Note: Descriptions are shown in the official language in which they were submitted.
Wo 95/14604 2 1 7 ~ 5 ~ 4 PCr/AUs4/00733
"VESSEB ~AVING A HIGH--SPEED PLANING OR SENI-PLANING HULL"
THIS INVE~TION relates to high speed marine craft hull
forms of both mono hull and multi-hulled form.
The invention relates particularly to improving the
llydLudy-lamic efficiency of high speed marine craft,
principally to mono-hulled or multi-hulled vessels which
would otherwise be of a planing or semiplaning nature, by
the introduction of a very shallow but pressurised air
cavity in the bottom of the craf t ' s rigid hull . The
L~ t in overall lly~h~dy~lamic ~ ffiri~nr~y of ship
hulls has been the subject of much research and the concept
of introducing air beneath a ship ' s hull with the intention
of improving it's llydLudy~lamic ~ff;rif-nl-y is not new. The
non-i 5;h;nus side wall hovercraft (otherwise knowi. as a
surface effect ship, SES) is a prime example of such an
application, although there are many others. Other
examples of such prior art comprise US3742888, US4393802,
US1824313, ~S1389865, AU--A--33446/84, AU--A--87515/83, AU--A--
44236/79, GB2112118, GB2060505, GBl311g35, JP3--243489, DE--
A-3208884, DE-A-2831357, WO-A-85/00332 and EP-A-0088640.
In regard to that prior art however, the power requirement
to maintain the air cavity at it ' 8 working pressure has
been a relatively high proportion (typically 15% to 50%) of
their main propulsion power requirements. Nany of these
designs also have the disadvantage of requiring f lexible
seals to ~-;nti~;n the air cavity in place. Another feature
of these existing designs is the relatively large volume or
depth of cavity employed which makes it ~l;ff;~nllt to
maintain the design air pressure in disturbed sea
conditions where air can rapidly leak from the cavity.
This ~; ff; C~ll ty is a contributing factor to the normally
high ~ supply system pow--: requirement.
Wo 95/14604 PCTIAU94/00733
217~56~ - 2 -
The invention relates to the ; ~ u" L of ~Iy-lLudyllamic
ef f iciency of a mono or multi hulled high speed marine
craft. This i8 brought about by supporting a significant
proportion of the craft weight on pressurised air, in the
f orm of a thin f ilm of air which is maintained under the
bottom of the hull. This air film is maintained within the
bounds of a shallow cavity integrated into the lower hull
of the vessel. The arrangement reduces the resistance
(both frictional and residuary resistance) to forward
motion of the craft compared to an equivalent craft without
the invention employed.
Accordingly the invention resides in a vessel having a high
speed planing or semiplaning hull comprising;
( a ) 2 f irst portion located at the bow and conf igured
to provide a forward planing portion;
(b) a second portion a~t of the first portion
comprising a shallow cavity having a forward end
defined by a step r~lrtr~ ; n~ across the hull at the
forward end of the second portion and a rib located to
each side of the hull for the length of the second
portion;
(c) a pressurised air source being provided in the
vessel and connected to the cavity to deliver air
under pressure to the cavity through an outlet whereby
the air is distributed substantially evenly into the
cavity and in a manner which does not disturb the
surface of the water below the cavity; and
(d) a third portion aft of the cavity providing a seal
at the aft end of the cavity and ~ormed with one or
more ~h~nnf.l ~ extending from the cavity to the stern
Wo 95/14604 2 1 7 ~ 5 G 4 PCr1AUs4100733
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to permit the controlled loss of air from the cavity
auch that a substantial portion of the third portion
has no contact with the air flowing from the cavity.
