Subject: [harryproa] Re: Building methods / materials
From: "Tim Barker" <clairebarker5@bigpond.com.au>
Date: 4/11/2008, 7:10 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

--- In harryproa@yahoogroups.com.au, "Robert" <cateran1949@...> wrote:
>This is where test methods usind drop weights are far from what
actually happens in a collision, and the results dont always reflect
the realworld suitability of a material, apart from a grounding in a
mud bank any collision involving something sharpish will result in a
rip in the skin , the trouble is with a composite panel once the one
skin is breached the strenght of the structure is dramatically
reduced.

While at Cols a boatbuilder from Airlie beach dropped in to report on
the multiple groundings after the recent weather up there, while i
dont have details it would appear that the composite boats in general
didnt fare too well and worst of all were the panel kit boats.

I suppose at the end of the day you have to be comfortabe with the
choices you make, the last place you want to be worring about wether
you should have built your hull differently is in the middle of a
serious blow.

Cheers Tim
> I don't care what type of hull you have, if the rock is sharp and
> tough, then you are going to have a rip in the skin.
> A welded hull would not have the dissimilar metals or the stress
> concentrations of a pop riveted one.
> I don't think I would like the puncture proofing of a 3mm ply skin,
> unless I had kevlar on the outside. Possibly you could use kevlar as
> your outer skin. Certainly gluing , rather than screwing reduces the
> corrosion and point loading.
> I have done a fair bit of welding of aluminium boats. I built a
small
> tri out of aluminium and sailed it from PNG to Australia, and I
> researched pretty thoroughly the pros and cons. I assure you there
is
> a corrosion and point stress problems in marine use unless a lot of
> care is taken. Have you looked at aluminium crossbeams on old beach
cats?
> Skin on frame is a sound technique but be careful of the choice of
> materials.
> --- In harryproa@yahoogroups.com.au, "Tim Barker" <clairebarker5@>
> wrote:
> >
> > The beauty of the design Rob is working on for us is that the
hulls
> > will need little or no lining, Col is going to get some figures
to
> > gether re weight per square mtr for comparison, im not saying
this
> > method is for me , more that when new things come along people
can be
> > dismissive or suspiscious (me included) and that a open mind is
one
> > that learns.
> >
> > Its a funny thing in this world but very often things arent done
a
> > certain way because thats the best way but because thats how
> > everybody else is doing it , im sure Rob is very familar with
that
> > promoting a design that makes eminent sense but meets with huge
> > paranoia and resistance .
> >
> > Im also sure thatRob is familar with people that say something
wont
> > work and state a very plausable reason why but at the end of the
day
> > his designs are out there sailing despite the reasonings to the
> > opposite.
> >
> > When looking at something as different as this i think we need to
> > realise that not everything will be obvious at first look. Rob
just
> > realized something quite significant recently re the load
carrying of
> > Proas, now if it only just occured to he who has spent a
significant
> > portion of the last ten years thinking "proa" then ill keep
> > investigating, for fun and edification .
> >
> > Just to add a little to the pot, what if the skins were 3mm ply
what
> > weight then .Remember the function of the skin is now only a
> > waterproof barrier. What if the skin was pure fibreglass, same or
> > better point loading no need for epoxy as with ply do it up on a
> > table to size . Col has had one example in the water for two
decades
> > still going strong, although this had the frame welded which
would
> > actually detract from its strength. the skins can actually be
glassed
> > to the stringer frames so little or no screw fastening is
possible.
> >
> > Come on guys lets do a little brain storming !
> >
> > What do you think would happen with this type of construction in
a
> > collision versus a cored hull. Not a dinky weight dropped on a
panel
> > that bounces, 3-4 tonn of boat doing 10knts doesent bounce when
> > striking a pointy bit of rock you get a long rip .
> >
> > Cheers Tim
> > --- In harryproa@yahoogroups.com.au, "Robert" <cateran1949@>
> > wrote:
> > >
> > > Looked at he website, and the internal frames are covered with
some
> > > kind of skin. Any skin has to add at least 1kg /m2.If you have
to
> > have
> > > an inner skin, it may as well be part of the sandwich. You are
also
> > > hiding the frames and can't check for corrosion easily.
Stainless
> > > steel into alloy can cause corrosion. The stainless steel
screws
> > into
> > > the ply , unless as Rob pointed out, you drill and presaturate
the
> > > hole, are a means of getting rot. The chines still need to be
> > rounded,
> > > glassed and faired, though the glassing could be part of the
final
> > > exterior glasing This seems a a fair amount of work and risk
to me.
> > > --- In harryproa@yahoogroups.com.au, "Robert" <cateran1949@>
wrote:
> > > >
> > > > Not sure how you do one and a half sheets of double bias. I am
> > > > assuming the extra sandwich thickness and glass are to
eliminate
> > the
> > > > internal framing
> > > >
> > > > Looking at the weights
