The object of the present invention is a swim fin with a longitudinally moulded blade designed for swimming lessons and swimming in sport and rehabilitation as well as for diving by increasing the swimming speed and efficiency of upward and downward oscillatory leg movement (in the sagittal plane), especially when swimming front crawl or butterfly stroke, and of backward and outward leg movements (in the coronal plane) in breaststroke swimming.

There are many of swim fins both for swimming and diving known in the prior art. Some of them are designed to provide proper body position when diving under water, while others to increase the swimming speed.

For example, from US3171142A there are known "swimming shoes" adjusted and adapted to different types of swimming generally used and the capabilities of the swimmer for a particular technique wherein adjustable rods disposed close to toes limit the amplitude of the strokes of the flipper blade and can be positioned preferably independently of each other, as to adjust the amplitude of the strokes and the angles of the incidence of the flipper blade.

From US4025977A there are known "angular foot fins" having an angular blade orientation at an optimum angle of the drive plane with regard to a user's foot. The invention comprises a swim fin having an angular blade orientation relationship that can be changed with respect to a user's foot. The angular relationship allows for walking with the blade in a planar relationship with the sole of a user's foot. When the blade is bent downwardly, it permits the user to swim in an optimum manner.

From WO1988001523A1 there are known „improved swim fins" consisting of the shoe and the blade, separated and distinct parts, articulated and unlocked or locked together in any of a chosen fixed angular position. The shoe has inserted a device that at the front and lateral has two axes, in the central and frontal part evolves an arc like part with slots that hold the lock that is attached to the axis with "H" shaped device. This part has two extensions that are inserted in the blade and into the shoe. Swim fins with angularly adjusted blades allows the user to choose the best blade orientation to suit his needs, and are detachable and interchangeable with other fin blades of various sizes.

In other known patent description GB2331940A are disclosed swim fins having a block with hinges and latching mechanism to connect the fin blade at a specified angle. The possibility to release the blade after swimming or diving facilitates moving in shallow water, walking on land or coming aboard a water ship.

From patent description US5292272A there is known a "dual mode swim fin" designed both for swimming and walking. The fin consists of the boot and a bulbous connecting member providing an enlarged surface for increasing propulsive thrust.

From patent description EP0819450A1 there are known "swim-shoes for divers or swimmers" that have apparently the main characteristic features of normal shoes with an upwards lengthened shoe-instep in the form of a swim-blade with moulded profile of flow. This lengthened shoe-instep in the form of a swim-blade is oscillatory at will through the foot-joint, thereby all swim-styles are possible.

From FR2565498A1 there are known "swim fins" comprising a sandal and a flexible paddle that is connected to the sandal by means of an articulation device with a horizontal spindle in order thus to be held practically in line with the sole of the sandal or a walking position, in which it is raised upwards over the front end of the sandal. This solution is to facilitate walking by the swimmer out of the water after raising the paddle upwards over the front end of the sandal.

From US4752259A there are known "swim fins" which can be used either for swimming or walking. This solution is an improved swim fin construction which is efficient and practical in the water, while allowing the diver-swimmer to convert from the swim mode to a walking mode on any type surface including the water's bottom, on diving platforms, on ladders, in boats, and anywhere around a swimming environment. The swim fin consists of a rubber shoe and a fin integrally attached thereto by a rotating hinge. The outer portion of the fin may be folded upwardly on top of the shoe portion in the walking position or folded under the shoe. Suitable latching mechanisms are provided to keep the fin extended when used during swimming and retracted in the walking position.

The next patent description GB2237747A discloses a "swimming flipper" adapted to be used for swimming and for walking, having a foot engaging portion adapted to be worn by a user and a two-part fin formed of an inner portion and outer portion which are connected to each other and rotatable with respect to each other using a suitable hinge assembly so that the outer portion may be folded on top of or under the foot wearing portion to facilitate walking and to enable the outer portion to be extended to facilitate swimming. Suitable locks are provided to maintain the fin portions in the extended or folded positions. The main object of this invention is to reduce effort when swimming. By using a two-part fin or separated fin and shoe it is possible to adjust an angle between fin and shoe, thus also to distribute the pressure along the sole of feet and not only on tiptoes.

From EP2324889B1 there is known "flipper provided with an asymmetrically bending blade". This solution relates to a fin consisting of an open -heel bootee secured with a strap, and a flexible wing extending in the direction of the length under the flexible wing when moving in the water from up to down. The flexible wing on the opposite side of the flipper is then recumbent. Thereby the flexible element works as a stiffener that is effectively loaded when the flipper is moved downward and unencumbered when it is moved upward.

Form patent description FR2455905A1 there is known "variable curve swimming flipper" that has a flexible ribbing on the blade axis consisting of tabs overlapping each other, and enabling the blade inclination to be changed and its bending to be limited. The overlapping tabs are not distributed uniformly, thus the length of rigid blade sections is variable. The tabs are hinge-connected and have stops to limit fin blade bending. From patent description US6152794A there are known "swim fins" consisting of a foot pocket and a blade connected to it, wherein the foot pocket has a slopping upper face and a slopping sole respectively slopping from the heel thereof toward the blade that forwardly extends from front and two opposite lateral sides of the foot pocket and terminates in a forked end, having a thin middle portion, two thick side portions at two opposite lateral sides of the thin middle portion, two side rails respectively formed integral with the thick side portions at an outer side and a plurality of ribs respectively formed at top and bottom side walls thereof. The contained angle defined between the axis longitudinally extended from the back side of the blade and the upper face of the foot pocket or top side wall of the blade exceed 180° angle, and the reactive force which is produced from the water against the swim fin is effectively used to push the user forwards.

