Fin for underwater swimming

Abstract

 A fin (1) for underwater swimming, comprising a blade (2), which is made of a material having a high elastic response, is flat and substantially rectangular and has two surface portions (5, 14) that are mutually inclined and generated without discontinuities, in which the initial portion (5) is inclined, and a foot pocket (3), which is made of substantially soft material, the blade and the foot pocket being mutually associated by way of connecting means. The blade (2) has a thickness that decreases gradually from its initial portion (5) to its end portion (14), the end tip (14) of the blade (2) being provided with a substantial centered and protruding surface portion (15), which is narrower than the width of the blade (2) and has a length that is substantially proportional to the length of the blade (2), and the initial portion (5), when the blade (2) is fitted below the foot pocket (3), remains entirely below the sole (13) of the foot pocket (3), the corner region (19) at which the inclined portion (5) begins being proximate to the area of the foot pocket (3) intended to accommodate the articular region between the metatarsus and the phalanxes of the foot (12) when the blade (2) is fitted below the foot pocket (3).

Description

[0001] The present invention relates to a fin for underwater swimming.

[0002] To facilitate the movement of underwater swimmers and increase their speed, the solution that is currently universally adopted is to increase the surface of the swimmer's organs of propulsion, i.e., the feet.

[0003] The choice to use footgear having a large flat surface (substantially an inclined plane that is appropriately connected to the foot) is therefore the most widespread.

[0004] The fin is composed of a part into which the foot is to be inserted (termed foot pocket) and a flat part, the mechanical behavior of which entails propulsion (termed blade). The blade flexes due to the motion of the foot (kicking) and of the fluid drag of the water.

[0005] The blade of a fin is made of materials that allow the best elastic response to forces, ensuring flexing with minimum energy absorption.

[0006] Depending on the application, the need for propulsion is different: in diving with self-contained breathing apparatus, the user employs, for vertical movements, an inflatable element, by means of which he neutralizes the flotation or sinking components, said element therefore allowing him to remain stationary at the chosen depth; in free diving, the user uses only the propulsion of his legs both for vertical travel and for horizontal travel.

[0007] A free diver needs to have fins (or a monofin) in which the blade has an excellent elastic behavior, minimizing the dissipated energy without however being too rigid, as this would entail rapid fatigue.

[0008] Currently commercially available free-diving fins use blades made of polymeric or composite material.

[0009] The best propulsion results, associated with minimum energy expenditure on the part of the free diver, have been obtained with blades made of composite material, particularly with laminated blades of carbon fiber immersed in a substantially polymeric or resin-based matrix.

[0010] Currently commercially available blades have a thickness that decreases starting from the region where they blend with the foot up to the tip: the purpose of this taper is to make the deformation line of the profile of the blade during use approximate as closely as possible a quadric curve (ideally, a parabola). The fins of fish, during swimming, assume a parabolic curvature, maximizing propulsion for an equal energy expenditure.

[0011] The tip of the blade cannot be thinner than a minimum limit set by the manufacturing process and by the need to withstand breakage and wear: during flexing, the blade undergoes a deformation, varying conspicuously from the ideal parabolic shape, as a consequence of the excessive thickness of its tip portion. The fluid threads, with non-parabolic flexing, cling more to the blade, increasing its friction with respect to the water.

[0012] The structure of a fin of this type entails a connection between the soft foot pocket (in order to improve fit) and the more rigid blade: this connection is a critical point for the transmission of energy from the foot to the blade. Further, the fit of the foot in the foot pocket is not sufficiently comfortable, since foot pockets all have the same fit for both feet (for an equal size), and said fit is not even adjustable. Therefore, the foot pocket must be sufficiently oversized with respect to the foot in order to accommodate equally the right or left foot; the play between the foot and the foot pocket contributes to the dissipation of energy and easily allows skin abrasion due to the rubbing of portions of the foot pocket against the foot.

