Note: Descriptions are shown in the official language in which they were submitted.
~25~3:2~
Naval architects of today have at their disposal a
number of fundamental dispositions for designing surface ships,
of which the buoyancy is obtained by adopting more than one hull.
For example, boats are known to be supported by three hulls.
The best known of these boats are equipped with hulls
which, understandably, are partly submerged, but also partly
emerged : this is the case illustrated for example in French
Patent 1 414 492. Other types of boats, less known of the
public, but of an already older design, are equipped with fully
submerged support hulls, such as described for example in U.S.
Patent 1 825 286.
Other designs are also known and even more pro;ects of
surface crafts of this last type, the buoyancy of which is
achieved by a plurality - two, three or four - of torpedo-like
hulls connected with the rest of the boat by partly submerged
high and narrow strut members playing a part in the buoyancy.
The effective part of such a boat is situated above the water
surface and the assembly constituted by the hull proper and by
the submerged part of the strut member is conventionally called a
"semi-submersible float".
Designs of "semi-submersible crafts" have, these last
few years, been concerned with saving and viability, and no
longer with the sole fact of finding new lines. But the number
of crafts built is few and the acquired experience remains
limited.
This novel design, however, is promising as far as the
construction of boats with good seaworthiness and comfort is
concerned. Yet there remains to determine the particular
dispositions which will lead to a minimum drag, hence to the
construction of crafts inexpsnsive to run.
Not one of the known boats that are e~uipped with
"semi-submersible floats" has -the nautical
2~
properties, such as the drag, whlch will make it an
attractive propositlon to run, thLs probably being why
all the pending projects generally appear so lnactive
and non-productive.
So lt is one of the objects of the present
invention to optimize the shapes and relative positions
of semi-submersible floats when working out those
special novel dispositions.
To this effect, the invention relates to a
boat with three semi-submersible floats connected to a
deck via strut members, a central float being provided
at the fore part, and two side floats being symmetrically
positioned with respect to the longitudinal plane of
said central float, according to the prlnciple disclosed
15 in U.S. Patent No. 1 815 286 for example
The main preoccupation of any naval architect
when designing a craft of this type is therefore to solve
the problem of reducing the drag, and more particularly
reducing the effect of wave action~ problem which past
projects have come up against, without really solving
it.
It is true that a number of solutions have
been proposed for boats with non semi-submersible sur-
face hulls, and French Patent 1 414 492~ for example,
defines the principles of dispositions which, for that
type of boats, permit to reduce the effects of waves.
~Z56~
The inventive act has been perormed in the present
invention when the Applicant has provided that, in the boat in
question:
a) the ratio of the ordinate of the area curve of the
complete boat at the crossing point of the area curves of the
side floats, on the one hand, and of the cen-tral float, on the
other hand, to the maximum ordinate of said area curve of -the
complete boat is at least equal to 0.45; and,
b) the ratio of the sum of the volumes of the side
floats combined, on the one hand, and of the volume of the
central float, on the other hand, is between 0.3 and 1.7.
The following advantageous dispositions are also
preferably adopted:
- for each float, the ratio of the depth
~5~2~
of immersion of the maximum part of the area curve of the
horizontal sections (namely TcL), to the equivalent diameter of
said float is between 0.6 and 1.4;
- the coefficient of asymmetry of the boat is less
than 0.3;
- the aspect ratio of each float is between 5 and 10;
- at least one substantially horizontal fin connects
each side float with the central float;
- the two side floats are, on the one hand, identical
to, and on the other hand, separate form the central float.
The invention will be more readily understood on
reading the following description with reference to the
accompanying drawings in which:
- Figure 1 is a view, following arrow F of Figure 2,
of a boat according to the invention;
- Figure 2 is a view, following arrow G of Figure 1,
of the same boat;
- Figure 3 is a cross-section along line III-III of
Figure 1;
- Figures 4, 5, 6, 7 and 8 are area curves of ths boat
according to the invention, shown as several separate
embodiments.
~ eference is made hereafter to a number of notions,
whose unusual nature invites a definition, this being given in
the accompanying schedule, presented as forming part of the
present patent application.