This present invention is therefore related to such a swim fin that produces less resistance and improves propelling speed when swimming in the water.

From patent description US20160287941A1 there is known a "swim fin". This solution relates to the new structure of the fin blade end that consists of segments with a positive incline and segments with a negative incline arranged alternate along the blade forming the shape of a wave, a triangle, a trapezium. Individual segments can be flat or curved in the shape of a wave. The lengths of two neighbouring segments with a transition define its total length. The heights of segments, total length and transition length can be equal, they can increase or decrease linearly, progressively or regressively. Segments can be arranged across the entire width of the blades surface or optionally in one part of the fin. The height of the segment is the highest at the root of the blade and decreases towards the ending of the blade until the transition to the flat part. The objective of the invention is to remove the noise in dynamically loaded blades made of materials with a high elastic modulus. The invention solves the said technical problem by creating a new shape of the blade. Due to its special shape, the blade, otherwise creating noise under dynamic pulsating load, is prevented from generating such surface tension, which would create noise.

From patent description US6758708B2 there are known "swim fins with energy storage and release system for improved angle of attack and water flow characteristics consisting of a foot pocket and a blade bending within a narrow range of angles of attack under a wide range of loads by providing varying resistance by one or more non-linear ribs. A “correct' angle of attack optimizes the conversion of kicking energy of the swimmer to propulsion through the water. When this angle is small, the blade is at a low angle of attack while this angle is high, the blade is at a high angle of attack. As the angle of attack increases, the flow collides with the fins attacking surface at a greater angle. This increases fluid pressure against this surface.

From US20040102110A1 there are known "swim fins" consisting of a foot pack and a blade, joined to each other to minimize the kick force. The blade swings up and down due to soft and flexible material used. The blade is designed in accordance with a shape of the tail fin of a whale or a stingray such that how to transmit the foot movement done by the wearer to the blade and to actuate smoothly with less effort. The blade is connected to the foot pack with rods of different hardness. The push force produced during up kick is about 60-70% of the push force during down kick.

From patent description WO2019053751A1 there are known "fins for underwater swimming" consisting of a foot pocket and a blade which has a first smaller portion and a second portion having a significantly larger surface with a substantially flat and elongated shape thus limiting lateral slip of the blades. The second portion is asymmetric with respect to the longitudinal plane arranged substantially at the centerline of the foot pocket and is narrower in its inner half-portion and wider in its outer half-portion. The first blade portion is rotated with respect to the longitudinal axis of the second portion. In order to reduce lateral slips during the fin kick (which cause a diagonal movement of the blade, reducing thrust efficiency), the protruding edges (lateral crests) arranged on the sides of the blades with the function of water flow channeling elements are provided.

From patent description US4007506A there are known "swim fins" consisting of a foot and a blade that includes a plurality of transversely spaced longitudinally extending ribs that are connected to each other by a web member. The ribs are comprised of a plurality of elongated flexible members juxtaposed upon each other with the elongated members being biased to interlocking tangs and grooves on the juxtaposed elongated members prevent lateral separation of the members. A pin passing transversely through the elongated members acts to limit the longitudinal displacement of one elongated member with respect to another. It is an object of the present invention to use an improved blade structure that allows the flexible blade to develop a reverse curve configuration during the kicking stroke.

In all disclosed solutions the inventors strived to improve the functionality of swim fins by changing materials or the shape of blade swinging from up to down and from down to up in the sagittal plane. There are also available in the market swim-shoes for breaststroke swimming with a portion added under the foot but without blade, while there are no general purpose fin that could allow, due to dynamic changes in longitudinal geometry of the active surface area (a longitudinally moulded blade), efficient oscillating movements of legs from up to down and from down to up in the sagittal plane used especially when swimming front crawl and butterfly stroke or outward and inward leg movements in the coronal plane in breaststroke swimming. The authors of the present invention aimed at developing such a swim fin.

The essence of the invention is a swim fin with a longitudinally moulded blade comprising a foot pocket configured to receive and secure a swimmer's foot, and containing a sole, sides and upper part of the slipper-shaped foot pocket or having a strap closure system and a blade being a working element of the fin acting as swimmer's propulsive thrust characterised in that the blade consists of two longitudinal profiles having V-shaped or U-shaped cross-section with a contained angle from 20 to 150 degrees, preferably of 90 degrees, attached to the front edge of the foot pocket, wherein the cross- sectional area of each profile increases in the direction opposite to the foot pocket, and longitudinal profiles are connected to each other in the end zone of inner edges of each of the profiles, preferably are spot joined with corners of the inner edges of each of the profiles, and between profile inner edges, the joint of these edges and the front edge of the foot pocket there is an opening forming a flow passage in a triangle-like shape. This opening when oscillating the legs during swimming allows water flow between profiles, thus reducing resistance and energy used by a swimmer when moving the legs in the preliminary phase (in front crawl and butterfly stroke from down to up and from up to down in back crawl).

Preferably, each of the blade longitudinal profiles is fitted with a flat stabilising slat positioned in the profile outer edge, preferably over its entire length, in such manner that slat branches extend both above and below the arbitrary plane being an extension of the foot pocket sole plane and the slat is preferably perpendicular to this plane, thereby ensuring the desired water flow direction. The stabilising slat reduces the lateral hydrodynamic drag by minimising turbulences occurring in the profile outer edges. Most preferably, the slat is made at the blade manufacturing stage by using two-component injection moulding.