[0013] Conventional foot pockets are coupled to the blade by means of grooves, provided in appropriate lateral longitudinal members of the foot pocket, within which the edges of the initial part of the blade are inserted, while the end part is free: the initial end is inserted below the foot pocket in an appropriately provided receptacle. This coupling affects only a small portion of the foot pocket and therefore the initial end of the blade affects only on the initial half of the foot, causing (after prolonged use) intense fatigue of the body part, caused by intense specific pressure below the sole of the foot. The longitudinal members mate with the blade only in an initial portion of its length.

[0014] Recently, in order to increase the channeling of the stream of water displaced by kicking during swimming with fins, lateral profiles have been introduced in many fin models which are designed to be fitted laterally to the blades and have a substantially T-shaped cross-section, the vertical portion of the T-shape being affected by a groove so that it is possible to accommodate the edge of the blade inside said groove. The horizontal portion of the T-shape, which is perpendicular to the blade after assembly, constitutes an edge for containing the stream of water, increasing blade efficiency. The mechanical characteristics of the profile (rigidity, elasticity) are constant along its length, and the profile therefore causes a generic stiffening of the blade that is in contrast with the need to have a flexibility that increases gradually toward the end tip in order to approximate a parabolic deformation.

[0015] On the other hand, the profiles are fitted exclusively in the lateral end part of the blade, since in the initial part the edges of the blade are already coupled to the longitudinal members of the foot pocket (which also perform a conveyance function, albeit a weaker one, caused both by their shape and by their partially transverse placement with respect to the direction of motion of the fluid): therefore, in addition to a discontinuity in the channeling of the stream of water (between the longitudinal member and the profile), the profile acts on (and stiffens) the end part of the blade, which instead would require the maximum possible flexibility.

[0016] The aim of the present invention is to obviate the above-mentioned drawbacks and to meet the mentioned requirements, by providing a fin for underwater swimming in which flexibility increases gradually from its initial tip to its end tip, in order to undergo deformation so as to approximate a parabola during use, improving the separation of the fluid threads from its surface.

[0017] Within this aim, an object of the present invention is to provide a fin in which the blade is coupled to the foot of the user at the region of the foot where forces are applied naturally (substantially the articulation region of the foot between the metatarsus and the phalanxes).

[0018] Another object of the present invention is to provide a fin for underwater swimming in which the foot pocket mates firmly with the foot, avoiding relative movements and ensuring a comfortable fit.

[0019] Another object of the present invention is to provide a fin for underwater swimming, in which the foot pocket and the blade are mutually associated so that the foot acts on the initial part of the blade.

[0020] Another object of the present invention is to provide a fin for underwater swimming in which the water conveying profiles are distributed along most of the length of the blade.

[0021] Another object of the present invention is to provide a fin that is simple, relatively easy to provide in practice, safe in use, effective in operation, and has a relatively low cost.

[0022] This aim and these and other objects that will become better apparent hereinafter are achieved by the present fin for underwater swimming, of the type that comprises a blade, which is made of a material having a high elastic response, is flat and substantially rectangular and has two surface portions that are mutually inclined and generated without discontinuities, in which the initial portion is inclined, and a foot pocket, which is made of substantially soft material, said blade and said foot pocket being mutually associated by way of connecting means; characterized in that said blade has a thickness that decreases gradually from its initial portion to its end portion, the end tip of said blade being provided with a substantial centered and protruding surface portion, which is narrower than the width of said blade and has a length that is substantially proportional to the length of the blade; and in that said initial portion, when the blade is fitted below said foot pocket, remains entirely below the sole of the foot pocket, the corner region at which the inclined portion begins being proximate to the area of the foot pocket intended to accommodate the articular region between the metatarsus and the phalanxes of the foot when the blade is fitted below said foot pocket.

