Note: Descriptions are shown in the official language in which they were submitted.
127~530
This invention relates to a marine planing hull
which is suitable for boats operating above
displacement speed through the water, and is directed
to the achievement of superior qualities with regard to
softness of ride through rough water, stability, and
general seaworthiness.
BACKGROUND OF THE INVENTION
For many years designers have strived to provide
the preceding qualities in their hulls, and the "deep
V" hull, the catamaran or tunnel hull and the hydro-
field designs have evolved. However, in gaining the
ride softness, the designs have always b~en a trade-off
to degrading some other quality. In the case of the
"deep V", increased draft and lack of stability at
rest, the catamaran has increased cost of manufacture,
increased draft and requires twin powerplants if heavy
loads are carried, and the hydrofield requires a narrow
beam and shows a lack of buoyancy in the bow.
The development of understanding of planing
hulls has taken place only in the last 40 years, and
the basic authority is a book entitled "Naval
Architecture of Planing HullsN by Dr Lindsay Lord
(Cornell Maritime Press, Inc, Cambridge, Maryland,
USA). On page 31 of the Third Edition of said book
there is a reference to the lifting forces and the
suction forces which exist in a planing hull, and it is
stated (apparently correctly) that it is the change of
directional momentum of water particles striking the
plane that kinetic energy is transferred. In terms of
useful work, lift occurs only at those points where
kinetic energy is being impressed upon the water. The
amount of lift at these points will vary approximately
as the cosine of the true planing angle at a gi~en
point.
The most commonly used planing hull has a V-shaped
bottom with smooth surfaces and the dead rise angle
rapidly increases at the forefoot end of the bottom.
~27~;30
Accordingly in many instances, under normal usage,
water will flow upwardly over the planing surfaces at
the forefoot end, and although that flow will cause a
considerable degree of lift, it will cause an upwardly
directed bow wave which necessarily results in loss of
lift and wastes energy. Furthermore the bow wave on
each side of the central longitudinal plane of the
bottom will cooperate with the bow wave on the other
side to define an angle which may be in the vicinity of
90 and is sometimes obtuse so that the lifting
pressure rapidly diminishes rearwardly of the
forefoot.
Referring further to the Lord textbook, on page 63
of said edition, reference is made to the forebody
lS sections, and the advantages and disadvantages of
various shapes are discussed. The effect of dead rise
is discussed and further advantages discussed with
respect to lateral plane on page 67, where it is
pointed out that a hull suited to blue water cruising
has a "more generous lateral plane, distributed fore
and aft throughout the underbodyn.
These considerations led Lord to the conclusion
that monohedron lines were the most desirable and that
running lines shall be "straight and parallel with each
othern. The development since that time has been based
upon the accurate statements of Lord which can be shown
to be correct, but there are necessarily compromises
- which are reached in the design, and any advantages,
for example due to the cross-sectional shape of the
hull bottom is accompanied by disadvantages. For
example, by having the shape of the hull bottom to
comprise a pair of downwardly concave planing surfaces,
the water displaced by the hull can be redirected
downwards by the curvature and thereby increase the
available lift, but hulls which are constructed to this
shape pound (that is, hydraulically bottom) and produce
extremely high shock loading on to the hull structure
~279S30
upon encountering rough water and there is also more
tendency for them to broach than with the more
conventional convex hull shapes.
By increasing deadrise into a deep "V" shape, the
lateral plane is increased quite effectively and the
steeply sloping plane surfaces of the bottom upon
tilting result in a correcting moment which is much
higher than with bottoms of small deadrise (say 10)
but there is an increased draft and also an instability
when the boat is at anchor and does not have the
benefit of the dynamic righting forces. An object
therefore of this invention is to provide a hull shape
which will provide required softness of ride without
the instability at anchor and without unnecessarily
large lateral planes.
The statements contained in the Lord textbook
relating to parallel running lines are obviously
correct, but in this invention parallelism is either
reduced or completely obviated and consequently some of
the benefits due thereto are lost, but experience and
tank tests have indicated that the compromise is much
in favour of this invention, that is, there is much
improvement in the softness of ride for a very small
cost in the planing efficiency.