According to a preferred feature of the invention the
forward planing portion is formed with a central rib which
extends to each side of the central longitudinal axis and
which extends from a position in the region of or forward
of the water line to the step or a position forward of the
6tep . The prof ile of the lower surf ace of the rib can be
generally of corresponding profile to the hull to each side
of the rib while the sides pre6ent a step in the profile of
the hull. If desired, the depth of the step can vary along
it6 length whereby it is at its maximum at an int~ te
position alon~ its length. If desired the deadrise of the
rib can vary along its length being at its minimum towards
its aft end. In addition, the rib may t~rTni n~te forward
of the step and in such a case the hull may be generally of
constant profile between the aft end of the rib and the
step . If desired the ~ ~wer edges of the rib may extend
beyond the face of tne step. According to a preferred
feature of the invention the rib is formed as a member
supported from the hull which is capable of adjustment to
vary the degree of protrusion of the rib from the hull. If
desired, the rib is r~s; 1 i~ntly supported from the hull.
According to a pref erred f eature of the invention the
forward planing portion i6 provided with a plurality of
secondary ribs to each side of the central axis and which
are configured and placed to control the water flow past
the forward pl~ning portion such that the water flow is
substantially axial.
According to a preferred feature, the substantial
portion of the third portion is formed as one or more
regions of positive deadri~e.
Wo 95114604 , PCr1~U94100733
2 1 7 7 ~ 6 4 4
According to a further preferred feature the third portion
has negative deadrise such that the substantial portion of
the third portion i6 located to either side.
According to a preferred feature the ribs extend for at
least a portion of the third portion.
According to a preferred feature the face of the third
portion is ;nrl ;n~d downwardly from the second portion to
the stern. In addition, if desired the upper wall of the
cavity is ;nrl;nP~ downwardly towards the stern.
According to a further preferred feature of the invention
the substantial portion of the third portion is adapted to
a~- '^te propulsive units.
According to a preferred feature o~ the invention, the
second portion is formed with a plurality of longit---l;niql ly
spaced shallow cavities each defined by a gtep PlrtPn~;ng
transversely across the hull at its forward end and a rib
located to each side of the hull, the pressurised air
source being provided in the vessel and connected to the
cavities to deliver air under pressure to each of the
cavities through an outlet. If desired, the air source to
each cavity can be; n~l~p~n~ nt of the other cavities and
the air pressure maintained in the each cavity can vary
f rom the air pressure in the other cavities or can be
equal. In addition, the air pressure in the cavities can
be varied
In addition, if desired the forward cavities communicate
with the adjacent aftmost cavity through passageways. If
desired the pasE~ y~ may be A~sor; ~tPd with means to
regulate the degree of ~ ; cAtion where the regulation
i8 governed by aspects of hull motion such as hull speed,
pitch and roll.
Wo 95114604 2 1 7 ~ 5 6 ~ PCT/A1~94/00733
A benefit of the invention has been found to comprise
re~ c~ion in resistance of up to 35~ with a total air
supply power requirement of less than 5~ of the required
design propulsive power requirement. This means that the
air supply system can be very small relative to the main
propulsion r~eh;n~ry of the vessel.
Although the invention is applicable to what would
otherwise be Vee or Round bottom high speed craft, the
introduction of the invention Pi~n;~;cAntly changes the
underwater shape of the craft such that these conventional
descriptions would no longer apply. The craft with the
invention would be an essentially flat buL ~ vessel with
small side ribs and a very low deadrise underwater Vee bow.
It is the nature of these 8; ~n i f i ~Ant changes and the
effects that they have, which provides the high gain in
overall ef f j ~iency which makes the present invention 80
different from the prior art. As a result, the hull is
capable of a higher speed than is available in equivalent
craft without an increase in power which would be expected
with equivalent cr~ft of a conventional form.
According to a preferred feature the sides of the cavlty
are sealed by straight or swept side ribs. The inner edges
of the side ribs and the aft edges of the forward planing
step are shaped to promote clean water separation and
minimum turbulence.
