Hulls For Power Boats

Abstract

A hull for a power boat has a bottom configuration comprising two subhulls providing a catamaran-type structure, with an additional intermediate subhull, and this last is formed on the bottom with a rearwardly facing step, nearer the fore-end than the afterend, to provide a local sectional change of a tunnel defined by the said two subhulls.

Description

This invention concerns hulls for power boats and particularly relates to the bottom configuration of a hull, which configuration affects the efficiency of the boat in terms of, for instance, drag, i.e., the resistance to forward motion in still water, and tendency to develop pitching and/or rolling motion as speed increases.

Drag can be reduced to a considerable degree by known techniques of streamlining and surface finishing. Tendency for a boat to roll is related, inter alia, to its lateral stability as represented by the relation between its length and beam at the waterline in combination with any particular configuration of its transverse section which presents resistance to pendulum motion about the axis of buoyancy. A construction known as catamaran, in which at least the bottom configuration has the form of two identically and conventionally shaped subhulls bridged by a common top structure, has been adopted to provide, inter alia, improved lateral stability. Such a structure exhibits what may be termed a central tunnel which is flared at its forward end due to the ordinary fairing of the surfaces of the bows or peaks of the component subhulls and of the underneath of the top structure, which fairing plays some part in causing the forepart of the boat to rise, at speed, to decrease the area of contact with the water and therefore the drag.

At speed, such a catamaran form tends to develop a pitching motion which may become very violent, so that porpoising effect may be produced, thereby destroying the smooth forward motion of the boat with consequent loss of efficiency and resulting in considerable discomfort to the occupants. I believe that this phenomenon is due to the building up of the pressure of air as it is funnelled into the tunnel, the air pressure being released spasmodically at the afterend as that end is first raised by the built-up pressure and then falls as the pressure momentarily falls following each violent increased expulsion of air.

The main object of the invention is to provide a form of hull whereby the last-mentioned defect will at least be considerably reduced and may be completely eliminated.

In accordance with the invention a hull for a power boat has a bottom configuration in the form of two identical side subhulls, and a central subhull symmetrically between and in juxtaposition with the side subhulls, and, nearer the fore-end than the afterend of the central subhull, a rearwardly facing step on the central subhull to provide a local change in section of the tunnel extending fore and aft between the side subhulls.

The bottom surfaces of each subhull, as viewed endwise, preferably converge as two sides of a triangle, the angle of convergence for the central subhull being greater rearwardly of the step than forwardly thereof.

Two power boat hulls constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, wherein:

FIG. 1 is a side elevation of one hull;

FIG. 2 is a front elevation of the same hull;

FIG. 3 is a rear elevation of the same hull;

FIG. 4 is a bottom elevation of the same hull;

FIG. 5 is a sectional elevation in the central fore-and-aft plane of the same hull;

FIG. 6 is a bottom elevation of the second hull;

FIG. 7 is a rear elevation of the second hull;

FIG. 8 is a front elevation of the second hull; and,

FIG. 9 is a sectional elevation in the central fore-and-aft plane of the second hull.

Referring first to the hull illustrated in FIGS. 1-5, the hull is a one-piece molding below the upper boundary or coaming line. In plan the hull is almost rectangular at the coaming line, as is apparent from FIG. 5, with parallel squared fore and aft ends 1 and 2 respectively, and sides 3, 4 which are gently curved to a maximum beam at about the midship position. The exterior of the hull has a generally trimaran form wherein the side subhulls 5 and 6 are identical and the central subhull 7 is generally wider than each side subhull. The central subhull 7 is also shallower at its after end 8 than the after ends 9 and 10 of the side subhulls 5 and 6 and is deeper at its fore-end 11 than the fore-ends of the side subhulls.

