[Paddlewise] Kevlar/Graphite

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..


John Winters answers:
>>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.<<

Which boats only lasted a few months? Mixed weave of Kevlar/graphite like
Dan is asking about? What happened to them?

>>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.<<

John, it appears to me you are describing the kind of mixing of different
fabrics into a laminate that I warned against earlier. One built of
individual layers of differing materials (which tend to delaminate between
the layers). When I say "mixed weave" I mean that strands of Kevlar and
strands of graphite are woven together so each layer of fabric contains
about 1/2 of each material evenly woven together. This way each layer of
this material bonded together in a laminate have the same characteristics
and are much less likely to delaminate between layers due to differing
elasticity.

John wrote:
>>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.<<

Our experience with Tsunami Rangers and their kind in California (those who
surf in in ocean rock gardens) is that the mixed weave is the way to go when
you want both light (to accelerate quickly to catch a fast wave) and tough
(for when that wave breaks on you and/or drags you into the rocks).

<SNIP>
John wrote:
>>So, yes, I have reservations about these mixed weave fabrics and at least
one of the weavers strongly recommends against them in canoes.<<
<SNIP>

John, here you use the words "mixed weave" which I have described my meaning
for above. You seem to be referring back to the Swift Canoes in rental use
when you say "So, yes". I'm confused, are you defining "mixed weave" to mean
what I mean by mixing materials in different layers of a laminate or a
single layer of fabric woven made of two different materials (the way I am
using it) or are you saying that Swift made canoes for rental use out of
fabrics which contained both Kevlar and graphite in the same weave that only
lasted for a few months? Which one of the weavers do you know for sure (the
"at least one") recommends against "mixed weave fabrics" for canoes
(whatever it is you mean by "mixed weave")? I would like to talk to them
about their experiences.

Matt Broze
http://www.marinerkayaks.com



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