MAST FOR A SAILBOARD

Abstract: To counteract stress peaks on a sailboard exerted by the bottom end of the mast, this bottom end is provided with a shock absorber formed by an oil filled cylinder and a piston with piston rod displaceable therein. The piston is provided with passages. The flow of oil through these passages is governed by valve means.

Description: The invention relates in the first instance to a mast for a sailboard. In the course of sailing with a sailboard, high peak stresses are exerted on the board by the bottom end of the mast during heavy weather. Extremely high stresses occur in particular in competition sailboard­ ing. They can lead to damage to the board. It is known to provide an elastic element between mast and board. The elastic element has little effect on absorbing the up and down movement of the mast. The mast remains moving and, through the elastic deformation of the ele­ ment, the amplitude of the mast movement in a direction perpendicular to the board will even be greater than the amplitude of the board movement in the same direction. The often jerking, turbulent movement of the mast also has an adverse effect on the joints of the sailboard. The object of the invention is to eliminate these disadvantages and to produce a sailboard mast which fol­ lows the up and down movement of the sailboard on which it is fixed, in such a way that the stress peaks on the board are counteracted to a considerable extent and the mast exhibits a smoother movement pattern. According to the invention, the mast is to this end characterized in that the bottom end thereof is provided with a shock absorber, formed by a cylinder filled with oil and a piston with piston rod displaceable therein, while in the piston provision is made for passages, and the flow of oil through said passages is governed by valve means. The oil meets with resistance when passing through the passages and the valve means. Energy is con­ verted to heat in the process. It is expected that, through the more stable mast position, the sailboard can travel faster. In any case, the sailboard will be less likely to suffer damage due to jolting stresses through the mast. The combination of springing and shock absorption is achieved if the shock absorber is also provided with a gas spring. In order to be able to fix the shock absorber in a simple manner to the bottom end of the mast, it can be pushed into the bottom end of the mast and held in place by an adaptor which is detachably connected both to the bottom end of the shock absorber and to the bottom end of the mast. The adaptor is preferably screwed to the shock ab­ sorber and connected to the mast by spring-loaded pins projecting through holes into the mast. The invention also relates to a sailboard with a mast of the above-described type. The piston rod of the shock absorber is fixed at its bottom end to a coupling element which gives in various directions. The coupling element is preferably a cardan joint, although a simple elastic element, for example in the form of a diabolo, is also possible. In order to limit the movements towards each other of mast and board without jolts, provision is made be­ tween the bottom end of the mast and the coupling ele­ ment for an elastic stroke limiting device. The invention will now be explained in greater detail with reference to the figure, in which an example of an embodiment is shown. The figure shows part of a sailboard with the bottom part of the mast thereof in cross section. The sailboard is indicated by 1, and the hollow mast by 2. Slid into the mast is a shock absorber 3, comprising a cylinder 4, a piston 5, a piston rod 6, and a guide head 7 for guiding the piston rod. Disposed in the piston 5 are passages 8 which are regulated by non-­ return valves 9, 10, in a manner known per se, in such a way that both on the ingoing and the outgoing stroke of the piston the oil flows from one side to the other and thereby meets with considerable resistance and produces the shock absorption. Fitted in the top end of the shock absorber is a gas spring 11, comprising a quantity of compressed gas which is separated from the oil by a sealed partition 12. The outward thrust of the gas spring can be brought into balance with the overall mast load by means of a filling system 20. For the purpose of retaining the shock absorber 3 in the desired position in the mast, the guide head 7 has a collar 13, which is provided with an external screw thread, and on which an adaptor 14 provided with an internal screw thread is screwed. This adaptor projects partially into the mast and has a number of pins 15 which are movable against spring action and project through openings into the bottom end of the mast 2. It will be clear that the shock absorber can easily be replaced by pressing the pins 15, sliding the com­ bination of shock absorber 3 and adaptor 14 out of the mast, unscrewing the adaptor from the shock absorber, screwing another shock absorber (for example, one with a different shock absorption characteristic) onto the adaptor, and sliding all this into the mast until the pins 15 project again through the openings into the mast. The bottom end of the piston rod is provided with screw thread and is connected by means of a screw con­ nection to a universal (cardan) joint 16 known per se, which permits hingeing in two directions perpendicular to each other. The said screw connection is secured by a nut with spring ring. This universal joint is incor­ porated in a bellows 17 and is fixed to a plate 18 which is anchored either in a fixed position or movably in a slide on the sailboard 1. Disposed on the top part of the universal joint is a disc 19, which serves to support an elastic stroke limiting device 21. It will be clear that many modifications are possible within the scope of the invention. For example, the shock absorber 3 could be disposed between the bottom end of the mast 2 and the stroke limiting device 19, in­ stead of in the mast. The universal joint 16 could be replaced by an ordinary diabolo-type elastic element which permits movements in all transverse directions. For the connection between the shock absorber and the mast there are many possibilities. Nor are there any limits to the way in which the bottom end of the piston rod is connected to the universal joint or diabolo. What is important is that peak stresses which would be exerted by the mast on the board are absorbed by a shock absorber which is provided on the bottom end of the mast, and which is preferably provided with a gas spring, although a steel screw spring or a spring ele­ ment made of elastic material are also conceivable.

Claims: 1. Mast for a sailboard, characterized in that the bottom end thereof is provided with a shock absorber, formed by an oil-filled cylinder and a piston with pis­ ton rod displaceable therein, while in the piston provision is made for passages, and the flow of oil through said passages is governed by valve means. 2. Mast according to Claim 1, characterized in that the shock absorber is also provided with a gas spring. 3. Mast according to Claim 2, characterized in that the gas spring is provided with a filling system, in or­ der to permit adjustment of the pressure to various weights of the mast/sail unit. 4. Mast according to one of the preceding claims, characterized in that the shock absorber is inserted into the bottom end of the mast and held in place by an adaptor which is detachably connected both to the bottom end of the shock absorber and the bottom end of the mast. 5. Mast according to Claim 4, characterized in that the adaptor is screwed onto the shock absorber and con­ nected to the mast by means of spring pins which project through holes into the mast. 6. Sailboard with a mast according to one of the preceding claims, characterized in that the piston rod of the shock absorber is connected by its bottom end to a coupling element which gives in various directions. 7. Sailboard according to Claim 6, characterized in that the coupling element is a cardan joint. 8. Sailboard according to Claim 6 or 7, charac­ terized in that an elastic stroke limiting device is fitted between the bottom end of mast or shock absorber and the coupling elements.

Inventors: DE VOS, JACOB
Applicants: KONI B.V.
Application year: 1987
Main classification: B63B15
IPC codes: B63B35