SWIM FLIPPER

The invention relates to swimming aids, underwater movement, and muscle training, and can be used in the construction of a swimming fin that can be attached to the foot.

A swimming fin with a foot part attachable to the swimmer's foot and a fin vane attached to the tip of the foot part is known from FR 2931690 A1. The fin vane has an elongated holder and at least two streamlined blades. The blades are mounted on both sides in the elongated holder, pivotable back and forth by a predefinable angle in both directions around pivot axes running transversely to a longitudinal axis of the elongated holder. The blades are mounted in the elongated holder using a common axis. The foot part attachable to the swimmer's foot comprises a sole with reinforcement, to which the elongated holder of the fin vane is attached. The longitudinal axis of the elongated holder is inclined at an angle of 12° to the sole of the foot part. During fin stroke movements, the elongated holder rotates and/or bends in relation to the foot part attachable to the swimmer's foot. The material of the elongated holder is stiff enough not to deform excessively during bending and torsion.

A swimming fin with a foot part attachable to the swimmer's foot with a toe section and a fin vane attached to the foot part is known from WO 2010/140965 A1. The fin vane has an elongated holder and at least one streamlined blade extending transversely to a longitudinal axis of the elongated holder. The blade is mounted on both sides in the elongated holder, pivotable back and forth by a predefinable angle in both directions around a pivot axis running transversely to a longitudinal axis of the elongated holder. The elongated holder is rigidly attached to the toe section at an angle between 20° and 60° of its longitudinal axis relative to the sole of the foot part. The blade can be designed hollow to fill with water when diving. The blade tips, also referred to as side edges, can be bounded by vertical wall sections. The elongated holder can additionally be arranged protruding at an angle deviating from the longitudinal axis of the foot part.

The technical solution closest to the swimming fin known from FR 2 931 690 A1 comprises a shoe connected to one or more blade devices. The blade device includes an elongated holder with a cylindrical receiving bore running through it perpendicular to its longitudinal direction. It further includes a propulsion part consisting of two streamlined blades. These are mounted with their side surface on both sides of an axis. The inflow edge of the blades runs parallel to this axis, which is rotatably mounted in the receiving bore of the holder.

For clarity, it should be specified that the terms “angle of attack”, “leading edge”, “chord line”, and “blade” are borrowed from aerodynamics.

The use of the above swimming fin is based on kicking movements of the swimmer's legs in the water. The blades rotate freely in relation to the axis until they reach their stop at the limiter. Then the blades push off from the water, transferring the reaction force to the swimmer. Although the blade rotation angle is said to change automatically depending on the swimmer's speed of movement, no effective system for automatic adjustment is provided.

The description contains a fin design that has blade (blade) rotation limiters. These are connected to a rod that can move inside the holder. The rod is threaded at the end. A knurled knob for adjustment is screwed onto it. The swimmer must turn the knurled knob located at the end of the holder by hand to adjust the blade (blade) inclination angle. This changes the blade (blade) inclination angle in relation to the holder.

The swimmer must interrupt and pause their movement in the water each time to make the above adjustment. It should also be noted that it is not very convenient to perform this procedure without removing the fin from the foot.

The description of the above technical solution mentions several times that the holder is designed to be rigid. This is to avoid deformation during use of the swimming fin. A rigid, dimensionally stable holder is also said to be necessary to prevent jamming of the device for adjusting the angle of attack of the blades. The description also states that the holder is inclined by about 10 degrees in relation to the sole of the foot. Such a holder construction makes entering the water from land with the fins already on significantly more difficult.

All the patents mentioned above claim that the use of multiple blades mounted in one or two longitudinal strips (holders) increases the efficiency of the swimming fin.

The efficiency of the swimming fin was evaluated on a dynamometric test stand. The schematic diagram of the test stand is shown in FIG. 12. The procedure for evaluating fin effectiveness was as follows:

- The swimming fin to be evaluated was placed on the lower horizontal bar of the test stand.
- The test stand drive generated up and down movements of the horizontal bar at a constant frequency.
- Throughout the entire test cycle, the rotation angle of the horizontal bar, the force required to drive the test stand, and the reaction (impact) force were measured.
- The efficiency of the swimming fin was calculated and graphs were created.

Comparative tests in a swimming pool on the dynamometric test stand have shown that the swimming fin designed according to French patent No. 2931690 has a slightly higher efficiency compared to the current classic fin (from the AQUALUNG brand).

There are two main reasons for its insufficient effectiveness:

- 1. Classic swimming fins are currently manufactured from high-quality modern materials using new technologies and have good efficiency,
- 2. The dynamics of a swimming fin with multiple blades mounted in one or two longitudinal strips (one or two holders) is imperfect, see FIG. 10. This figure shows that the blade angle of attack is small in the initial phase of the fin's stroke movement. The water flow G does not encounter significant resistance when acting on the blade. As the fin's stroke movement progresses, the resistance to water flow increases. The reaction force reaches its maximum at the moment the fin passes through the bisector of the stroke angle. After the fin passes through the angle bisector, however, the reaction force begins to decrease. In contrast, the blade's resistance to water flow increases abruptly. The change in forces during the fin's stroke movement is more clearly illustrated using the example of a single blade in FIG. 11.

During a stroke movement, the water pressure P acts on the blade surface. This generates a force Q, which is directly proportional to the product of this pressure and the blade surface projection.

Q=kPS Sin α.

- Where:
- K: a constant coefficient for the given flow velocity,
- P: water pressure,
- S: blade surface area,
- α: blade angle of attack.

The force Q is perpendicular to the blade plane. Due to the force Q, a reaction force R is created, which acts forward in the direction of the axis of movement. The reaction force R is calculated using the following formula:

R=Q Cos α

During the stroke movement of the swimming fin, the blade must overcome the water flow resistance. The force of the flow resistance is:

F=Cw Q

Where Cw is the flow resistance coefficient.

