Field of invention

The invention relates to a diving fin.

Prior Art

Due to a small surface area and inappropriate geometry of the human foot, diving fins were developed to provide a good thrust for the swimmer when swimming. They function in a similar way to a fish tail, but with the difference that, due to human anatomy, the thrust is generated mainly by the upward movement of the foot. In this movement, the fin blade moves upwards at an angle, pushing the water away. The fins have a rail along the longitudinal edges which helps to direct the flow of water along the fin. A wider fin blade also helps to improve the swimmer's thrust. Traditionally, diving fins were made of rubber. More recently, however, diving fins have been developed from polymer materials reinforced with carbon, glass or other high elastic modulus fibre fabrics, which provide a higher thrust force and thus greater diving fin performance.

Technical problem

The technical problem is how to further increase the efficiency of diving fins. A more efficient diving fin means a better thrust for the swimmer for the same effort input, or the same thrust for the swimmer for less effort input. Solution to the technical Problem

The relative terms such as distal, proximal etc. are defined with respect to the user when the diving fin is in use.

The technical problem is solved by a diving fin that comprises: a foot portion and a fin blade connected to the foot portion at its distal end, the fin blade comprising two support layers extending along the entire length of the fin blade and a plurality of inner layers between the two support layers extending from the proximal end of the blade towards the distal end over at least a portion of the longitudinal dimension of the fin blade, each support layer and inner layer comprising resin-impregnated fibres, wherein, at least in the support layers, the number of fibres per length unit oriented substantially in the longitudinal direction of the diving fin is greater than the number of fibres per length unit oriented substantially in the transverse direction of the diving fin, preferably with a ratio of at least 1.5 between the number of fibres per length unit oriented in the longitudinal direction and the number of fibres per length unit oriented in the transverse direction of the diving fin.

The advantage of the diving fin according to the invention over known diving fins is the increased efficiency of the diving fin. The diving fin therefore enhances the kick, allowing faster swimming.

Figure 1 : Diving fin

Figure 2: Blade layers of the diving fin

Figure 3: Wavy fin blade

The invention is described in more detail hereinbelow. The technical problem is solved by a diving fin 1 that comprises: a foot portion 2 and a fin blade 3 connected to the foot portion 2 at its distal end, the fin blade 3 comprising two support layers 4 extending along the entire length of the fin blade and a plurality of inner layers 5 between the two support layers extending from the proximal end of the blade towards the distal end over at least a portion of the longitudinal dimension of the fin blade, each support layer 4 and inner layer 5 comprising resin-impregnated fibres, wherein, at least in the support layers 4, the number of fibres per length unit oriented substantially in the longitudinal direction of the diving fin is greater than the number of fibres per length unit oriented substantially in the transverse direction of the diving fin, preferably with a ratio of at least 1.5 between the number of fibres per length unit oriented in the longitudinal direction and the number of fibres per length unit oriented in the transverse direction of the diving fin.

The technical effect of increased efficiency of the fin occurs if the number of fibres per length unit oriented in the longitudinal direction of the diving fin is greater than the number of fibres per length unit oriented in the transverse direction of the diving fin, but the effect is in fact noticeable if the ratio between the number of fibres per length unit oriented in the longitudinal direction and the number of fibres oriented in the transverse direction of the diving fin is 1.5. If the ratio between the number of fibres per length unit oriented in the longitudinal direction and the number of fibres oriented in the transverse direction of the diving fin is 9 or greater, the efficiency of the diving fin is greater, but this has a negative impact on the mechanical strength of the diving fin in the transverse direction. The most preferred embodiment is the one, in which the ratio between the number of fibres per length unit oriented in the longitudinal direction and the number of fibres oriented in the transverse direction of the diving fin is 2 to 4. The diving fin may further comprise two protective layers 6 disposed on the outside of each of the support layers. The protective layers may be formed of, for example, polyester or glass fibre felt impregnated with resin. The protective layers can also serve as carriers for graphic printing.

The fibres of the support and inner layers may be selected from carbon fibres, glass fibres or other fibres having a Young's modulus of at least 60 GPa and a tensile strength of at least 500 MPa, or combinations thereof.

The longitudinal and transverse fibres are preferably woven. Examples of suitable weaves: plain weave (80/20), twill (3/1), Basket weave, Jacquard weave, Dobby weave, etc.

Different numbers of fibres in the longitudinal and transversal directions in the fabric can be achieved in different ways. For example, a plain weave fabric can be used, wherein the threads in the longitudinal direction have a higher number of fibres than the threads in the transverse direction. Alternatively, a fabric may be used in which the threads in the longitudinal and transverse directions are the same, but the density of the longitudinal threads per length unit is greater than that of the transverse threads. It is also possible to combine the two ways, i.e. the number of fibres in the longitudinal threads is greater than in the transverse threads and the density of the longitudinal threads per length unit is greater than that of the transverse threads.

The resin can be chosen from epoxy resin, phenolic resin, bio resin or polyester resin.

The number of the inner layers may be 3 to 16, preferably 3 to 5.

The fin blade is preferably made by the infusion process, where layers of dry fibres are stacked on top of each other and then impregnated with resin. The advantage of the infusion process over the prepreg process, which uses pre-soaked fibres stacked on top of each other and then heat bonded, is that the final product is almost completely free of micrometre air bubbles, which has a positive effect on the lifetime of the fin blade. When manufacturing the fin blade, care must be taken that there is not excess resin in relation to fibres, as this can have a negative impact on the mechanical properties of the product.

However, when testing the diving fin according to the invention, it turned out that the flat fin blade according to the invention, due to dynamic loads (i.e. alternating compressive and tensile loads), makes more noise than the known diving fin, which is heard as a "clicking" sound when the diving fin is used in the water. Such sounds scare away fish, which is of course undesirable when spearfishing, watching or photographing fish. It has furthermore proved that there is no increase in noise if the fin blade is shaped in a wavy pattern with the crests of the waves in the transverse direction of the fin blade. Such a diving fin is a preferred embodiment of a diving fin according to the invention and will be described in more detail below.

According to a preferred embodiment, the fin blade is formed by a plurality of concave and convex segments 7a, 7b alternating from the proximal portion to the distal portion of the fin blade, with the crests of the concave and convex segments oriented transverse to the longitudinal direction of the fin blade. The amplitude of the successive concave and convex segments preferably decreases towards the distal end of the fin blade. The wave length of the successive concave and convex segments along the fin blade may be equal or decrease towards the distal end of the fin blade. The distal end of the diving fin may be formed flat, i.e. without concave and convex segments. The longitudinal edge of the fin blade may be provided with a rubber profile in the form of a wing to prevent the lateral flow of water when the diving fin is in use, thereby stabilising the movement of the diving fin in the swimming direction.

The performance of the diving fin was tested on a fin with three inner layers of glass fibre felt. The two support layers were made with a plain weave fabric having the same number of threads per length unit in the longitudinal and transverse directions, but with the threads having 12000 fibres in the longitudinal direction and 3000 fibres in the transverse direction.