The boat illustrated by way of example is a surface-
type boat with three floats, called "trimaran". It is
constituted by:
- an entirely emerged platform 1 comprising a deck 2
and containing the effective volume of the boat (transporting
holds, cabins, etc...)
- a front cen-tral hull 3, which is oblong and has a
vertical longitudinal plane of symmetry S, and which is
~251~i32~
entirely immersed below the water surface ~;
- two side hulls 5, which are disposed symmetrically
with respect to the plane of symmetry S, at the back of the
central hull 3, are identical and entirely immersed;
- a strut member 6 which extends vertically and
substantially parallel to the plane of symmetry S ancl connects
-the central hull 3 with the lower face 7 of the platform 1;
- two strut members ~, extending vertically,
substantially parallel to the plane of symmetry S, each one
connecting a side hull 5 with the lower face 7 of the platform 1;
- two substantially horizontal fins 9, which connect
both side hulls 5 to the central hull 3.
The special features have been observed:
- the assembly of a hull and the corresponding
strut member (central hull 3 and a strut member 6, each side hull
5 and its strut member 8) constitutes a semi-submersible float;
- each semi-submersible float has a positive
buoyancy, the assembly of three semi-submersible floats
conferring its buoyancy to the boat;
- the hulls 3,5 and their strut members 6,8 can
be constituted of tanks or water-ballasts, but they can also be
constituted of compartments containing the installations o~ th~
boat; for example, three "Diesal" type engines, a main one, and
two lower-powered ones, may be installed in the central hull 3
and in the side hulls 5, to drive the propellers; likewise, the
hollow strut members 6,8 are designed to enable the passage of
numerous connections (electric cables, piping, access), between
the hulls 3,5 an~ the deck 2;
- the transverse vertical planes passing
through the ends of the area curves of the vertical transverse
sections of the semi-submersible floats 3-6 and 5-8 are marked:
V 3 AR : plane passing through the aft end of the area
curve of the semi-submersible float 3-6;
V 3 AV : plane passing through the forward end of the area
curve of the semi-submersible floa-ts 3-6,
V 5 AR : plane passing through the aft ends of the area
curve of the semi-submersible floats 5-8,
V 5 AV : plane passing through the forward ends of the area
curve of the semi-submersible floats 5-8,
and it is noted that there is an overlapping in the longitudinal
direction, parallel to plane S, of the relative posi-tions of the
semi-submersible central float 3-6 and of the semi-submersible
side floats 5-8, (see figure 2) plane V 5 AV being situated ahead
of plane V 3 AR.
Figures 4 to 8 show the curves of the surfaces
according to several different embodiments and corresponding, for
each one:
- curve A 3 to the semi-submersible float 3,
- curve A 5, to the whole assembly of the two semi-
submersible floats 5-~,
- curve A 1, to tall three semi-submersible floats,
namel~ to the boat itself.
Due to the aforesaid overlapping, curves A 3 and A 5
have an intersecting point I contained inside a transverse
vertical plane VI, situated between planes V 3 AR and V 5 AV.
Also represented are:
- the value ~I of the surface of the cross-section of
the boat (curve A 1) situated inside the plane VI,
- the maximum value AM1 of curve A 1.
~2~ i3;~4
In the embodiment which corresponds to
- Figure 4, AI is substantially equal to AM3 and AM5.
A*ll is therefore equal, substantially to any one of said
three values. Curve Al is flat between planes V3~ and
V5~ . This is very helpful to reduce the efEect of wave
action for speeds corresponding to a number of Froude
of between 0.4 and 0.6 approximately (curve Al
"balanced" between the front and the rear of the boat
and free of trough or accentuated crest, particularly
in thearea of plane VI). Moreover, the volume of the
two semi-submersible side floats5-8, on thè one hand,
and the volume of the semi-submersible central float
3-6, on the other hand, are substantially equal ~areas
of the curves of parts A3 and A5 substantially equal)
this permitting, in the adopted design of trimaran,
to reduce even further the effect of wave action.