As viewed from fore and aft (FIGS. 2 and 3), the upper parts 14, 15 of the sides of the hull are inwardly inclined, at a little less than 90.degree. to the horizontal, to the upper boundaries of the outsides 16, 17 of the side subhulls 5, 6, those outsides 16, 17 being more steeply inclined at about 45.degree. to the horizontal. The outsides 16, 17 of the side subhulls 5, 6 are interrupted by spray rails 18 which extend to and are faired into the foreparts of those outsides 16, 17. The inner sides 19, 20 of the side subhulls 5, 6 are set at about 90.degree. to the outer sides 16, 17 thereof. At the afterend (FIG. 3) the outer sides 21, 22 of the afterpart of the central subhull 7 are inclined to one another at about 135.degree., the two lines of junction between the sides 21, 22 of the central subhull and the inner sides 19, 20 of the side subhulls 5, 6 being at about the level of the junctions between the upper parts 14, 15 of the sides of the hull and the outer sides 16, 17 of the side subhulls. As seen from the afterend (FIG. 3) the maximum width of the end 8 of the central subhull is greater than that of each of the ends 9, 10 of the side subhulls, and, as indicated above, the depth of the end 8 of the central subhull is less than that of the ends 9, 10 of the side subhulls.

The afterend 23 of the hull is a substantially planar surface inclined inwards and downwards at a small angle, for instance 14.degree., to the vertical, and it extends as the after ends 8, 9 and 10 of the central and side subhulls.

As viewed from below, the subhulls 5, 6, 7 extend substantially parallel to one another from one end to the other of the hull.

At a position between one-half and two-thirds of the overall length from the afterend, the central subhull is formed with a rearwardly facing, substantially vertical step 24 extending at right angles to the fore-and-aft centerline. This provides that forwardly of the step 24 of the line 11 of junction of the sides 25, 26 of the forward part of the central subhull is lower than the line of junction of the sides 21, 22 of the afterpart of the central subhull; but at the step 24 the upper boundaries of the sides 25, 26 and 21, 22 of the forward and after parts respectively of the central subhull are at the same level. Thus forwardly of the step 24 the angle between the sides of the central subhull is increased. It will be seen, as indicated in FIG. 3, that the step 24 as viewed from the afterend presents two elongated triangular faces inclined symmetrically upwardly and away from one another at a shallow or obtuse angle.

As previously explained, the provision of the step 24 on the bottom of the central subhull 7 modifies the form of the tunnel extending between the side subhulls 5, 6 in a manner which at least reduces any tendency of a boat of which the hull is the basis to porpoise.

Forwardly of the step 24 the surfaces of the subhulls are faired gently upwardly and together, but for none of the subhulls is the fairing continued to the vertical nor to pointed peak. From the upper front boundary 1 of the hull, as is visible in FIG. 2, there extend downwardly three generally isosceles triangular surfaces 27, 28, 29, referred to as snub faces; the snub faces 27, 28, 29, being formed one on each of subhulls, curve downwardly and inwardly, as indicated in FIG. 4, to meet the sides of the subhulls, the snub faces 27, 29 on the side subhulls being curved sharper than the snub face on the central subhull. The fairing of the sides of the subhulls terminates on the sides of the triangular snub faces.

The fore part 11 of the central subhull is deeper than the fore parts 30 of the side subhulls, and the lower peak of the fore part of the central subhull extends forwardly of the lower peaks of the fore parts of the side subhulls to meet its associated snub face 28 at a sharper angle than do the lower peaks of the foreparts of the side subhulls meet their associated snub faces 27, 29. Preferably the lower peaks of the side subhulls are smoothly curved into their associated snub faces 27, 29.

The purpose of the snub faces 27-29 is to prevent the boat lifting to such an extent at its forward end that it might tend to be turned over backwards.

In the second form of hull, shown in FIG. 6-9, the rearwardly facing step as seen from below is V-form with the apex 31 of the V forwardly on the fore-and-aft centerline 32 of the central part hull 33 and the sides 34, 35 of the V diverging rearwardly to the outer boundaries of the outer sides of the central subhull 33. As in the first-described arrangement, the depth of the middle line 32 of the central sub hull is reduced at the step 31, so that at and rearwardly of the step 31 the middle line 32a is higher than its forward part 32. However, rearwardly of the step 31 the sides 36, 37 of the rear part of the central subhull 33 meet the inner sides 40, 41 of the side subhulls 42, 43 along the same lines 44, 45, that is at the same levels, as the sides 38, 39 meet the inner sides of the side subhulls 42, 43 forwardly of the step 31. Thus, as in the first-described arrangement, the step as seen from the afterend presents two faces 34, 35 each of elongated triangular form inclined upwardly and away from one another at a shallow or obtuse angle, but in this case the faces 34, 35 are also divergent rearwardly as indicated in FIG. 6.

