Note: Descriptions are shown in the official language in which they were submitted.
WO91/09768 PCT/NO90/00188
2072~70 ~
Vessel hull
,
The pcesent invention concerns a hull particularly for
ships and similar marine structuces of the type stated in
the introduction to Claim 1.
~ackground
In a traditionally designed ship hull, the plating and
bracing system is acranged so that the external pressure
primarily is cacried by bending stresses in the hull
plating. Loads are led from the plating to the primary
10 braces (usually longitudinal braces) then to the secondary
braces (usually transverse frames) and finally to the ship s
side/- longitudinal bulkhead for distribution along the ;
~ship's beam~. In smaller vessels the plating is often given
a double curvature. In a double curved plate the external i ~
15 pressure will mainly be carried by compressive in-plane ~ -
stresses (shell se~esses).
When a ship s hull i6 traditionally designed, it can be ~ ;
optimi~ed for weight or production costs. A weigh~ optimized
structure is characterized by relatively thin hull plates
ZO and a dense framework of primary and secondary braces. This
results in a complicated structure with high production
costs. The complicated structure introduces several
problems. It brings about a range of complicated connections
between the various bracing componehts in steel and
25 aluminium hulls, as well as in glassfibre hulls ~GRP). This
can easily lead to cracking because of fatigue or
delamination in GRP hulls.
All hull components are normally designed so that the
stress level is below an accepted elastic stress level. When
30 plate sections are exposed to excess loading there will be
local deformation in the plates at the connection to the ,
bracing and the stresses in the plates will gradually change
rom bending stress to tensile stress (membrane stress). The
result will be permanent deformities in metal hulls and
35 local cracking in glassfibre hulls (GRP-hulls).
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WO91/09768 PCT/NO90/00188
2072~70 2
Objective
The main objective o~ the pcesent invention is to
create a hull for ships, barges and othe~ marine structures,
that permits weight and cost reductions in the production of
hulls made of steel, aluminium or composltes.
The invention also has the objective of reducing the
number of structural details which are particularly exposed
to damage. It is also an object to simplify the connections
between the plating and the braces.
A fucther objective of the invention is to find new -
methods of fabricating hulls that will help to re~uce costs.
Invention
The invention is defined in Claim l, and other
15 advantageous features of the invention are given in the
subsidiary claims.
The invention is based on the use of what is known as
m~embrane tension, i.e. a concave section of plating that
supports external pressure by means of tensile membrane
20 stress. The concave plates are placed between and fixed to
longitudinal braces which ace supported on transverse frames
that in principle are not attached to the skin hull plates
of the ship. In cases where the hull plating is connected to
other members than the longitudinals, by for ~;
25 example a transverse bulkhead, this is achieved without any
real forces being transferred directly fEom the hull plating
to the transverse member. The use oE membrane sections can
be combined with parts of a hull where a traditional bracing
system is used.
The new proposed type of structure can be produced in a
known manner.
There are numerous differences between a traditional
structure and this new one. The use of a membrane section
should bring about a considerable weight reduction. In
35 addition, it will be much less expensive to produce a hull
in accordance with the invention. In a metal hull the number
of welded meters will be reduced and there will mainly be
simple continuous welds. It will only be necessary to a
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WO91/09768 PCT/N~90/00188
207257~
minor extent to have bent or rolled transverse frames.
The invention is particularly favourable where weight
reductions are essential such as in high-speed vessels.
When a membrane section is used, it is the maximum
permitted tensile stress in a material that decides the load
carrying capacity. This means that steel, aluminium and
glassfibre can be loaded at about the same stress level.
Thus the invention results in considerable weight savings ~ -
when glassfibre or aluminium are used.
In a glassfibre structure, the problems associated with
the connection of internal bracing to the hull, will be
reduced. Furthermore the problems related to cracking and
redistribution of stresses will be almost avoided when a
hull section is overloaded.
The invention can be used for all types of ships hulls,
hulls for barges and other marine structures. The only
precondition is that the hull must generally only be exposed
to external lateral pressuce. This is particulacly the case
for high-speed vessels, either catamarans or
Z0 single-hulled ships and naval vessels, for example.
Example
The invention will now be described in more detail by
refecence to the enclosed drawings, where:
Fig. 1 shows a schematic cross-section of a small
vesseI,
Fig. 2 shows a detail of a catamaran cross-section with
a laminated skin, (sandwich construction).
Figs. 3-5 show details of the hull in Fig. 2, with the
3G bottom, side and transition of the deck/side cespectively,
in different variants of materials and design details, while
Fig. 6 shows a cross-section from the hull of a larger
vessel.
Fig. 1 shows a design where the present invention is
used on a single hull, in a small high-speed vessel such as
a patrol craft. The figure shows a midship frame in the
hull. The hull structure consists of a transverse frame 11
.
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WO9l/~976X PCT/NO90/00188
that is connected to a deck beam 12 and an internal bcace
13, that i~ necessary can be used as a support for the
interior deck. The transverse frames 11 are connected to the
longitudinals 14. The example shows two longitudinal
braces 14a and 14b on each side, and a V-shaped keel 16. The
keel 16 is further braced by transverse plates 17 at each
transverse frame.