According to a preferred feature the upper surface of the
cavity top, which forms the upper boundary of the air
cavity can be angled down, from its forward most end
towards its aft end and the third portion is also angled
down with an increased inclination. As a result, the third
portion at least, by virtue of its increased angle of
inclination compared to the second portion is contacted by
Wo 95/14604 PCr1AU94100733
217~56~ - 6 -
the water to create a seal at the aft end of the cavity,
which is profiled to have 1lydLu~iyllamic ~ffir;.on~y and to
control the loss of air from the cavity. The third portion
of the hull is formed with one or more ~hAnn~l R to allow
the air to escape to the stern of the hull through the one
or more ahAnn~l R formed in the third portion. The
presence of the ~hAnnel ~ serves to control and minimise the
air :Elow rate from the cavities and substantially reduces
the cavity air ref ill rate in rough sea conditions . In
addition, the rhAnnf~l R ensure that the L- i nrl~r of the
third portion is substantially free from any contact with
the air from the cavity. This enables propulsion units to
be located at the l~ ; nrl~r of the third portion whereby
their pelLuL111a11ce will not be inhibited by the air flowing
f rom the cavity .
According to a pref erred f e~ture of the invention at least
A rear part of the third portion is displacable vertically
with respect to the hull to vary the inclination of the
third portion. In this regard, the whole of the surface of
the rear part of the third portion between the side ribs
can be movable or it can be subdivided into segments
located between the ~hAnnf~l R . The movable rear part can
have or can provide one or more channels positioned in
uulle~l~u~ nce with the one or more ~h~nn~l ~ in the third
portion. Support ~or the movable rear part may be of a
resilient form to provide for the at least partial
absorption of shocks and the like, The movable rear part
serves to enhance stability of vertical ~,~ t and to
reduce excessive 1OA~1;n~R on the stern portion of the
ves sel .
A vessel designed in accordance with the above has a
distin~-iRhins feature that the total volume of the air
cavity is small compared to the static displaced volume of
the hull. Typically the ratio of total air cavity volume
to total static displaced volume is from 0 . 05 to 0 . 2 .
Wo 95114604 2 1 7 7 ~ 6 ~ PCTI~U94/00733
-- 7 --
-
An example of the vessel designed in accordance with the
above has a distin~l;~h;ng feature that the power required
to supply the air film is only a small percentage of the
power required to propel the craft. Whilst the design flow
rate of the air supply is related to the sealinq
arrAn ~, -t.s of the particular cavity design, the design
f low rate of the air supply is such that when multiplied
by the design air pressure and divided by the efficiency of
the pressurised air supply system, the resulting power is
no greater than 5~ of the Delivered Power required to
propel the craft at its design speed in its design
condition ~where the Delivered Power is the power required
to be delivered to the propulsion device to propel the
craf t at a certain speed ) .
A vessel designed in accordance with the above has a
distinguishing feature that the pressure of the air in the
cavity is such that this pressure multiplied by the non-
wetted platform area of the cavity is equal to a
~ir~n;f;r~nt proportion of the design weight of the craft
which typically is of the order of 30~ to 60~ of the design
weight of the craft.
According to a preferred feature the forward end of the
upper surface of the cavity is formed with a transverse
second step which reduces the depth of the cavity towards
the forward end, said air being delivered to the cavity
across the end face of the step and from a plurality of
op~n;n~ on the lower face of the step. Preferably the
majority of the air flow is from across the end face of the
step. According to a preferred feature the second step is
formed by a plate member mounted transversely across the
cavity. I'he entry of air into the cavity is such that the
surface of the water below the cavity is not ,l~f~ ' by
the air f low f rom the second step .
Wo gs/l4604 ~ PCrlAU94/00733
f~l77~iG~ - 8 - ~
In an _'i t of the invention, the pressurized air is
introduced from behind f a flat plate mounted horizontally
within the forward end of the cavity. The plate is
provided with openings in its lower face to allow some air
into the forward portion of the cavity. The air is
rrnt~;nf~d in the cavity by planing Yectors of the hull at
the forward end which terminate in a straight or swept
planing step. This step which forms the forward end of the
cavity, is substantially forward in the craft, being a
distance of 396 to 3596 of the static waterline length of the
craft aft of the forward perp~nA;r~ r. The lower portion
of this forward planing sector of the hull is made in the
form of low deadrise Vee section.
