Note: Descriptions are shown in the official language in which they were submitted.
~ 10760~3
The present invention relates to a method of con-
structing a boat hull or other hollow articles.
Foam Reinforced Plastic, commonly known as FRP,~is
used for constructing boat hulls. FRP consists of a low
density core between outer layers of highc'density material.
The core is shaped as required and the outer layers secured
to it by a mechanical bond. The core material must be of
sufficient stiffness and sufficiently shearproof to hold
the outer skins apart. PVC Foam is an example of a core
material of this type which possesses, in addition, *he
capacity for recovery after compression loading and there -
fore resistance to vibration. PVC Foam Glass Fibre and
Polyester Resin are typical materials suitable for sand-
wich construction.
A known method of sandwich construction used in boat
building is familiarised as the "Male Plug" or "Male Mould"
Method. This method is to make a plug or mould constructed
in the form of the required boat hull upside down and
secured to a flat floor. It consists of athwartships
frames or ribs fixed parallel to each other and to which
battens are fixed longitudinally. The battens are spaced
a few inches ~a~,a~t. PVC foam sheets are cut and "tailored"
to the form and strained, heated or preformed so as to wrap
approximately around the mould. These PVC foam panels are
then secured to the wood battens from within the mould by
wood screws, or by headless nails or spikes driven from the
outside through foam and batten so as to hold the foam
securely to the battens. Each panel of foam is butted
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j- against that which has been secured to the mould until
- the whole surface of the hull is covered, after which the
gaps and butt joints between panels of foam are filled with
~i grout and sanded fair, ready for the application of the out-
er skin.
~' C ~ext~ an outer skin lay-up in ~ proceeds with the
application of a quick cure polyester resin applied to ths
~ surface of the PVC foam followed by layers of glass fibre
l' in the form of chopped mat, unidirectional and/or woven
J ~ . . . .
¦ 10 rovings, wetted and fully impregnated with polyester resin.
he surface is usually finished at this stage b~ ~rinding
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~ mooth.
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he hull, consisting of PVC foam with an outer skin
- of GRP is moved from the wooden mould. Screws, nails or
¦ 15 fastenings are removed from the inside to rel~ase the in-
ternal surface of the foam from the wood battens. The hull
is then lifted clear of the mould, turned over and placed
¦ upright in chocks made ready to receive it.
-! ~ext an inner skin of GRP is provided in a similar
manner as that of the outside of the hull, so as to form a
"sandw~ch" of PVC foam between two skins of GRP mechanically
- bonded to each surface.
~he construction of the deck, or "top section" of the
hull proceeds either in the ~ame manner as that of the hull
' 25 or is built up with separate panels upon beams.
~he disadvantages of the"Male Plug Method" are that:
a. '~ailoring and cutting of foam in panels to fit com-
pound curves is wasteful and requires a high degree of
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- ski
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b. ~ertain portions of PVC foam must be fastened under
` varying degrees of tension to the wood battens of the mould.
; Since heat is generated by polyester resin in the course
,;
- j of curing, the surface of the PVC foam in contact with
5 _ G~P laminations appliéd to it, is warmed thereby reducing
the rigidity of the foam. At the same time, shrinkage
i - occurs in the curing of the skin lamination. ~he effect
'- ~ o~ this action is to create distortions in the surface of
the hull which appear as the skin cures and hardens. If
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` l~ 10 a slow cure resin is used to minimise heat transference
' from lamination to foam, there is a danger of styrene being
il released from the resin upon the foam and causing soft-
.
ening and similar distortion, particularly in those areas
!; whsre pressure has been applied to secure a tight fit
between foam and mould.
c. Application of GRP laminations over a fixed mould
` from the horizontal at the centre of the hull to vertical
~1 at the gun~Jhale line cause inevitable variations in lay-up
, and consequent waste.
I, i . .
d. Standardised control of lay-up of both outside and
j inside skins becomes problematical when scaffolding is
- , required to enable operators to handle resin and glass
, materials over the whole surface of the hull. Special
ventilation must be provided for working upon the inside
; 25 GRP skin.
e. ~he common use of slow cure resin enables an operat-or
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~ - . to complete one lamination of glass fibre and to allo~J this
; to cure partially before applying subsequent laminations.
However, in this case it is necessary to grind and remove
rough edges from the partially cured surface between each
- i 5 application of laminations.
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. ! :
. Removal of the wood male-plug tend to cause damage
j to the plug itself and to the inner surface of the fo~m.
g. ~ifting, turning and lowering the partially fabricated
- - hull to enable the internal surface lay-up to take placemakes demands upon the time and expertise of the builder~
-: including the realignment of the hull in its upright posit-
- ion so as to avoid distortions developing during subsequent
~ nternal skin lay-up.
