melius, covers an
"ergonomic swim fin apparatus" consisting of a foot-pocket,
provided laterally with two "channeling scoops" and a "flexible
blade" which runs beyond the toes, parallel with the swimmer's
sole, to a trailing edge' to which a wing shaped tail fin is
secured. The channeling scoops are claimed to preferentially direct
water over the blade and tail fin, thus enhancing lift and
thrust.
[0018] This is a modification of U.S. Pat. No. 6,375,531. The area
of the foot-pocket is extended on both sides of each foot by means
of "scoops" intended to increase the amount of thrust-producing
water displaced during flapping. Actually, the increase of the area
of the foot pocket (transverse to the direction of the flapping
movement) will increase the power consumed by the swimmer, more
than the amount of thrust produced. If an improvement is seen in
the swimming speed, it is gained on the expense of
disproportionately large increase of power expenditure.
[0019] A similar approach is taken in U.S. Pat. No. 7,614,928
(2009) to Grivna, which installs to both sides of each foot pocket
two "lateral fins" for increasing the volume of the water moved by
the flapping feet. The extra amount of water moved by the lateral
fins will be ejected in directions which are not favorable for
producing useful thrust, but a substantial drag increase will
result.
[0020] U.S. Pat. No. 7,040,942 (2006) to Houck, describes a fin
consisting of a sleeve which surrounds the lower leg (or the arm)
of the swimmer, to which two fins are attached. The fins are
extended laterally and form surfaces parallel to the legs and
normal to the plane in which the flapping is performed. The fins as
described will displace more water than the flapping legs alone.
Being tied to the shins of the swimmer, only a small fraction of
the water displaced will be pushed in the direction parallel to the
axis of the body, and generate thrust. Their efficiency is
diminished by the feet which "stick out" from between the fins and
will disturb the direction of propelling streams.
[0021] In U.S. Pat. No. 7,083,485 (2006) to Melius, the swim fin is
a blade shaped as a flat projection of a fish, (including pectoral
fins, caudal fins and tail), on top of which the foot pocket is
attached. The distal portion of the swim fin has the shape of a
fish tail, claimed to produce lift/thrust, which propels the
swimmer forward.
[0022] This is a further expansion of the U.S. Pat. Nos. 6,375,531
and 6,893,307. The soles of both feet of the swimmer's are attached
to the flat blade. The sheens stick out of the plane of the blade
at a large angle. The drag produced by the planar blade and the
poor hydrodynamic profile of the foot pocket represent an important
power waste. Also, a large fraction of the produced thrust will not
be parallel to the axis of the swimmer's body and thus will not
contribute to the movement in the desired direction. Several US
patents, such as U.S. Pat. No. 6,146,224 (2000) to McCarthy, U.S.
Pat. No. 6,379,203 (2002) to Kuo. U.S. Pat. No. 7,115,011 (2006) to
Chen, U.S. Pat. No. 7,753,749 (2010) to Mun, describe fin blades
which are provided with a variety of openings, through which the
water can flow from one side to the other side of the blade. While
the formation of such water streams is claimed to reduce the drag,
it for sure reduces the efficiency of the conversion into thrust of
the power used by the swimmer. Indeed, a portion of the water which
was moved by the blade moves from the high-pressure side of the
blade to the low-pressure side without producing thrust.
[0023] One of the advanced designs in the class of monofins is the
PowerSwim device, developed by DEKA [Popular Mechanics, November
2007, p. 22], U.S. Pat. No. 7,988,508 (2011) to Langenfeld et al.,
which is based on the early concept of U.S. Pat. No. 3,122,759
(Gongwer). This device consists of two hydrofoils. One of them has
a high aspect ratio (approx. 10), with a span of 1.80 m, which
oscillates at about the midriff, in the front of the swimmer. The
blade is connected to a lever which is fastened between the ankles
and the knees of the swimmer. The second hydrofoil, of a smaller
aspect ratio and span is fastened to, and oscillates right above
the ankles of the swimmer. It is claimed that a swimmer using the
PowerSwim device can achieve 150% higher velocity than with regular
fins.
[0024] The device of U.S. Pat. No. 6,881,113 (2005) to Smith uses
as blade a rigid hydrofoil, connected to the feet of the swimmer in
a flexible manner. While the movement of the blade relative to the
foot pockets is controlled, no effort is made to control the
direction of the water streams produced by the flapping movement,
around the "support structure" the feet or the rigid blade in order
to increase the thrust or reduce the drag.
[0025] The main deficiencies of the fins of the prior art may be
summarized as follows. [0026] In order to increase the amount of
water pushed by the fin, the surface of the fin including the foot
pocket is expanded either laterally or axially. In both cases the
gain in thrust is accompanied by an even greater increase of the
drag and of the power which is consumed for flapping the fins.
[0027] In order to reduce the drag, a variety of gaps, holes,
windows are practice in the blade. Some of the water pushed by the
blade will escape through these holes thereby reducing the drag. In
the same time the power efficiency of the flapping is diminished
since less water will form the propelling jets which push the
swimmer forward. These opposed approaches indicate a lack of
understanding of the flow pattern needed for producing thrust by
the flapping feet and fins and of the methods to be used for
reducing drag. [0028] The blade of the fin is usually parallel to
the sole of the foot. This results in difficulties in pushing the
water displaced by the fins in direction along the general axis of
the swimmer's body, and thus in reduced power efficiency. Several
of the fins of the prior art are designed so as to be easily worn
when walking. The angle between the blade and the foot sole causes
the water to be pushed by the blade in directions not suitable for
producing thrust. [0029] Much of the water moved by the fins and
monofins of prior art forms streams which are not directed
backwards and do not produce thrust. Also, the shape and
orientation of the foot pockets leads to significant drag which
consumes much of the power spent by the swimmer.