If desired the plate can be angled and extended aft to a
distance no more that half the length of the air cavity and
provided with a sharp trailing edge to ensure clean
separation of any water that should impinge on it. The
deadrise angle of this plnte may be equal to or less than
that at the forward planing step. This feature can lead to
i ~ uv~:d perfrr~~nrr of the air cavity in disturbed sea
conditions .
Furfh~ if desired, the plate can be constructed in an
angled, stepped form all the way to the stern, with the
deadrise angle of each step being equal to or less than the
one immediately in front of it, the forward most step
having a deadrise angle equal to or less than that of the
forward planing step. This feature can lead to i uve:d
pe.L ~ ~- - re in calm and disturbed sea conditions
particularly for high length to benm ratio vessels.
Accordins to a pref erred f eature of the invention the
rh~nn~ may be provided with regulation means which are
able to regulate air flow from the cavity. The regulation
means may comprise vanes of the like which can be moved to
WO 95/14604 ~ 1 7 7 ~ ~ ~ PC r/AUs4/00733
vary the cross-sectional area of the channels. The
regulation of air flow can serve to provide a control for
the trim~ and heel of the vessel.
According to a f eature of an ; ).~ of the invention,
the ribs are of substantially constant width throughout
their length . Alternatively in another : ~ i L the ribs
may decrease in width rearwardly of the step.
According to another pref erred f eature of the invention the
transverse distance between the chines of the hull in the
region of the step is at most equal to the transverse
distance between the chineg of the hull Ami~lRhiE.-2.
The invention will be more fully understood in the light of
the following description of several specific embodiments.
The description is made with reference to the ~ nying
drawings of which:-
Figure 1 is an underneath plan view of a hull
according to the f irst
F~ gure 2 is a sectional elevation of a hull according
to the first ~ L;
Figures 3A, 3s and 3C are cross-sectional views of the
hull of Figure 2 at lines A-A, B-B, C-C respectively;
Figures 4A, 4B, 4C, 4D, 4E, 4F, 4G and 4H illustrate a
variety of profiles for the . ~~i L along line D-D
of Figure 2 and of Figure 10;
Figures 5A and Ss illustrate the relationship between
the forward cavity depth and d~th of the planir,g step
area of the forward and rearward portion of the cavity
respectively;
~U~IllU~ SHEET (Rulc 2~j
Wo 95/14604 PCTIAU94/00733
2~ 64 - lo -
Figure 6 is an lln~ rn~ath plan view of a second
~ _-ir L having an r~Yfr n~ plate;
Figure 7 is an underneath plan view of a third
~ ` '; L having a set of extended plates;
Figure 8 grArhir~lly illustrates the results from
model tests of an example of the first embodiment
where resistance trim, heave and the pressurised air
pressure and f low rate are all shown as a function of
ship forward speed;
Figure 9 is an underneath ~lan view of a hull
according to the f ourth ~ L;
Figure 10 is a sectional elevation of a hull according
to the fourth: ` -ii L;
Figure llA, llB, llC are cross-sec~;on 1l views of the
hull of Figure 10 at lines A-A, B-B, C-C respectively;
Figure 12 is a side elevation of a form of the forward
portion of a hull which can be utilised in each o~ the
~"ho~; Ls; and
Figures 13A, 13B, 13C, 13D, 13E, 13F and 13G are cross
sections along lines A-A, B-B, C-C, D-D, E-E, F-F, G-G
of the f orward portion shown at Figure 12 .
Figure 14 is a schematic view of the stern of a vessel
according to another . - ' i - L .
In all of the drawings the abbreviations CL mean Centreline
and SWL means Static Water ~ine.
~ WQ 95~14604 21 7 7 5 ~ ~ PCT/AU94/00733
rrhe f irst ~ of the invention as shown at Figures
1, 2 and 3 comprises a high speed planing hull 11 which i8
formed with a forward portion 12 which has a generally
conventional planning cnnf i ~lration except it incorporates
a low deadrise planing section in its lower portion; and a
second portion 13 which A' I~lAt~ the cavity 14. The
forward portion 12 i8 6eparated from the second portion 13
by a step 15 which defines the forward boundary of the
cavity 14. The sides of the cavity 14 are defined by a
narrow ribs 16 to each side of the hull of equal width or
gradually becoming wider as they extend from the stern to
the forward end of the cavity and forming lateral
extensions of the forward portion. The wetted area of the
hull at design co~ditions is shown crosshatched at Figure
1.