`~' 3' ! h. As the result of a,b,c,d,e and f, abovej a considerable
j 15 amount of filling and grinding is required to produce a
tandard of finiSh comparable with hulls built bg other
- methods.
he "Male Plug Method" is usually employed for the
construction of "one off" hulls or small numbers of hulls.
~urthermore the structural advantages of the monocoq
Sandwich Construction, in which compound curves are so
effectively achieved, together with the ease with which
local areas of the hull may be stressed by the use of ~oven
` and unidirectional fibres, must be balanced against the
cost of effective lag-up control and finishing.
An object of this invention is to provide a method of
-; constructing a boat hull by which the advantages of Sandwich
I - Construction are preserved~ the disadvantages reduced or
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avoided and the best use made of the materials employed~
~he present invention consists-in a method of con-
structing boat hulls or other hollow articles comprising
providing a male mould~covering the mould with a first
~- 5 layer or layers of resin impregnated fibre~ then with a
- winding of at least one layer of synthetic foam about the
fibre, and winding at least a further layer of fibre impre-
gnated with resin about the foam to form a sandwich of foam
between the layers of fibre.
It is possible to remove the mould by cutting the sand-
wich into two parts and then to produce two hulls from one
mould by making o~e said part as one complete hull. Alter-
natively a single, decked boat can be produced by using the
method according to this invention. A further advantage of
-15 the present invention is that the method may be used by
semi-skilled labour and for long productio line operat;ion.
According to one convenient method of applying the
invention, by way of example, a small-craft hull is made
specifically in relation to the opportunities offered by
method and material. In this example, a yacht hull and
deck is considered as one unit, the "top" and "bottom"
sections of which are designed to absorb compression and
tension loads exerted by fore and back stays.
An example of the method of construction is as follows:
A rotatable mould is provided and the materials
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required for sandwich lay-up are mounted on a trolley
alon~side.
~he ~ould is ~irtually a complete hull and deck unit
smaller in diameter of section than the finished hull by
the thiclDless of the finished sandwich lay-up. ~he mould
is supported at either end, motorised and geared to revolve
- - .
~ elowly so that the materials may be unwound and applied
from their trolley mounting and wound in sequence and under
- : tension onto the male mould. ~he mould is first coated
- 10 with a release agent such as ~VA or wax. Polyester
,
resin is activated and applied in suitable width to the
- ¦ - mould. Woven glass rovings of the same width and under
~ tension are applied to the wetted resin. This in turn is
!i -
followed up by a second application of resin and woven
; 15 rovings and so on to the desired number of laminations of
the inner skin, PVC foam of appropriate width, being wound
under tension onto the last quick-cure wet lamination.
~his may be followed by a light wide mesh glass roving
¦ - wound dry over the surface of the PVC foam to ensure
that it is compressed firmly and accurately into the surface
of the inner skin. ~hen follows the application of a
coat of quick-cure resin. ~ay-up of the outer skin lamin-
ations commences as soon as the quick-cure resin application
to the PVC foam surface has sealed it sufficiently against
styrene action. At this stage any faults in lay-up may
be rectified by the application of fillers. ~aminations
proceed as with the inner skin, to the desired specification,
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; ~3ina1 finish can be achieved by the positioning Or a
¦ "float", blade or wiper, set so as to smooth out and
' dist-ribute excess resin as the mould revolves.
~t this stage in a modification of the described
method it is advantageous to pro~ide a final finish by
bandaging with a strip of material such as Melan/ex
Q,oo
(Registered Trade Mark), aluminium foil of 1.009 inch
- thickness, or suitable polyester resistant film.
~; ~he final stage in the manufacture of the complete
~` 10 hull involves the removal of the male mould from within it
l~ by cutting the hull in half, removing the mould intact and
,j - ~oinin`g the two halves together again. This may be
- conveniently done, if for example, prior to the application of
, the release agent, an insert is provided in the mould
' 15 horizontally and at the point of maximum beam running round
¦ the hull to define a groove in the sandwich lay-up. By
inserting a knife or saw at this point through the sandwich
~ - lay-up into the groove, a clean and precise cut may be
- ¦ guided round the hull to sever top from bottom. The top
section is then removed and hoisted clear and the mould hoisted
out of the bottom section. ~oam from the top edge of the
,,
lower hull section may conveniently be gouged out to a
suitable depth. Resin is then applied and a preformed tongue
inserted into the groove. ~ similar groove is made in the
j 25 lower edge of the top "deck" section of the hull. The
¦ tonvue insert having been coated with resin, the top deck
section is lowered onto the tongue and excess resin
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, ` ` . , .
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~ . wiped away.