In the first preferable embodiment, the foot pocket is made of plastic with Shore hardness between 30 and 120, preferably of thermoplastic elastomer, while the blade is made of Kevlar or a mixture of Kevlar and rubber or plasticised polycarbonate or polyurethane or silicone with Shore hardness between 30 and 120.

In the second preferable embodiment, the foot pocket is made of plastic with Shore hardness between 30 and 120, preferably of thermoplastic elastomer, while the blade is made of carbon fibre, preferably reinforced with a resin or a mixture of carbon fibre and resin or plasticised polycarbonate or polyurethane or silicone with Shore hardness between 30 and 120.

In the third preferable embodiment, the foot pocket and the blade are made of thermoplastic elastomer in the form of polyurethane with Shore hardness between 30 and 90.

Preferably, the stabilising slats are made of:

- Kevlar or mixture of Kevlar with rubber or plasticised polycarbonate or polyurethane or silicone with Shore hardness between 30 and 120, or

- carbon fibre, preferably reinforced with a resin or carbon fibre with rubber or plasticised polycarbonate or polyurethane or silicone with Shore hardness between 30 and 120, or

- polyurethane of Shore hardness between 30 and 120, most preferably, the stabilising slats are made of the same material as the blade.

Preferably, the blade length is between 20 and 250% of the foot pocket length and most preferably is equal to 80% of the foot pocket. An increase of the blade length above the preferable value involves increased loads in ankle and knee joints during swimming. The longer blade the higher load on joints, which during prolonged use may lead to osteoarthritis in both joints. But decreasing the blade length below the preferable value will limit the working (active) surface area, thus resulting in loss of thrust/propulsive force while reducing the resistance created by the fin.

Preferably, in the embodiment with a blade made of a high hardness material, i.e. Shore hardness above 45, the plane of the blade is inclined downward with respect to the foot pocket sole by 5 to 40 degrees, preferably 20 degrees.

Preferably, the fin contains reinforcing rods made of carbon fibre built in the blade along the longitudinal axis. The use of rods provides additional stiffening of the structure and prevents changes in fin geometry during dynamic swimming.

The foot pocket is appropriately profiled to be fit to swimmer's foot, preferably with slightly inclined downward to toe-ends (due to the vector of generated propulsive force) and has a flat sole, i.e. without folds or protrusions to allow free walking on the water's bottom or out of the water.

Preferably, the foot pocket comprises anti slip pads on the outer surface of the sole made of any flexible material, especially silicone or rubber.

Most preferably, the foot pocket sole is made of thermoplastic elastomer with Shore hardness between 60 and 90, while the sides and upper part of the foot pocket are made of thermoplastic elastomer with Shore hardness between 30 and 60.

Preferably, a thermoplastic elastomer used for manufacturing the foot pocket is admixed with an antimicrobial and antifungal substance in the form a mixture of silver and copper nanoparticles, preferably with an addition of nanosilica suspended in an alkoxide or oil performing a role of a stabilising agent at the amount from 0.05 to 10%, preferably 0.2% of the protective substance with respect to the base material, and proportions of nanoparticle mixture to the stabilising agent are from 0.1:1 to 15:1, preferably 1:1, while proportions of individual nanoparticles in protective substance are as follows: silver nanoparticles: copper nanoparticles : nanosilica are from 0.1:0.1:9.8 to 5:5:0, preferably 1:3:6. Preferably, propylene glycol or ethylene glycol is used as an alkoxide in which a mixture of nanoparticles is suspended. Preferably, an organic or mineral oil, most preferably silicone oil, is used as an oil in which a mixture of nanoparticles is suspended.

Preferably, the stabilising slats at its ends, i.e. distal parts of the blade have a height between 2 and 5 cm that steeply decreases towards the foot pocket, where it reaches the value of 1 to 2 cm at the joint with the foot pocket.

Preferably, the foot pocket is made of:

- Kevlar of Shore hardness between 30 and 60, or

- resin reinforced with carbon fibre with Shore hardness between 230 and 60, or

- polyurethane with Shore hardness between 30 and 90, or

- plasticised polycarbonate with Shore hardness between 30 and 90, or

- rubber with Shore hardness between 30 and 60, or - mixture of Kevlar with rubber or plasticised polycarbonate or polyurethane or silicone with Shore hardness between 30 and 120, or

- mixture of carbon fibre with rubber plasticised polycarbonate or polyurethane or silicone with Shore hardness between 30 and 120.

An advantage of composite materials is that we gain advantage from using various types of materials, thus eliminating or reducing drawbacks of individual components used such as abrasion or brittle fracture defects.

The fin according to present invention, despite of its relatively short working element, has four preferably perpendicular blade longitudinal surfaces that provides a large actual surface area of the working element, thus minimising drawbacks resulting from the use of long fins when using different swimming styles, including breaststroke. Such fin construction improves hydrodynamic characteristics by providing laminar and directed water flow during swimming. The fin is advantageous both for swimming courses as well as for improving breaststroke swimming and for other sport swimming techniques because of large lateral drag resulting from enlarged side surface of the profiles. The fin can work both in the sagittal plane, as in front and back crawl techniques, as well as it has a quite high lateral drag, enabling the swimmer to generate an appropriate propulsive force when he moves legs in the coronal plane as in breaststroke swimming, or for a rescuer towing the victim while swimming backstroke by using leg movements as in breaststroke swimming. The fin construction allows the lateral drag to be used more effectively, while increasing swimmer's speed, thus reducing swimmer's fatigue, while increasing an actual swimming speed of a sportsman or rescuer.