Figures 3A, 3B, 3C provide an indication of the
cross-sectional t~nnf i g~lration of the hull on the lines A-A,
B-B, C-C of Figure 2.
A8 shown in Figures 3B and 3C the upper surface of the
cavity 14 is substantially planar and as shown at Figures 2
and 3s and 3C the upper surface is in~l in~d downwardly
towards the stern of the hull . The ribs which f orm the
sides of the cavity in the central portion extend to the
third portion aft of the cavity and can have a low positive
deadrise at the inner side of the rib. In addition, the
mid-portion of the third portion can be f ormed to have a
portion of positive deadrise to each side of the central
axis .
As a result of the ~nn Fi ~uration of the cavity and the
third portion of the hull, the air in the cavity is
maintained in the cavity and any 1088 of air i8 generally
controlled. Furthermore, the loss of air from the rear of
the cavity past the third portion is effected through
~-hAnnf.1~ 20 formed between the cavity and the stern a~d
4,30g dS -- 12 -- PCrlAU94100733
Figures 4A - 4H illustrate a variety of profiles available
for the third portion along line D-D of Figure 2 where the
third portion i6 formed of ~hAnn~l ~ 20 which extend between
the cavity and the stern. The presence o the channels
serves to control the 1055 of air from the cavity and
ensures that a substantial portion of the third portion is
not in contact with air or air bubble5 flowing from the
cavity. This enables the location of propulsion units such
a5 propellors or the like in the 5ub5tantial portion
whereby they are not af f ected by the air f lowing f rom the
cavity. The rhAnn~ can if desired incorporAte a flow
control in the form of vanes which can be used to vary the
cross-sectional area of the rhAnnRl ~ . In 80 doing some
control can be provided for the trim and heel of the
ves sel .
The cavity 14 is pressuri6ed from a pressure source (not
shown) a~ '~ted within the vessel which is connected to
an outlet 17 provided in the upper wall Qf the cavity 14
towards its forward end. The outlet is associated with a
plate 18 which extends across the cavity in the region
below the outlet 17 int~ te of the depth of the
cavity. Air delivered from the outlet 17 i8 delivered into
the cavity from the rear edge of the plate 18.
Figures 5A and 5s illustrate the proportions between the
depth H1 of the f orward portion and rear portion of the air
cavity respectively compared to the depth H2 of the planing
step area of the rib portion 16. The relat;~n~hip between
these values in the forward portion of the cavity area is
such that the depth H1 of the air cavity in that region is
10% to 40% greater than the depth H2 of the planing step
area of the rib . Pref erably in the f orward region of the
cavity the ratio of H1 and H2 is generally less than O . 5
and can incre~se in the aft portion of the c~vity to be
more than O . 5 .
~VI~ U~ SEIEET (Rule 26)
W0 95/14604 `2 L 7 7 ~ 6 ~ PCTI~Ug4100733
-- 13 --
The rela~;nn~hir between the ~orward portion 12 is 3uch
that the distance L2 between the step 15 ~iPfin;n~ the
forward end of the air cavity and the forward end of the
waterline of the vessel 19 as compared to the waterline
length Ll of the vessel is of the order of 0 . 05 and 0 . 40 .
If desired the plate 18 may be extended such that it
extends for a distance equal to up to half of the length of
the air cavity as shown at Figure 6.
In addition, according to a third em})odiment as shown at
Figure 7 a plurality of air outlets may be provided in the
upper wall of the air cavity 14 and each may be associated
with a ventilating plate 18 at a spaced intervals along the
cavity .
