Chuck,

What's the diff between kevlar and fiberglass?

Kevlar is the brand name for an aramide fiber. In itself this fiber
is very strong and tough, but _only_ relatively: according to some
measurements Kevlar is 5 times stronger than steel. BUT according to
that same measurements, fiberglass is 2 times stronger than
steel...!
Using Kevlar in a canoe does help to get a few kilograms lighter and
a bit stronger boat than a canoe made from fiberglass, BUT only when
applied properly.

Problem is that Kevlar has some characteristics that have to be
dealt with, to get a stronger and lighter canoe, than the same canoe
made with mostly fiberglass. To take advantage of the better
strength of Kevlar one must use a better laminating material than
the normally used polyester. Otherwise the bond between the kevlar
and the resin will fail on impact, before the better strength of
Kevlar will be useful... Most knowledgeable canoe builders use
vinylester, and some even use epoxy as a laminating material. Other
'problem' is that using only Kevlar has proven to give problems with
impact and such. The best kevlar laminates have to be combinated
with some stiffer materials like S-glass (a much stronger version of
fiberglass) on the outside, to be really successful.

In order to get a very much lighter canoe (say 5 kg / 11lb. less
than a fiberglass one), using Kevlar alone is not good enough. You
have to combine it with lightweight core materials like foams or
balsa wood, and or carefully use carbon fibers. And then difficult
decisions have to be made regarding stiffnes, strength and
durability. Making a canoe very lightweight without losing too much
strength, means that it will be more flexible. You can make it
sufficiently rigid and very lightweight, but this will make the
canoe less strong, especially when you do not use the right core
materials and building methods, etc.! If a canoe builder is very
good, this compromise will turn out better than with a bad canoe
builder, who will make the canoe either too heavy or too flexible or
not as strong as possible! How will the canoe builder know whether a
canoe is as light as possible but still strong enough etc.?
Ultimately only the customers can tell... And if the company who
makes the canoes has many customers, and listens to them well
enough, then they should be able to produce strong enough Kevlar
boats.

If you really want a very strong canoe and don't care much about
weight, just ask the builder for an all-cloth kevlar canoe with a
layer or two of Kevlar extra in the middle of the lay-up -- it will
make the canoe as heavy as Royalex but almost as strong
and last a lot longer.

Dirk Barends