The fin vane (blade) can be considered as a plate in this case. Cw is approximately 1. Accordingly, F can be assumed to be equal to Q. The force applied to the swimming fin to overcome the flow resistance F corresponds to the expenditure of energy that is converted into the reaction force R. The efficiency r of the blade (blades) is therefore calculated according to the following formula:

$η = R / Q .$

Three diagrams (a, b, c) in FIG. 11 clearly show that the highest efficiency of the blade occurs in the initial phase of the fin stroke movement. In the middle phase of the fin stroke movement (diagram b), the force R reaches its maximum value while the efficiency decreases. Subsequently, the reaction force R decreases, while the resistance force increases rapidly. This leads to a significant reduction in blade efficiency.

A simple calculation shows that in the special case according to diagram “a”, the efficiency η is equal to 0.88. In the special case according to diagram “b”, η is equal to 0.64, and according to diagram “c”, η is equal to 0.34. Consequently, the insufficient efficiency of such a swimming fin with multiple blades as a whole is due to a sudden decrease in fin efficiency after passing through the bisector of the stroke angle. The above results are based on calculations of the ideal efficiency. However, the actual efficiency is always below the ideal value.

All of this proves that the fin efficiency stated in FR 2931690 A1 can only be insufficiently realized. This is precisely the technical problem of the prototype design discussed here.

Another technical problem with all the fins mentioned above is the attachment of the blades to the longitudinal arms of the blade, also referred to as holders. All possibilities for connecting blades to holders can be divided into 4 types:

- using an axis that runs through the body of the holder or is attached to one side of the holder (FR 2 931 690 A1; WO 2010/140965 A1; U.S. Pat. Nos. 3,084,355; 3,081,467),
- using an elastic hinge, usually made of an elastic material such as rubber (DE 20 2007 004 633 U1; US 2012/0115377 A1),
- rigid attachment to an arm. The effect is achieved through the elasticity of the blade material itself (FR 2 929 127 A1; WO 94/25116 A1; WO 2017/175151 A1),
- a combined method using an axis, an elastic hinge, and internal stops (U.S. Pat. No. 4,944,703).

By attaching the blades to one or more holders using axes, the problem of pivoting or rotating the blades by a larger angle is solved. However, this creates a so-called idle stroke of the fin. In this case, the swimmer performs a leg kick movement without generating propulsion. This happens for the following reason. At the moment of movement reversal of the fin stroke, the blades must also reverse to the opposite position. This allows pushing off from the water. To achieve this, the swimming fin must start its stroke movement in the opposite direction from a reversal point called the dead point. In the initial phase of the stroke movement, the blade first rotates into a position where it begins to push off from the water. Only then does the working stroke movement of the fin begin. During this initial phase of the fin stroke, the aforementioned idle stroke occurs. This idle stroke leads to a significant reduction in swimming fin efficiency.

Tests have shown that the problem of idle stroke is more pronounced the larger the dimensions of the blades. Reducing the size of the blades diminishes the problem, but does not completely solve it.

Connecting the blades to the holder via elastic hinges allows the blades to return to the neutral position at the end of the stroke. This reduces the idle stroke by half, and the problem becomes less pronounced. However, it is difficult to find a compromise between the elasticity of the hinge material and its mobility. This means that if the hinge material can overcome the water mass when the blade returns to the neutral position, it then does not allow the blade to rotate by a significant angle during the turn. Elastic hinges are poorly regulated and do not allow the blade to rotate more than 30 degrees.

It is also known that elastic materials such as rubber and thermoplastic elastomers quickly lose their properties when exposed to ultraviolet light.

The above problems also exist with a rigid attachment of the blade to the holder, where the effect is achieved due to the elasticity of the blade material itself.

The combined method using axes and elastic hinges (Patent U.S. Pat. No. 4,944,703), in addition to all of the above, is also very complicated. Another problem with this connection of the blades to the holders is the high susceptibility to clogging with sand and algae.

The technical problems described above are eliminated by a swimming fin with the features of claim 1.

The foot part attachable to the swimmer's foot generally comprises a sole with reinforcement, to which the elongated holder of the fin vane is connected. The elongated holder is advantageously articulated to the sole reinforcement of the foot part attachable to the swimmer's foot. The joint can be provided with at least one return spring. The holder is designed to be elastically deformable or rigid.

The elongated holder can be designed to be elastically deformable and rigidly connected to the sole reinforcement of the foot part attachable to the swimmer's foot.

The elongated holder can have internal spaces, external ribs, and openings of various shapes. The internal spaces can be both closed and communicate with the external environment to allow water entry.

The longitudinal axis of the elongated holder is directed forward from the foot part attachable to the swimmer's foot. It is advantageously positioned at an angle of 0° to 20° to the longitudinal axis of the elongated holder.

The blades are generally mounted in the elongated holder using a common axis.

In another configuration, oppositely arranged blades are interconnected by means of a crossbar. The crossbar passes through an opening present in the elongated holder. The opening in the elongated holder is larger than the crossbar passing through it. The opening has a non-round shape. Inside the opening, there are stops to limit rotational movements of the crossbar around the pivot axes of the respective blades. The surface of the opening can be covered with a material to dampen the contact between the stops and the crossbar. FIG. 15 shows possible shapes of openings in the elongated holder. The openings provided in the elongated holder can also have a different shape.

The elongated holder of the fin vane can be at least partially assembled from modules of streamlined blades.

The elongated holder is provided with at least one protrusion on at least one side to limit the rotation of the streamlined blade.

The technical result of the invention consists in increasing the efficiency of the swimming fin.