The solution according to the present invention has many advantages over the prior art, and the most important among them are described below.

Due to the variable geometry of the fin active surface (with longitudinally moulded blades) according to the invention, the fins enable faster and more efficient swimming when oscillating the legs from up to down used primarily in front and back crawl swimming as well as when swimming butterfly stroke or breaststroke.

The solution according to the present invention due the variable geometry of the blade active surface (with longitudinally moulded blades) gives it higher stiffness when oscillating the legs from up to down and generates stronger and more streamed (oriented) forces pushing water backwards, thus making leg movement more efficient than conventional fins of the same contour. The swimmer using conventional fins when oscillating from up to down presses water with the flat blade surface, and water runs down equally both backwards and on sides. The swimmer by using the fins according to the present invention due to dynamic variable geometry of the longitudinal blade active surface (fins with longitudinally moulded blades) and proportionally less effort achieves higher power and related speed than with the conventional fins. When attempting to use equivalent effort by using conventional fins, the swimmer can use fins with a dynamic variable geometry of longitudinal active surface of clearly smaller blade. The fin according to the present invention due to the variable geometry of the blade active surface (with longitudinally moulded blades) causes that during the return leg movement from down to up when oscillating the legs in front crawl and symmetrical leg movements as in butterfly stroke (or vice versa, i.e. from up to down when oscillating the legs during swimming in back crawl) the fin due its cone shaped outer surface or U-shaped blade and a flow passage opening between the profiles over which water flows easier and significantly lower drag is generated then when moving the same fin from up to down, thus requires less user's effort, and thereby causes less leg fatigue. When using a conventional fin during the return leg movement the fin presses water at unfavourable angles of attack with its entire flat surface, thus requires the same high effort as when oscillating the legs from up to down, while achieving a significantly lower swimming effect.

The solution according to the present invention due to the variable geometry of the blade active surface causes that when oscillating the legs during swimming the fins as a whole are set at the same angle of attack, thus the entire blade surface generates similar thrust. In addition, the angle of attack is also adjusted when oscillating the legs during swimming and return movement due to flexible (not rigid) connections between the foot pocket and the blade. When oscillating the conventional fin the blade is most often more rigid close to the foot pocket and more flexible at the blade ends, thereby its more rigid proximal portion of the foot pocket presses water at less favourable angles of attack, thus reducing the resultant of favourable angles of attack.

The solution according to the present invention due to the variable geometry of the blade active surface causes that when oscillating the legs from the position when the legs are stretched and connected by bending at the hip, knee and ankle joints, and moving the legs backward and outward, the generated propulsive force allows efficient and fast breaststroke swimming due to significantly enlarged side surfaces of the blade and the foot pocket.

The flat stabilising slats provided to improve efficiency of the working element, i.e. blade, enable to direct the force backwards behind the swimmer, thus producing less resistance when the leg returns when oscillating from down to up, minimising energy loss when directing the water vertically downward. In addition, both side stabilising slats ensure more streamlined, laminar water flow through the working element. The stabilising slats stabilise the fin during oscillatory and undulatory swimming such as front or back crawl, and generate additional lateral drag and prevent cavitation when using symmetrical techniques like butterfly stroke or breaststroke. The slats prevent from generating turbulent motions in the fine side area. Furthermore, the slats reinforce and stiffen blade profiles, directing the energy backward instead of vertically, downward and upward, thus improving swimmer's efficiency and reducing his fatigue, increasing the speed and efficiency. Further, such system reduces the load on the locomotor system, e.g. ankle and knee joints, by generating the force only along lower limbs without any additional lateral loads.

In one embodiment wherein Kevlar or a mixture of Kevlar with rubber or plasticised polycarbonate or polyurethane, or, carbon fibre, preferably reinforced with a resin or a mixture of carbon fibre and rubber or plasticised polycarbonate or polyurethane or silicone, i.e. materials of low density and high strength, especially of high fatigue resistance and tensile strength, were used, the fin of very low weight (ultralight) was obtained that gives the target fin the best possible strength-to-weight ratio.

The use of carbon fibre considerably reduces the weight with respect to other organic materials, while maintaining high tensile strength, shape stability, dimensional stability and fatigue resistance, that is hard to achieve for other materials.

In an embodiment of the fin wherein polyurethane was used an additional advantage is a moderate cost of his material, thereby the fins can be widely used also in amateur swimming and swimming lessons. Furthermore, the use of polyurethane in the manufacture of fins ensures an effective and uncomplicated application of processing methods with a wide range of tolerances, thus reducing costs and complexity of manufacturing processes. Thereby, the fin can be manufactured without a highly qualified and specialised personnel. This fin type is suitable for small batch production.

The fin according to the present invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings, where Fig. 1 shows a front perspective view of the fin, Fig. 2 shows a back perspective view of the fin, Fig. 3 shows a top view of the fin, Fig. 4 shows a side view of the fin, Fig. 5 shows a back view of the fin, Fig. 6 shows a front view of the fin, Fig. 7 shows a front perspective view of the fin with stabilising slats, Fig. 8 shows a front view of the fin with stabilising slats, and Fig. 9 shows a side view of the fin with stabilising slats.