BRIEF SUMMARY OF THE INVENTION
In an embodiment of this invention a marine hull
includes a plurality of channels extending rearwardly
and inclined, in plan, with respect to the central
longitudinal vertical plane of the hull, the cross-
sectional shape of each channel being curved so that
its surface intercepts water when the hull is mobile
and that water is caused to leave each channel in a
downward direction thereby imparting lift over a major
portion of the length of the hull.
More specifically, in this invention, a marine
hull has a bottom shape which includes surfaces which
define a plurality of channels which extend rearward~
and are inclined, in plan, with respect to the central
~Z'79~30
--5--longitudinal vertical plane of the hull, the cross-
sectional shape of each said channel being such that
its said surface intercepts water when the hull is
mobile and the water so intercepted moves firstly
upwardly and rearwardly and then downwardly and rear-
wardly with respect to the hull thereby imparting
kinetic energy to that water and transforming that
kinetic energy into lift, sufficient length of said
bottom having said channels that said lift occurs over
a major porltion of the length of the hull.
With this invention, there are three major advan-
tages over prior art hulls. The channels deflect the
flow of water over the hull bottom from the forefoot
area, and this reduces the tendency to pound
(hydraulically bottom). Secondly, the channels entrap
air which cushions the pounding. Thirdly, it is but a
simple matter to achieve a much more even distribution
of lift at the centre and rear portions of the hull
bottom than with a conventional hull, so that a hull
which becomes airborne from riding a wave can descend
to the water surface with much less pounding than a
conventional hull.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is applicable to a wide range of
shapes and proportions, and several embodiments are
described hereunder in some detail with reference to
and are illustrated in the accompanying drawings in
which:
FIG. 1 is a side elevation of a hull which
embodies the invention,
FIG. 2a shows the cross-sectional shape of an
inboard channel of FIG. 1,
FIG. 2b shows the cross-sectional shape of an
inboard channel of FIG. 1,
FIG. 2c shows a cross-sectional shape similar to
FIGs. 2a and 2b, but modified to have a step,
gL;~7~;3~)
--6--
- FIG. 3 is a part section taken on line 3-3 of FIG. 1,
FIG. 4 i6 a part section taken on line 4-4 of FIG. 1,
FIG. 5 is a part section taken on line 5-5 of FIG. 1,
FIG. 6 is an underside perspective view showing a hull
according to a second embodiment,
FIG. 7 is a rear end elevation of a hull according to a
third embodiment,
FIG. 8 is an underside view of FIG. 7,
FIG. 9 is an underside view of a hull according to a
fourth embodiment,
FIG. 10 is an underside view of a hull according to a
fifth embodiment, and
FIG. 11 is a side elevation of a hull according to FIG.
10 .
Referring first to the embodiments of FIGS. 1 through to 5
a marine planing hull 10 has a "trimaran" front 11, and a
bottom 12 which comprises a plurality of channel surfaces 13,
all of which extend laterally outwardly and rearwardly from the
central longitudinal plane 'P', adjacent surfaces 13 between
them defining channels 14 which at least partly guide the flow
of water relative to the hull bottom when the hull is mobile
t~rough the water.
The channels 14 on one side of the central longitudinal
vertical plane 'P' of the hull bottom define (in plan) an angle
with corresponding channels on the other side thereof which is
an acute angle at least in the forebody 15, but in this
embodiment all the channels 14 on each side of the hull are
parallel to each other but are inclined to plane 'P' (as they
are also in FIG. 6). In this embodiment there is a "trimaran"
or triple front 11 and the two outer hull portions define with
the inner hull portion a pair of large channels 17. ~hese are
illustrated in detail in FIGS. 2a, 2b, 3 and 4. In all
instances, the channel
,,~A~
, .
127~530
surfaces 13 of each channel 14 or 17 include side sur-
faces and an intermediate surface 18 which is
downwardly concave. Further, the outboard side surface
19 are steeper than the inboard side surfaces 20 of each
channel. The ribs 22 shown in FIGS. 2a and 2b are
optional to the invention but are useful in further
softening the ride, since they appear to separate some
air from the water.
FIG. 2c shows a minor variation of FIGS. 2a and
2b, wherein the step 23 assists in causing a reduction
of the "wetted surface" of the bottom 12, without sub-
stantial loss of lift.