The swimming fin to be applied for is schematically shown in the drawings. They show:

FIG. 1 the swimming fin in axonometric view,

FIG. 2 an exploded view of the swimming fin in axonometric representation,

FIG. 3 a side view of the swimming fin with a joint connecting the sole reinforcement and the elongated holder,

FIG. 4 functional phases of the swimming fin during its downstroke movement,

FIG. 5a, 5b schematically the function of the swimming fin during its upstroke and downstroke movement,

FIG. 6 a streamlined blade,

FIG. 7a the side view of a swimming fin with rigid connection of the sole reinforcement and the elongated holder,

FIG. 7b,7c schematically the function of the swimming fin with an elastically deformable elongated holder during its upstroke movement,

FIG. 8 the swimming fin to be applied for with a fin vane in modular design,

FIG. 9 a swimming fin in detachable design,

FIG. 10 functional phases of a swimming fin prototype according to French patent No. 2931690 during the downstroke movement,

FIG. 11 schematically the effect of forces on blades of the swimming fin prototype according to French patent No. 2931690 in individual downstroke movement phases,

FIG. 12 the schematic diagram of the dynamometric swimming fin test stand,

FIG. 13 the position of planes of the elongated holder,

FIG. 14 an exploded view of the swimming fin with blades attached using crossbars,

FIG. 15 design variants of openings present in the elongated holder,

FIG. 16 the “crossbar-blade” connection,

FIG. 17 various examples in 17a, 17b and 17c of structural elements of the elongated holder.

REFERENCE NUMBERS IN FIG. 1 TO 17

- 1—foot part attachable to the swimmer's foot,
- 2—fin vane,
- 3—foot part attachable to the swimmer's foot, designed as a shoe,
- 4—foot part attachable to the swimmer's foot, designed as a pocket with fastening straps,
- 5—elongated holder,
- 6—foot part tip,
- 7 to 7i, 8 to 8i—streamlined blades,
- 9—longitudinal axis of the elongated holder,
- 10—longitudinal axis of the foot part attachable to the swimmer's foot,
- 11—module of streamlined blades,
- 12 to 12i—holes in the elongated holder,
- 13 to 13i—common rotating connecting axis of the streamlined blades,
- 14—blade symmetry plane,
- 15—upstroke movement of the swimmer's leg,
- 16—downstroke movement of the swimmer's leg,
- 17—leading (inflow) edge of a streamlined blade,
- 18—trailing edge of a streamlined blade,
- 19—rotation axis of a streamlined blade,
- 20—side edge of a streamlined blade,
- 21—streamlined blade surface, blade
- 22—length (chord line) of a streamlined blade,
- 23—width of a streamlined blade,
- 24—continuous water flow-through openings,
- 25 to 25i—protrusions on the elongated holder that serve as rotation limiters for streamlined blades,
- 26—foot sole reinforcement, sole reinforcement
- 27—joint,
- 28—fork piece,
- 29—joint axis,
- 30—return spring,
- 31—stabilizer,
- 32—connection,
- 33—swimming fin drive,
- 34—fin stroke angle sensor,
- 35—dynamometer,
- 36—horizontal bar,
- 37—vertical bar,
- 38—swimming fin to be tested,
- 39—pull rod,
- 40—test stand frame,
- 41—control unit,
- 42—recording device,
- 43—vertical plane,
- 44—horizontal plane,
- 45, 45i—hole or opening in the elongated holder,
- 46—crossbar,
- 47—crossbar movement limiter,
- 48—crossbar movement limiter,
- 49—rib,
- 50—opening,
- 51—interior space,
- 52—joint cover,
- α—blade angle of attack,
- β1, β2_i, β3 . . . μ_i—angles between the blade symmetry plane and the longitudinal axis of the elongated holder in rigid design, which occur during a fin upstroke movement,
- γ1, γ2_i, γ3 . . . γ_i—angles between the blade symmetry plane and the longitudinal axis of the elongated holder in rigid design, which occur during a fin downstroke movement,
- φ—angular deflection of the axis of the elongated holder from the fin stroke angle bisector.

The swimming fin comprises a foot part 1 attachable to the swimmer's foot and a fin vane 2 attached to the foot part 1.

The foot part 1 is advantageously made of rubber and/or thermoplastic elastomer and designed as a shoe 3 (FIG. 1). However, other designs are possible, for example in the form of a pocket (a half-shoe) 4 with several fastening straps (FIG. 2).

The foot part 1 is provided with a stiff sole and may contain a sole reinforcement 26 for stiffening purposes. The sole reinforcement 26 can be made unitarily with the shoe 3 from a polymer. It can also be made of another material, such as metal, polymer reinforced with carbon and/or other fibers, plywood, fiberglass, etc. The sole reinforcement 26 can be connected to the sole of the foot part 1 using rivets, threads, adhesive or welding and/or be injected into the “body” of the sole of the foot part 1.

The front part of the foot part 1 has a fork piece 28 for connection to the elongated holder 5.

The fin vane 2 comprises an elongated holder 5 directed forward from the tip 6 of the foot part 1. The fin vane 2 further comprises at least two streamlined blades 7 and 8.

The longitudinal axis 9 of the elongated holder 5 runs in its longitudinal direction advantageously parallel to the longitudinal axis 10 of the shoe 3. However, it can also be positioned at an angle of up to 20° to the longitudinal axis 10 of the shoe 3. The elongated holder 5 is attached to the foot part 1 by means of a joint 27 (FIG. 3).

The joint 27 comprises a fork piece 28, which can be designed unitarily with both the elongated holder 5 and the foot part 1. The joint further comprises the counterpart of the joint 27 and an axis 29. The joint 27 allows the elongated holder 5 to rotate in relation to the foot part 1. In doing so, the longitudinal axis 9 of the elongated holder 5 can change its position in relation to the longitudinal axis 10 of the foot part 1.

The joint 27 is provided with at least one return spring 30. The spring 30 alone or as part of a spring device returns the elongated holder 5 to its middle basic position after the leg stroke movement is completed. The characteristic of the spring 30 or the spring device is tuned in such a way that the force expended by the swimmer is effectively utilized. The characteristic of the spring 30 or the spring device can be both linear and non-linear.

The elongated holder 5 is designed to be rigid (FIGS. 3 and 4), but can also be elastically deformable (FIGS. 7a, 7b and 7c).

The elongated holder 5 can have internal spaces 51, external ribs 49 and openings 50 of various shapes. The internal spaces 51 can be both closed and connected to the external environment to allow water entry. A preferably combined use of ribs, openings and internal spaces allows regulation of elastic deformation of the elongated holder both in the vertical plane 43 and in the horizontal plane 44 (see FIG. 13 and FIG. 17).