[0023] Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment of a fin for underwater swimming, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a side view of a fin for underwater swimming according to the invention;

Figure 2 is a top view of a fin for underwater swimming according to the invention;

Figure 3 is a sectional view, taken along the line III-III of Figure 2, of the foot pocket of a fin for underwater swimming according to the invention;

Figure 4 is a perspective view of a conveyance profile for a fin for underwater swimming according to the invention;

Figure 5 is a top view of the blade of a fin for underwater swimming according to the invention;

Figure 6 is a side view of the blade of a fin for underwater swimming according to the invention;

Figure 7 is a sectional view, taken along the line VII-VII of Figure 6, of the blade of a fin for underwater swimming according to the invention;

Figure 8 is a top view of the blade of a fin for underwater swimming according to the invention, associated with a foot pocket of a conventional type;

Figure 9 is a top view of a monofin for underwater swimming according to the invention.

Figure 10 is a longitudinal sectional side view of a fin for underwater swimming, illustrated worn on the foot of a user.

[0024] With reference to the figures, the reference numeral 1 generally designates a fin for underwater swimming according to the invention.

[0025] The fin 1 is constituted by a blade 2 and a foot pocket 3, which are mutually coupled by way of a receptacle 4 of the foot pocket 3, in which the initial portion 5 of the blade 2 is inserted, and by way of fixing means 6, which are arranged in the initial portion of the foot pocket 3 (and in the corresponding position also in the blade 2), which can be for example pairs of threaded elements that mate with each other. The receptacle 4 provided on the bottom of the foot pocket 3 can reach the region intended to accommodate the heel of the foot 12, the initial portion 5 of the blade 2, when said blade 2 is fitted to the foot pocket 3, being fully comprised therein and being therefore rigidly coupled to the entire sole of the foot 12. As an alternative, the receptacle 4 may also be of a conventional type, ending at the region intended to accommodate the concave part of the foot 12 (between the heel and the forefoot).

[0026] The foot pocket 3 is provided, in an upper region, with a contoured portion 7 shaped like an inverted letter U, which is provided without discontinuities so that the lateral arms of the U-shape are blended respectively with the right flap 8 and with the left flap 9 of the upper 10.

[0027] The contoured portion 7 has a plurality of through holes 11, which are aligned in pairs: said holes 11 are adapted to accommodate a lace (not shown in the figure), by means of which it is possible to move mutually closer the two facing sides of the contoured portion 7 and accordingly move the right flap 8 closer to the left flap 9, tightening the upper 10 around the foot 12 so as to improve the fit. As an alternative to the lace, it is also possible to provide screw-and-nut pairs, each of which is inserted in a respective hole 11, so that their tightening entails the mutual approach of the two flaps 8 and 9, fastening the foot 12 within the upper 10.

[0028] The foot 12 can be inserted within the foot pocket 3 by means of an opening 12a, which is located in the rear upper portion of the foot pocket 3, and rests on the sole 13 of the foot pocket 3. It should be noted that the foot pockets 3 are provided according to two different configurations (left foot pocket 3 and right foot pocket 3) in order to further improve comfort and ensure maximum stability of said foot pockets on the foot 12 (all relative movements caused by the presence of voids between the foot pocket 3 and the foot 12 are avoided).

[0029] The blade 2 is constituted by two parts: the initial portion 5 (which will be associated with the foot pocket 3 and therefore is tapered) and the end portion 14 (which is much longer and has a substantially constant width).

[0030] The end portion 14 has a substantial centered and protruding surface portion 15 that is narrower than the width of said blade and has a length that is substantially proportional to the length of the blade (hereinafter termed flap 15) at its free end 16.

[0031] The flap 15 has a substantially trapezoidal shape, since the side that would constitute the longer parallel side is rigidly coupled to the free end 16 (since it is a continuation thereof), the side that constitutes the shorter parallel side is constituted by the tip edge 17, and the two oblique sides are constituted by the lateral edges 18. The lateral edges 18 may be linear or curved, and are curved in the preferred embodiment shown in the figures. The approximate dimensions of the flap are closely correlated to the dimensions of the end portion 14 of the blade 2: generally, a length of no more than 20% of the length of the portion 14 and a width comprised between 20% and 70% of the width of the end tip 16. The flap 15 has a surface area that substantially does not exceed 10% of the surface area of the portion 14 but reaches, in a preferred embodiment, approximately 5% of the surface area of the portion 14.