In the embodiment of FIG. 6, the channels 14 ter-
minate in a shelf 24 which is forward of the transom 25,
but in some other embodiments the channels extend
through to the transom. Shelf 24 may be flat or of
convex shape, or may be corrugated. It is in a
horizontal plane and arranged so that most or all of
its surface is just clear of the water when the hull is
planing, and this reduces wetted surface area.
Under displacement conditions, shelf 24 is beneath the
surface of the water and provides some buoyancy. Shelf
24 does not necessarily extend right across the hull,
but may be flanked by channels which extend to the
stern.
FIGs. 7 and 8 illustrate a further embodiment
wherein the underside view (FIG. 8) of the lower
portion of the hull is generally triangular, the hull
being provided with surfaces 13 which form channels 14
on each side which diverge from the channels 14 on the
other side from the central longitudinal plane 'P', and
between the surfaces 13, a central bottom portion 28
bridges the innermost channels and is downwardly
convex. This is a relatively small portion which is
triangular in plan as shown in FIG. 8. The central
portion 28 can be so arranged that it is immersed at
displacement speeds but clear of the water at planing
speeds of the hull. Small downwardly convex triangular
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areas 29 at the junctions of channels 14 further reduce
pounding (FIG. 8). The rear edges of these areas 29
are transverse, and there is a clean break-away of the
water from these areas.
A model shape which has been produced and tested
in a tank indicates that the flow of water encountering
the strakes 13 is directed into channels 14 by its
surfaces but the flow through the channels is not
simple. The flow is complex and is different for
different speeds.
At all angles of the channels 17 to the plane
'P' other than parallel, the lower outer edge of each
surface 13 tFIG. 2b) shields the internal volume
beneath the concave surface 18 from direct contact with
lS approaching waves. At the moment of contact with a
wave, a layer of water is forced upward by the inboard
surface 13, around the surface 18 in a clockwise
direction until it emerges vertically downward having
transformed its kinetic energy into vertical lift on
the surface 18. Just before the wave rises above lower
edge of 19, this high speed layer of downward moving
water now meets the surface of the wave forcing
entrained air below the wave surface. This mixture of
turbulent water and air is then forced back against the
surfaces 13 and 18 as the wave rises further and thus
cushions the impact and spreads it over a greater time
period and area of the hull, greatly reducing impact
forces and making hydraulic bottoming or pounding
impossible.
To allow the hull to start planing with less power
a conduit or conduits 26 may connect to each channel
such that air is allowed to be drawn into the channel
14 while in motion.
One of the causes of loss of direction which is
frequently encountered is when waves strike a hull from
a forward quarter and cause the hull to rotate about a
vertiçal axis so as to change direction. This
invention reduces the effect of such wave motions in
~;~7953~
g
that the surface water of the waves is distributed
across the channels 14l and the channels function as
shock absorbers because they are likely to include
pockets of air.
Intercepting the upwardly directed bow wave by use
of this invention increases the lift available to the
hull and ensures spray from the boat is directed
downwardly close to the hull so that it cannot be blown
back inside the boat by wind.
By decreasing the cross-sectional area of each
channel 14 in the vicinity of the bow, the bow shape is
allowed to be sharp or fine at the forefoot, and each
channel above having increased length of curvature, the
bow becomes rounded or full at deck level allowing
superior performance with a following sea.
Water which freely enters the channel spaces and
is accommodated thereby during the passage of the hull
through the water has a large component of downward
movement as it leaves the channels. Because the
channels run at an angle to the central plane (FIG.8),
and because maximum lift is when the water leaves the
channels vertically downwardly, it is preferable to
reduce the outward displacement and this can be
achieved by angling surfaces 19 (FIG.2) inwardly and
downwardly. Flowever, near the rear ends of the
channels, each surface 19 may be made to slope
downwardly ancl outwardly to reduce generation of spray
near the hull.
The cross-sectional area and shape of the channels
need not be constant along their entire length. It has
previously been mentioned the progressive reduction in
area as the channels near the bow improve the shape of
the bow. It is also generaly preferred to have the
surfaces 13 of the channels 14 curved as shown in FIG.