An elastically deformable holder 5 can also be rigidly connected to the foot part 1, for example by means of a coupling piece 32. In this case, the longitudinal axis 9 of the elongated holder 5 bends along with the holder 5. This occurs in relation to the longitudinal axis 10 of the foot part 1 due to elastic deformation of the holder 5 itself during a leg stroke movement and/or due to a thinned area present in the elongated holder 5.

The elongated holder 5 is generally made of one piece. However, it can also be at least partially assembled from several modules 11 of streamlined blades 7i and 8i (FIG. 8).

The elongated holder 5 has at least one stabilizer 31 in the form of a widening at the holder end in one plane. This plane runs perpendicular to the rotation axis 19 of streamlined blades 7-7i or 8-8i.

The elongated holder 5 can be made of metal, a polymer reinforced with carbon and/or other fibers, plywood, fiberglass, etc. Streamlined blades 7 and 8 are pivotally mounted in the elongated holder 5 on both sides on a common rotating connecting axis 13. This connecting axis 13 is installed in the bore 12. Generally, there is the possibility of co-rotation of the streamlined blades 7 and 8 together with their connecting axis 13 in both directions in relation to the above-mentioned elongated holder 5 by a predefined angle. Generally, rotation in one direction is possible by an angle β_ibetween the longitudinal axis 9 of the elongated holder 5, which runs in its longitudinal direction, and the symmetry plane 14 of the i-th streamlined blade 7 or 8 during an upstroke movement 15 of the swimmer's leg. Rotation in the opposite direction is possible by an angle γ_ibetween the above axis 9 and plane 14 during a downstroke movement 16 of the swimmer's leg. The symmetry plane 14 of the i-th streamlined blade 7 and 8 runs through the leading edge 17 of the blade 7 and 8, its trailing edge 18 and the rotation axis 19 of the blades 7 and 8. Rotation angles β_iand γ_iof the blades 7-7i or 8-8i can differ from blades arranged close to the foot part 1. They can also differ from the blades arranged at the distant end of the holder 5 in the fin vane 2.

As a special case, the streamlined blades 7 and 8 can be detachable from the elongated holder 5. The outline of the streamlined blades 7 or 8 is advantageously trapezoidal with rounded corners. However, the outline can also have a different shape. Each of the streamlined blades 7 or 8 has a leading (inflow) edge 17 directed towards the foot part 1, a trailing edge 18, two side edges 20 and two streamlined surfaces 21 in between (FIG. 6). A common rotating connecting axis 13 is inserted into each of the streamlined blades 7 and 8. The connecting axis 13 is positioned in the first third of the length 22 (chord line) of the blade 7 or 8 on the side of the leading edge 17.

The blade leading edge 17 is curved and/or straight, but positioned at an angle to the rotation axis 19 of the blade 7 or 8. The leading edge 17 of the blade 7 or 8 can also be designed as a kinked straight line.

The streamlined blades 7 or 8 on one side of the elongated holder 5 can have the same or different dimensions. This can be the case, for example, with regard to their length 22 and/or width 23, compared to the streamlined blades 8 or 7 arranged on the other side of the elongated holder 5. The blades 7 and 8 can be provided with continuous openings 24 for water flow-through and reduction of pressure on the blades 7 and 8.

A common rotating connecting axis 13 of the streamlined blades 7 or 8 can also serve to increase the stiffness of these blades. In this case, the above-mentioned axis 13 is inserted quite deeply into the blade 7 or 8.

The fin vane 2 is generally provided with two or more pairs of streamlined blades 7-7i and 8-8i. The dimensions of each pair of streamlined blades are advantageously the same, but can also be different. This applies to all blade pairs as well as to only one or more pairs. The streamlined blades 7 or 8 are advantageously designed to be stiff. They retain their shape under the influence of water flow. However, they can also be elastic, bendable in the longitudinal and/or transverse direction in relation to the longitudinal axis 9 of the elongated holder 5 on its long side.

The fin vane 2 has a limiter for the rotation of the streamlined blades 7 or 8 by a predefined angle, advantageously together with their connecting common rotation axis 13. The limiter can be designed as at least one protrusion 25. It is arranged on the elongated holder 5. The limiter has the possibility of abutting against the protrusion of at least one of the streamlined blades 7 or 8 in its end rotation position (FIG. 5a, 5b). The protrusion 25 on the elongated holder 5 is advantageously cylindrical. It is arranged on the side surface of the elongated holder. However, it can also have a different shape. Generally, each pair of streamlined blades 7-7i and 8-8i corresponds to a protrusion 25-25i.

Limiting protrusions 25 can be formed on the opposite side surfaces of the elongated holder 5 for each streamlined blade 7 or 8. At least one protrusion 25 on the opposite sides in relation to the rotation axis 19 of the streamlined blades 7 or 8 is possible. Protrusions 25 can be made in one piece with the elongated holder 5 or attached to it as separate parts.

The protrusion 25 for limiting the rotation of the blades 7 and 8 can be covered with rubber material to dampen the contact between the blades 7 or 8 and the protrusion 25. Other materials with contact damping properties are also suitable for this purpose. The protrusion 25 itself on the elongated holder 5 can be made entirely of a material that guarantees damping and/or a smoother contact between the blades 7 or 8 and the limiting protrusion 25.

As a variant, the blades 7-7i or 8-8i can be attached to the elongated holder 5 using a so-called free joint (FIGS. 14 and 15). In this case, the blades 7-7i or 8-8i are interconnected by means of a crossbar 46, for example in the form of a plate. This passes through an opening, for example a hole 45, 45i, present in the elongated holder 5. The opening 45, 45i in the elongated holder 5 has larger dimensions than the crossbar 46 passing through it. The opening 45, 45i has a non-round shape. Inside the opening 45, 45i, there are stops 47 and 48 to limit rotational movements of the crossbar 46 around the pivot axes of the respective blades 7-7i or 8-8i, also referred to as rotation axes 19. The surface of the opening 45, 45i can be covered with a material to dampen the contact between the crossbar 46 and the stops 47, 48. This makes the recurring contact between the stops 47, 48 and the crossbar 46 connected to the blades 7-7i or 8-8i gentler with each fin stroke.