Power Efficiency.
[0030] In order to generate propulsion which results in velocity,
human swimmers as well as fishes or aquatic mammals need to spend
power (energy per unit time). For the present discussion only the
power consumed by the swimmer for moving the legs will be
considered.
[0031] Cetaceans and fishes of the tuna or marlin families produce
propulsion by the oscillating movement of the rear 1/3rd part of
the body (carangiform and thunniform movement), while the front
part of the body does not oscillate practically at all. Human
swimmers can use the same swimming style. However, the movement of
the body of human swimmers using swim fins and practicing the
"dolphin kick" style is closer to the "anguiliform", where the
propulsion is produced by a wave-like movement of the body. The
body bends in a progressive manner as if a wave passes through it,
from the head to the end of the toes (and the end of the swim fin).
In the animal realm, the anguiliform style is less efficient and
results in lower velocities than the carangiform or thunniform
movement.
[0032] The mechanism by which flapping tails or fins generate
propulsion is as follows: at each up- or down-stroke, or half cycle
of the flapping of the tail or fin (by a cetacean or by a human
swimming face down or on the back), a certain amount of water is
pushed backwards and as reaction to it, the body of the swimmer is
propelled forwards. The water is pushed as a backwards-directed
stream (jet). The force (thrust) by which the swimmer is propelled
forward at each stroke of the fin depends on the size, shape and
orientation of the blade during the stroke, the amplitude and
frequency of the flapping movement and on the flow conditions
(water streams) produced as result of the flapping movement in the
space close to the fin and to the body of the swimmer.
[0033] Despite the ability to closely copy the shape, size,
elasticity, texture and movement of the flukes of cetaceans
[References: Bose, N. et al. Proc. R. Soc. London B 242 (No. 1305)
pp 163-173(1999), Fish, F. E. et al., Bioinsp. Biomim. 1 (2006) pp
42-48] and of tails of fast swimming fishes, the swimming
performance of the man-made swim fins is not matching that of the
model animals. The efficiency of converting the power consumed by
the swimmer into propulsion is much lower for humans than for the
aquatic animals used as models for designing the swim fins. For the
same power consumed, a human swimmer will generate less propulsion
than a dolphin of the same weight and height.
[0034] The power consumed or used by the animal or human swimmer
can be perceived as consisting of several components:
Pt (total power consumed by swimmer)=Pp (power used for generating
thrust)+Pd (power used for overcoming the body drag)+Pw (power
wasted during the flapping of the legs and swim fin).
[0035] For a given swimmer and conditions, Pt is given. In order to
maximize Pp, one needs to minimize Pd and Pw. Only small reduction
of Pd has been achieved by using body suits, such as Spandex. The
swim devices covered here address the reduction of Pw.
[0036] The power wasted Pw, can be seen as having two
components:
Pw=Ppf (power wasted by producing parasitic, i.e. non-thrust
producing water streams)+Pdf (power wasted to overcome the drag of
the flapping feet)
[0037] The designs of the swimming devices of prior art have no
methods for reducing the parasitic (called here also "shunt"
streams or currents) streams, which do not produce thrust, or for
reducing the power wasted as drag, during the flapping of the
legs.
DESCRIPTION OF THE FIGURES
[0038] FIG. 1. Shows in a simplified manner the main water flows
produced by a moving plate and the parasitic (shunt) currents for
conditions not according to this patent.
[0039] FIG. 2a, 2b, 2c, show the main outlines and movements of a
blade connected to the end of a flapping rod (2a), cylinder (2b)
and cone (2c).
[0040] FIG. 3a, 3b. Show the water streams set in motion by a swim
fin of this invention, shown as a ghost side view in two positions
of a flapping foot and a ghost plan view of a foot wearing a swim
fin.
[0041] FIG. 4 is a ghost plan view of the monofin of this
invention, with feet held parallel in individual foot pockets, the
narrow (necking) distal end of which is fastened to a common blade
(monofin).
[0042] FIG. 5 shows a ghost plan and a side view of a monofin of
this invention, (crossed feet), for achieving a reduced frontal
area of the cowling, and a lower drag.
[0043] FIG. 6 shows a ghost plan and a side view of a monofin of
this invention, (parallel feet). Letters M, N, P and R refer to
transverse cross-sections through the cowling, at the levels
indicated.
THE POWER WASTED DURING THE FLAPPING OF SWIM DEVICES
[0044] There are two main ways in which a portion of the power
expended by the swimmer for moving the flapping legs/fins is wasted
(Pw).
A. Power Wasted as Parasitic Streams (Ppf).
[0045] An important fraction of the expended power is wasted by the
blade setting in motion a mass of water which will not be part of
the thrust-producing jet (Ppf), as discussed below.
[0046] Here, the convention is made to call "in front" or "ahead" a
position facing, or streams flowing in the same sense as the
instantaneous movement of the fin, or adjacent to the "front" side
of the fin. Positions or streams flowing in the opposite sense of
the instantaneous movement of the fin are called "behind", as they
are adjacent to the "back" side of the fin. The front and back of
the fin switch at every up- and down-stroke of the fin.
[0047] For a swimmer in "ventral" position, the flapping action is
divided into a "dorsal" or "up-stroke" and a "ventral" or
"down-stroke".