- , At this sta~e, when the resin skins are still in the
I ~`process of curing, apertures, such as cockpit, hatches and
;! - windows may be cut out without fear of distortion. ~ffective
bonding may also be achieved in this state i.e. before
`¦ final cure has taken place, of internal bulkheads, keel
¦ ~ stringers, floors and furniture, to the internal and external
kins of the hull.
~ariations of lay-up procedure may be employed, for
I 10 example for the application of unidirectional fibres long-
: . . ..
- itudinally by hand lay-up to the mould surface prior to the
lay-up procedure of the inner skin, and again to the outer
~¦ sur~ace of the cured foam prior to lay-up of the outer skin.j Heat may be applied locally to either surface of the
P~C foam during lay-up.
`1 Widths of PVC foam may be increased by using foam in
j which grooves have been cut on one or both surfaces so that
only the centre area is compressed in bending.
C ~ of thickness of foam core 'o GRP skins in~ ~and-
¦ 20 wich boat hull construction may be about 6:1 for a PVC foam
core of density of 5 lbs per`cu.ft. Variations of skin
~ thickness and in the composition of glass fibres in the skinj laminations may be made to absorb local loading. Compression! Or "distance" pieces may be inserted in place of the PVC core
where, for example, bolts are used through the core, having
the effect of spreading the load between both skins. At
, these points it may be desirable to appl~ additional lamin-
! ations to spread the load over a larger area of the skin
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surf~ce tha~ that of the compression insert. Compression
plugs or plates a~ electrical circuits ma~ co~veniently
be inserted into the PVC foam core prior to the application
of the outer skin.
In the application of this example of the invention, a
sandwich construction is used which æimplifies the building
of boat hulls in ~RP. X~tation of the mould combined with
the ability to control under tension, the application of
materials laid up over compound curves is the basic advantage
- 10 of the system. ~his applies in particular to PVC loam used
as a core which is bonded effectivelg within the outer GEP
sk~s.
- By slight modifica~ions to both hull design and the
make-up of materials used in FRP construction, without
detriment to the performance of hull or the mechanical and
structural qualities of the materials, material wastage is
eliminated, standardised structural control is achieved and
much labour saved in relation to the present customary
method of sandwich construction. ~he invention may be
used both as a hand lay-up and a mechanised lay-up technique
for the purpose of building production ru~s from the male
mould.
~urther advantages of the method according to the
invention are as follows. Air bubbles within the resin are
forcedfrom each lamination to the sur~ace by the tensioning
of materials in narrow widths about the mould~
Shrinkage of resin while curing causes increased
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, tensioning of glass fibre around the mould a~d ensures an
- accurate mechanical bond between the foam and glass fibre.
~ A che~ical bond is established between the inner and '
'~ outer layers of glass fibre along but-t joints in the foam.
}
i~ 5 ~his area of butt joint may be reinforced during lay upj, ' with strands of fibre so as to provide an "H" section of
GRP.
~'i ' ' Quick-cure resin may be used not onl~ to increase the
' speed of lay~up but to reduce or eliminate styrene action.
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' In the case of polyester resin and semi-rigid unplasticised
' , PVC foam, the foam is locally softenéd and distorted b~
' , slow curing resin.
j' ' ' Application of local heat to brittle or rigid PVC
' foam strips makes possible the use of this type of foam'~' 15 - for bending around compound curves. Local heat at the
, point of lay-up may also increase the resin cure and lay-
' up speed. Resin pigmented in one or more colours may
¦ ,be used in both inner and outer skin laminations to provide
internal and external colour finish.
~he finished hull may be cut in two or more sections
for removal from the mould within about fifteen minutes
of completing the lay-up and virtually no distortion
~ ' takes place. Because of the absence of distortion
'! æections can be stored separately to cure without the
need for chocks. A,fter curing the parts can be fitted
together with no misalignment or mating troubles. ~his
would not be possible using conventional GRP methods
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P-re-stressing fibres durin~ lay-up combined with
exact control of resin to fibre ratios provides an
improved strer~th to weight characteristic over conv~tional
~EP methods.
~lthough the inve~tion has been described primarily
with the obaect of constructi~g boat hulls, the method is
suitable for pipes, oontainers, wheelbarrows or any other
articles suitable for the application of glass fibre and
foam i~ the method described.
In the case of hollow article construction, the article
may be made with parallel or tapered sides, and the mould
can then be directly withdrawn from one end after construc-
tio~ has finished. A tube i9 an example of such an article.
It would also be possible for the mould to be collapsed
inside the finished moulding, and for the mould partæ to
be subsequently withdrawn from the interior of the article.
~he above methods of mould remo~al are disclosed as
examples o~ly. Ar~ other appropriate method can be used.