FIG. 15 shows possible shapes of openings 45, 45i in the elongated holder 5. The openings 45, 45i provided in the elongated holder 5 can also have a different shape.

Due to the complexity of manufacturing processes and design solutions, stops 47, 48 for limiting the rotational movement of the crossbars 46 can also be arranged outside the free joint directly on the holder 5.

The crossbar 46 is advantageously positioned in the front half of the blades 7-7i or 8-8i (FIG. 16). The crossbar 46 is advantageously flat, but can also have a different design.

The free joint can be provided with covers 52 on the sides (FIG. 14). The covers 52 form vertical wall sections in relation to the holder 5 on the inner sides of the streamlined blade surfaces 21 of the blades 7, 7i, 8, 8i facing the holder 5. The covers 52 can be formed by discs, encompass such discs or be encompassed by discs. The covers 52, for example formed by discs, advantageously span planes on which the respective pivot or rotation axes 19 of the blades 7, 7i, 8, 8i stand perpendicular. Contamination of the openings in the elongated holder 5, for example designed as holes 45, 45i, is effectively prevented by the aforementioned covers 52. For example, the covers 52 prevent the openings 45, 45i from becoming clogged with algae. The covers 52 can be both recessed into the body of the holder 5 and protrude outwards.

As a special case, the fin can be made of materials with positive buoyancy.

The swimming fin functions as follows:

When moving through the water, the swimmer performs upstrokes 15 and downstrokes 16 with their legs, as shown in FIGS. 4, 5a, 5b and 7b.

During the upstroke 15, in the course of an upward movement (FIG. 5a) of the swimming fin, the streamlined blades 7 or 8 are rotated by an angle β_iunder the influence of water pressure. The rotating blades 7 and 8 hit against the limiting protrusions 25 present on the elongated holder 5 when they reach their end position. Subsequently, the blades 7 or 8 push off from the water. The push-off force is transferred to the swimmer via the elongated holder 5 and the foot part 1. As the swimming fin upstroke continues, the water pressure effect on the fin vane 2 increases. The reason for this is that the angle of attack of the streamlined blades 7 or 8 has increased. The elongated holder 5 overcomes the force of the spring 30 under increased water pressure. It rotates in the joint 27 by which it is connected to the foot part 1. The rotation of the elongated holder 5 causes a reduction in the angle of attack of the streamlined blade, which leads to a reduction in resistance on the fin vane 2 and an increase in the push-off force. With further execution of the stroke movement with the swimming fin and the increase in water pressure effect on the fin vane 2, the elongated holder 5 is rotated by an even greater angle in relation to the foot part 1. This reduces the angle of attack of the blade 7 or 8. Thus, the resistance of the fin vane 2 can be reduced. When the stroke movement of the swimming fin stops, the fin vane 2 returns to its initial position in relation to the foot part 1 under the action of the spring 30 of the joint 27. This gives the swimmer an additional impulse.

Then, during the downstroke 16 of the fin (FIG. 5b), the streamlined blades 7 or 8 are rotated by an angle γ_iunder the influence of water pressure. The rotating blades 7 and 8 hit against the limiting protrusions 25 present on the elongated holder 5 when they reach their end position. Subsequently, the blades 7 and 8 push off from the water. The push-off force is transferred to the swimmer via the elongated holder 5 and the foot part 1. As the downstroke movement of the swimming fin continues, the water pressure effect on the fin vane 2 increases, as the angle of attack of the streamlined blade 7 or 8 has increased. The elongated holder 5 rotates under increased water pressure in the joint 27 attached to the foot part 1. The rotation of the elongated holder 5 reduces the angle of attack of the streamlined blade 7 or 8. This leads to a reduction in resistance of the fin vane 2 and an increase in the reaction force. With further execution of the stroke movement of the swimming fin and increase in water pressure effect on the fin vane 2, the elongated holder 5 is rotated by an even greater angle in relation to the foot part 1. This reduces the angle of attack of the blade 7 or 8. Thus, the resistance of the fin vane 2 can be reduced. When the stroke movement of the swimming fin stops, the fin vane 2 returns to its initial position in relation to the foot part 1 under the action of the spring 30 of the joint 27. It gives the swimmer an additional impulse.

Another swimming fin design contains an elastically deformable elongated holder 5. The holder 5 can be rigidly attached to the foot part 1 (FIGS. 7a, 7b and 7c). In this case, the streamlined blades 7 and 8 are rotated by an angle β_iunderwater pressure during an upstroke 15 of the swimming fin (similar to FIG. 5a). The rotating blades 7 or 8 hit against the limiting protrusions 25 present on the elongated holder 5 when they reach their end position. Subsequently, the blades 7 and 8 push off from the water. The push-off force is transferred to the swimmer via the elongated holder 5 and the foot part 1. As the upstroke movement of the swimming fin continues, the water pressure on the fin vane 2 increases because the angle of attack of the streamlined blade 7 or 8 has increased. Under increased water pressure, the elongated holder 5 deforms elastically. Its longitudinal axis 9 bends in relation to the foot part 1. The bending of the elongated holder 5 reduces the angle of attack of the streamlined blade. This leads to a reduction in resistance of the fin vane 2 and an increase in the reaction force. As the stroke movement of the swimming fin continues and the water pressure effect on the fin vane 2 increases, the elongated holder 5 bends by an even greater angle in relation to the foot part 1. It thereby reduces the angle of attack of the blade 7 or 8. This causes a reduction in resistance of the fin vane 2 and an increase in the push-off force. When the stroke movement of the swimming fin stops, the elongated holder 5 elastically straightens. The fin vane 2 returns to its initial position in relation to the foot part 1, giving the swimmer an additional impulse.