[0048] During both the up- and down-movements of the swim fin, a
zone of transient, high dynamic pressure (caused by the movement of
the fin) forms in front of the fin. Simultaneously, a zone of
lowered dynamic pressure is produced behind the fin. The push
exerted by the fin produces powerful stream of water
(propulsion-generating or propelling jet) directed backwards, away
from the body, along a path which is generally parallel to the axis
of the swimmer's body. The size and direction of these water jets
is controlled by the pattern in which the blade moves (flapping
amplitude, orientation) and by the size and design (shape, profile)
of the blade. Propulsion of the swimmer's body results as reaction
to these propelling jets of water.
[0049] Not all the water corresponding to the volume swept by the
fin during a half stroke will be part of the propelling jets.
Observations show that portions of the water mass pushed by the
dorsal or ventral sides of the swim fin (during the dorsal or
ventral movement, respectively) separate from the direction of the
main streams and turn around the borders of the swim fin to flow
"backwards", into the space which during that half of the flapping
cycle is "behind" (i.e. ventral or dorsal respectively) the moving
fin. These streams do not produce propulsion. Thus, the power which
was spent for accelerating the corresponding water mass is
wasted.
[0050] The shunt streams flow from the high pressure zone produced
ahead of the plate, during its movement, around the borders of the
plate, into the low-pressure zone generated behind the plate. FIG.
1 depicts the zones of transient dynamic high pressure and the
flows generated by a flapping plate, simulating a fin not of this
patent, submerged in water. A flapping plate 1 with a central axis
4 is connected to a lever 2, having an axis line 5, by means of a
hinge 3 which allows for a limited rotation of plate 1, to maximum
angles S and S' respectively, on both sides of the position in
which the axis 4 of plate 1 is parallel to the axis 5 of lever 2.
The flapping movement is caused by lever 2 pivoting around a pivot
point P to positions corresponding to angles V and V', on opposing
sides of a neutral position indicated by a line N. For reasons of
simplicity, only the "down" stroke of the flapping cycle is shown,
as indicated by an arrow 6. The "up" stroke (shown in dotted lines)
is symmetrical with respect to the neutral axis N.
[0051] In the drawing, lever 2 is at the maximum amplitude
(measured by angle V), during the oscillating (flapping) movement
about the neutral position N. As it moves downwards, plate 1 exerts
in front of it (in the direction of the movement), a push on the
water, manifested as a dynamic pressure increase in the zone marked
"in front", which forms a jet, moving as indicated by the arrows 8.
As result of the movement of plate 1, a zone of lowered pressure is
formed on the opposite side of the blade, in the zone marked
"behind". In order to balance the pressure difference between the
two sides of plate 1, a portion of jet 8 will leave the
high-pressure zone, will turn around the borders of plate 1 and
will enter the low-pressure zone, as parasitic, or shunt streams 9.
The water contained in shunt streams 9 is subtracted from the water
which was initially part of jet 8 and thus, reduces the size of the
propelling jet. As result, the power consumed by the swimmer for
accelerating the water ending as shunt streams 9 is wasted.
[0052] In none of the swim devices of the prior art are there
attempts made to reduce the amount of wasted power, by reducing the
streams which flow from the front to the back of the flapping blade
and diminish (shunt) the flow of water which generates
propulsion.
B. Power Wasted as Drag (Pdf).
[0053] A significant portion of the power consumed by the swimmer
is lost for overcoming the drag associated to the flapping of the
legs. In order to advance, a human swimmer will flap the feet/legs
in the sagittal plane of the body, dorsally and ventrally (if the
body is in prone position, this will correspond to up and down).
Hydrodynamic studies have shown that cylinders (and by analogy, the
sheens and legs of the swimmer) moving in water produce significant
drag if the direction of the movement is normal to the axes of the
cylinders (cross-flow). (Reference: S. F. Hoerner, "Fluid Dynamic
Drag" 1965. Library of Congress No. 64, 1966). The drag is
proportional to the "frontal area" and to the square of the
velocity of the water in cross-flow over the cylinders. The frontal
area is defined as the largest cross-section of the submerged body,
normal to the direction of the water flow. The drag is also
strongly dependent on the shape of the submerged body. A body with
a hydrodynamic cross section e.g. elliptical, with the long axis
parallel to the direction of flow, and the short axis perpendicular
to it, with the ratio of the long axis A to the short axis B of
A/B=2 will experience only approx. 70% and for A/B=4, only 50% of
the drag of a circular cylinder with the diameter equal to the axis
B of the ellipsoid.
[0054] None of the swim fin designs of prior art, addresses in
specific manner the reduction of the drag generated by the flapping
movement of the legs of the swimmer, by giving a hydrodynamic shape
to the foot pocket. On the contrary, many of the fins of the prior
art increase the frontal area of the foot pocket in the attempt to
increase the volume of the water pumped at each stroke. This
results in a moderate increase of the thrust but in a much higher
increase of the drag.
EXPERIMENTS
[0055] The existence of an interaction between the blade and the
flapping feet/legs of the swimmer was investigated by means of
simplified models. A blade mimicking a dolphin fluke was built at a
reduced scale of 1/10 and was attached by means of a hinge to an
elongated body, simulating the feet/legs of a swimmer which was
oscillated to an angle "V" of about 35 degrees up and down, around
a pivoting axis "PA", perpendicular to the longitudinal axis "LA"
of the elongated body. (FIG. 2a,b,c). The hinge allowed the blade
to deviate to an angle "S" of about 35 degrees, on both sides of
the neutral position defined by the axis of the elongated body.
Three shapes were tested for the elongated body: a thin rod (FIG.
