Ships – Hull or hull adjunct employing fluid dynamic forces to... – Having hydrofoil
Patent
1998-04-17
2000-02-15
Basinger, Sherman
Ships
Hull or hull adjunct employing fluid dynamic forces to...
Having hydrofoil
114 3924, 114 611, B63B 126, B63B 130
Patent
active
060240415
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to shipbuilding, and more particularly to a hydrofoil system of sailing-trimarans.
DESCRIPTION OF THE PRIOR ART
It is known that, as a watercraft gathers speed, its drag increases dramatically. An efficient way to diminish the drag is to use the hydrofoils which generate, at sufficient speeds, a hydrodynamic lifting capacity and lift a hull clear of the water. At such high speeds, the drag of hydrofoils is a number of times lower in comparison with the drag of a floating hull.
The use of hydrofoils is also very efficient in increasing the speed of windpowered watercraft. Modern windpowered multihulls, particularly the trimarans, are sufficiently high-speeded and light to be lifted, due to hydrodynamic lift, completely or partially clear of the water, and thereby, the drag is essentially diminished. A specific requirement regarding the windpowered watercraft is to provide the required stability, because the total force of a wind, as well as its direction and magnitude can vary in a wide range. The hydrofoil system of a cruising/racing yacht oriented to real conditions and to a wide range of yachtsmen must also be efficient in a rough sea, but, at a light breeze, when the speed is not sufficient to generate the lift, the drag of the hydrofoil system should be minimal. Such a hydrofoil system should not increase substantially the costs of a boat and cause additional inconvenience in operating. Existing hydrofoil systems meet these requirements only partially, therefore their use is still limited.
For example, in U.S. Pat. No. 5,168,824 a hydrofoil assisted watercraft of a trimaran type is described. The disclosed construction of foil suspended watercraft can only be used for short trips in waters sheltered from the high, breaking waves and is efficient only with sufficiently strong wind, when a hull and the outriggers are completely lifted clear of the water by hydrodynamic lift. At a light breeze, when a craft floats on the hull and the outriggers, the hydrofoils having maximal attack angle, the cantilevers and the canards all together generate great additional drag. The cantilevers and the canards hinder a mooring, but deep-positioned hydrofoils cause additional inconvenience in the shallow water.
Another hydrofoil system assisting in offshore cruising trimaran is described in Multihull International, June 1984, No. 197, 141-144, and it consists of two curved, liftable foils, arranged one on each outrigger, and of a daggerboard on a central hull. The main shortcoming of this system lies in the fact that, as the side wind pressure and hydrofoil lift increase, the stability of the trimaran decreases. The weight of the trimaran is transferred to the leeward outrigger which receives the concentrated force of the hydrofoil's dynamic lift, which lessens the waterplane moment of inertia of an outrigger and increases the pitching amplitude. Submersing of the forepart of the outrigger causes the decrease of hydrofoil's attack angle and of hydrodynamic lift force, but the lifting of the forepart of the outrigger causes an increase in said attack angle and lift force. As the hydrofoil is displaced forward from the axis of pitching oscillations, the alteration of hydrodynamic lift force stimulates an increase of pitching amplitude and decreases even more the longitudinal stability of the trimaran.
The closest prior art to the present invention is a construction of an offshore racing trimaran with a hydrofoil system consisting of an inclined foil on each of the outriggers and a keel with an A-shaped additional foil, where the keel is moved aside the centre of central hull in the direction of its stern, shown in the Multihull International, January 1984, No. 192, p. 10-11.
This placement of hydrofoils also illustrates the main shortcoming of the scheme described above, namely, the decrease of the longitudinal stability with the increasing of side wind pressure and hydrofoil lift. The distance in a longitudinal direction between the A-shaped foil on the keel and the
REFERENCES:
patent: 3598076 (1971-08-01), Saxton
patent: 3802366 (1974-04-01), Mankawich
patent: 3949695 (1976-04-01), Pless
patent: 4027614 (1977-06-01), Jones
patent: 5054410 (1991-10-01), Scarborough
patent: 5168824 (1992-12-01), Ketterman
Multihull International No. 192, vol. 17, Jan. 1984, pp 10-11.
Multihull International No. 197, vol. 17, Jun. 1984, pp 141-144.
Abrahams Colin P.
Basinger Sherman
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