During the downstroke movement 16 of the swimming fin, the streamlined blades 7 and 8 then rotate under water pressure by an angle γ_i(similar to FIG. 5b). The rotating blades 7 and 8 hit against the limiting protrusions 25 present on the elongated holder 5 when they reach their end position. Subsequently, the blades 7 and 8 push off from the water. The push-off force is transferred to the swimmer via the elongated holder 5 and the foot part 1. During the subsequent upstroke movement of the swimming fin, the water pressure effect on the fin vane 2 increases due to the increase in the angle of attack of the streamlined blade. Under increased water pressure, the elongated holder 5 deforms elastically. Its longitudinal axis 9 bends in relation to the foot part 1. The bending of the elongated holder 5 reduces the angle of attack of the streamlined blade 7 or 8. This leads to a reduction in resistance of the fin vane 2 and an increase in the reaction force. As the stroke movement of the swimming fin continues and the water pressure effect on the fin vane 2 increases, the elongated holder 5 elastically bends by an even greater angle in relation to the foot part 1. It thereby reduces the angle of attack of the blade 7 or 8. This can reduce the resistance of the fin vane 2 and increase the reaction force. When the stroke movement of the swimming fin stops, the elongated holder 5 elastically straightens. The fin vane 2 returns to its initial position in relation to the foot part 1. It gives the swimmer an additional impulse.

Advantageously, the elasticity of the elongated holder 5 in a vertical plane 43, briefly vertical plane 43, is higher than in a horizontal plane 44 arranged perpendicular to it, standing normal to the vertical plane 43 and spanned by the streamlined blades and including the longitudinal axis 9 of the holder 5, briefly horizontal plane 44 (FIG. 13). The fin efficiency can be increased through elastic deformation of the elongated holder 5 in the vertical plane 43. However, simultaneous elastic deformation in the horizontal plane 44 is disadvantageous.

At the same time, swimming fin deformation in the horizontal plane 44 has a negative effect, as the fin begins to deflect laterally during leg kicks. This dislocates the swimmer's ankle, leading to greater muscle exertion.

Therefore, adjusting the elasticity of the elongated holder 5 in both the vertical plane 43 and the horizontal plane 44 is important. Optimally, the elasticity of the elongated holder 5 in the vertical plane 43 should be higher than the elasticity in the horizontal plane 44. At the very least, the holder 5 should have the same elasticity in the vertical plane 43 as in the horizontal plane 44.

The elasticity of the elongated holder 5 in the vertical plane 43 and in the horizontal plane 44 can be regulated by the following structural elements: ribs 49, openings 50, and the interior spaces present in the holder 5. The interior spaces 51 of the holder 5 can be closed. However, they can also communicate with the external environment to allow water entry. Through combined use of ribs, openings and interior spaces, elastic deformation of the elongated holder can be regulated in both the vertical plane 43 and the horizontal plane 44 (FIGS. 13 and 17).

The described swimming fin makes it possible to optimize rotation angles β and γ of each pair of blades 7-7i and 8-8i. The swimmer receives a stronger impulse at smaller values of rotation angles β and γ of blades 7-7i and 8-8i, while larger rotation angles β and γ of blades 7-7i and 8-8i contribute to economical use of the swimmer's muscle power.

By changing the position of the longitudinal axis 9 of the elongated holder 5 in relation to the longitudinal axis 10 of the foot part 1, the swimmer's muscle power can be highly effectively utilized when executing a fin stroke movement.

Another factor in increasing the efficiency of the depicted swimming fin is the elastic deformation of the blades 7 and 8 under water pressure. A bending of the blade that increases from the rotation axis 19 towards the trailing edge 18 contributes to reducing the hydrodynamic resistance of the blade.

A significant increase in blade effectiveness can also be achieved through continuous water flow-through openings 24 in the streamlined blades 7-7i and 8-8i (FIG. 6).

The impulse can be influenced by changing the surface area of the streamlined blades 7 and 8.

During fin strokes, the blades 7, 7i, 8, 8i perform limited rotational movements around their pivot or rotation axes 19 running transversely to the longitudinal axis 9 of the holder 5. The crossbar 46, which connects the two blade surfaces protruding on both sides of the holder 5 of a blade 7, 7i, 8, 8i, performs back-and-forth tilting movements between the stops 47 and 48.

Here, blade surface refers to the streamlined blade surface 21.

During fin strokes, the crossbar 46 connecting the blades 7 and 8 is freely tilted within the opening 45, 45i between stops 47 and 48 that limit the blade movement. This free tilting movement of the blade from one end position to the other requires significantly less time compared to a rotation. Accordingly, the idle stroke is reduced. Test stand trials have shown that the problem of swimming fin idle stroke is practically completely eliminated by reducing the blade dimensions while simultaneously increasing their number and having a free joint.

The use of only one elongated holder 5, connected to the foot part 1, can contribute to a significant reduction in hydrodynamic resistance during stroke movements of the swimming fin.

Since the swimmer performs back-and-forth movements with their legs during propulsion through the water, the fin weight influences the inertial force that must be overcome during propulsion. By using only one elongated holder 5, the swimming fin weight can be reduced. This also improves the effectiveness of utilizing the swimmer's muscle power.

The use of only one elongated holder 5 also simplifies the problem of separating it from the tip portion of the foot part 1 (FIG. 9). The separation possibility allows reducing the overall dimensions of the swimming fin, and its transport to the place of use can be simplified.

Unlike other design variants, the use of only one elongated holder 5 contributes to simplifying the attachment of the streamlined blades 7-7i and 8-8i to the holder and their separation from the holder. This additionally facilitates the transport of the swimming fin to its place of use.

The simple attachment and separation of the streamlined blades 7-7i and 8-8i makes it possible to use several blade sets with different characteristics. The elongated holder 5 with the foot part 1 attachable to the swimmer's foot (basic part of the swimming fin) remains unchanged. Sets of streamlined blades 7-7i and 8-8i can be optimized for specific purposes, one set for swimming with powerful thrust and the other for calm swimming with minimal energy expenditure.