Example 1

The solution according to this exemplary embodiment is a swim fin with a longitudinally moulded blade, consisting of a foot pocket 1 securing the swimmer's foot, and containing a sole, sides and upper part of the slipper- shaped foot pocket, and a blade 2 being a working element acting as swimmer's propulsive thrust. The blade 2 consists of two longitudinal profiles 2' and 2" having V-shaped cross-section with a contained angle of 90 degrees, attached to the front edge 1' of the foot pocket 1 wherein the cross-sectional area of each profile increases in the direction opposite to the foot pocket, and longitudinal profiles 2' and 2" are adhesively connected to each other in the end zone of the inner edges of each of the profiles, forming the joint 4.

There is an opening 3 between the inner edges of the longitudinal profiles 2' and 2", corner joint 4 of these edges and the front edge 1' of the foot pocket 1, being a flow passage in a triangle-like shape.

The length of the blade 2 is 120 % of the length of the foot pocket 1.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 50 and 70, wherein the foot pocket sole is made of thermoplastic polyurethane with Shore hardness of 70, and the side and upper part of the foot pocket is made of thermoplastic polyurethane with Shore hardness of 50. Polyurethane contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 1:3:6, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The amount of the protective substance to the base material is 0.2%.

The blade 2 is made of polyurethane with Shore hardness of 70.

Example 2

The fin of basic construction as in Example 1, wherein each of the longitudinal profiles 2' and 2" of the blade 2 is further provided with a flat stabilising slat 6 positioned in the profile outer edge over its entire length in such manner that slat branches extend both above and below the arbitrary plane being an extension of the foot pocket sole plane, and the slat 6 is perpendicular to this plane. The stabilising slats 6 at its ends, i.e. distal parts of the blade 2 have a height of 5 cm that steeply decreases towards the foot pocket 1 , and reaches 2 cm at the joint with the foot pocket.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 50 and 60, wherein the foot pocket sole is made of thermoplastic polyurethane with Shore hardness of 60, and the side and upper part of the foot pocket is made of thermoplastic polyurethane with Shore hardness of 50. Polyurethane contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide, wherein proportions of individual nanoparticles in protective substance are 1:3:6, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 0.8%.

The blade 2 and stabilising slats 6 are made of polyurethane with Shore hardness of 70.

Example 3

The solution according to this exemplary embodiment is a swim fin with a longitudinally moulded blade, consisting of a foot pocket 1 securing the swimmer's foot, and containing a sole, sides and upper part of the slipper- shaped foot pocket, and a blade 2 being a working element acting as swimmer's propulsive thrust. The blade 2 consists of two longitudinal profiles 2' and 2" having U-shaped cross-section with a contained angle of 80 degrees, attached to the front edge 1' of the foot pocket 1, wherein the cross-sectional area of each profile increases in the direction opposite to the foot pocket, and longitudinal profiles 2' and 2" are adhesively connected to each other in the end zone of the inner edges of each of the profiles, forming the joint 4.

There is an opening 3 between the inner edges of the longitudinal profiles 2' and 2", corner joint 4 of these edges and the front edge 1' of the foot pocket 1, being a flow passage in a triangle-like shape.

The length of the blade 2 is 80 % of the length of the foot pocket l .

The fin contains four reinforcing rods 5 made of carbon fibre built into the blade 2 along the longitudinal axis. The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 40 and 50, wherein the foot pocket sole is made of thermoplastic polyurethane with Shore hardness of 50, and the side and upper part of the foot pocket is made of thermoplastic polyurethane with Shore hardness of 40. Polyurethane contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 1:2:5, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 0.9%.

The blade 2 is made of polyurethane with Shore hardness of 65.

Example 4

The fin of basic construction as in Example 3, wherein each of longitudinal profiles 2 and 2 of the blade 2 is further provided with a flat stabilising slat 6 positioned in the profile outer edge over its entire length in such manner that slat branches extend both above and below the arbitrary plane being an extension of the foot pocket sole plane, and the slat 6 is perpendicular to this plane. The stabilising slats 6 at its ends, i.e. distal parts of the blade 2 have a height of 5 cm that steeply decreases towards the foot pocket 1, and reaches the value of 2 cm at the joint with the foot pocket.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 40 and 50, wherein the foot pocket sole is made of thermoplastic polyurethane with Shore hardness of 50, and the side and upper part of the foot pocket is made of thermoplastic polyurethane with Shore hardness of 40. Polyurethane contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 1:2:5, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 0.1 %.

The blade 2 and stabilising slats 6 are made of polyurethane with Shore hardness of 65.

Example 5

The solution according to this exemplary embodiment is an ultralight swim fin with a longitudinally moulded blade, consisting of a foot pocket 1 securing the swimmer's foot, and containing a sole, sides and upper part of the slipper- shaped foot pocket, and a blade 2 being a working element acting as swimmer's propulsive thrust. The blade 2 consists of two longitudinal profiles 2' and 2" having V-shaped cross-section with a contained angle of 90 degrees, attached to the front edge 1' of the foot pocket 1 wherein the cross-sectional area of each profile increases in the direction opposite to the foot pocket, and longitudinal profiles 2 and 2 are adhesively connected to each other in the end zone of the inner edges of each of the profiles, forming the joint 4. There is an opening 3 between the inner edges of the longitudinal profiles 2' and 2", corner joint 4 of these edges and the front edge 1' of the foot pocket 1, being a flow passage in a triangle-like shape.