Figure 8 illustrates the results of testing an example of
the ~ ; L shown at Figures 1, 2 and 3. The test model
was representative of a vessel of a length of 74 metres and
a displ~ L of 700 tonnes. The l~::yr ese:l-Lations provide
an indication of the resistance values, degree of trim, the
degree of heave, the variation in air cavity pressure and
variation of air supply or f low rate . In Figure 8A the
solid line indicates the resistance curve of a vessel of
corresponding configuration but not in.u~oLcLting a cavity
while the broken line illustrates the relatinn~hir of
resistance and hull speed of the example of the
L .
Similarly, in relation to Figure 8B that figure illustrates
by the solid line the angle of trim of an ordinary vessel
of corresponding conf iguration to the example while the
broken line illustrates the angle of trim of the example of
the hull according to the ~ L.
WO 95/14604 ~ PCr/AU94/00733
~7~6~ - 14 -
Similarly Figure 8C illustrates the variation in heave for
the vessel without the invention (the solid line) as
compared with the vessel with the invention (the broken
line ) .
Figures 8D and 8E illustrate the variation in air cavity
pressure and air supply flow rate in a hull inuuLyoLaLing
the invention as a function of hull speed.
The fourth ~ t of the invention as shown at Figures
9, 10 and 11 has a high speed planing hull 111 which is
formed with a forward portion 112 which has a generally
conventional ~r~nf; gl~ration except that it in~ul~ola~es a
low deadrise planing section in its lower portion and a
second portion 113 which inuul~ulAtes a plurality of
longit~ inAl ly spaced cavities 114. The forwardmost cavity
114 is separated from the forward portion 112 by a first
step 115 which defines the forward boundary of the
forwardmost cavity 114. In addition, each of the
subsequent cavities is formed with a forwardmost step 115
which each represents the termination of the upper surf ace
of the adjacent ~ùlw~ cavity 114. In Figure 9 the
wetted area of the hull under design condition is shown as
crosshatched .
Figures llA, s and C provide an indication of the
cross-sectional c~nfigllration of the hull on the lines A-A,
B--B and C-C of Figure lO.
The side of each cavity is defined by a narrow ribs 116 to
each side of the hull of equal with or gradually becoming
wider f rom the stern to the f orward end of the cavity and
which in each case forms lateral and longitudinal
extensions of the portion of the hull forward of the
respective step.
~ Wo gSl14604 2 ~ 7 7 5 ~ ~ PCT/AU94l00733
-- 15 -- ~ -
The upper walls of each cavity 114 are 5ubstantially
planar but as shown in Figure g are inrl inPd downwardly
towards the stern of the hull where~y the ribs 116 of the
respective cavity terminate on the upper wall of that
cavity intersecting the plane of the ribs. This occurs
immediately prior the transverse axes of the step of the
following cavity. The cavities 114 are interconnected by
second rhAnnpl R 125 to enable air to flow between the
cavities. If desired each second channel may be provided
with regulating vanes or like elements which can be
adjusted to control the degree of flow through the second
~hAnnRl ~ 114. The adjustment of the regulating vanes or
the Like can be effected manually or automatically
according to the hull of the vessel and for the degree of
roll of the vessel.
The ribs which form the sides of the cavity in the central
portion can extend into the third portion aft of the cavity
and can have a low positive deadrise at the inner side. In
addition, the mid-portion of the third portion is formed to
have a positive deadrise to each side of the central axis.
A~ a result of the t~nnf i ~lration of the cavity and the
th ~ rd portion of the hull, the air in the cavity is
maintained in the cavity and any 10~8 of air is generally
controlled. Fur~h~ L~:~ the 1088 of air from the rear of
the cavity past the third portion is permitted in a
controlled manner through channels 125 which are between
the cavity and the 6tern.
The relafinnRhi~ between the forward portion 112 is such
that the ratio of distance L2 between the f orward
perpendicular of the fuLw~L' ~t extent of the waterline
which i6 marked FP and the ~olwc~l, ,.,L cavity step 115 to
the waterline length of the vessel Ll is between 0 . 03 and
0.35 .