2a), a circular cylinder (FIG. 2.b) and a cone with an apex angle
"A" of 35 degrees (FIG. 2.c). The diameter of the cylinder and the
maximum diameter of the cone were approx. 30% of the wingspan of
the blade. The models were submerged in a container filled with
static water. Each model was separately oscillated manually (so as
to simulate the flapping of the feet/legs of a swimmer) and the
movement of water in the neighborhood of the elongated body and the
blade was observed by following the movements of small neutrally
buoyant particles suspended in water.
[0056] The oscillation of the blade attached to the rod of FIG. 2a
produces water streams (jets) directed away from the blade, more or
less along the median position of the axis of the oscillating rod.
No significant movement was visible along the rod.
[0057] For the case of the blade connected to the cylindrical body
(FIG. 2b), significant turbulence, with erratic currents were seen
along the oscillating cylindrical body, which interacted with the
water displaced by the blade, generating a less structured movement
pattern of the water (weaker jets along the axis of the body).
[0058] The blade connected to the apex of the oscillating conical
body (FIG. 2c) produced the strongest axial jets and significantly
less turbulence around the oscillating body, than when connected to
the cylindrical body. A careful observation indicated that at each
half-stroke, water close to the oscillating conical body moved from
the side "ahead" of the cone (high dynamic pressure), towards the
apex and across the axis of the cone, in the narrowed portion, and
to the side "behind" the blade (low dynamic pressure). The
direction of these "cross-over" streams changed at each
half-stroke, but the water jets leaving the blade along the median
position of the axis of the body were stronger than for either of
the other models. This is an un-expected finding, not mentioned
before in the rich scientific literature on propulsion by
oscillating foils of marine animals, humans or crafts. It led to
two conclusions: [0059] (1) in order to improve the swimming
efficiency one needs to control not only the shape and movement of
the swim device itself, but also the flow pattern, that is, the
water streams around the flapping feet in the zone upstream of the
blade. The flow pattern is improved by shaping the part of the swim
device upstream of the blade, to make possible the rapid filling of
the low-pressure zone formed behind the blade at each half-stroke.
[0060] (2) The foot pocket should be shaped so as to produce the
least possible drag and not to "pump" water, as in most of the
prior art devices.
[0061] A mechanism by which the cross-over currents lead to
increase efficiency of the conversion of the energy expended for
flapping into thrust will be discussed below. (FIG. 3a, b). As it
will be shown, the present invention describes swim devices of a
design, which has no antecedent in the prior art. The design is
based on new insight gained from own above experiments on the water
streams generated by the flapping movement.
OBJECT OF THE INVENTION
[0062] Consequently, this invention addresses swim devices which
are shaped with the objectives of improving the overall efficiency
of converting the power exerted by a swimmer into thrust, by
favoring the formation of producing of currents which will cross
over the long axis of the flapping feet and balance the dynamic
pressure difference between the two sides of the flapping blade,
thereby resulting in less wasted energy by the shunt currents, as
well as in less the drag experienced by the flapping legs and
feet.
DETAILED DESCRIPTION
Preferred Embodiments
[0063] The swim devices of this invention achieve these objectives
and comprise: [0064] A structure of a generally prolate shape
(called foot pocket) which surrounds and is fastened to each foot
of a human swimmer. The proximal end of each of the foot pockets is
provided with an opening through which the foot enters. The distal
portion of the foot pocket is shaped as a taper, with the
transversal cross-section of preferably elliptical shape, having
the long axis parallel to the plane of the flapping movement. The
taper ends distally in a "necking" to which the blade is attached.
The necking has a substantially smaller frontal cross-section than
the rest of the cowling. The cowling has transversal cross-sections
of hydrodynamic shapes and possesses sufficient rigidity, to
maintain its shape during the oscillating movement imposed by the
flapping feet. [0065] Each foot pocket may be attached to one
individual blade. The two swim fins so obtained allow the swimmer
to move the feet separately, in flapping movement. [0066] The foot
pockets for the two feet may be attached to one common blade,
building a monofin. [0067] A structure of a generally prolate shape
hereinafter called "cowling", which surrounds both feet of a human
swimmer. The proximal end of the cowling is provided with an
opening through which the feet and possibly also a portion of the
legs of the swimmer are accommodated. The cowling is attached
distally to a blade, thus forming a monofin. [0068] A taper, at the
end section of the cowling which extends distally along a certain
axial distance along the feet and beyond the soles of the swimmer,
to a "necking" with a substantially smaller frontal cross-section
than the rest of the cowling. The cowling has transversal
cross-sections of [0069] hydrodynamic shapes and possesses
sufficient rigidity, to maintain its shape during the oscillating
movement imposed by the flapping feet. [0070] A blade of
predetermined shape, size and profile, connected to the necking of
the tapered end of the cowling, and capable to oscillate in the
sagittal plane, to predetermined angles, on both sides of a neutral
position, in a manner which generates thrust. The blade may be of
any desired shape, preferably mimicking the fluke of dolphins, the
lunate tail of tuna, marlin, etc., as well as a hydrofoil with
straight or curved leading edge. [0071] A connecting means (such as
a lever or similar device) for assembling in a functional
relationship the blade to the necking in the taper of the foot
pocket or to the cowling and to the feet and legs enclosed therein,
of the swimmer.
[0072] The drawings of FIGS. 3a and 3b show fins of this invention
worn on each foot. The drawings of FIGS. 4, 5 and 6, depict the
monofins of this invention.
[0073] In FIG. 3, a foot pocket 11, surrounds each foot 10.