The proposed swimming fin can also have a modular design. This means that the swimming fin in its basic design comprises, for example, three pairs of streamlined blades 7, 7a, 7b, 8, 8a and 8b and functions according to the principles described above. With 3 blade pairs, calm swimming with minimal energy expenditure is assumed. For the purpose of increasing propulsive force, a module 11 of streamlined blades 7i and 8i, also referred to as an additional module, can be mounted (FIG. 8).

The return spring 30 or the spring device can also be easily replaced by another device with different characteristics. This results in another possibility to obtain a swimming fin for use with powerful thrust capability or for calm swimming.

As a design variant, the blades 7-7i or 8-8i can be attached to the elongated holder 5 using a so-called free joint (FIGS. 14 and 15). In this case, the blades 7-7i or 8-8i are interconnected by means of a crossbar 46, for example in the form of a plate. The crossbar 46 passes through an opening 45, 45i present in the elongated holder 5. The opening 45, 45i in the elongated holder 5 has larger dimensions than the crossbar 46 passing through it. The opening 45, 45i has a non-round shape. Inside the opening 45, 45i, there are stops 47 and 48 to limit rotational movements of the crossbar 46 around the pivot or rotation axes 19 of the respective blades 7-7i or 8-8i. The surface of the opening 45, 45i can be covered with a material to dampen the contact between the crossbar 46 and the stops 47, 48. This makes the recurring contact between the stops 47, 48 and the crossbar 46 connected to the blades 7-7i or 8-8i gentler with each fin stroke. FIG. 15 shows possible shapes of openings 45, 45i in the elongated holder 5. The openings 45, 45i provided in the elongated holder 5 can also have a different shape.

The crossbar 46 is advantageously positioned in the front half of the blades 7-7i or 8-8i (FIG. 16). The crossbar 46 is advantageously flat, but can also have a different design.

The free joint can be provided with covers 52 on the sides (FIG. 14). The covers 52 can be formed by discs, encompass such discs or be encompassed by discs. The covers 52, for example formed by discs, advantageously span planes on which the respective pivot or rotation axes 19 of the blades 7, 7i, 8, 8i stand perpendicular. Contamination of the openings 45, 45i in the elongated holder 5 is effectively prevented by the aforementioned covers 52. For example, the covers 52 prevent the openings 45, 45i from becoming clogged with algae. The covers 52 can be both recessed into the body of the holder 5 and protrude outwards.

It is important to emphasize that a swimming fin shown in whole or in part in FIG. 1 to FIG. 17c) comprises:

- a foot part 1, 3, 4 attachable to the swimmer's foot, and
- a swimming fin vane 2 arranged on the foot part 1, 3, 4, for example attachable to it.

The swimming fin vane 2, briefly fin vane, comprises an elongated holder 5 with streamlined blades 7, 7i, 8, 8i, 21 rotatably arranged on it. At least two streamlined blades 7, 7i, 8, 8i are provided, rotatably arranged protruding laterally from the holder 5. The blades can be rotatably arranged around pivot or rotation axes 19 running, for example, transversely to a longitudinal axis 9 of the aforementioned elongated holder 5. The blades are thereby rotatably arranged in oppositely back-and-forth pivoting directions, briefly in both directions by a predefined angle.

According to a first object of the invention, the swimming fin is characterized by a movable arrangement of the elongated holder 5 relative to the foot part 1, 3, 4 attachable to the swimmer's foot, at least during fin stroke movements.

According to an alternative or additional second object of the invention, the swimming fin is characterized in that the streamlined blades 7, 7i, 8, 8i protruding on opposite sides in relation to the longitudinal axis 9 of the holder 5, or their blade leaves 21 formed by streamlined blade surfaces 21, are interconnected via a plate-shaped crossbar 46. The crossbar 46 runs through a hole 45, 45i in the elongated holder 5. The hole 45, 45i in the elongated holder 5 is equipped with blade movement limiters 47, 48 in the form of protrusions. The hole 45, 45i is larger than the crossbar 46 passing through it.

The streamlined blades 7, 7i, 8, 8i, 21 can be provided with discs 52 at their ends facing the holder 5, which close off the holes 45, 45i in the elongated holder 5.

Each blade 7, 7i, 8, 8i comprises at least one blade leaf formed by a streamlined blade surface 21. The blades 7, 7i, 8, 8i preferably consist of two blade leaves referred to as streamlined blade surfaces 21. One blade leaf is located on each side of the holder 5. The streamlined blade surfaces 21 of the blades 7, 7i, 8, 8i advantageously protrude on opposite sides of the longitudinal axis 9 of the elongated holder 5 in the direction of pivot or rotation axes 19 running transversely to its longitudinal axis 9. These can be individual or pairwise common pivot or rotation axes 19. With an individual pivot or rotation axis 19, a blade 7, 7i, 8, 8i comprises only one blade leaf protruding on one side of the holder 5. With pairwise pivot or rotation axes 19, a blade 7, 7i, 8, 8i comprises two blade leaves protruding on opposite sides of the holder 5. The blades 7, 7i, 8, 8i can perform predefined, limited back-and-forth rotational movements around the pivot or rotation axes 19.

According to this, the blades 7, 7i, 8, 8i or their blade leaves comprising streamlined blade surfaces 21 can protrude on both sides of the elongated holder 5.

Advantageously, the blade leaves arranged opposite each other on a pairwise pivot or rotation axis 19 are connected to each other non-rotatably to form a blade 7, 7i, 8, 8i.

The blades 7, 7i, 8, 8i protruding on opposite sides in relation to the longitudinal axis 9 of the holder 5, or their blade leaves comprising streamlined blade surfaces 21, can thus be rotatably mounted around a common axis 19 in the elongated holder 5.

In this context, it is conceivable that oppositely arranged blade leaves are indeed rotatably arranged back and forth around a common, pairwise pivot or rotation axis 19. However, they can perform their rotational movements independently of each other. The blade leaves are not connected to each other non-rotatably via a common connecting element.

Advantageously, a movable arrangement of the elongated holder 5 relative to the foot part 1, 3, 4 attachable to the swimmer's foot is provided, at least during fin stroke movements. The elongated holder is thereby articulated to the foot part.