If the solution illustrated in Figure 4
may appear as an ideal solution from the aforesaid
points of view, it nevertheless remains obvious that other
solutions, although they may not be as good, may still
be satisfactory.
For example, in the embodiment illustrated
in Figure 5, AMl = AM5; AM3 is slightly less than AM5
and AI/AMl = O.45. The volumes of the semi-submersible
side floats 5-8 and central float 3~6 are substantially
equal. This is a limit case, adapted for high speeds
(Fn 0.6), AI/AMl should in principle be selected to be
higher than 0.45 in order -to allow a maximum reduction
of -the effect of wave action.
The embodiment illustrated in Figure 5
is characterized by a strong unbalance between the
volumes o-E the semi-submersibIe side floats 5-8 on
the one hand, and of the semi-submersible central float
3-6 on the other hand : the ratio of these volumes
is equal to 0.3. Thereagain, the limit is a minimum
limit which should not be exceeded. In addition, AI/AMl
is substantially equal -to 1, which is satisfactory.
32~
Figure 7 shows an embodiment in which the volume of the
semi-submersible side (and rear) floats 5-8 is equal to 1,7 times
that of the semi-submersible central (and front) float 3-6. This
embodiment constitutes the upper limit not to be exce0ded.
Moreover, AI is substantially equal to AM1. The curve A1 is
relatively flat between the crests of curves A3 and A5, hence the
fact that a relatively poor effect of wave action is obtained for
speeds corresponding to Fn=0.4 to 0.6.
Figure 8 illustrates an embodiment in which the curves
of the surfaces Al of the boat is strongly asymmetrical. The
coefficient of asymmetry DIS of the boat is equal to 0.3, this
constituting the maximum limit below which it is recommended to
stay. Semi-submersible side (and rear) floats 5-8 are bulgy with
respect to semi-submersible central (and front) float 3-6.
For the boat illustrated in Figures 1 to 3 (semi-
submersible floats 3-6 and 5-8 shown in block lines in Figure 1)
the aspect ratio of the floats is about equal to 7. To obtain a
compromise between the effect of wave action and the resistance
to friction reducing the overall drag, the shapes should be so
selected that the aspect ra-tio lies between 5 and 10.
Finally, to derive the maximum advantages from said
technique of semi-submersible floats, it is important, first to
immerse the floats 3-6;5-8 to depths that are sufficient to
reduce the movements of the boa-t and to reduce the effsct of wave
ac-tion, and second, to limit the immersion of said floats to
depths which will eliminate any great structural problems from
the construction of the boat, and which will keep the wet surface
to a reasonable value. This is -the reason why the ratio TcL/Deq
of the immersion depth of the maximum
of the curve of the surfaces of horizontal section to the
equivalent diameter, is, ~or every semi-submersible float,
between 0.6 and 1.4, this corresponding -to the drawings in broken
lines shown in Figure 1 : the drawing of -the floats closest to
the water surface corresponds to TcL/Deq = 0.6 and that farthest
from the water surface corresponds to Tcl/deq = 1.4.
The boat definition given hereinabove obviously confers
on that boat all the ~ualities specific to all semi-submersible
bloats, but, in addition, it gives it a new optimization of its
drag. For the first time, a semi-submersible boat has a yield
substantially equivalent to that of a conventional surface boat
of identical capacity, which makes the technique a viable one.
Compared with semi-submersible boats of the catamaran
type, the effect of wave action is considerably more advantageous
than that between the two semi-submersible floats of the
catamaran, because there is a deliberate longitudinal overlapping
of the curves of areas A3 and A5 to prevent damaging
interferences be-tween the flow along the semi-submersible central
float 3-6 and the semi-submersible side floats 5-8, and
thereagain, to reduce the effect of wave action. The very choice
of the curve of areas A1, preferably the flattest between the two
crests of the curves of parts A3 and A5, and close to point I,
is, on this point, a sign of an important reduction of the drag.