7, but not necessarily of circular shape. Also if the
channels are of increasing vertical angle (as are
surfaces 13b in FIG. 7), the ride is softer but more
propulsion power is required. Thus in the area near
~;27~ 30
--10--
the stern, at the lowest part of the hull, the angles
tend to be shallowerr as are surfaces 13, and both at
the bow and in the channels 14 higher on the side of
the hull, the angle is more nearly vertical.
If the channels are inclined slightly upwardly
when nearing the point of the bow, the bow tends to
lift. If the forward end of the outer edge 13 (FIG.
2b) is inclined downwardly, the hull gives a "softer"
ride, reducing pounding in an approaching sea.
In the interests of soft ride, the most favourable
ratio of propulsion power to ride comfort is when the
area and number of horizontally arranged channels is
sufficient to just lift the hull at normal load and
cruising speed, and the channels 14 are arranged simi-
larly to FIG. 7. wherein the topmost curves of the
channel surfaces 13 are all nearly at the same hori~on-
tal height as are their lower edges. Deepening of the
central portion of the hull (eg. at 29 in FIG. 8 making
the central curvature more convex downwardly) at the
localities of the junctions of the channel pairs also
reduces the pounding effect in that area. The effect
of this modification to the front portion 29 (FIG. 8)
has the effect of limiting "porpoising". Its rear
surface can be made to slope upwardly and rearwardly
with some advantage.
Succeeding channels above this level are arranged
with greater variation of height and angled more
vertically to reduce their lifting effect.
At the most rearward point of each channel 14 the
shape of surface 13 is modified to prevent excess water
which would not be caught by curve 18 from being forced
upward. This can be done by changing the inboard rear
portion of surface 13 to run parallel to the keel at
its rear end, the surface generated by this change
sloping upwardly and outwardly away from the keel.
This is not illustrated.
Under certain conditions it is found that spray
will rise vertically from the rear portions of the
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channels, eg in turns. To remedy this situation an
inverted curved section runs from a relatively high
point at the bow, rearward to the region where the
curve of the bow finishes, and then drops more acutely
following the points where each channel finishes
forming a chine, to the stern of the hull. This chine
redirects spray, improves the appearance of the hull,
protects the edge of the strakes and allows a portion
of the chine to facilitate loading on and off a
trailer.
In respects other than those described above the
principles set forth in the Lord textbook essentially
apply. For example, in elongate hulls the channels can
converge near their forward ends but constitute
parallel running lines rearwardly of the central
portion of the hull. It is profitable to provide a
keel which connects the successive channel joining
points.
Reference is now made to FIG. 9 which is an
underside view wherein the channels 14 follow a zig-zag
path, and in this embodiment the channels divide the
bottom of the hull 10 into a forwardly located diamond-
shape portion 30 and a rearward area portion 31 which
may be flat but in this embodiment each of these
portions constitutes conic surfaces or repeated
arrangements of channels in zig-zag pattern shown in
FIG. 9.
It will be seen that the channels are
inclined in plan with respect to the longitudinal
vertical plane 'P' of the hull, and thereby intercept
the water so that, as in the other embodiments, it
moves firstly upwardly and rearwardly and then
downwardly and rear-wardly to impart kinetic energy to
the water in the channels 14 and then transform that
kinetic energy into lift, as the water is discharged
both at the ends of the channels, and along the length
of the channels.
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The same effect is achieved also with the
further embodiment illustrated in FIGs. 10 and 11. In
this further embodiment (which is really an extension
of FIG. 9) the envelope shape of each surface
designated 33 is conic, and the rearwardly and upwardly
sloping surfaces 34 comprise a series of trans-
versely curved longitudinal portions arranged in
step fashion, each step having a vertical transversely
extending portion 35 and a horizontal transversely
extending curved portion 36, and this stepped shape
reduces the suction drag which might otherwise occur.
When outboard motors are used, they are best carried on
rearward extensions (not shown) behind the, or the
respective, conic surfaces 33.
The invention reduces planing angle, reduces
wetted surface, improves softness of ride, improves
stability under rough water conditions, and reduces
draft, when compared with V-bottom hulls having the
same performance.
