Boat Forum / Building / September 2007

I use this site for info on constructions methods for my outrigger
canoe project.  He has a few plywood kayak designs.

http://oneoceankayaks.com/stitchglue/stitchkayaks.htm

Ian Oughtred's Puffin?

See www.customware.nl/boats
And that one is entirely glued with epoxy.

Meindert

That;s not quite correct. Polyester dissolves some foams; notably
styrene. PVC foam and urethane foam are not affected. PVC foam is the
best for strength and longevity, but not cheap. It can also be used to
make compound (smooth) lines with a little effort.

Human bevaviour: Bestiality with a brain

Yes... but.  Lew's Knitted glass - when bought in 'roll' quantites is
about a dollar-a-pound more expensive than woven roving.  Traditional
thinking is that woven fabric is used primarily with fiberglass 'mat'
in a polyester layup, one between the other.  The basic reason for
this is that the woven, i.e. "over, under, repeat" nature of the w.r.
causes "hollows" where the 'high' strands cross-over the 'low' strands
of glass.  The mat (in addition to providing significant bulk, and
sucking up a lot of resin) is thought to "tie" the woven layers
together, by bridging these 'hollows.'

Now, in a large epoxy resin layup one can significantly reduce the
cost, while maintaining adequate strength by continuing to use woven-
roving.  The mat is forsaken in favor of a slurry of milled fibers and
a little cab-o-sil mixed to a 'light cream' consistency.  That is,
layer of w.r. wet out with straight epoxy.  Squeege.  Trowel in a
slurry of epoxy / milled fibers / cab-o-sil, then next layer of w.r.
Finish wet-out with straight epoxy. Squeege.  Repeat.

The milled fiber + cab-o-sil slurry is filling the hollows and
providing a tie for the next layer of woven fabric.  A 10 lb bag of
cab-o-sil is like way cheap, and will last the entire project.  A 50
lb bag of milled fibers is similarly inexpensive.

And, becuase we've eliminated the mat, resin-to-glass ratio's of 50 /
50 are easily achived.

So, in a large project where cost is a concern my belief is that one
ought not write-off woven roving as being a suitable material.

MW

After the fact, yes.

It was my problem.

Lew

Woven fabric looks like a burlap bag, a very coarse weave.

Knitted fabric looks like suit fabric, very fine, tightly knitted
fabric.

Do a Google for Knytex, then DB170.

That will get you to a double bias (+/-45), 17 oz/sq yard material.

It is about all I use these days.

There are also what are known as "Uni" fabrics which have the fiber
oriented either 0 or 90 degrees to the run of the roll.

Lew

Knitted glass consists of two or more layers of unidirectional glass which
are knitted together.  It's available with the glass at 0 and 90 degrees and
with the glass at +-45 degrees.  It is less expensive per pound than glasss
fabric.  Because the fibers are not crimped by weaving, it's stronger and,
for a given glass content, thinner and therefore it needs less epoxy to
fill.  So, for structural purposes, it's superior to mat & roving and to
cloth.  It often does not finish as smooth as cloth, so a top laminate of
cloth is a good way to finish .