It has been found that with a somewhat shorter boat, the V-form step is even more effective than that first described.

It is found that the performance of a boat may be further improved by slightly inclining the lower middle line 32a of the central subhull rearwardly and downwardly from the step 31. The angle of inclination of the line 32a to the horizontal will be quite small, for instance about 11/2.degree., so that at its extreme after end this line 32a will still be above the lowest lines 46, 47 of the side subhulls 42, 43.

The hull shown in FIG. 6-9 differs in some other respects from that shown in FIGS. 1-5. For instance, as seen from the fore- and afterends, the sides of the side subhulls are asymmetrical, in that their inner sides 40, 41 are more steeply set, for instance at 15.degree. to the vertical, and their outer sides 50, 51, on which the spray rails 52 are provided, are at an angle of less than 45.degree. to the horizontal. Also the forward end 53 of the hull is not square with the sides as in the previously described arrangement, but is set at an oblique angle with a central nose portion 54. The forward part 55 of the central subhull is faired to the nose portion, as indicated in FIGS. 6 and 9, and the forward parts 56 of the side subhulls are faired to positions slightly rearwardly of, but at the same level as, the nose portion 54.

As in the first described arrangement, the forward part 31 of the step is between a half and two-thirds of the length of the hull from the after end.

Some typical dimensions of the hulls illustrated in the drawings are as follows:

Figs. 1 to 5

Overall length--15 feet.

Beam--6 feet.

Width of step-- 2 feet 1 inch.

Depth of step on center line-- 4 inches.

Distance of step from afterend-- 8 feet, 4 inches.

Figs. 6 to 9

Overall length-- 13 feet.

Beam-- 5 feet, 6 inches.

Width of step-- 2 feet, 6 inches.

Depth of step, on centerline-- 6 inches.

Distance of step from afterend-- 7 feet, 6 inches.

It has been found that with the improved hull shape, a boat has greatly improved stability when turning at speed, in that it has less tendency to heel over.

Claims

I claim:

1. A hull for a power boat, the hull having a bottom configuration of two identical side subhulls and a central subhull symmetrically between, and in juxtaposition with, the side subhulls, and, nearer the fore-end than the afterend of the central subhull, a rearwardly facing step on the bottom of the central subhull, the bottom surfaces of each subhull converging downwardly to meet in a fore-and-aft extending vertical plane, and the angle of convergence of the bottom surfaces of the central subhull being greater rearwardly of the step than forwardly thereof.

2. A hull for a power boat, the hull having a bottom configuration of two identical side subhulls and a central subhull symmetrically between and in juxtaposition with the side subhulls, and, nearer the fore-end than the afterend of the central subhull, a rearwardly facing step on the bottom of the central subhull, the bottom surfaces of each subhull converging downwardly to meet in a fore-and-aft extending vertical plane, and the angle of convergence of the bottom surfaces of the central subhull being greater rearwardly of the step than forwardly thereof, the step being, in plan, of symmetrical V-form with the apex of the V-form forwardmost in the fore-and-aft middle vertical plane of the hull, the limbs of the V-form diverging rearwardly and symmetrically about said middle vertical plane, and said limbs presenting vertical faces each of a triangular shape which is convergent away from the apex of the V-form.

3. A hull for a power boat, the hull having a bottom configuration of two identical side subhulls and a central subhull symmetrically between, and in juxtaposition with, the side subhulls, and, nearer the fore-end than the afterend of the central subhull, a rearwardly facing step on the bottom of the central subhull, the bottom surfaces of each subhull converging downwardly to meet in a fore-and-aft extending vertical plane, and the angle of convergence of the bottom surfaces of the central subhull being greater rearwardly of the step than forwardly thereof, the step being, in plan, of symmetrical V-form with the apex of the V-form forwardmost in the fore-and-aft middle vertical plane of the hull, the limbs of the V-form diverging rearwardly and symmetrically about said middle vertical plane, and said limbs presenting vertical faces each of a triangular shape which is convergent away from the apex of the V-form, and, rearwardly of the step, the line of convergence of the bottom surfaces of the central subhull inclining downwardly towards the after end of the hull.