Subject: [harryproa] Re: Building methods / materials
From: "Robert" <>
Date: 4/9/2008, 8:03 PM

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

--- In, "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 .
> > 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 .
> >
> > 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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