Subject: Re: [harryproa] Building methods / materials
From: George Kuck
Date: 4/9/2008, 10:30 AM

I would also agree plywood sealed in epoxy is not the best way to build.  The epoxy only seals in moisture and in time will be prone to rot !  I built a TT720 in 1991 that was sealed with System 3 inside and glassed on outside.  The main hull has held up OK except for some isolated areas that got rain water in and I have rebuilt small areas as needed.   But the outer float hulls have been a constant problem.  The moisture gets trapped in them and it is impossible to keep dry.  After abought 10 years it started having rot problems.  Two other boats built at the same time by a friend had even worse problem and he used "West system epoxy.  The "epoxy saturation does not actually saturate the wood but puts it in a envelope that will trap water.  If you do use wood I would recomend only glassing the outside and using a conventional marine paint on inside that will allow the wood to breath.
I am planning on building new outer float hulls with Airex R63.8 foam and glass sandwich construction and vinylester resin.
George Kuck
Chestertown, MD
Jan Iversen <> wrote:
Hey Tim

I build a 10 m catamaran using high quality marine plywood and glass. I also used the best epoxy money could buy. After 10 years I could start to renew plywood here and there due to ROT. This seems to be an ongoing experience, so my advice to you will absolutely be: Stay away from plywood and use ordinary fibreglass/foam construction instead.

Jan Iversen

2008/4/9, Tim Barker <>:
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 .

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

Cheers Tim

Med venlig hilsen

Jan Iversen
Lundvej 223
6800 Varde

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