WATERSKI WITH IMPROVED TORSIONAL CHARACTERISTICS

Abstract

A water ski with improved torsional characteristics delimited on the upper side by the upper surface, on the bottom side by a concave surface and on the sides by curvilinear sidewalls. The ski has a tip at the front side and a tail on the rear side. On the central part of the ski, on the upper surface, a longitudinal groove is provided having a flat bottom surface connected with vertical longitudinal sides of the groove by rounded surfaces, wherein the groove decreases torsional and flexural strength, which depth and width reduce torsional and flexural stiffness of the central part of the ski. The width of the groove may be 30-80% of the width of the ski, and the depth of the groove may be 20-95% of the thickness of the ski.

Claims

1-5. (canceled)

6. A water ski with improved torsional characteristics, the water ski having a given thickness and a given width, comprising: an upper side having a curved upper surface; a bottom side having a concave surface; sides having curvilinear sidewalls configured to narrow a front end and a rear end of the water ski; wherein said water ski has a tip at the front end and a tail at the rear end, character-ized in that a central part of the water ski on the upper surface is provided with a longitudinal groove, the groove having a flat bottom surface connected with vertical longitudinal sides of the groove by rounded surfaces, wherein the groove decreases torsional and flexural strength of the central part of the water ski; and wherein the groove has a width that is 30-80% of the width of the water ski; and a depth that is 20-95% of the thickness of the water ski.

7. The water ski according to claim 1, having a given total length, wherein the groove is 20-50% of the total length of the water ski.

8. The water ski according to claim 7, wherein the groove is 30-40% of the total length of the water ski.

9. The water ski with improved torsional characteristics according to claim 1 or 2, wherein the groove has a trapezoid cross-section.

10. The water ski with improved torsional characteristics according to claim 1 or 2, wherein the groove has a rectangular cross-section.

11. The water ski with improved torsional characteristics according to any of the above claims wherein the ends of the groove are of the same or of a different shape and in that the ends of the groove are in the form of a semi-circle or angle.

12. The water ski of claim 1, wherein the width of the groove is 40-50% of the width of the central part of the water ski.

13. The water ski of claim 1, wherein the groove has a depth corresponding to 80-95% of the thickness of the water ski.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0016] Water skies with improved torsional characteristics will be described herein below based on an example of embodiment and the attached drawings. The embodiment example disclosed in the detailed description and illustrated in the drawings is a non-limiting example of the invention the protection thereof is requested in the claims. The example is given for a better understanding of the invention. The following is shown in the drawings:

[0017] FIG. 1 is an axonometric projection of a ski embodiment according to the invention;

[0018] FIG. 2 is a longitudinal sectional view of the ski embodiment taken along line A-A in FIG. 3;

[0019] FIG. 3 is a top view of the ski embodiment;

[0020] FIG. 4 is a cross-section view of the ski embodiment taken along line B-B in FIG. 4. In this embodiment the ski embodies a core and an outer layer, however, the invention is not limited to only this embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0021] FIG. 1 shows an embodiment of the ski 1 with improved torsional characteristics according to the invention. The invention refers not only to the presented embodiment of the water ski 1 but also to the other types of skis. The ski 1 is on the upper side delimited by the upper surface 2 which in its major part is in fact a curved surface and bent upwards in the region of the tip 4 of the ski 1. From the bottom side the ski 1 is delimited by the bottom surface 3 (also see FIG. 4). The bottom surface 3 is concave, respectively curved outward to the body of the ski 1 viewed from the cross-section and, viewed lengthwise, the bottom surface 3 of the ski 1 is curved being convex to the outside (from the skier's perspective). On the side, the ski 1 is delimited by the sidewalls 7 which follow the form of a double curvature and can be of a different shape depending on the type of the ski 1. The sidewalls 7 narrow the ski 7 at the front end where there is the tip 4 and at the rear end where there is the tail 5. The sidewall at the tail can follow a straight line perpendicular to the longitudinal axis of the ski 1. In the disclosed embodiment the ski 1 at the tail 5 has a slot 9 for the attachment of a fin. In this embodiment, on the upper surface 2 openings are also provided for the attachment of additional equipment. All the elements described so far are characteristic of the skis available in the market and known to those skilled in this field of art. The ski 1 according to the invention has a longitudinal grove 6 provided on the upper side which longitudinal axis coincides with the longitudinal axis of the ski 1 (FIGS. 1 and 3). The longitudinal groove 6 runs on the central part of the length of the ski 1 and it is not provided on the rear end of the ski 1 with the tail 5 or the front end of ski 1 with the tip 4. The length of the longitudinal groove 6 is 20 to 50% total length of the ski 1 and, viewed lengthwise, the part of the ski 1 on which the groove 6 is provided represents the part of the ski 1 that more easily elastically deforms to torsion and flexure or, in other words, has different torsional stiffness from the part of the ski 1 where the groove 6 is not provided. More suitable range of the length of the ski 1 where the groove 6 is provided is 30 to 40% of the ski length. Size of the length of the ski 1 provided with the groove 6 depends on the area of the ski 1 that requires altered torsional characteristics of the ski 1, that is, in which part of the ski 1 is required a reduced torsional stiffness, which is conditioned by the intended use of the ski. In any case, within the scope of the present invention, various variations of the length of the groove 6 are possible in accordance with the intended use and type of the ski 1. The form of the cross-section of the groove 6 of the ski 1 (FIG. 4) is preferably trapezoid as shown in FIG. 4 but it may be rectangular or have any other suitable form. The form of the cross-section of the groove 6 depends on the shape of the walls of the groove 6; they may be at a right angle with respect to the upper surface 2 or slanting thereto. The width and depth of the groove 6 of the ski 1 (see FIGS. 2 and 4, longitudinal section and cross-section) are of particular importance, i.e. the ratio between the depth of the groove 6 and the thickness of the ski 1, as well as the ratio between the width of the groove 6 and the width of the ski 1. The depth of the groove 6 of the ski 1 is in the range from 20 to 95%, preferably 80 to 95% of the thickness of the ski 1 at the place of the groove 6, i.e. down to the last layer of the material (laminate). The width of the groove 6 is in the range from 30 to 80%, preferably 40 to 50% of the width of the ski 1 at the place of the groove 6. The groove length, width and depth are mean values depending on the shape of the groove wall and groove end, as already stated above. The sizes of the width and depth of the groove 6 specified herein are of crucial importance for the application of the ski 1 according to an embodiment and represent the results of the tests of the ski 1 prototype. Actual depth and width of the groove 6 from within the identified range depend on the type and intended use of the ski 1 but also on the material from which the ski 1 is made. Is the depth and width of the groove 6 would be smaller that the specified dimension ratio, the stiffness of the ski 1 to torsion would not be considerably reduced and the ski 1 would not function in the desired manner. In such case it could be said that shallow and narrow grooves represent decorative grooves and do not have effect on the ride characteristics of the ski 1, that is its functioning, and that the skier would not feel a difference between a ski of a full profile and the ski 1 according to the invention. The front and rear end of the groove 6 may be of a different or same shape. In addition to the already presented semicircular shape of the end of the groove 6, a semi-elliptic or angular shape of the end of the groove 6 is also suitable; however, other suitable forms may also be used.