It should also be noted that the recommended structure
is especially strong. It is a known fact that, catamarans for
example, have particularly delicate structures, considering the
very great strains normally developing thereon. The new
"trimaran" type struc-ture which is proposed, has none of the
fragility of the prior
~Z~;iE;3~
designs, since, on the one hand, the boat is supported
overall on three points instead of 4 for the catamarans,
and on the other hand , the ailerons 6 close up the
structure constituted by the struts 6 and 8 and by the
hulls 3 and 5. Thus, any stresses in the area where
the struts 6 join up to the body 1 are less than those
existing in the equivalent joining up areas in a semi-
submersible catamaran in the central point thereof.
The invention is in no way limited to the
description given hereinabove and on the contrary
covers any modifications that can be brought thereto
without departing from its scope or its spirit.
.
2 ~
11
SCHEDULE
The object of the present schedule is to facilitata an
understanding of some of the terms used herein and the following
definitions are not to be taken as limiting the scope of the
invention as defined herein.
Area curve of a boat
The immersed part of the hull of a boat is usually
defined by the values of its successive vertical cross-sections
between the verticals passing through the outermost submerged
points of the hull, and called forward perpendicular and aft
perpendicular in the lengthwise direc-tion of the boat. The
plotting in y-axis of the areas of the cross-sections, and in x-
axis of the distances between said cross-sections and a reference
point of origin, enables to draw -the curve of the areas.
Volume of a semi-submersible float
-
This volume is equal to the surface defined under the
graph of the curve of the areas of vertical cross-sections, by
said curve of the areas and the x-axis.
Semi-submersible float
An immersed body can be defined, at least partly, by
horizontal sections.
By semi-submersible float is meant a float showing a
posi-tive buoyancy, of which the curve of the areas of its
horizontal sections (or water lines) has a maximum under the
water surface at a depth TCL.
In such a float, the value of said maximum is
preferably greater than twice the value of the area of the
horizontal section of the waterline.
Said maximum may be realized for various depths of
waterlines. In this case, TCL designates the arithmetical mean
of said depths.
~ 5~;~
In conventional manner, a semi-submersible float is
constituted by the assembly of an entirely submerged hull and a
strut joining it at least to the water surface, and then to an
above surface platform.
Equivalent diameter
It is often difficult to distinguish the strut from the
totally submerged hull to which it is joined. Then it is
advantageous to refer to the diameter De~ of a circle of which
the area is equal to that of the maximum cross-sectional area of
the semi-submersible float (assembly of strut -~ totally submerged
hull).
Aspect ratio of a semi-submersible float
The aspect ratio is the ratio of the length of the area
curve (ie. length between perpendiculars) of the vertical cross-
sections to the equivalent diameter of said semi-submersible
float.
Coefficient of asymmetry
The curve of the areas of the ver-tical cross-sections
of a float extends along the total len~th of said float, namely:
x, the abscissa, marking the position of a vertical
cross-section, measured from a point of origin O
situated at the median abscissa of the curve of
the areas. The median abscissa of the curve of
the areas is the abscissa of the vertical cross-
section which separates the boat in two e~ual
volumes
A(x), the value of the area of the vertical cross-
sec-tion corresponding to abscissa x
V , the total volume of the submerged part of the
float
Xav , abscissa of the front end of the curve of the
areas
Xar , abscissa of the back end of the curve of the areas
Xmax , the higher of the two values Xav and Xar.
~L2~
13
The lon~itudinal asymmetry of the float
corresponds to the differences of values of the areas of
vertical cross-sections corresponding to abscissae x and
t-x), symmetrical with respect to the origin of the abs-
cissae~
The quantity ~_ x max
IA(X) ~(-X) ¦dx
is a representation of said asymmetry. It has the di-
mensions of a volume and it is possible, and obviously
preferable, to convert it in order to obtain a coefficient
without dimension. It suffices, to do so, to divide it by
the volume V of the float.
With ~ xav
1 A(x) dx ,
V J xar
the coefficient of asymmetry DIS of a float is defined
by : r xmax ~ ~ xav
DIS ~ 1 ¦ A(x)-A(-x~ldx J / ~Jxar A(x) dxJ