Distally, foot pocket 11 forms a taper 17, ending in a necking 13,
with a hinge device 16, to which a blade 12 is attached. Inside
foot pocket 11, foot 10 is fastened to a foot plate 14 which is
connected to a lever 15, attached by means of hinge device 16 at
necking 13 to blade 12. The flapping takes place in the sagittal
plane of the swimmer, to angles V and V', of approx. 30-50 degrees
on each side of a neutral position defined by the longitudinal axis
of the swimmer's body. The up-stroke and down-stroke movements of
the fins generate a thrust 19 and cross-over streams 18, as
indicated. The transversal cross-section of foot pocket 11 is of
hydrodynamic shape, as indicated by the letters M, N, P and R, at
the marked position along the length of the foot pocket. The angle
T of taper 17 is of 35-50 degrees, as shown in FIG. 2b.
[0074] A further embodiment of this invention is shown in FIG. 4.
Each foot 20 is surrounded by a foot pocket 21, which is identical
to that described in FIG. 3. Each foot pocket 21 extends beyond the
toes of the swimmer as a taper 23, ending as a narrow necking 24,
provided with a hinge device 27, to which a single blade 22 is
attached, thus resulting in a monofin. Inside each of foot pockets
21, a foot plate 25 is located, to which feet 20 are fastened in a
functional manner. From each foot plate 25, a lever 26 is extended
distally, through neckings 24, and connected to blade 22 by hinge
device 27. In plane view, the angle T of tapers 23 is of 35-50
degrees.
[0075] Another embodiment of this invention is a monofin where both
feet are fastened within a single containment, called cowling,
depicted in FIG. 5. A cowling 31 surrounds the feet 30, possibly
extending to the level of the ankles of the swimmer. In order to
reduce the volume and the frontal area of the cowling, the feet are
placed in overlapped position (crossed). Cowling 31 extends beyond
the toes of the swimmer as a taper 32 which ends as a narrow
necking 34, to which a single blade 33 is attached. A foot plate 35
located within the cowling is connected to a lever 36, which passes
through necking 34 and attaches to blade 33. In plane view, taper
32 encloses an angle T of preferred 35-50 degrees.
[0076] In a variation of this embodiment, the cowling can extend
from the region of the ankles up, to the region of the knees, as
marked by 37. The transversal cross-section of extended cowling 37
has a hydrodynamic, low drag shape.
[0077] A still further embodiment of this invention is a monofin
where both feet are fastened within the cowling, depicted in FIG.
6. Thus, cowling 31 surrounds feet 30, possibly extending to the
ankles of the swimmer. In this configuration, the feet are placed
in parallel position (side by side). Cowling 31 extends distally
beyond the soles of the swimmer as taper 32 which ends as narrow
necking 34, to which single blade 33 is attached. Foot plate 35
located within the cowling is connected to lever 36, which passes
through necking 34 and attaches to blade 33. In plane view, taper
32 encloses an angle T of preferred 35-50 degrees.
[0078] In FIG. 5, transversal cross-sections M, N, P and R depict
the shape of extended cowling 37 at the indicated positions. When
progressing distally, from the rim of the cowling (in the region of
the knees), the shape of the cowling changes from approximately
circular to elliptical. The approximate ratio A/B of the long axis
A (in the sagittal plane), to the short axis B (in the frontal
plane) of the ellipses vary from A/B=1 (corresponding to a circle)
at position M, to A/B=1.3 at position N, A/B=1.5 at position P and
A/B=4.0 at position R.
The Foot Pocket and the Cowling.
[0079] The foot pockets cover individually each foot of the swimmer
up to the region of the ankles and confer to them a hydrodynamic
shape which generates low drag, during the flapping movement. The
foot pockets may be attached each to one blade, as in regular swim
fins, or both to one single blade, resulting in a monofin.
[0080] The cowling covers the joint feet and a predetermined length
of the flapping legs. The cross-section of the cowling is designed
with a hydrodynamic shape, for minimizing the drag encountered
during the flapping movement.
[0081] More or less of the length of the legs may be covered by the
cowling, as illustrated in FIGS. 5 and 6. In one embodiment, the
cowling covers only the feet, and its proximal rim is located in
the region of the ankles. The cowling may extend proximally to
about the region of the knees, as marked by 37, in dotted lines.
The proximal rim of the cowling should not impede the flexing of
the knees, required for the flapping movement. The more of the
length of the legs is covered by the cowling, the smaller will be
the overall drag encountered during flapping.
[0082] In a further embodiment, in order to reduce the frontal
area, of the flapping cowling, the swimmer may assume a posture
with feet crossed. (FIG. 5). In this posture, the coronal
cross-section (frontal area) is smaller than for the posture with
parallel feet (FIG. 6). The drag resulting by flapping a cowling
sized for accommodating the crossed feet of the swimmer, will be
less than by flapping a cowling designed for parallel feet.
[0083] When assuming the crossed feet position, either foot can be
placed above (ventrally) the other one, which is placed below
(dorsally).
[0084] Inside the foot pockets 11 (FIG. 3a) and 25 (FIG. 4) and
inside cowling 31 (FIGS. 5 and 6), means are provided for attaching
the legs to the blades (respectively 12, 21 and 31) in a functional
relationship. One or both feet may be attached to the blade, by
means of a suitable device, such as a foot plate (respectively 14,
25 and 35), and a connecting lever 15, 26 and 36, respectively. In
a preferred arrangement, only one of the feet, namely the one which
is located dorsally is fastened to the foot plate 35 in FIG. 4. In
order to assure a proper division of the power load between the two
legs, in a preferred arrangement, the feet or the legs are
connected to each-other by any convenient means (not shown),
including strips of material (moldable after the shape of the feet,
stretchable or not, etc.) making possible the secure fastening of
the foot pocket or cowling to the legs, without producing unduly
inconvenience to the swimmer.