[0032] The initial portion 5 and the end portion 14 of the blade 2 are mutually separated by a corner region 19, along which the two surfaces are blended: such surfaces are in fact mutually inclined with an angle that is generally comprised between 15 and 25° (said angle is preferably 20°). The presence of such an inclination between the portions 5 and 14 is intended to maximize the thrust provided by the swimmer for an equal energy expenditure thereof, further improving the comfort and ergonomics of the use of blades 2 having this configuration.

[0033] Profiled elements 20 that have a substantially T-shaped cross-section are fitted on the lateral surface of each blade 2. The vertical portion of said T-shape is provided with a longitudinal groove 20a, along the longitudinal extension of the profiled element 20, which is suitable to accommodate the lateral edge of the blade 2, while the horizontal portion of the T-shape has a variable length along the extension of the profiled element, giving the profiled elements 20 a shape (if viewed from the side) that substantially resembles an elongated teardrop.

[0034] The horizontal portion of the T-shape has a minimum length, which may even be negligible, at the two tip regions of the profiled element 20, and a maximum length in an intermediate region that is comprised, when the profiled element 20 is fitted to the blade 2, between the corner region 19 and the midpoint of the end portion 14: this configuration gives the various sections of the blade 2 variable flexibility, improving their elastic response.

[0035] To use a fin 1 according to the invention, the user inserts his feet 12 through the openings 12a into the foot pocket 3. Once the foot 12 has been inserted, the corner region 19 lies below the articulation region between the metatarsus and the phalanxes (the sort of pad before the toes). This location improves, with respect to conventional embodiments, the transfer of energy from the foot 12 to the blade 2, since the blade 2 is rigidly coupled to the part of the foot 12 that has no articulations, thus eliminating all the muscular efforts caused by the increase in the distance of application of the forces (lever arm) transferred through the toes of the feet 12 for the stiffening required for a correct fin stroke.

[0036] The portion of the foot 12 that is constituted by the articulation region between the metatarsus and the phalanxes is the natural place through which a force is transferred from the leg to an external element. Consider for example the working point of the foot 12 on the pedal of a bicycle: the coupling between the foot and the pedal is fixed by means of appropriate fastening elements in order to keep the pedal constantly associated with the articulation region between the metatarsus and the phalanxes. When climbing stairs, too, support is provided in the articulation region between the metatarsus and the phalanxes in order to improve force application without causing fatigue of the toes of the foot 12. The placement of the corner region 19 below the region of articulation between the metatarsus and the phalanxes must therefore be considered a fundamentally important detail, because the efficiency of the fin stroke is improved by transferring forces at the region of the foot 12 that is naturally intended to do so and at the same time the load that the toes must withstand is reduced, avoiding pain and fatigue.

[0037] Adjustment of the foot pocket 3 according to the shape of the foot 12 is performed by taking care to fasten the lace arranged between the holes 11 in order to move the flaps 8 and 9 of the upper 10 mutually closer.

[0038] The effort required for the fin stroke is minimized by the presence of the flap 15 and by the configuration with gradually decreasing thickness (from the corner region 19 to the end 16) of the end portion 14. The shape of the profiled elements 20 also contributes to improve the elastic response of the fin 1, which can undergo deformation during use with a curvature that can be likened to a parabola. The combination of the presence of the flap 15 and of the particular configuration of the profiled elements 20 ensures that the blade 2 flexes progressively, also improving fluid thread separation.

