U.S. patent number 3,625,173 [Application Number 04/848,593] was granted by the patent office on 1971-12-07 for hulls for power boats.
Invention is credited to Les Mitton.
United States Patent |
3,625,173 |
Mitton |
December 7, 1971 |
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.
Inventors: |
Mitton; Les (Birmingham, 20,
EN) |
Family
ID: |
25303738 |
Appl.
No.: |
04/848,593 |
Filed: |
August 8, 1969 |
Current U.S.
Class: |
114/61.33;
114/291 |
Current CPC
Class: |
B63B
1/20 (20130101); B63B 2001/203 (20130101); B63B
2001/202 (20130101); B63B 2001/005 (20130101); B63B
2001/186 (20130101); B63B 2001/201 (20130101) |
Current International
Class: |
B63B
1/20 (20060101); B63B 1/16 (20060101); B63b
001/10 () |
Field of
Search: |
;244/66.5S,61 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Farrell; Andrew H.
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.
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.
* * * * *