The length of the blade 2 is 120 % of the length of the foot pocket 1.

The surface of the blade 2 is canted 15 degrees downward with respect to the plane of the sole of the foot pocket 1.

The fin contains four reinforcing rods 5 made of carbon fibre built into the blade 2 along the longitudinal axis.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 50 and 60, wherein the foot pocket sole is made of thermoplastic polyurethane with Shore hardness of 60, and the side and upper part of the foot pocket is made of thermoplastic polyurethane with Shore hardness of 50. Polyurethane contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 2:0.5:6, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 6%.

The blade 2 is made of Kevlar with Shore hardness of 120.

Example 6

The fin of basic construction as in Example 5, wherein each of longitudinal profiles 2' and 2 of the blade 2 is further provided with a flat stabilising slat 6 positioned in the profile outer edge over its entire length in such manner that slat branches extend both above and below the arbitrary plane being an extension of the foot pocket sole plane, and the slat 6 is perpendicular to this plane. The stabilising slats 6 at its ends, i.e. distal parts of the blade 2 have a height of 5 cm that steeply decreases towards the foot pocket 1, and reaches the value of 2 cm at the joint with the foot pocket.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 50 and 60, wherein the foot pocket sole is made of thermoplastic polyurethane with Shore hardness of 60, and the side and upper part of the foot pocket is made of thermoplastic polyurethane with Shore hardness of 50. Polyurethane contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in protective substance are 1:3:6, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 0.4%.

The blade 2 and stabilising slats 6 are made of Kevlar with Shore hardness of 120.

Example 7 The solution according to this exemplary embodiment is an ultralight swim fin with a longitudinally moulded blade, consisting of a foot pocket 1 securing the swimmer's foot, and containing a sole, sides and upper part of the slipper- shaped foot pocket, and a blade 2 being a working element acting as swimmer's propulsive thrust. The blade 2 consists of two longitudinal profiles 2' and 2" having U-shaped cross-section with a contained angle of 90 degrees, attached to the front edge 1' of the foot pocket 1 wherein the cross-sectional area of each profile increases in the direction opposite to the foot pocket, and longitudinal profiles 2' and 2" are adhesively connected to each other in the end zone of the inner edges of each of the profiles, forming the joint 4.

There is an opening 3 between the inner edges of the longitudinal profiles 2' and 2", corner joint 4 of these edges and the front edge 1' of the foot pocket 1, being a flow passage in a triangle-like shape.

The length of the blade 2 is 150 % of the length of the foot pocket 1.

The surface of the blade 2 is canted 20 degrees downward with respect to the plane of the sole of the foot pocket 1.

The fin contains four reinforcing rods 5 made of carbon fibre built into the blade 2 along the longitudinal axis.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 60 and 60, wherein the foot pocket sole is made of plasticised polycarbonate with Shore hardness of 50, and the side and upper part of the foot pocket is made of plasticised polycarbonate with Shore hardness of 50. Polycarbonate contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 2:2:3, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 8%.

The blade 2 is made of Kevlar with Shore hardness of 110.

Example 8

The fin of basic construction as in Example 7, wherein each of the longitudinal profiles 2' and 2" of the blade 2 is further provided with a flat stabilising slat 6 positioned in the profile outer edge over its entire length in such manner that slat branches extend both above and below the arbitrary plane being an extension of the foot pocket sole plane, and the slat 6 is perpendicular to this plane. The stabilising slats 6 at its ends, i.e. distal parts of the blade 2 have a height of 5 cm that steeply decreases towards the foot pocket 1, and reaches the value of 2 cm at the joint with the foot pocket.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 40 and 50, wherein the foot pocket sole is made of thermoplastic polyurethane with Shore hardness of 50, and the side and upper part of the foot pocket is made of thermoplastic polyurethane with Shore hardness of 40. Polyurethane contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 1:2:5, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 1 %.

The blade 2 and stabilising slats 6 are made of Kevlar with Shore hardness of 120.

Example 9

The solution according to this exemplary embodiment is an ultralight swim fin with a longitudinally moulded blade, consisting of a foot pocket 1 securing the swimmer's foot, and containing a sole, sides and upper part of the slipper- shaped foot pocket, and a blade 2 being a working element acting as swimmer's propulsive thrust. The blade 2 consists of two longitudinal profiles 2' and 2" having V-shaped cross-section with a contained angle of 80 degrees, attached to the front edge 1' of the foot pocket 1 wherein the cross-sectional area of each profile increases in the direction opposite to the foot pocket, and longitudinal profiles 2 and 2 are adhesively connected over a section with length of 10 cm of each of the profiles, forming the joint 4.

There is an opening 3 between the inner edges of the longitudinal profiles 2' and 2", corner joint 4 of these edges and the front edge 1' of the foot pocket 1, being a flow passage in a triangle-like shape.

The length of the blade 2 is 85 % of the length of the foot pocket 1.

The surface of the blade 2 is canted 15 degrees downward with respect to the plane of the sole of the foot pocket 1.

The fin contains four reinforcing rods 5 made of carbon fibre built into the blade 2 along the longitudinal axis.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between of 60, wherein the foot pocket sole is made of Kevlar with Shore hardness of 60, and the side and upper part of the foot pocket is made of rubber with Shore hardness of 60. Kevlar contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 1:2:6, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 2%.

The blade 2 is made of a mixture of Kevlar and plasticised polycarbonate with Shore hardness of 100.

