Re: [Paddlewise] Best Construction / Whatever It Costs

Jerry wrote;


>A manufacturer told me that he puts 3 layers in a sea kayak hull: A 3/4
>layer of fiberglass next to the gelcoat, then 2 other layers of
fiberglass.
>A kevlar hull will have one of the full layers of Kevlar, but the 3/4 and
>other layer still fiberglass.  He also uses a carbon/Kevlar hybrid, and
>sometimes a carbon layer.
>
>Do you still consider that a carbon/Kevlar hybrid is a "great sin"?

Yes. Rather extensive testing by myself and others indicates that the best
use of carbon and Kevlar is when the materials are used in their own
discrete layers to take best advantage of their characteristics I.e. layer
of Kevlar/ layer of carbon/layer of Kevlar rather than mixing the two in
the same layer.
>
>So you have 4 possible materials: fiberglass, Kevlar, carbon, or hybrid.
>Assuming that you need fiberglass next to the gelcoat, that leaves 2
layers,
>each of which can be chosen in 4 ways.  Therefore there are 16 possible
>constructions of the hull.  (Not to mention various choices for the
resin.)
>
>WITHOUT CONSIDERING COST AT ALL, what is the best construction if you want
>the lightest and strongest boat?

The layer of fiberglass  on the outside is nice (it does not fuzz when
abraded) but not essential. An ideal lay-up might have a 2 oz. S glass
cloth
on the outside, a Kevlar/carbon knit (Kevlar facing out) - a syntactic foam
core and another Kevlar/ carbon knit with the Kevlar facing in on the
inside of the boat. The weights of the cloth would depend upon how much
durability I wanted. The best finish (also lightest) would be one of the
two part polyurethanes such as AWLGRIP or Dupont Imron.

If I were vacuum bagging I would replace the syntactic core with honeycomb
and heavier skins. I might also use Spectra Instead of Kevlar. Of course,
you said money was no object so one might look into Boron fibers or maybe
even ceramic whiskers. Haven't been keeping up with such things but they
are
reported to be as strong as they are expensive.


Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/




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