US 3094959 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
June 25, 1963 u. FOX 3,094,959
MULTI-HULLED CRAFT 4 Filed Sept; 7, 1961 2 Sheets-Sheet 1 IN ve/vrom- Filed Sefit. 7, 1961 2 Sheets-Sheet 2 Z/WM/w' UFFA Fox 3,094,959 MULTI-HULLED CRAFT Ulla Fox, The Commodores House, Cowes, Isle of Wight, England Filed Sept. 7, 1961, Ser. No. 136,529 Claims priority, application Great Britain Aug. 2, 1961 1 Claim. (Cl. 114-61) This invention relates to multi-hulled craft, such as twin-hulled catamarans, and triple-hulled trimarans, i.e. of the kind wherein the hulls are relatively widely separated laterally.
Where such a craft is entirely without a ballast keel either on the hull or elsewhere, the craft is easily capsized and inherently non-self-righting, and once it has passed beyond the 90 angle of turn about its fore-andaft axis, will be subject to an over-turning couple which increases with further turn and results in complete capsize of the craft.
The object of the complete invention is to provide an improvement in such multi-hulled craft whereby they tend to be non capsizing and become automatically selfrighting irrespective of the degree of turn to which they may be subject, i.e. able to restore themselves to even keel from the completely capsized condition.
According to the present invention, in a multi-hulled craft of the kind referred to, there is provided a ballast keel on or near the centre line of separation of the hulls, whereby upon positioning of the craft in water at any inclination to the level there is exerted a restoring turning couple constituted by the Weight of the ballast keel means acting downwardly in a first plane and the buoyancy re action of the immersed part of the craft acting upwardly in a second plane spaced horizontally from the first plane.
In a preferred form, the ballast keel means consist of a single ballast keel, mounted for example on a depending keel fin, positioned centrally and symmetrically between two hulls, e.g. of a catamaran.
The restoring force is most effective if the centre of gravity of the ballast keel means is below the immersed portion of the hull or hulls, or at least below the flotation centre thereof, and it is preferable if the ballast keel means is relatively dense, compared with water, so as to have its effective weight reduced as little as possible by immersion.
In a preferred practical embodiment, the weight of the ballast keel means would be approximately half of the total weight of the craft, e.g. rnast, rigging, upperworks, etc., and including the ballast keel means.
A form of catamaran incorporating the invention has two similar or dissimilar hulls relatively widely spaced by a superstructure disposed generally above the water line, a depending keel fin being formed on the superstructure and being positioned with its centre line in the median plane between the two hulls, a ballast keel being mounted at the base of the keel fin at a level below the two hulls such that the positioning of the craft in water at any inclination to the level causes the exertion of a restoring turning couple constituted by the weight of the ballast keel, immersed or otherwise, acting downwardly in a first plane, and the buoyancy reaction of the remaining immersed part of the craft, i.e. a hull or part of the superstructure or both, acting upwardly in a second plane spaced horizontally from the first plane.
In order that the nature of the invention may be readily ascertained, an embodiment of multi-hulled craft in accordance therewith, and its manner of operation for selfrighting, is hereinafter particularly described by way of non-limiting example with reference to the figures of the accompanying drawing, wherein:
Patented June 25, 1963 FIG. 1 shows schematically the craft in even keel position.
FIG. FIG. FIG.
2 shows the same in a 30 tilted condition. 3 shows the same in a 60 tilted condition. 4 shows the same in a tilted condition. 5 shows the same in a tilted condition.
FIG. 6 shows the same in a tilted condition.
FIG. 7 shows the same in a tilted condition, i.e. fully capsized.
In this drawing, the craft is shown only schematically because other details of its construction are incidental only and do not form part of the invention.
The craft has a superstructure 1 incorporating twin hulls 2 and 3 which are separated by substantially the maximum width of the superstructure. Centrally below the superstructure is provided a dependent keel fin 4 with ballast weight 5. The ballast weight 5 is best formed from conventional ballast material for marine use such as lead, iron, or the like which is many times more dense than water. The keel fin 4 is symmetrically arranged between the two hulls 2 and '3, and the areas 6, 7 of the superstructure lie clear of the water line 8 in the upright condition of the craft.
The superstructure is shown as having a deck formation at 9, at each side, and inwardly tilted side walls 10 define, for example, cabin works or the like.
The shaded areas of the hulls 2 and 3 represent those portions which lie beneath the water level 8 for the various conditions illustrated in these figures.
By way of example, the weight of the ballast keel weight 5 could be half of the total weight of the craft, i.e. the weight of the ballast keel is equal to the combined weights of the remainder of the hull, superstructure, rigging, masts, etc.
The centre of gravity of the ballast keel weight 5 is indicated at x and the flotation centre of the immersed portion of the structure is indicated at y.
It will be seen that, in the even keel condition of FIG. 1, the two centres are vertically one above the other and in a stable condition. The immersed weight of the ballast keel 5 acting downwardly is counterbalanced by the symmetrical upward thrusts exerted on the two hulls 2 and 3.
Referring now to FIG. 2, in which the craft is tilted at 30 to the vertical, the centres x and y are now separated by a horizontal distance a. The immersed weight of the ballast keel 5 still acts downwardly and an increased thrust is exerted on the hull 2 in an upward direction. The result is a turning couple, constituted by the forces acting at x and y and separated by a distance a, which acts to restore the craft to equilibrium in the even keel condition of FIG. 1.
A restoring couple is similarly exerted on the craft in the position of FIG. 3, but is increased because the distance a is greater and a, the reaction at y has increased because more of the hull has become immersed, and the immersed weight of the keel at x has increased because less of it is in the water.
In the horizontal position of FIG. 4, there is a maximum restoring couple exerted, because although the distance a has reduced slightly, the keel weight 5 is now fully out of the water and the whole of its weight acts downwardly at x.
In the 120 position of FIG. 5 the restoring force has again been reduced but is still considerable because the weight of the keel 5, acting at x is equal to the weight of the whole of the remainder of the vessel.
In the 150 position of FIG. 6 the restoring force is again somewhat reduced but is still adequate to turn the craft back towards the even keel condition.
In the 180 position of FIG. 7, the weight of the keel acts at x which is vertically above the upward buoyancy thrust acting at y. This is a position of unstable equilibrium; in practice however the whole would inevitably tilt to one side or the other of vertical after a very short time, whereupon a restoring couple would be exerted and the craft would pass'through the series of positions described until it was back again in the even keel position of FIG. 1.
A multi-hulled craft having two buoyant hulls relatively widely spaced by a superstructure positioned generally above the water line, a depending keel fin formed on the superstructure and positioned with its centre line in the median plane between the two hulls, a ballast keel mounted at the base of the keel fin at a level below the two hulls, said hulls and keel fin extending both above and below the normal water line in the upright condition of the craft, such that upon positioning of the craft in water at any inclination to level there is exerted on the craft a restoring turning couple constituted by the weight of the ballast keel acting downwardly in a first plane and the buoyancy reaction of the remaining immersed part of the craft acting upwardly in a second plane spaced horizontally from the first plane.
References Cited in the file of this patent UNITED STATES PATENTS 2,997,974 Hamlin Aug. 29, 196 1 FOREIGN PATENTS 58,0 29 Germany Aug. 4, 1891 331 Great Britain 1896 822,861 France Oct. 4, 1937 1,164,373 France May 12, 1958 1,169,344 France Sept. 8, 1958