Re: [Paddlewise] Fiberglass laminate

At 10:16 AM 2/27/02 -0500, Michael Daly wrote:
>From: "Jim" <jfarrelly5_at_home.com>
>
> > I watched a show on the Discovery Channel Monday night about new bridge
> > building technology.  They showed an interesting way to make a piece of
> > fiberglass "board" by taking foam board and sandwiching it between 
> fiberglass
> > cloth and then injecting it with fiberglass threads in an x pattern.
>
>The x pattern fibers will pick up the shear forces that the foam is not
>strong enough to carry.  This makes it significantly stronger than
>just a normal foam/fiberglass sandwich.
>
>Quite some time ago we had a discussion on PW about using core materials
>to make stiffer and stronger kayaks.  The problem is finding a core with
>enough shear strength to make it work.  After that discussion, I thought
>about using a 3D woven material (vaguely like the tricot lining in
>3 layer GoreTex) that combines two surface layers with a lattice of
>crossed fibers internally.  Inject with foam and coat with resin and
>you're done.  I talked to a couple of folks about it, but it probably isn't
>cost effective.
>
>You wouldn't need a very thick core to create a stiff kayak.  However,
>two groups would likely chime in.  The stitch and glue crowd will
>eagerly point out that glassed okoume kayaks are just as good, cheap
>and easy to make and the skin on frame gang will point out that
>kayaks are best when they're flexible.

As one of the "stitch and glue" crowd I'll respond to the invitation to 
chime in.  Typically stitch and glue kayaks using fiberglass over okoume 
don't create a "core" because the fiberglass cloth is often only on the 
outside of the hull and in strategic place where a little more 
protection.  On my S&G boat there is cloth tape down the keep line and 
lighter cloth over the entire outside of the hull.  On the inside, the 
seams have fiberglass cloth, and even though it wasn't required in the 
building instructions I put down cloth on the bottom of the cockpit area 
for abrasion resistance, behind the cockpit to stiffen it up for reentries, 
and around the hatch openings (I made flush hatches).  The deck has no 
fiberglass cloth on it whatsoever.  I would imagine that very few S&G wood 
kayaks are actually fiberglass-wood-fiberglass sandwich for the entire boat.

However, kayaks or canoes built using strips (usually cedar) *are* 
constructed using a fiberglass-wood-fiberglass sandwich (I'm currently 
building one of those too) and would have similar benefits.

I also wouldn't put too much credence into the benefits of a foam core as a 
significant aid to floatation.  I haven't particularly noticed that my wood 
kayak floats better than my fiberglass boat or a plastic boat.  The 
floatation doesn't come from the material as much as the use of bulkheads 
or inflatable bags to displace water (ever seen a cement boat?).  If a 
fiberglass kayak and foam core were both completely full of water, the foam 
core boat might float a bit higher instead of being neutral but both boats 
are going to be pretty useless until most of the water is emptied from the 
inside of the hull.

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