Re: [Paddlewise] carbon-kevlar weave

Dan wrote;

>
> I have seen the results of Matt's hammer and folding tests, and
> laminates with a carbon-kevlar weave seem to be very resistant to abuse
> of this type. However some time ago John Winters expressed serious
> reservations about this material (the details of which I have
> forgotten). What are the potential drawbacks of a carbon-kevlar weave?
> Has anyone subjected a kayak made with this material to long-term abuse?
> Enquiring minds want to know...
>

The Swift Canoe Company tested boats built using these types of materials in
their rental fleets. The results  disappointed them. The boats sometimes
lasted less than a few months where their normal Kevlar boats last as much a
five years in their fleet. Their "mixed" laminate boats ("S"
Glass/carbon/Kevlar) last two to three years. Impacts usually resulted in
visible  delamination running along the carbon fibers and extending well
beyond the impact point. Since the company provides a lifetime guarantee you
can appreciate that they would not continue using the materials even though
the data from lab tests looked promising.

Admittedly the use (and abuse) probably exceeds that which most sea kayaks
will get.

Now, before anyone goes rushing off in all directions recognize that fabrics
come in an extraordinary range of weaves etc. What Matt tested may not have
much resemblance to what Swift tested nor did the test methods have a lot of
similarity. I recall Darryl Lideigh beating on his mat canoes with  a hammer
and saying they were just as strong as anyone's else's Kevlar canoes and
even challenging other builders to duplicate his hammer test.  There are
tests and there are tests.

While the rental fleet test hardly qualifies as a controlled and repeatable
test procedure it does have the merit of having some similarity to "real
life". I recall how, in the yacht business, a lot of things that worked well
in the lab just "couldn't be done" on the shop floor and simply did not work
out in the "real world". It tends to humble one to have some old fart with
forty years experience show you (the snotty nosed kid) that your brilliant
idea that has lots of science behind it just won't cut it.

Maybe I am saying that because I am closing in on forty years of experience
:-)

So, yes, I have reservations about these mixed weave fabrics and at least
one of the weavers strongly recommends against them in canoes. That does not
mean they don't "work" or won't work. It just means that one has to exercise
caution with construction techniques that do not have a long term proven
track record. They may serve quite well for some uses but not others just a
mat serves quite well for some uses but not others.

As I have mentioned before, we really don't know how strong "strong enough"
is. Paddlers and builders seem to have a lot of opinions though. You can
take 'em or leave 'em.

Cheers,

John Winters
Redwing Designs
Web site address, http://home.ican.net/~735769







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