Example 10

The solution according to this exemplary embodiment is an ultralight swim fin with a longitudinally moulded blade, consisting of a foot pocket 1 securing the swimmer's foot, and containing a sole, sides and upper part of the slipper-shaped foot pocket, and a blade 2 being a working element acting as swimmer's propulsive thrust. The blade 2 consists of two longitudinal profiles 2' and 2" having V-shaped cross-section with a contained angle of 90 degrees, attached to the front edge 1' of the foot pocket 1 wherein the cross-sectional area of each profile increases in the direction opposite to the foot pocket, and longitudinal profiles 2' and 2" are adhesively connected over a section with length of 5 cm of each of the profiles, forming the joint 4.

There is an opening 3 between the inner edges of the longitudinal profiles 2' and 2", corner joint 4 of these edges and the front edge 1' of the foot pocket 1, being a flow passage in a triangle-like shape. The length of the blade 2 is 80 % of the length of the foot pocket 1.

The surface of the blade 2 is canted 10 degrees downward with respect to the plane of the sole of the foot pocket 1.

The fin contains four reinforcing rods 5 made of carbon fibre built into the blade 2 along the longitudinal axis.

Each of longitudinal profiles 2' and 2" of the blade 2 is provided with a flat stabilising slat 6 positioned in the profile outer edge over its entire length in such manner that slat branches extend both above and below the arbitrary plane being an extension of the foot pocket sole plane, and the slat 6 is perpendicular to this plane. The stabilising slats 6 at its ends, i.e. distal parts of the blade 2 have a height of 5 cm that steeply decreases towards the foot pocket 1, and reaches the value of 2 cm at the joint with the foot pocket.

The foot pocket 1 of the fin is made of thermoplastic polymer with Shore hardness between 40 and 50, wherein the foot pocket sole is made of Kevlar with Shore hardness of 100, and the side and upper part of the foot pocket is made of plasticised polycarbonate with Shore hardness of 40. Plasticised polycarbonate contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in protective substance are 0.2:3 :5, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 5%.

The blade 2 and stabilising slats 6 are made of a mixture of Kevlar and plasticised polycarbonate with Shore hardness of 120.

Example 11

The solution according to this exemplary embodiment is an ultra-strong swim fin with a longitudinally moulded blade, consisting of a foot pocket 1 securing the swimmer's foot, and containing a sole, sides and upper part of the slipper-shaped foot pocket, and a blade 2 being a working element acting as swimmer's propulsive thrust. The blade 2 consists of two longitudinal profiles 2' and 2" having V-shaped cross-section with a contained angle of 90 degrees, attached to the front edge 1' of the foot pocket 1 wherein the cross-sectional area of each profile increases in the direction opposite to the foot pocket, and longitudinal profiles 2 and 2 are adhesively connected to each other in the end zone of the inner edges of each of the profiles, forming the joint 4. There is an opening 3 between the inner edges of the longitudinal profiles 2' and 2", corner joint 4 of these edges and the front edge 1' of the foot pocket 1, being a flow passage in a triangle-like shape. The length of the blade 2 is 120 % of the length of the foot pocket 1.

The surface of the blade 2 is canted 15 degrees downward with respect to the plane of the sole of the foot pocket 1.

The fin contains four reinforcing rods 5 made of carbon fibre built into the blade 2 along the longitudinal axis.

The foot pocket 1 is made of thermoplastic elastomer with Shore hardness between 50 and 60, wherein the foot pocket sole is made of thermoplastic polyurethane with Shore hardness of 60, and the side and upper part of the foot pocket is made of thermoplastic polyurethane with Shore hardness of 50. Polyurethane contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 2:0.5:6, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 0.5%.

The blade 2 is made of carbon fibre with Shore hardness of 120.

Example 12

The fin of basic construction as in Example 11, wherein each of longitudinal profiles 2' and 2" of the blade 2 is further provided with a flat stabilising slat 6 positioned in the profile outer edge over its entire length in such manner that slat branches extend both above and below the arbitrary plane being an extension of the foot pocket sole plane, and the slat 6 is perpendicular to this plane. The stabilising slats 6 at its ends, i.e. distal parts of the blade 2 have a height of 5 cm that steeply decreases towards the foot pocket 1, and reaches the value of 2 cm at the joint with the foot pocket.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 50 and 60, wherein the foot pocket sole is made of thermoplastic polyurethane with Shore hardness of 60, and the side and upper part of the foot pocket is made of thermoplastic polyurethane with Shore hardness of 50. Polyurethane contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 1:3:6, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 10%.

The blade 2 and stabilising slats 6 are made of Kevlar with Shore hardness of 120.

Example 13

The solution according to this exemplary embodiment is an ultra-strong swim fin with a longitudinally moulded blade, consisting of a foot pocket 1 securing the swimmer's foot, and containing a sole, sides and upper part of the slipper-shaped foot pocket, and a blade 2 being a working element acting as swimmer's propulsive thrust. The blade 2 consists of two longitudinal profiles 2' and 2" having U-shaped cross-section with a contained angle of 90 degrees, attached to the front edge 1' of the foot pocket 1 wherein the cross-sectional area of each profile increases in the direction opposite to the foot pocket, and longitudinal profiles 2' and 2" are adhesively connected to each other in the end zone of the inner edges of each of the profiles, forming the joint 4.