[0022] The use and functioning of the water skis 1 according to the invention are described herein below. In water skiing the ski 1 is exposed to a complex load which is the consequence of the traction force and hydrodynamic conditions prevailing during the movement of an object on or through water and there is the transfer of force in both directions from the water, via the skis 1, the skier, and rote to the towboat. From the analysis of the complex load and from the experience it is known that one of the dominant components of the load is torsion and flexure. This is particularly noticeable in specific moments of the ride, e.g. when making turns or in slalom. To control the skis 1 it is necessary that the skier gets inclined with respect to the water surface. It is also favourable that the ski 1 adapts to the hydrodynamic conditions of skiing. In order for this to be achieved it is necessary that the rear end of the ski 1 with the tail 5, the central part of the ski 1 and the rear end with tip 4 of the ski 1 have different torsional characteristics, more precisely that the central part of the ski has reduced stiffness to elastic torsional deformation. Application of various calculation models is possible although significant simplification of the model would have to be made relative to the actual skiing conditions and the load action to the ski 1; however, the following is indisputable. It is known from the material resistance that deformation to twisting (torsion), i.e. the angle of twist is directly proportional to the torsional moment, the force acting length, and inversely proportional to the cross-section characteristic, i.e. the torsional moment of inertia that depends on the shape and dimensions and, hence, also the area cross-section. The angle of twist depends also on the constant that represents the characteristic of the material, i.e. it is inversely proportionate to the shearing modulus. The inventors have recognized decreasing the cross-section area where the angle of twist is measured results in a decrease of the respective cross-section characteristic and an increase of the angle of twist. In this way, providing of the groove 6 of sufficient size, i.e. sufficient depth and width in the central part of the ski 1 results in the change of its torsional properties, i.e. to their improvement in terms of the control and easier skiing on water. The front end of the ski 1 where there is the tip 4 and the rear end of the ski 1 where there is the tail 5 and where the longitudinal grove 6 is not provided retain their original torsional properties so that at the same load there is a different torsion of the different parts of the ski 1. In other words, the groove or depression on the top surface of the ski changes cross-sectional characteristics of the ski making it more flexible and reducing its stiffness on torsion and flexion and chosen dimensions are dependent on mechanical characteristics. Also, as can be seen in the Figures and as described herein, the vertical longitudinal sides of the groove are connected with the bottom surface of the groove by rounded surface and it has no channels which can be a cause of the stress concentration and lead to damage of the ski. The direct consequence of different, to a certain degree less dependent, angles of twist of the different parts of the ski 1 results in easier controllability of the skis 1 and better adaptation of the ski 1 to the current hydrodynamic conditions of the movement on water. The ride of the ski 1 is also easier because it is easier to take a desired angle between the ski 1 and the water surface. The control of the ski 1 is made easier; it requires less physical effort because tipping of the ski 1 to lateral surface is facilitated; it is easier to take position, i.e. the skiing direction and angle with respect to the towing device. In this way the skiing is made easier in particular to less strong skiers and becomes more accessible to women and younger persons. The ski 1 with improved torsional characteristics can be used by all categories of water skiers from the beginners through recreational skiers of various physical strengths to competitors. Advantages offered by the ski 1 according to the invention are manifested in various kinds of skiing: slalom, jumps, tricks, and other. It is necessary to emphasise once again that the relationships between the dimensions of the groove 6 and the overall dimensions of the ski 1 represent the intrinsic characteristic of the present invention, that they are defined on the basis of tests and that they inevitably represent the subject of protection. Shallow grooves, i.e. grooves of smaller dimensions provided only for the purpose of decoration of the upper ski surface and with no effect on the mechanical characteristics of a ski, in particular torsional strength, do not provide for the functioning of the ski 1 according to the present invention in the desired manner. On the other hand, grooves of dimensions greater that those specified would result in a risky decrease of strength, i.e. increase of the probability of ski damage or break. The ski 1 according to the invention is made from materials that are customarily applied in the manufacture of water skis such as fibreglass, graphite and others, not excluding the use of composite laminates as innovative materials. The water ski 1 according to the invention is made by standard technologies known to those skilled in this art so that big investments into new equipment are not necessary for the changeover to production of the ski 1 according to the present invention.