The membrane section 18, that is the concave plating
section, is connected to the longitudinal 14 so that they
10 extend from the bow to the stern. The membrane sections are
welded in the longitudinals 14 and the keel 16 by continuous
longitudinal welds. The hull plates form concave sections
between the longitudinals. The plates have a radius of
curvature that is sufficient to give pure tensile stress.
The longitudinal frames 14 are placed so they follow
the lines of the hull. The transverse frames 11 can be
welded only to the longitudinals 14. Thus the transverse
frames 11 will only be exposed to compressive forces under
normal load conditions. In this example metal plates are
20 used as the membrane sections 18.
A similar type of structure can be used for hulls with - :
glassfibre hull plates. The plating or the membrane sections
18 must here be laid continuously over the longitudinals 14.
The fibres in such a glassfibre membrane are to be laid in
25 the direction that gives the optimal utilization of the
tensile strength of the material.
In a hull that has membrane sectionfi designed in
accordance with the invention, the forces that are
transferred from the plating to the braces will mainly be
30 forces acting perpendicularly to the hull surface. Thus the
strength requicements on the connection between the hull
plating (membrane sections) and the longitudinal braces are
not high.
Fig. 2 shows a catamaran hull with a laminated outer
35 hull plating (sandwich plates). The hull consists of a
transverse bulkhead 20 that acts as a support for a deck
beam 21 and outer transverse frames 24 and inner transverse
frames 25 that extend down towards the keel area.
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W09l/09768 PCT/NO90/0018~
5 2072570 ;~
In the shie~s side, the deck beam~ 21 are attached to a
longitudinal 26. Similar longitudinals 27 and 28 are located
one under the other along each side of the ship. In the
transition to the keel area there is a longitudinal 29 on
each side. The deck 30 is built in a t~aditional manner.
F~om the deck next to frame 26 and down towards the keel
area (longitudinal 29) the hull plates are laid as membrane
sections 31. Traditional means of construction are used by
the keel 33 and the longitudinal frames are connected to a
10 local web 33 in the keel region. From the longitudinal 29B
close to the keel membrane sections 32 cover the hull up to
the centre line 22. Longitudinal braces 27B and 28B are
found as indicated in Fig. 2. In the central part of the
hull (wet deck) the hull plates are attached to the
transverse
15 bulkhead 20.
Fig. 3 shows the details of the aeea that are close to
the keel region. The transverse brace 24 in this example has
a quadratic fiection, and can be made of glassfibre for
example. The hull plate 31 has a sandwich construction with
20 covering layers of glassfibre-reinforced plastic and with
foam as the core material.
~ ig. 4 shows the equivalent details as Fig. 3 for the
attachment of the hull plates 31 at the transition to the
deck. Here, the transverse frames are alsomade of
25 glassfibre profiles 24, with longitudinals 26 and 27 built
into the transverse frame structure.
Fig. 5 shows the arrangement of a longitudinal 2'7 used
in a modified hybriol design where an aluminium transverse
frame 25 is used. Here the longitudinal 28A is attached with
30 two aluminium brackets 49 that are welded to the transverse
frame 24. In this example, laminated single hull plates 31
are used, These could be made of glassfibre.
In both these examples the hull plates will have pure
tensile stresses, apart from in the area where the hull
35 plates lie against the transverse frames. The tensile ;
stresses result in lateral forces that are carried by the
longitudinals 26, 27, 28 and 29.
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W091t09768 PCT/NO90/00188
2~ o 6
Fig. 6 shows a section through a tanke~ designed in
accordance with ~he invention. The hull has a transverse
frame 34 that is divided into sections with intecmediate
longitudinals 35. The transverse frame sections 34A-E
S support the bottom plates 36, that focm the inside base o~
the tank 37. The longitudinal frames 35A-F that support the
concave skin plates 38 are welded to the transverse frames.
At the transition between the bottom and the ship s
side. the transverse frame 34F has closely spaced
10 longitudinal braces 35I using ~nown methods, and is covered
by an extension of the hull plates 38. The ship s sides have
two sections 34G and 34H with a transverse frame and ;~
interior walls 39 in a known manner. The outer part of the
longitudinals 35G-J is welded to the hull plates 40. The
15 hull plates are formed so that a concave arched membrane ;~
section 41 is formed in an equivalent manner as at the
bottom.
The topside of the vessel is designed by known means,
with a transverse frame 42, longitudinal braces 43 and
20 plates 44 midship. In addition, there are membrane sections
45 and 46 at the sides of the midship plates 44 and a
traditional braced plate section 47 in the upper part of the
ship s side, between the outer membrane section 46 and
membrane section 41.
With the alternative desiqn of a tanker as in Fig. 6,
the bottom plates 36 can be shaped as membrane sections,
with or without connection to the transverse frames. Also
the interior wall, or parts of this can be shaped as -~
membrane sections, with or without connection towards the
30 transverse frames along the sides of the ship. This gives
the same advantages as when a membrane section is used for
the outer hull plating.
The invention will provide a basis for a simplified
production that will in tu~n give considerable reductions in
35 cost.
If the frames are correctly positioned it is possible
for example to lay the hull plates out by being unwound from
a,plate spool. Further, the invention enables more ratlonal
WO91/09768 PCT/NO90/0018~
7 2072~70 ~ `
assembly of machinery. equipment and the like before the
hull plates are attached.
The invention can be combined with parts of hulls that
a~e designed by traditional means.
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