Diving board

Abstract

A diving board comprising a layer extending over its full length, at least one of its upper and lower surfaces being provided with thin sheets of reinforcing material, said sheets having different lengths, the lengths of said sheets diminishing from the front and the rear ends of the diving board to a portion of said diving board lying between its both ends, which portion is destined for resting on a support of said diving board. The diving board has a light primary layer to take up part of the total bending force thereon with at least an upper or lower surface with reinforcing material provided so that the amount of reinforcing material is substantially adapted to the moment acting in each cross-section of the diving board. BACKGROUND OF THE INVENTION The present invention relates to a diving board for a swimming pool, said driving board being of the cantilever type having its rear end attached to a stationary support and resting on a fulcrum at a place between its front and rear ends. A driving board of the cantilever type is a diving board with a fixed or pivoting rear end and resting at a place between its front and rear ends on a fulcrum. The invention also relates to a method for the manufacture of such a diving board. The object of the present invention is to obtain a diving board with a practically unlimited durability without impairing other properties such as flexibility and inertia particularly under circumstances as usually prevail in public swimming pools, where the board is frequently used by the public as well as by top-divers. The importance of the above mentioned properties will be elucidated hereunder. The durability can be predicted on the basis of a fatique-bending test. If the front end is repeatedly deflected by a force of 500 kg and its withstands 100.000 cycles, before it breaks, it will show a lifetime of about 3 years in actual practice. Since the object of the invention is to obtain a diving board having a practically unlimited lifetime, the constructions thereof to be described are calculated in such a way, that none of the used materials can be subjected to the maximum stress, which is allowable when fatique must be excluded. In order to check the resistance against fatique a diving board according to the invention has been executed to a bending-test, which has been extended to more than 1.000.000 cycles. After said test not the slightest deformation of the diving board was detectable. The flexibility of the board can be measured by the deflection of the front end under a certain static load. For the best type of board, such as is used in international contests and Olympic Games, this deflection amounts from 13 to 21 cm per 100 kg, dependent on the place of the fulcrum, which -- in accordance with the rules for diving boards of the "Federation Internationale de Natation Amateur" -- must be adjustable by the diver. The inertia, i.e., the inertia of the front end -- in mechanics called the "reduced mass" is the property, which determines, whether the board gives the diver the experience of "light" or "heavy" behaviour of the board. It should be clearly distinguished from the total mass of the board. It is actually the "apparent mass" of the front end. It could be defined as the mass, that ought to be fixed to the front end of a hypothetically weightless board, to give it the same dynamic behaviour as the real board possesses. For a diving board of uniform cross-section this inertia amounts to one third of the mass of that part of the board that protrudes over the fulcrum in forward direction. The inertia is however greatly reduced, if the front part of the part, that protrudes over the fulcrum is tapered towards the front end. This tapering also enlarges the flexibility. If carried out in the correct way it will not impair the bending-strength. Tapering of the rear part towards the rear end also increases the flexibility, but hardly influences the inertia for a given fulcrum position. But, as the latter tapering increases the flexibility, at a constant fulcrum position, it allows a more forward position of the fulcrum for a required deflection of the front end. Therefore tapering towards the rear end will also reduce the inertia at a given deflection. The principle of tapering has been described in many patents (U.S. Pat. Nos. 2,070,494, 2,951,701, 2,805,859, U.K. Pat. Nos. 710,595, 746,647). Tapering of diving boards towards both ends is nowadays general practice for diving boards of reasonable performance. Up to the present the mutual connection between durability, flexibility and inertia is insufficiently recognised. Improvement of one of these proportions without impairing the other properties, is the basic problem of the construction of a good diving board. All claims, often made that boards have a better performance or a better lifetime are worthless, if this mutual connection is not taken into account. The actual situation of the last 50 years, that swimming pool proprietors must make a choice between a board of excellent performance and a board with a very long lifetime, has not substantially changed. There is still a great demand for an excellent diving board, which lasts longer and the growing awareness that the supply of base materials is not unlimited gives a strong support to the design of more durable goods. SUMMARY OF THE INVENTION This has been the starting point for the design of the new type of the diving board according to the invention according to which said diving board comprises a primary layer substantially extending over its full length, said layer having a low density, at least one of its surfaces being provided with reinforcing material over at least a portion of said surface at both sides of said fulcrum. The basic idea of the present invention is to use a primary layer which does not need to be tapered and which in itself can undergo the required deflection without surpassing the maximum allowable bending stress. This primary layer cannot withstand the total bending force (500 kg) that is exerted in actual practice on the diving board, but usually only a rather small part of this force, say 20-30%. The maximum deflection may therefore already be achieved, when the front end is loaded with 100-150 kg. However, of this primary layer, preferably both upper and lower surface -- and in special cases only one of these surfaces -- are reinforced in a very special way, viz. such that the amount of reinforcing material is adapted to the particular moment, acting in each cross-section of the diving board. Generally this means that the application of reinforcing material begins at a certain distance from the front end as well as from the rear end and that this amount increases almost lineary to the point of the most rear ward fulcrum position of the diving board. Since the reinforcing material is usually applied in layers of different lengths, this would imply a stepwise increase of the amount of reinforcing material. In order to avoid such a stepwise increase according to the invention the amount of reinforcing material gradually may increase from a distance from at least one end of said diving board towards the place of the most rearward position of said fulcrum. In order to obtain this in an easy way the ends of the reinforcing sheets may have the shape of a triangle and may have their apexes on the longitudinal centre line of the diving board. A very important feature of the invention is, that also a combination of different materials can be used for one and the same diving board. Thus material which in itself is not very strong, but has a very low density, can be used at places, where low density is more important than strength. On the other hand material of great strength and high density can be used at places, where strength is more important than low density. Thus it may be of great advantage to use a material of low density for the primary layer and a material of very high strength as a reinforcing material. The fact, that the reinforcing material is applied at places which lie as far as possible from the neutral line, means that practically all reinforcing material is subjected to its maximum allowable stress. Thus optimal use is made of the strength of this material. It is also possible to use different materials for the upper and lower surfaces. Reduction of the inertia is very important for the following reasons. 1. A board with a lower inertia will allow the diver to jump higher, because the energy left behind in the moving board, after the diver has left it, is not available to throw the diver upward. This energy loss is proportional to the inertia for a given inertia of the front end. 2. From a viewpont of safety a low inertia should be preferred For it often occurs that a diver, after having left the board, collides on its front end with either head or limbs. The severeness of injury increases with the inertia of the board. 3. A board with a lower inertia will make it more suiteable for younger people. In the past the high inertia of diving boards has often been the reason, why youngsters could not participate in the art of diving at an early age. From the above described connection between durability, deflection and inertia it follows that inertia could certainly be further reduced if less rigid requirements would accepted for the durability.

Dependencies are inferred from the claim text.