A joint 27 can be arranged between the elongated holder 5 and the foot part 1, 3, 4. The joint 27 provides a movable, especially preferably articulated arrangement of the elongated holder 5 relative to the foot part 1, 3, 4 attachable to the swimmer's foot. The elongated holder 5 is thereby articulated to the foot part 1, 3, 4 at least during fin stroke movements.

Advantageously, a spring loading acting against deflection is provided for the articulated arrangement of the elongated holder 5 relative to the foot part 1, 3, 4.

For this purpose, the joint 27 can be provided with at least one return spring. The holder 5 can be designed to be elastically deformable. Alternatively, the holder 5 can be designed to be rigid. In the rigid version, it has a sufficiently high bending stiffness to prevent deformations due to human force effects.

The elongated holder 5 can rotate and/or bend relative to the foot part 1, 3, 4 attachable to the swimmer's foot during fin stroke movements.

Advantageously, the elasticity of the elongated holder 5 in a vertical plane 43 is higher than in a horizontal plane 44 arranged perpendicular to the vertical plane 43, standing normal to the vertical plane 43 and spanned by the streamlined blades and including the longitudinal axis 9 of the holder 5.

The elongated holder 5 can have ribs 49 and/or openings 50 also referred to as holes and/or inner cavities 51 filled with water or free of water. The mentioned measures can serve to adjust the elasticity of the holder 4 in the vertical 43 and horizontal plane 44.

The elongated holder 5 of the fin vane 2 can be at least partially assembled from modules 11 with streamlined blades 7, 7i, 8, 8i.

The foot part 1, 3, 4 attachable to the swimmer's foot can comprise a sole with reinforcement—briefly sole reinforcement 26. The elongated holder 5 of the fin vane 2 is advantageously attached to such a sole reinforcement 26.

Especially preferably, the elongated holder 5 is articulated to the sole reinforcement 26 of the foot part 1, 3, 4 attachable to the swimmer's foot.

A joint 27 serving the articulated arrangement is advantageously arranged between the sole reinforcement 26 of the foot part 1, 3, 4 attachable to the swimmer's foot and the elongated holder 5.

The elongated holder 5 can be provided with at least one protrusion 25, 25i on at least one side. The protrusion 25, 25i limits the rotation of the streamlined blades 7, 7i, 8, 8i around their pivot or rotation axes 19.

The longitudinal axis 9 of the elongated holder is preferably directed forward in relation to the longitudinal axis 10 of the foot part 1. The longitudinal axis 9 of the elongated holder 5 is advantageously positioned downward at an inclination angle of 0° to 20° to the longitudinal axis 10 of the foot part 1.

If a joint 27 is provided between the foot part 1 and the holder 5, the inclination angle refers to a middle neutral position of the holder 5 relative to the foot part 1. From the middle neutral position, the holder 5 arranged at the joint 27 can be deflected upward and downward at approximately equal angles. In the middle neutral position, the mobility of the joint 27 is approximately equal in both directions.

It is apparent that the invention can alternatively or additionally be realized by a swimming fin comprising:

- a fastening device on the swimmer's foot, also called foot part 1, 3, 4, and
- a swimming fin vane 2 that is attached to the fastening device on the swimmer's foot and contains an elongated holder 5 and at least two streamlined blades 7, 7i, 8, 8i. The blades 7, 7i, 8, 8i are pivotally mounted on an elongated holder 5, preferably with one blade leaf comprising a streamlined blade surface 21 on both sides thereof. This creates the possibility of limited movement relative to the above elongated holder 5 in both directions.

The swimming fin is characterized in that the elongated holder 5 rotates and/or bends relative to the fastening device on the swimmer's foot at least during fin stroke movements. The elasticity of the elongated holder 5 in the vertical plane 43 is higher than in the horizontal plane 44.

The fastening device on the swimmer's foot can contain a sole with a sole reinforcement 26 to which the elongated holder 5 is attached.

The elongated holder 5 is advantageously elastically deformable and rigidly attached to the sole reinforcement of the fastening device.

The elongated holder 5 is preferably attached to the sole reinforcement of the fastening device on the swimmer's foot by means of a joint 27.

The joint 27 is preferably provided with at least one return spring, while the holder 5 is elastically deformable.

The joint 27, also referred to as a hinge, can alternatively be equipped with at least one return spring, while the holder 5 is designed to be rigid.

The elongated holder 5 can have ribs 49 and/or holes 50 and/or inner cavities 51 filled with water or free of water. These serve to adjust the elasticity of the holder 5 in the vertical plane 43 and in the horizontal plane 44.

The swimming fin vane 2 can be at least partially assembled from modules 11 with streamlined blades 7, 7i, 8, 8i.

Alternatively or additionally, a swimming fin comprising:

- a fastening device on the swimmer's foot, also referred to as foot part 1, and
- a swimming fin vane attached to the fastening device for attachment to the swimmer's foot. The swimming fin vane comprises an elongated holder 5 and at least two streamlined blades 7, 7i, 8, 8i, which are pivotally mounted on the elongated holder 5 on both sides thereof. There is the possibility of limited movement relative to the above elongated holder 5 in both directions,
  
  can be characterized in
  
  that the streamlined blades are interconnected via a plate-shaped crossbar 46. The crossbar 46 runs through a hole 45, 45i in the elongated holder 5. The hole 45, 45i in the elongated holder is equipped with blade movement limiters 47, 48 in the form of protrusions and has a larger size than the crossbar 46 passing through it.

The streamlined blades 7, 7i, 8, 8i can contain discs 52 that close off the holes 45, 45i in the elongated holder 5.

It should be mentioned that the embodiments described above only represent the presented device, but do not limit it. Experts in the field are capable of developing a variety of alternative implementations without deviating from the scope of the attached claims. The mere fact that certain criteria are listed in different dependent claims should not mean that the combination of these criteria cannot be used to achieve the positive effect.

The invention is commercially applicable particularly in the field of development and manufacture of diving or swimming fins.

SWIM FLIPPER

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