[0039] The blade 2 of the fin 1 according to the invention can also be fitted to conventional foot pockets 21 provided with a lower receptacle (not shown in the figures), which affects only the initial part (in practice from the region below the region designed to accommodate the toes to the region below the region intended to accommodate the arch of the foot 12): in this case, it is necessary to resort to a particularly shaped blade 2a. For this type of use, the suitable blade 2a has an initial portion 22 that is shorter than the initial portion 4 of the blade 2 and has at least one hole 23 for coupling to the foot pocket 21. The foot pocket 21 also comprises two lateral longitudinal members 24, which by being provided with a groove on their internal surface are interlocked on the part located proximate to the corner region 19 of the lateral surfaces of the end portion 25 of the blade 2a. Profiled elements 26, shaped like the profiled elements 20 but shorter, are accommodated on the part of the lateral surface of the blade 2a that is left free by the longitudinal members 24. The profiled elements 26, when viewed from the side, are less elongated than the profiled elements 20 although being likewise teardrop-shaped (in a different embodiment, the profiled elements 26 may also have a constant thickness along their entire extension). The blade 2a ends with a flap 26a that is shaped like the flap 15 and has the same dimensional characteristics.

[0040] The fin 1 according to the invention can also be provided according to an embodiment (monofin 1a) provided with a double foot pocket 27, which has a first receptacle 28 that is contoured for insertion of the right foot 12 and a second receptacle 29 that is contoured for insertion of left foot 12, said receptacles being arranged side by side and being rigidly coupled to each other.

[0041] In order to provide to the monofin 1a, the blade 30 must have a suitable width, which is increased with respect to the width of the blades 2 for the foot pocket 3 with a receptacle 12a for a single foot 12.

[0042] Its initial portion can be associated stably with a receptacle provided below the double foot pocket 27, the corresponding angle of variation of the inclination (equal in breadth to the angle described for the blade 2) being arranged below the area of the region of articulation between the metatarsus and the phalanxes.

[0043] The blade 30 has substantially twice the width of the blades 2 for the foot pocket 3 provided with a receptacle 12a for a single foot.

[0044] The specifications of the monofin 1a are similar (except for the dimensional indications already described) to the ones described for the fin 1 in everything that regards the configuration of the profiled elements 31 (similar to the profiled elements 20), of the flap 32 (similar to the flap 15 also as regards its dimensional parameters), and of the means for fastening the foot pockets 27 to the feet 12.

[0045] The preferred material for providing the blades 2, 2a and 30 is a composite material constituted by a matrix of thermosetting resin with structural reinforcements made of high-performance fibers (for example carbon fiber, glass fiber or Kevlar) arranged appropriately so as to give the best elastic response along particular directions of deformation. As an alternative, the blades 2, 2a and 30 may be made of polymeric material with suitable mechanical characteristics.

[0046] The foot pockets 3 and 27 may be made preferably of polymeric material (such as polyurethane) and rubber. In an optional different embodiment, the foot pockets 3 and 27 (at least part thereof), too, are provided by using a composite material (for example a structural component constituted by carbon fiber, glass fiber or Kevlar immersed in an epoxy resin matrix) in order to strengthen their parts that are most intensely stressed during the fin stroke.

[0047] It has thus been shown that the invention achieves the intended aim and objects.

[0048] The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. All the details may further be replaced with other technical equivalent ones.

[0049] For example, the right flap 8 can accommodate a ratchet lever and the left flap 9 can accommodate the corresponding engagement element, in an embodiment in which the contoured portion 7 is not present (or is shaped differently), so that the two flaps 8 and 9 can be moved mutually closer by means of a fastening action performed with said lever.

[0050] In order to improve foot insertion comfort, in this case it is possible to provide a tongue (in a manner similar to what occurs in shoes for land use) that prevents the edges of the flaps 8 and 9 from rubbing against the instep of the foot 12.

[0051] In the embodiments described, individual characteristics, given in relation to specific examples, may actually be interchanged with other different characteristics that exist in other embodiments.

[0052] Moreover, it is noted that anything found to be already known during the patenting process is understood not to be claimed and to be the subject of a disclaimer.

[0053] The embodiment of the present invention shall be carried out in the most scrupulous compliance with the statutory and regulatory provisions related to the products of the invention or correlated thereto and following any required authorization of the corresponding competent authorities, with particular reference to regulations related to safety, environmental pollution and health.