[0085] The cross-sections M, N, P and R of FIGS. 3b and 6 show the
shape of the walls in the transverse plane at three positions along
the foot pocket and respectively the cowling, for the posture with
crossed feet. At all levels, the frontal area (projection in the
coronal plane) is smaller for the crossed-feet posture than when
the feet are held parallel to each-other.
The Taper.
[0086] As depicted in FIGS. 3b, 4, 5 and 6, the distal section of
the foot pocket and of the cowling (respectively 11, 21, 31, 31),
beyond of the toes of the swimmer, assumes a taper (respectively
17, 23, 32, 32) which is one of the important embodiments of these
swim devices. The taper decreases the frontal area of said foot
pocket and said cowling from that needed to contain the swimmer's
foot (as specifically indicated as sections N and P, in FIGS. 3b
and 6), to a small fraction thereof, corresponding to neckings
(respectively 13, 24, 34, 34, in FIGS. 3a/3b, 4, 5 and 6), and also
shown in cross-section, as section R in FIGS. 3b and 6.
[0087] With reference to FIGS. 3b and 6, the maximum width of the
foot pocket, and of the cowling, in frontal cross-section as shown
at position R should represent 5-15%, preferably not more than 10%
of the width of the cross-section at position N. While a very
narrow necking is desirable, the width at R should be sufficient
for containing lever (positions 15, 26, 36, 36) or any other means
for attaching in a functional manner the blade to the foot pocket
of the swim fin or to the cowling of the monofin and to the feet of
the swimmer.
[0088] As seen in the frontal sections in FIGS. 3b, 4, 5 and 6, the
angle T, enclosed by taper (respectively 17, 23, 32, 32), is less
than 90 degrees, preferably 30-50 degrees, most preferably 35-45
degrees. In the sagittal plane, the value of the angle enclosed by
the taper is less critical. It is determined by the dimensions of
the lever or other means used for connecting the foot pocket and
cowling to the blade. The shape of the transversal cross-section of
cowling 11, 21, 31, 31 is conveniently defined by the ratio of the
major axis to the minor axis, A/B of the ellipse. As exemplified in
FIG. 6, but valid for all drawings of this invention, this ratio
changes from approximately A/B=1.5, as shown in section P, to that
of section R, where the ratio is approximately B/A=4.0. This last
value is known to generate least drag, when placed in a flow
stream, parallel to axis A. (Hoerner, loc. cit.).
The Blade.
[0089] Blades (12, 22, 32, 32 of FIGS. 3a/3b, 4, 5 and 6,
respectively), of several shapes may be used as part of the swim
devices described here. Preferred shapes include blades which mimic
the flukes of cetaceans (FIGS. 3a/3b, 5,6), tails of fast-swimming
fishes, such as tuna (FIG. 4), marlin, sailfish, as well as
hydrofoils with straight or swept leading edges, or any other
shapes, as known in the art. Preferably, these blades are provided
with hydrodynamic chord profiles, in order to generate low drag and
good lift, as known in the art.
[0090] The aspect ratio AR=(L 2)/S (fin span L, squared divided by
the plane area S, of the fin) of the preferred fin is larger than
1. For fins using hydrofoils, the aspect ratio is preferably
AR=2-6. The blade may be rigid or may posses a certain span-wise
and chord-wise flexibility. The materials of which blades may be
made include synthetic rubber silicon rubber (both of which may be
reinforced by adequate spars or spines), polyurethanes, polyesters,
etc. By incorporation in the structure of the blade of reinforcing
ribs it is possible to control the elasticity, resilience and
degree of deformation during flapping, especially for larger AR
values. The materials of the ribs include metals, especially wires
or bars of metal, plastics, battens made of glass-reinforced
plastics, or of carbon fibers-reinforced plastics, which will
confer to the blade the desired elasticity and sturdiness etc.
[0091] Swim fins or monofins of this invention provide excellent
propulsion for blade spans of 0.3-0.5 m, which is in the same range
as the fluke spans of cetaceans with body weights and body-lengths
similar to those of human swimmers. [References: Bose, N. et al.
Proc. R. Soc. London B 242 (No. 1305) pp 163-173(1999), Fish, F. E.
et al., Bioinsp. Biomim. 1 (2006) pp 42-48],
Connecting the Parts.
[0092] With reference to FIGS. 3a/3b, 4, 5 and 6, the blade is
attached to the feet of the swimmer and to the foot pocket or the
cowling by means of a footplate 15, 25, 35, 35, respectively to
which the feet 10, 20, 30 and 30, respectively are fastened, and
one end of a lever 15, 26, 36, 36, respectively which, in its
simplest form is a bar. The other end of the lever is preferably
attached to the area of the center of the leading edge of the
blade. Possibility may be incorporated to adjust the angle between
lever and foot plate, to accommodate individual conformations of
the feet of the swimmer. The lever may posses a certain degree of
elasticity for bending, but should be quite un-yielding to torsion
or rotation around its axis.
[0093] The blade may be attached to the lever by a hinge means
which may be a rigid or elastic connection, as known in the art.
Spiral springs, torsion bars or slit pipe springs may be used to
this effect, as well as rubber or plastic parts which possess the
desired properties. The blade follows the flapping movement of the
foot pocket or cowling and, as reaction to the dynamic pressure it
exerts on the water, bends or pivots around said hinge means or in
its absence, around a pivot point in the necking, to limiting
angles schematically depicted in FIG. 1 as S and S', about its
neutral position N. The flapping movement of the foot pocket and of
the cowling and the bending of the blade, take place in the
dorso-ventral (sagittal) plane. The degree of bending allowed by
the blade-lever connection depends on the type of blade used. For
blades mimicking the flukes of cetaceans, the plane of the blade
may swing both sides of the neutral position to a maximum angle of
45-50 degrees, although angles of 25-45 degrees seem to confer
efficient propulsion.
