Ships – Watercraft with means used in providing sailpower – Having specifically defined hull shape
Patent
1993-10-04
1995-03-14
Avila, Stephen P.
Ships
Watercraft with means used in providing sailpower
Having specifically defined hull shape
114 93, B63B 3500
Patent
active
053968565
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a sailboard.
BACKGROUND OF THE INVENTION
Numerous types of sailboards are known which are generally adapted to receive on their upper surface a mast adapted to carry a sail and fixed by a mast foot on the board, and foot straps adapted to retain the feet of a user of the board and located rearwardly of the board relative to the mast foot.
It is known that a sailboard receives during its movements on the water dynamic forces of various natures: it receives on its lower surface in contact with the water forces due to the waves, to slapping, to landing after a jump; it also receives on its upper surfaces forces transmitted by the mast foot on the one hand, by the feet of the user retained by the footstrap on the other hand.
These various forces give rise to vibrations of the board. Generally speaking, these vibrations consume energy, requiring a supplemental physical effort on the part of the user of the board, and braking this latter. Moreover, certain of these vibrations, whose frequency corresponds to the frequency of the board itself, give rise to resonance phenomena which aggravate the recited drawbacks.
It is known that the frequency of the sailboard itself depends in particular on the distance separating the mast foot from the footstraps.
It is also known that for a given board, the emplacement of the mast foot is determined, for a given sail, by the position of the center of pressure of the sail, the conditions of navigation, the type and structure of the board. It is not therefore possible to modify this emplacement without risking loss of equilibrium and performance of the board.
Various internal structures of the board have been proposed: they have been able to improve the dynamic behavior of the board only in the case of low frequency vibrations, which are those that the user of the board can overcome at least partially by the action of his leg muscles.
It has also been proposed to mount the foot of the mast in a shock absorber adapted to absorb a portion of the forces transmitted by the latter: such a shock absorber can only function at the level of the amplitude of the vibrations, and not that of the creation of these latter.
SUMMARY OF THE INVENTION
The object of the present invention is to overcome the drawbacks of known sailboards, and to provide a sailboard in which the phenomena of resonance to low and medium frequency vibrations, which are the most troublesome, are at least to a great extent eliminated.
According to the present invention, the sailboard of the described type is characterized in that it comprises flexible means to support the mast foot in cantilever fashion above the board, and to transmit to the board in a region situated rearwardly of the mast head the forces transmitted by this latter.
The forces transmitted by the mast foot are thus transmitted to the board in a region situated rearwardly of the mast foot, therefore at a distance from the footstrap substantially less than on an ordinary board: the frequency of the board itself will thus be substantially offset toward the high frequency range, in which it is known that the corresponding vibrations have only a negligible effect on the performances of the board.
Moreover, because the mast foot is supported in cantilever fashion by flexible means, the forces and vibrations that it transmits will be at least in part absorbed before being transmitted to the board.
On the other hand, the emplacement of the mast foot remains unchanged on the board, such that the performances and equilibrium of this latter are in no way modified.
According to an interesting embodiment of the invention, the board also comprises flexible means to support the footstrap and the weight of the user of the board in cantilever above the latter and to transmit to the board in a region situated rearwardly of the mast head and in advance of the footstrap the forces transmitted by the feet of the user of the board.
This arrangement permits bringing toward each other a further substantial distance
REFERENCES:
patent: 4635578 (1987-01-01), Calcabrini et al.
patent: 4649847 (1987-03-01), Tinkler et al.
patent: 4730568 (1988-03-01), Campbell
patent: 4963111 (1990-10-01), Moulin
patent: 5018468 (1991-05-01), Peterson
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