The invention relates to swim fins, mostly with the shape of the fins' blade.

The fins used today by professional divers are made of materials with a high elastic modulus. Carbon fibres covered with different polymeric materials such as epoxy or polyester are most commonly used. Materials with a high elastic modulus increase the efficiency of the fin. During use, the fin's blade is under a dynamic pulsating load, as the leg and the fin are moved up and down. Compressive and tensile force are alternately applied to the external surface of the blade longitudinally with the flow of the medium, i.e. water. Due to this alternating application of compressive and tensile force to the fin's blade as well as movement, the blade makes a noise similar to a click, which can be heard in the water. This noise is disturbing because it prevents the diver from soundlessly approaching fish, for example, if he wants to observe, photograph or catch them. The larger the elastic modulus of the material of the fin or the fin's blade, the louder the noise generated by the blade during regular use. The necessity to make a fin or a blade that would reduce or remove this noise therefore occurred. The problem was solved by creating a special shape of the fin's blade, which, longitudinally, has an alternating incline of the blade or the blade's surface, for example in the shape of a sinusoid with decreasing amplitude.

The development in the field of fins was mostly aimed at different structures of fins and different materials of which the fins are made, enabling higher efficiency of the fin, the force, which should be applied by the user to maximize the effect of his work. The EP 2055353 patent application therefore describes the structure of the fin, which has two side parts extending along the entire length of the fin from the foot pocket, i.e. along the entire blade. The blade is attached to these side parts only in two spots, in the upper part, where the foot pocket extends into the blade, and towards the end of the blade. In the central part, the blade is flexible in the transverse up and down direction. The US 2012/0289105 patent application describes the structure of the fin, whose central part of the blade is attached to some kind of hinges at the end of the fin enabling the undulation of the fin in the transverse up-down direction, while a membrane limiting the movement of the blade is attached to the flexible blade along the left and right edge of the fin in the longitudinal direction. Since 1990, when first carbon-fibre fins creating noise during regular use appeared, people have been dealing with the problem of removing or limiting this noise. The purpose and objective of the invention is to remove the noise, the click, 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 or its surface, otherwise creating noise under dynamic pulsating load, is prevented from generating such surface tension, which would create noise or clicks.

In fins made of materials with a high elastic modulus, different thermoplastic or composite materials such as carbon, glass and other fibres covered with various polymeric materials, based on the state of the art, the blade is flat or mainly flat, while the entire surface is levelled or mainly levelled. During regular use of the fins, when the user is swimming with up and down strokes, compressive and tensile force are alternately applied to the surface of the blade longitudinally with the flow of the medium. When the blade is bent downwards, tensile force is applied to its external surface, i.e. the side turned towards the water surface during swimming, while compressive force is applied to the inner surface of the blade, i.e. the side turned towards the bottom during swimming. When the blade is bent upwards, the forces are interchanged. Tensile force is replaced by compressive force and vice-versa.

In ideal circumstances, which are never achieved, there would be no noise or click, the surface of the blade would be perfectly smooth, the blade would be completely rigid in the transverse direction, the distribution of forces on the blade under a load, when the user is swimming with up and down strokes, would be completely equal in the transverse direction, thus the force exchange from compressive to tensile force would be connective and not instantaneous. Due to the above- mentioned reasons, random surface parts, bent in the opposite direction as they should be according to the application of compressive and tensile forces to this part of the surface in the given moment, could not be generated on the surface of the blade.

In reality, the surface of the blade is not perfectly smooth, the blade is not completely rigid in the transverse direction and during use, when the user is swimming with up and down strokes, the blade is under dynamic load causing the local formation of areas with different force combinations. Consequently, random locally defined areas with opposite camber according to the forces applied to that part of the blade's surface in that moment, appear on the surface of the blade. This means that parts of the blade's surface bend concavely or convexly, in the opposite direction as they should according to the current application of tensile or compressive force to the surface of the blade. For example, the part of the surface should be bent concavely according to the forces, but it is bent convexly or vice-versa. Due to the application of tensile or compressive force, the camber of this part of the surface changes instantaneously, which creates noise: a click. The number of these random locally defined surfaces of the blade and the camber level, as well as the loudness of the noise or click are affected by the basic structure of the blade, i.e. its flatness, the flexibility of the material, the medium in which the fin is used, being mostly commonly water, and other factors.