[0094] For blades mimicking the tail of tuna (FIG. 3a/3b, 4) or for
hydrofoils of large aspect ratio, the connection between the blade
and the lever may be suitably rigid. The dynamic pressure generated
by the flapping movement, will cause a certain degree of span-wise
and chord-wise bending and twisting of the blade itself, which will
lead to efficient propelling action.
[0095] Other methods for connecting the blade to the feet of the
swimmer, can be practiced so as to fit specific material or design
peculiarities. For example, by building the foot pocket and the
cowling including the taper suitably sturdy, it is possible to
connect the blade directly to the necking at the distal end of the
taper of the foot pocket or cowling, to which the swimmer's feet
are attached. This is a suitable procedure for achieving a
functional connection between the feet of the swimmer and the blade
of the swim devices covered here.
The Fastening Devices.
[0096] The swim fin or the monofin are preferably built in a manner
which allows them to be rapidly attached to the feet/legs of the
swimmer, and rapidly disconnected from them. According to a
preferred construction, the foot pocket or the cowling consist of
two or more parts, which can be attached to each-other along
corresponding matching sides. In a more preferred construction, the
foot pocket and the cowling are made of two parts which have
matching sides along the legs of the swimmer, in the coronal plane.
The foot pocket or the cowling are thus divided into a dorsal and a
ventral part. Both parts may accommodate devices to attach the
parts to each other, as well as to the feet or legs of the swimmer,
and to the footplate, lever and blade itself. Said devices, will
allow for a rapid assembly and a rapid attachment and fastening of
the foot pocket and cowling, inclusive blade to the legs of the
swimmer and a rapid detaching and removal thereof. Preferred
devices may be fasteners, flexible and/or elastic tapes which may
be provided with the possibility to adjust the fastening tension,
such as clamps, Velcro closures, buckles fasteners, etc., as known
in the art. For the case of monofins, it is preferred that the feet
be attached to the foot plate in the cowling, one at the time.
Inside the cowling, at several convenient levels, supports may be
provided for means of further fastening if so needed, the legs of
the swimmer to each-other, to the cowling, and to the foot
plate.
[0097] In a preferred embodiment, within the taper, supports (not
shown) are provided for attaching and guiding the foot plate and
the lever in the desired orientation for suiting the individual
preference of the swimmer.
Materials and Construction.
[0098] The details of the design of the foot pocket and of cowling
and the materials of construction can vary. The thickness of the
shell is function of the material used in its manufacture. The foot
pocket and the cowling have to be sufficiently sturdy to maintain
their shape during the flapping movement. Adequate materials for
making the shell are: wood, metals (aluminum etc.), plastic
materials (such as PVC, polyethylene, polypropylene, ABS,
polyamides, polyurethanes, polyesters, etc.) glass-reinforced or
carbon fibers-reinforced plastics, etc.
[0099] The proximal rims of the foot pockets or cowling may be
protected by a soft and cushioning material which will prevent
injuring the legs/feet of the swimmer and will ensure a smooth (low
drag) transition for the water flowing along the legs, to the outer
surface of the cowling.
[0100] The space not occupied by the feet and the legs within the
foot pocket or cowling is preferably filled with materials to
ensure a tight connection between the feet and the cowling, without
however, unduly cramping the feet and legs. Preferred materials are
molded foams including rubber, polyethylene, poly-propylene,
poly-styrene, poly urethanes, etc. bags or pouches which may be
inflated with gas or filled with liquid, to achieve a suitable
tight fit (no play) between the foot pocket or the cowling and the
foot/feet/legs of the swimmer. The overall specific gravity of the
foot pocket and of the cowling as installed, including the legs,
may be lower, equal or higher than of water. A specific gravity
close to that of water is preferred, in order to confer neutral
buoyancy to the body of the swimmer. Added materials (preferably
inside the foot pocket or the cowling) can be used in order to
obtain the desired buoyancy.
[0101] In a further embodiment, the foot pocket and the cowling can
be built as massive entities (block, monolith) of the desired
outside shape, without a distinct shell, and provided with internal
cavities for accommodating the feet (and legs) of the swimmer, as
well as the means for connecting the legs to the blade. The block
may be made up of several shaped parts which are assembled together
and allow for the rapid fastening to the legs of the swimmer, and
removal there-from of the swim fins or monofin. This type of foot
pocket and of cowling may be made of a convenient plastic material
provided with voids (foam) in order to have the desired overall
specific gravity and be sufficiently sturdy, as required for
maintaining the prescribed shape when undergoing the flapping
movement.
Making the Fin and the Monofin.
[0102] The fabrication of the parts which make the fin and the
monofin is not a problem for someone skilled in the operations of
molding and casting plastic materials. The foot pocket and cowling
may be fabricated by operations including vacuum forming, hot
pressing or similar techniques. The details of the operation depend
on the properties of the material selected. The taper is best
fabricated as integral part of the foot pocket and of the cowling,
although other options are possible. The blade fabrication includes
methods such as casting (of silicon rubber or similar), injection
molding, forming by sculpturing or by bonding together pre-formed
sub-components. The other components, such as fasteners, tying
tapes, foot plate, lever, etc. can be either purchased on the
market or fabricated by using broadly available materials and
skills.
