Ships – Hull or hull adjunct employing fluid dynamic forces to...
Patent
1992-05-22
1996-03-19
Huppert, Michael S.
Ships
Hull or hull adjunct employing fluid dynamic forces to...
114 56, B63B 104
Patent
active
054995930
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a boat hull for high-speed planing hulls, the underside of which has a profile in a longitudinal section through or, respectively, parallel to the center plane similar to the profile of an aircraft wing having curvatures, the vertex point of the longitudinal sectional profile, with reference to the bow-side endpoint of the chord of the longitudinal sectional profile, being positioned in the front half of the entire length of the chord, and wherein the stern-side endpoint of the profile is positioned at the lower endpoint of the stern or, respectively, transom below the water level.
Boat hulls of similar kind are known, for example from the DE-PS 30 22 966 or, respectively, from the FR-PS 515 361; this known boat hull, however, has several disadvantages. By the relatively strong curvature of the profile of the boat hull according to the DE-PS in the front region of the profile, the flow around the boat hull is accelerated at this place, whereby a zone of low pressure is created and the boat hull in this region is "sucked on" by the water. This is called "inverse wing effect", which occurs also in connection with the underside of an aircraft wing. By reduction of the profile curvature in the rear region of the profile, the flow speed is reduced in this region with respect to the front region of the profile, whereby a zone of high-pressure is created which presses the rear end of the profile upwardly, therefore out of the water. By these two forces, namely the downwardly directed suction force in the front part of the profile and the upwardly directed pressure force in the rear part, a trim moment by the bow is created, that is a moment around a point at a place between the points of application of the lifting force and the depression force, which moment may press the bow of the boat to down, therefore downwards, so that the boat is trimmed by the bow. This trim effect generally is a function of the shape of the profile as well as of the speed of advance flow and of the inclination angle of the profile or, respectively, of the profile chord. In case of a boat hull according to the DE-PS 30 22 966, the inclination angle of the profile for the stillstanding, unloaded boat is almost 0, so that the hitherto described effect can be understood substantially as a function of the shape of the profile and the speed of advance. The just described effect that has its reasons in the shape of the profile of the boat hull, finally is superimposed by the effect of a flow against an inclined flat plate, wherein the term "flow against an inclined flat plate" must be understood as a terminus technicus.
If a watercraft vessel increases its speed, also its bow-wave is increased. If the speed of the watercraft vessel is greater than the wave propagation speed of the bow-wave of the watercraft vessel, the boat hull incides, that means it trims by the stern; in simplified words, the ship tries to ride on its own bow-wave. As already said, the boat hull thereby trims by the stern, the inclination angle of the profile is changed and thereby also the depression force of the profile changes. Substantial parts of the boat hull are no more hit by the inclined against flow as a "profile", but as a "flat plate", whereby in the forebody a buoyancy component is created which acts against the bow-heavy trim moment. Supposing that the boat can bring sufficient power, the boat reaches a planing condition, which, however, when compared with conventional planing hulls, due to the curvature of the profile in the forebody is characterized by an increased resistance caused by an increased wetted surface as well as an increased wave resistance.
Further, within this known boat hull the suction component created by the arch of the profile in the front region of the profile, due to the horizontal in-flow, is so strong that a transition into the planing condition is indeed possible, however at the same time significantly more energy is absorbed as if, for example by a reduction of the arch of the prof
REFERENCES:
patent: 912814 (1909-02-01), Clifford
patent: 1505113 (1924-08-01), Warnock
patent: 3342032 (1967-09-01), Cox et al.
patent: 4742739 (1988-05-01), Mader
patent: 5199366 (1993-04-01), Ranchi
Lindsay Lord, Naval Architecture of Planing Hulls, Cornell Maritime Press, New York, 1946, pp. 169-172.
Brahan Thomas J.
Huppert Michael S.
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