There is an opening 3 between the inner edges of the longitudinal profiles 2' and 2", corner joint 4 of these edges and the front edge 1' of the foot pocket 1, being a flow passage in a triangle like shape. The length of the blade 2 is 150 % of the length of the foot pocket 1.

The surface of the blade 2 is canted 20 degrees downward with respect to the plane of the sole of the foot pocket 1.

The fin contains four reinforcing rods 5 made of carbon fibre built into the blade 2 along the longitudinal axis.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 50 and 60, wherein the foot pocket sole is made of plasticised polycarbonate with Shore hardness of 60, and the side and upper part of the foot pocket is made of plasticised polycarbonate with Shore hardness of 50. Polycarbonate contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 2:2:3, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 0.5%.

The blade 2 is made of carbon fibre reinforced with a resin with Shore hardness of 90.

Example 14

The fin of basic construction as in Example 13, wherein each of longitudinal profiles 2' and 2" of the blade 2 is further provided with a flat stabilising slat 6 positioned in the profile outer edge over its entire length in such manner that slat branches extend both above and below the arbitrary plane being an extension of the foot pocket sole plane, and the slat 6 is perpendicular to this plane. The stabilising slats 6 at its ends, i.e. distal parts of the blade 2 have a height of 5 cm that steeply decreases towards the foot pocket 1, and reaches the value of 2 cm at the joint with the foot pocket.

The foot pocket 1 of the fin is made of thermoplastic elastomer with Shore hardness between 40 and 50, wherein the foot pocket sole is made of thermoplastic polyurethane with Shore hardness of 50, and the side and upper part of the foot pocket is made of thermoplastic polyurethane with Shore hardness of 40. Polyurethane contains an addition of a protective substance in the form of a mixture of silver and copper nanoparticles and nanosilica suspended in an alkoxide (ethylene glycol), wherein proportions of individual nanoparticles in the protective substance are 1:2:5, respectively, and the proportion of nanoparticle mixture to the alkoxide is 1:1. The ratio of the protective substance to the base material is 0.05%.

The blade 2 and stabilising slats 6 are made of a mixture of carbon fibre and rubber with Shore hardness of 110.

Example 15

The solution according to this exemplary embodiment is an ultra-strong swim fin with a longitudinally moulded blade, consisting of a foot pocket 1 securing the swimmer's foot, and containing a sole, sides and upper part of the slipper-shaped foot pocket, and a blade 2 being a working element acting as swimmer's propulsive thrust. The blade 2 consists of two longitudinal profiles 2' and 2" having V-shaped cross-section with a contained angle of 80 degrees, attached to the front edge 1' of the foot pocket 1 wherein the cross-sectional area of each profile increases in the direction opposite to the foot pocket, and longitudinal profiles 2' and 2" are adhesively connected over a section with length of 15 cm of each of the profiles, forming the joint 4.

There is an opening 3 between the inner edges of the longitudinal profiles 2' and 2", corner joint 4 of these edges and the front edge 1' of the foot pocket 1, being a flow passage in a triangle-like shape. The length of the blade 2 is 200 % of the length of the foot pocket 1.

The surface of the blade 2 is canted 10 degrees downward with respect to the plane of the sole of the foot pocket 1.

The fin contains four reinforcing rods 5 made of carbon fibre built into the blade 2 along the longitudinal axis.

The foot pocket 1 (both the sole, sides as well as the upper part) is made of carbon fibre mixed with plasticised polycarbonate with Shore hardness of 120.

The blade 2 is made of carbon fibre with Shore hardness of 120.

Example 16

The fin of basic construction as in Example 15, wherein each of longitudinal profiles 2 and 2 of the blade 2 is further provided with a flat stabilising slat 6 positioned in the profile outer edge over its entire length in such manner that slat branches extend both above and below the arbitrary plane being an extension of the foot pocket sole plane, and the slat 6 is perpendicular to this plane. The stabilising slats 6 at its ends, i.e. distal parts of the blade 2 have a height of 5 cm that steeply decreases towards the foot pocket 1, and reaches the value of 2 cm at the joint with the foot pocket.

The foot pocket 1 of the fin (both the sole, sides as well as the upper part) are made of thermoplastic elastomer in the form of a mixture of Kevlar and plasticised polycarbonate with Shore hardness of 70. The blade 2 and stabilising slats 6 are made of a mixture of carbon fibre and rubber with Shore hardness of 100. The solution according to the present invention can be used particularly in swimming lessons as well as in swimming in sports and rehabilitation as well as for water rescue and diving purposes.

In swimming in sports the use of swim fins according to the present invention expands the range of methods and means for shaping techniques and conditioning abilities by doing general and specific exercises.

In swimming in rehabilitation the use of swim fins according to the present invention enables persons working out in water for restoring their physical shape to move the legs in any pace and rhythm in all directions with a specified effort.

In water rescue the use of swim fins according to the present invention allows a rescuer to swim out to the victim and easier adaptation to the actual situation and to help the victim more effectively by offering the possibility of changing oscillating movements into symmetric ones and vice versa.

In diving with a breath held and when using a breathing apparatus the use of the present invention will enable effective descending and ascending by using oscillatory leg movements, and symmetric backward and outward leg movements as in breaststroke, when it is necessary to penetrate the bottom or to reduce the turbidity of water.

The swim fin according to the present invention is a flexible fin that strains the ankle and knee joint to a small extent. This fin is especially recommended for persons with an injury to their ankle or knee joints, and is suitable for spine rehabilitation and for strengthening deep core muscles.