Wo 95114604 ~ PCTl~1~94l00733 ~
21~564 - 16 -
Each cavity 114 i8 pressurised from a pressure source (no~
shown) P~ dated within the vessel which i6 connected to
an outlet 117 provided in the upper wall of each cavity 114
towards its forward end. Each outlet 117 i8 asBoCiated
with a plate 118 which extends Rcross the cavity in the
region below the outlet 117 int~ te of the depth of
the cavity. Air delivered from the outlet 117 is delivered
into the cavity 114 across the rear edge of the plate 118.
If desired the delivery of air to each of the outlets 117
may be effected from a common pressure source.
Alternatively the air may be delivered to each cavity ~rom
an ; n~ p~ntl~nt pressure source. This can improve the
p~=l r~ ..r~ of the embodiment in rough sea conditions and
in certain situations enables the air being delivered to
each cavity to vary, which serves to optimise control of
the motion and attitude of the vessel according to sea
conditions by the varying the cavity air volume in each
cavity. In addition, the pressure maintained in each
cavity may vary from the air pres8ure in adjacent
cavities .
As shown at Figures 12 and 13 the forward planing portion
12 of the hull of each of the e ' ';- I s can be formed to
have a central rib 26, which extends to each side of the
central axis. The rib has a cross-sectional profile which
is an extension of the profile of the hull to each side of
the rib, at ~ny particular location along the rib however
the rib serves to project its profile outwardly from the
profile of the L~ ; nrl~r of the hull . In addition, the rib
extends from a position forward of the water line B-3 to
the step 15.
The function of the central rib is to shape the surface of
the water in the region of the cavity and which f orms the
lower wall of the cavity such that the there will be no
~ ~0 95/14604 2 ~ 7 7 5 6 4 Pcr/AUg4/00733
collapse of that surface and whereby the integrity of the
cavity is maintained. The rib reduces in deadrise
rearwardly along the hull. If desired the rib can
terminate before the step in which case the profile of the
hull between the central rib and step remains substantially
constant .
In addition, if desired the rib can be formed as a support
member which is movable inwardly and outwardly with respect
to the hull according to the operating characteristics and
water conditions. In addition or alternatively the member
may be resiliently supported from the hull to provide some
shock absorbing preparation.
In addition, the forward planing portion may be formed with
(not shown) a plurality of secondary ribs in the form of
f ins or thin chines to each side of the central rib to
further control the flow of water past the forward most
portion to the second portion.
One ' ined benefit of these features is to reduce the
vertical forces or heave exerted on the vessel in rough sea
conditions .
If desired the plate of each of the embodiments may be
dispensed with and the upper surface of the cavity can be
formed with stepped cnnfi~ration where a~r is delivered
across the rear face of the step. The stepped upper wall
of the c~vity in.c~ LaLes the feature of the plate of
previous ' ~ Ls as an integral feature of the hull.
of course appropriate means must be provided to equalise
the distribution of air across the rear face of the step.
i
Air is delivered into the cavity in each of the ~ i r ts
at a pressure such that the vertical force applied to the
interior of the cavity is roughly equal to 309~ to 6096 of
WO 95114604 PCTIAU94/00733 ~
21~5~ - 18 -
the design weight oi~ the vessel. In addition, the total
cavity volume of the cavity iB of the order of 5% to 20% of
the displaced volume of the vessel.
According to ~mother embodiment as shown at Figure 14 the
surface of the third portion is formed to be displacable.
The 6urf~ce of the third portion is formed by several more
segments 230 which are pivotally supported ~rom their
forward edge to be pivotable downwardly to vary the
;ncl in.q1-;nn of the surface of the third portion. ~he
segments 230 are spaced to provide one or more rh~nnel ,:
which are in correspnnri~nrp with one or more channels 220
in the third portion. The 8upport for the segments (shown
schematically in Figure 14 at X) i5 resilient to provide
some shock ~hgQrhin~ properties. ~he rP~il ir~ntly
displacable segment serve to provide some stability against
vertical ~, L and reduce shock loadings on the third
portion in rough sea8.
It should be appreciated that the scope of the present
invention need not be limited to the particular scope of
the , ~ - 1; L described above. In particular the
invention has application to multi hulled vessels where
each hull is fQrmed with a cavity of the form described.