> > > > 20mm core 1.6kg/m2; glass 1.8kg/m2; resin-depending on type
of
> > core,
> > > > effort in edge joining, holes, shaping cuts, scrim for
polyprop
> > > > honeycomb` .9-1.5kg/m2. This gives a total of 4.3-4.9kg/m2
> > > > With internal frames, this could possibly reduce to 3.2kgm2.
I was
> > > > wondering how the internal frames are covered-That could add
> > > > significantly more weight
> > > > Epoxy saturated 6mm marine ply is in the order of 4.5kg/m2.
The
> > ply
> > > > still needs almost .5 kg abrasion and surface cracking
protection
> > on
> > > > the outside, and still needs the inner frame.
> > > > Costs of the foam sandwich depends on type of core, type of
> > resin,
> > > > and very much source of materials: for 20mm core $35-70/m2;
resin
> > > > $10-20/m2; glass $10-15/m2 I think you would find the costs
of
> > going
> > > > with the ply would be similar or slightly more with the cost
of
> > the
> > > > frame. I must admit the simple meccano approach to the frames
> > appeals,
> > > > but for the shape of a Harry, I don't see an advantage.
Simply
> > make
> > > > some big flat sheets,with judicious leaving out of glass
where you
> > > > want to bend, pull or push them into shape - possibly a
little
> > extra
> > > > shaping on the ends- and the basic hulls are there, except
for the
> > > > main bulkheads where the crossbeam loads are concentrated. I
> > reckon a
> > > > Visionarry hull up to topsides could be done with less than
4m2 of
> > > > external fairing and much of the internal work will be
covered by
> > > > internal furniture. Anyway, thats what I am aiming at. I hate
> > adding
> > > > good materials, only to sand it off again. Don't know how
much
> > fairing
> > > > is required on the aluminium frame set up
> > > > Robert
> > > >
> > > >
> > > >
> > > >
> > > > --- In harryproa@yahoogroups.com.au, "Rob Denney"
<harryproa@>
> > wrote:
> > > > >
> > > > > G'day,
> > > > >
> > > > > Col is a very smart bloke, has been designing boats for
yonks
> > and has
> > > > > always been full of ideas, most of them good.
> > Experimentation is a
> > > > > good thing and so is caution , so talk to Col and at least
a
> > couple
> > > > > of people who have built with it. Maybe build his little
canoe
> > as a
> > > > > test. Then do the numbers and decide which suits you best.
> > > > >
> > > > > I worry about corrosion of alloy and screw attachment of
ply,
> > which
> > > > > often rots around fastenings unless they are individually
over
> > > > > drilled, filled with glue and redrilled. I also think
> > > > > glass/ply/alloy will be heavier, maybe more expensive and
> > require
> > > > > more finishing. Could be wrong on all counts.
> > > > >
> > > > > If you talk to Col, say hi from me, tell him your boat
will
> > almost
> > > > > certainly be 20mm foam or Polycore with one and a half
layers
> > of 600
> > > > > double bias each side and some serious strength required
> > around the
> > > > > mast and the beams, but no other bulkheads. Surface area of
> > > > > Visionarry lee hull is 57 sq m. I will be very
interested to
> > see
> > > > > what he suggests, and how it competes with the panel build
> > method.
> > > > > Also ask him about the large flat)ish) cabin roof and floor
> > areas
> > > > >
> > > > > regards,
> > > > >
> > > > > Rob
> > > > >
> > > > > On Wed, Apr 9, 2008 at 3:40 PM, Tim Barker <clairebarker5@>
> > wrote:
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > Hi Rob/ all
> > > > > > Visited Col Clifford today , as much to see his radial
> > engine as
> > > > have a
> > > > > > yack about build methods, very interesting guy and very
> > cluey.
> > > > > >
> > > > > > What are your thoughts about the alloy internal frame
> > system , as a
> > > > > > person who has done quite a bit of metal fabrication it
makes
> > > > sense to
> > > > > > me and offers some build speed advantages as far as i
can
> > see .
> > > > Coupled
> > > > > > with the idea of glassed ply skins it should be very
cost
> > effective
> > > > > > tough and simple to build.
> > > > > >
> > > > > > For those on the site who arent familiar the method
involves
> > > standard
> > > > > > ally extrusions and cast ally fittings which allow the
frame
> > to be
> > > > > > fabricated from ally without welding, it is then skinned
in
> > ply or
> > > > > > composite however the skin basically only has to act as a
> > > waterproof
> > > > > > membrane not as a structural member and also to hold the
> > > structure in
> > > > > > tension, light strong simple . WWW.ccplans.com.au
> > > > > >
> > > > > > What are the various opinions out there.I myself am very
> > > > suspiscious of
> > > > > > ply or timber however i know that this is a fairly
basless
> > > predjudice
> > > > > > given modern methods and materials hence the ongoing
> > > investigation of
> > > > > > different methods and materials.
> > > > > >
> > > > > > Coupled with the relative costs of some of the composite
> > cores
> > > on the
> > > > > > market and the slowly dawning realization that using
these
> > > composites
> > > > > > may result in a craft not much lighter (if at all) but
> > > substantially
> > > > > > more expensive than a craft using ply skins has
certainly
> > eroded my
> > > > > > predjudices.
> > > > > >
> > > > > > Cheers Tim
> > > > > >
> > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

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