Subject: [harryproa] Re: Building methods / materials
From: "Robert" <>
Date: 4/12/2008, 1:00 AM

If you are looking at a skin on frame structure, you are after tensile
strength. Hence kevlar, with possibly a thin fibreglass coating and
--- In, "rattus32" <mike@...> wrote:
> Which is why Kevlar is recommended for *inner* skins rather than
outer ones - the benefit
> tends to be in tension rather than compression, although you lose
the abrasion resistance
> that way, unless penetration is severe.
> Perhaps a strong inner and light outer Kevlar (Twaron, not sure
about Nomex) may be the
> best solution. Hydrodynamically it would be a bust, but I've seen
and felt a Halvarsson
> Kevlar terrycloth-like vest claimed to be the most
abrasion-resistant protection a
> motorcycle rider can have sliding against pavement.
> "But Cap'n - it saved the boat but the barnacles are having a field
day afterward!"
> Mike
> --- In, "Rob Denney" <harryproa@> wrote:
> > G'day,
> >
> > Kevlar is amazingly good at resisting abrasion. A few years ago, John
> > West, a kevlar/foam/kevlar 12m/40' cat rubbed up against a large steel
> > mooring buoy. The external kevlar and the foam were removed pretty
> > quickly, the internal kevlar was still watertight after a couple of
> > hours.
> >
> > The problem with the stuff is that it goes fuzzy when abraded and
> > there is noway to get it smooth. Hence the layer of glass so you
> > don't sand through it, either on the beach or during fairing. It is
> > also very hard to cut and has peculiar, and low, compression
> > properties. A bit stiffer than fibreglass and as strong as carbon on
> > a weight for weight basis. As a last resort safety item, a layer of
> > kevlar on the inside has a lot going for it.
> >
> > regards,
> >
> > Rob
> >

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