Preferred Embodiments
Function
[0103] The taper at the distal end of the foot pocket and of the
cowling is of essence for improving the power efficiency of
propulsion generation by the flapping swim fin and monofin
described here. The simplified typical water flow patterns produced
by the fin and monofin of this invention are sketched in FIGS.
3a/3b and 5, and marked as "cross-over streams.
[0104] With reference to FIG. 3a, the movement of the swim fin, as
shown by arrows marked "UP-STROKE" and "DOWN-STROKE" causes a zone
of high dynamic pressure to form in front of blade 12, as origin
for propelling jet indicated by the arrows marked "THRUST". A zone
of lowered dynamic pressure will form behind blade 12. The forward
movement of the swimmer combines with the flapping movement of the
foot pocket or cowling to generate streams of water 18, which move
distally, and as allowed by the presence of taper 17, cross the
frontal plane of the foot pocket or cowling in the zone of necking
13, and flow into the zone of dynamic low-pressure formed behind
blade 12, thus equalizing the pressure difference between the two
sides of the blade. In this manner, the pressure driving force
which caused the formation of the non-propelling parasitic or shunt
streams (marked as 9, in FIG. 1) is removed. Since less water will
form the parasitic streams, more of the water pumped by blade 12
will remain as part of the thrust-producing propelling jet.
[0105] While the direction of the flows across the taper and
necking alternates for each half-stroke, the resulting propelling
jets have the same general direction. The stronger jets will
produce more thrust and higher power efficiency for the swimmer
than other devices where balancing the dynamic pressure difference
around the two sides of the blade is performed by shunting streams
flowing around the borders of the blade or through openings
practiced in the blade itself.
[0106] In conclusion, the swim devices covered here are built with
a hydrodynamic and tapered shape which, at each half-stroke of the
flapping feet, will cause that water from the higher dynamic
pressure area, in front and up-stream of the foot pocket or
cowling, moves across the necking of the taper, into the area of
lowered dynamic pressure, behind the flapping blade, thereby
improving the efficiency of converting the power expended by a
swimmer into thrust, and reducing the drag encountered during
flapping, compared to the devices of prior art. The swim device,
whether fin or monofin of this invention consist of the following
parts: [0107] A foot pocket of elongated shape, which surrounds
each foot of the swimmer, or a cowling of elongated shape which
surrounds both feet and a certain length of the legs of the human
swimmer. [0108] A taper of the distal end section of the foot
pocket or of the cowling ends in a necking which has a
substantially smaller width than the maximum width of the foot
pocket or of the cowling, respectively. At the necking, the foot
pocket or the cowling is connected to the blade, preferably to the
leading edge thereof. The foot pocket and the cowling have
transversal cross-sections of hydrodynamic shape which results in a
low drag. [0109] A blade of predetermined shape, size and profile,
connected in a functional relationship to the necking of the taper
of the flapping foot pocket or cowling. The blade acts upon the
water for generating thrust which efficiently propels the swimmer
forward. [0110] A lever or other means for connecting in a
functional relationship the blade to the feet of the swimmer and/or
to the foot pocket and to the cowling. [0111] The swim devices
possess sufficient rigidity, to maintain the desired shape during
the oscillating movement imposed by the flapping feet. Components
of the Swim Devices, Fin and Monofin of this Invention.
FIG. 1
[0111] [0112] 1 moving plate [0113] 2 lever [0114] 3 hinge [0115] 4
axis of moving plate 1 [0116] 5 axis of lever 2 [0117] 6 direction
of flapping movement [0118] 8 direction of thrust (propelling jet)
[0119] 9 parasitic (shunt) streams [0120] IN FRONT: zone of
increased dynamic pressure [0121] BEHIND: zone of decreased dynamic
pressure [0122] V, V' flapping angles between lever 2 and neutral
axis N, during down-stroke and respectively, up-stroke [0123] N
neutral axis; longitudinal axis of body of swimmer [0124] S, S'
angles between the axis of lever 2 and axis of moving plate 1,
during down-stroke, respectively up-stroke. FIGS. 2a, 2b, 2c.
[0125] A Apex angle of cone body [0126] LA Longitudinal axis of
flapping body [0127] N Neutral position of flapping body [0128] P
Pivot point [0129] PA Pivoting axis [0130] S, S' Angle between
blade and LA during down-stroke, respectively up-stroke. [0131] V,
V' Angle between LA and neutral position N, during down-stroke,
respectively up-stroke. FIGS. 3a, 3b [0132] 10 foot [0133] 11 foot
pocket [0134] 12 blade [0135] 13 necking [0136] 14 foot plate
[0137] 15 lever [0138] 16 hinge [0139] 17 taper [0140] 18
cross-over streams [0141] 19 direction of thrust [0142] M,N,P,R
transversal cross-sections at the indicated locations along the
foot pocket [0143] T angle of taper [0144] UP, DOWN: direction of
flapping movements
FIG. 4
[0144] [0145] 20 feet [0146] 21 foot pocket [0147] 22 blade [0148]
23 taper [0149] 24 necking [0150] 25 foot plate [0151] 26 lever
[0152] 27 hinge [0153] T taper angle
FIG. 5,6
[0153] [0154] 30 feet [0155] 31 cowling [0156] 32 taper [0157] 33
blade [0158] 34 necking [0159] 35 foot plate [0160] 36 lever [0161]
37 extended cowling [0162] 38 hinge [0163] 39 cross-over streams
[0164] A long axis of ellipse [0165] B short axis of ellipse [0166]
M,N,P,R transversal cross-sections through the cowling, at the
indicated locations [0167] T taper angle
* * * * *