If the blade of the fin changes in terms of its structure, the blade being produced in a form which enables all three dimensions and increased rigidity in the transverse direction of the blade, random local surfaces on the blade with reverse camber are reduced or even completely disabled, which minimises or removes the noise or click.

The invention is described by using examples and drawings showing the following:

Figure 1 : Structure of the fin based on the state of the art

Figure 2/1 : Different segment shapes with and without transitions and ground plan of the fin

Figure 2/2: Side view of the fin Figure 3: Example of a blade with triangular segments and straight transitions

Figure 4: Example of a blade with wave-shaped segments and straight transitions

Figure 5: Example of the most preferable blade with wave-shaped segments and connective transitions, in the shape of a sinusoid

Figure 1 shows the fin based on the state of the art. It consists of foot pocket 1 and blade 2. Foot pocket 1 can be made of rubber or various thermoplastic materials. Blade 2 is usually made of different thermoplastic or composite materials such as carbon, glass or other fibres. Side 3 can be rubber-coated across the entire length. Wings, which are not shown in the drawing, can be made or attached sideways to stabilise the fins. The rubber profile prevents the water from leaking sideways and also stabilises the movement of the fin in the direction of the swimming. According to the invention, the blade is made of S segments and T transitions, which follow each other along blade 2, while the inclines of individual S segments according to the longitudinal axis of the fin are alternately changing. If the initial SI segment at root 7 has an increasing incline, the following S2 segment has a decreasing incline, the third S3 segment an increasing one again and so on. The initial SI segment can also have a decreasing incline, which means the following S2 segment will have an increasing incline, the third S3 segment a decreasing one, etc. The segment inclines according to the longitudinal direction of the blade can therefore follow each other randomly, but the segment with an increasing incline must always be followed by a segment with a decreasing incline and vice-versa.

T transition from one S segment with an increasing incline to another S segment with a decreasing incline or vice-versa can be connective, as in a sinusoid, or it can include a transitional part, which may be flat or curved, or a break in the spot between two inclines. For example, two neighbouring S segments with a T transition can form the shape of a wave, a triangle, a trapezium or a tooth. Individual S segments can be flat, mainly flat or curved. Different examples of possible S segment forms are shown in figures 2/1 and 2/2. The lengths of two neighbouring S segments with a T transition define the total L length. Transitions in the drawing of the fin in figure 2/1 and 2/2 are marked with the number 5. In figure 2/2, the segment's height is marked with 11. H heights of S segments, total L length and T transition lengths can be equal, they can increase or decrease linearly, progressively or regressively. Random combinations of changing shapes, H heights of S segments, total L lengths and T transitions along blade 2 are possible. According to the invention, blade 2 includes at least three S segments. As a priority, H height of the segment is the highest at root 7 of blade 2, where foot pocket 1 is installed, and decreases towards ending 8 of blade 2, therefore HI > H2 > H3, etc., until the transition to flat part 10. As a priority, total L lengths of two neighbouring segments are equal or increasing from root 7 towards ending 8 of blade 2, therefore LI > L2 > L3, etc. Preferably, the lengths of T transitions are equal or increasing from root 7 towards ending 8 of blade 2, therefore Tl < T2 < T3, etc. S segments can be produced preferably across the entire width of blade 2 or optionally in one part of the fin. The most preferably, S segments are produced in the shape of waves with connective transitions, thus in the shape of a sinusoid.

The velocity of water outflow in the fin is the highest at the end of the blade, this is why the segments' height is connectively decreasing along the blade, which reduces turbulence. The introduction of an imposed form of the blade increases the rigidity of the blade mostly in the transverse direction, which has a positive impact on the fin's function. Increased torsional resistance of the fin leads to better control of the fin during use.