[0054] In practice, the materials used, as well as the shapes and the dimensions, may be any according to requirements without thereby abandoning the scope of the protection of the appended claims.

[0055] The disclosures in Italian Patent Application No. BO2004A000273 from which this application claims priority are incorporated herein by reference.

[0056] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A fin for underwater swimming, of the type that comprises a blade (2), which is made of a material having a high elastic response, is flat and substantially rectangular and has two surface portions (5, 14) that are mutually inclined and generated without discontinuities, in which the initial portion (5) is inclined, and a foot pocket (3), which is made of substantially soft material, said blade and said foot pocket being mutually associated by way of connecting means; characterized in that said blade (2) has a thickness that decreases gradually from its initial portion (5) to its end portion (14), the end tip (14) of said blade (2) being provided with a substantial centered and protruding surface portion (15), which is narrower than the width of said blade (2) and has a length that is substantially proportional to the length of the blade (2); and in that said initial portion (5), when the blade (2) is fitted below said foot pocket (3), remains entirely below the sole (13) of said foot pocket (3), the corner region (19) at which the inclined portion (5) begins being proximate to the area of the foot pocket (3) intended to accommodate the articular region between the metatarsus and the phalanxes of the foot (12) when the blade (2) is fitted below said foot pocket (3).

2. The fin according to claim 1, characterized in that the corner region (19) between said inclined initial portion (5) of said blade (2) and the end portion (14), when the blade (2) is fitted on said foot pocket (3), is arranged at the region where the region of articulation of the foot between the metatarsus and the phalanxes rests, rigidly associating said initial portion (5) with the sole of the foot (12).

3. The fin according to the preceding claims, characterized in that said foot pocket (3) has, in a lower region, a receptacle (4) at the sole (13), which is adapted to accommodate said initial portion (5) of the blade (2) and, in an upper region, on the upper (10), a contoured portion (7) shaped like an inverted letter U, which is provided without discontinuities in a longitudinal direction with fastening means that are designed to move the flaps (8, 9) of the right and left surfaces of said U-shaped portion mutually closer, firmly wrapping around the foot (12).

4. The fin according to claim 3, characterized in that said fastening means comprise a plurality of mutually facing through holes (11) in the lateral vertical faces, said holes being adapted to accommodate at least one traction element for moving said holes (11) mutually closer.

5. The fin according to claim 4, characterized in that said traction element is a lace made of a material having good mechanical properties.

6. The fin according to claim 3 and as an alternative to claim 4, characterized in that said fastening means comprise a ratchet lever, which is fixed on one of the two flaps (8) and the corresponding engagement element fitted on the other flap (9).

7. The fin according to claim 3 and as an alternative to claim 4, characterized in that said fastening means comprise a plurality of threaded elements of appropriate size and shape, which are adapted to fasten the U-shaped portion on the upper part of the upper (10).

8. The fin according to claim 1, characterized in that profiled elements (20) having a substantially T-shaped cross-section are fitted on the lateral edges of said blade, the vertical portion of said T-shape being provided with a longitudinal groove (20a) along the extension of the profiled element (20), said groove being adapted to accommodate the edge of said blade (2), the horizontal portion of the T-shape having a length that can vary along the extension of the profiled element (20).

9. The fin according to claim 7, characterized in that said horizontal portion of said T-shape has a minimum length, which may even be negligible, at the two end portions of said profiled element (20) and a maximum length in an intermediate portion that is comprised, when the profiled element (20) is fitted to said blade (2), between the corner region (19) and the midpoint of said end portion (14), said configuration being adapted to give variable flexibility to the various sections of said blade (2).

10. The fin according to claim 3, characterized in that said receptacle (4) of said foot pocket (3) reaches the region intended to accommodate the heel of the foot (12), said initial portion (5) of the blade (2), when the blade (2) is fitted on said foot pocket, being fully comprised within it and therefore being rigidly coupled to the entire sole of the foot (12).

11. The fin according to claim 2, characterized in that said foot pockets (3) are provided in different models, a first model that is contoured for insertion of the right foot (12) and a second model this is contoured for insertion of the left foot (12).

12. The fin according to one or more of the preceding claims, characterized in that said substantial surface (15), which can be termed flap (15), has a length that substantially does not exceed 20% of the length of the blade (2) excluding the initial portion (5) that is suitable for insertion in the appropriately provided receptacle (4) of said foot pocket (3).

13. The fin according to one or more of the preceding claims, characterized in that said substantial surface (15), which can be termed flap (15), has a width comprised between 20% and 70% of the width of the end tip (16) of said blade (2).

14. The fin according to one or more of the preceding claims and as an alternative to claims 12 and 13, characterized in that said substantial surface (15), which can be termed flap (15), has a surface area that substantially does not exceed 10% of the surface area of the blade (2) except for the initial portion (5), which is suitable for insertion in the appropriately provided receptacle (4) of said foot pocket (3).

15. The fin according to claim 14, characterized in that said substantial surface (15), which can be termed flap (15), has a surface area that is preferably on the order of approximately 5% of the surface area of the blade (2), excluding the initial portion (5) that is suitable for insertion in the appropriately provided receptacle (4) of said foot pocket (3).

16. The fin according to according to one or more of the preceding claims, characterized in that said substantial surface (15), which can be termed flap (15), is tapered and has its maximum width at the section for blending with the tip (16) of the blade (2) and its minimum width at its end edge (17).

17. The fin according to claim 16, characterized in that the lateral edges (18) of said substantial surface (15), which can be termed flap (15), are substantially curved and blend the blade (2) with the end edge (17) of said flap (15).

18. The fin according to one or more of the preceding claims, characterized in that the lateral edges (18) of said substantial surface (15), which can be termed flap (15), are substantially linear and join the blade (2) to the corners of the end edge (17) of said flap (15), said flap having a substantially trapezoidal shape.

19. The fin according to one or more of the preceding claims, characterized in that said blade (2a) is associable with a conventional foot pocket (21), said initial portion (22) of the blade (2a) having dimensions that are suitable to occupy the interlocking receptacle provided below the sole of conventional foot pockets (22).

20. The fin according to claim 19, characterized in that said lateral profiled elements (26) are fitted exclusively in the end part of the edges of the blade (2a), the initial part of said edges being associated with longitudinal members (24) for coupling the conventional foot pocket (3) to the blade (2a).

21. The fin according to one or more of the preceding claims, characterized in that said foot pocket (3) is made of a polymeric material such as polyurethane.

22. The fin according to one or more of the preceding claims, characterized in that said blade (2) is made of a composite material such as carbon fiber immersed in an epoxy resin matrix.

23. The fin according to one or more of the preceding claims, characterized in that said blade (2) is associated with the corresponding foot pocket (3) by way of at least one detachable connection element, which is constituted for example by at least one threaded element.

24. The fin according to claim 23, characterized in that said detachable connection elements are three, one being arranged along the axis of symmetry of the blade (2), the other two being arranged laterally in a symmetrical configuration with respect to the axis of symmetry of the blade (2).

25. The fin according to one or more of the preceding claims, characterized in that the foot pocket (27) is a double foot pocket and is provided with the first receptacle (28) that is shaped for the insertion of the right foot (12) and a second receptacle (29) that is shaped for the insertion of the left foot (12), said receptacles being arranged side by side.

26. The fin according to claim 25, characterized in that a blade (30) having a width increased with respect to the width of the blades (2) for the foot pocket (3) with a receptacle (12a) for a single foot (12), can be stably associated with the receptacle provided below said double foot pocket (27), the corresponding corner region for varying the inclination being arranged below the area of the foot (12) where the toes are joined to said foot (12).

27. The fin according to claim 26, characterized in that said blade (30) having an increased width is substantially twice as wide as the blades (2) for a foot pocket (3) with a receptacle (12a) for single foot (12).

Drawing