During the construction of the fins, the desired hardness or rigidity of the fins is established based on tests. This is why an optimal ratio between the segments' height and length, enabling the removal of noise or click, suitably increasing the rigidity of the fin and also having a minimum impact on the user's increased power intake to achieve equal action as if the blade was flat, needs to be defined. It is desirable that the ratio between H height of the S segment and total L length at root 7 of blade 2 is between 0.15 and 0.015 and then decreases towards 0 until the transition to flat part 10.

Preferably, the highest HI height of the S segment is between 2.5 and 5 mm, while the total L length is between 4 and 6 cm. The number of S segments depends on the fin's length.

With an imposed blade form created in line with the invention, areas bent concavely or convexly on the surface of the blade are accurately defined in advance and this way, random reverse camber of the blade's surface according to the force currently applied to the entire surface of the blade is less likely or even prevented. As a result of the suggested form, the surface of the blade is pre-stressed and has no straight sections, the rigidity of the blade is increased in the transverse direction, which minimises or removes the noise or click. The invention will be presented in detail using the examples.

Figure 3 shows an example of blade 2 with triangular S segments and straight T transitions. The fin consists of foot pocket 1 and blade 2. Two neighbouring S segments form the shape of a triangle with a straight T transition, while blade 2 near foot pocket 1 begins with the S 1 segment and increasing incline continuing into the S2 segment with a decreasing incline through straight Tl transition and then continuing into the S3 segment with an increasing incline through straight T2 transition and so on until the transition to flat part 10, which closes blade 2. The segments follow each other in the longitudinal direction towards ending 8 of blade 2 across the entire surface of blade 2. HI height of the segment is the highest at root 7 of blade 2, where foot pocket 1 is installed, and decreases towards ending 8 of blade 2, therefore HI > H2 > H3 ... . The total LI length is the shortest at root 7 of blade 2 and increases towards ending 8 of blade 2, therefore LI < L2 < L3 ... . The length of the straight transition is the shortest at root 7 of blade 2 and increases towards ending 8 of blade 2, therefore Tl < T2 < T3.

Figure 4 shows an example of blade 2 with wave-shaped S segments and straight T transitions.

The fin consists of foot pocket 1 and blade 2. Two neighbouring S segments form the shape of a wave with a straight T transition, while blade 2 near foot pocket 1 begins with the SI segment and increasing incline continuing into the S2 segment with a decreasing incline through straight T transition and then continuing into the S3 segment with an increasing incline through straight T transition and so on until the transition to flat part 10, which closes blade 2. The segments follow each other in the longitudinal direction towards ending 8 across the entire surface of blade 2. HI height of the segment is the highest at root 7 of blade 2, where foot pocket 1 is installed, and decreases towards ending 8 of blade 2, therefore HI > H2 > H3 ... . The total LI length is the shortest at root 7 of blade 2 and increases towards ending 8 of blade 2, therefore LI < L2 < L3 ... . The length of the straight transition is the shortest at root 7 of blade 2 and increases towards ending 8 of blade 2, therefore Tl < T2 < T3 ... .

Figure 5 shows an example of the most preferable blade 2 with wave-shaped S segments and connective transitions, in the shape of a sinusoid.

The fin consists of foot pocket 1 and blade 2. Two pairs of neighbouring S segments form a wave. Blade 2 is made of wave-shaped S segments with connective T transitions, while the waves form a sinusoid. Blade 2 begins near foot pocket 1 with the SI segment and increasing incline connective ly continuing into the S2 segment with a decreasing incline and then continuing into the S3 segment with an increasing incline and so on until the transition to flat part 10, which closes blade 2. The waves or segments follow each other in the longitudinal direction towards ending 8 of blade 2 across the entire surface of blade 2. HI height of the segment is the highest at root 7 of blade 2, where foot pocket 1 is installed, and decreases towards ending 8 of blade 2, therefore HI > H2 > H3 ... . The total length does not change and is constant across the entire length of blade 2, therefore LI = L2 = L3 ... .

The shown examples do not limit the use of other segment forms regarding length, height and shape.