On Sat, 18 Aug 2007 20:19:58 -0700, "Lew Hodgett"
wrote:


"Richard Casady" wrote:

Strong as wood, heavy as steel, about sums it up.

Steel is lighter than wood. of equal strength. Aluminum is lighter
than wood. For the same weight aluminum and steel are equally strong.

Compared to an Airex cored hull with epoxy and knitted glass skins, all of
the above are a joke.

The very best plastic may be stronger. I think if Boeing is using it
that says something.
Be interesting to see a table comparing the S/N for various materials.
I know the latest fiberglass [and other plastic] is a lot better than
it used to be.
Been my experience that the older fiberglass boats are heavier than a
comparable aluminum boat. In any case, I got a 22 foot aluminum boat,
in the usual good shape, for two grand, instead. I laughed all the way
to the bank. If the available steal had been a plastic boat I might
well have bought that. It is well known that you can build a decent
boat from any of the popular materials. That is why they are popular,
after all. The family has a plastic boat that has been in use for
fifty years. It is pretty heavy. A turbocraft, first of the jet boats,
SN 10. It finally got painted after forty years. On the other hand,
the local aluminum boats of that vintage are still doing fine with the
original bare metal. We have a couple of neighbors with 1940's
fiberglass sailboats. The material was not well understood, they used
too much, and the boats are way heavy. They are, however, still in
good shape. Something called Rebels, they are among the earliest of
the production glass boats. Plastic [not necessarily glass], _is_
lighter than aluminum if it is done right, the aircraft industry is
proving that. As for glass, it is heavier than graphite or kevlar, and
you can get those materials in boats. Titanium is lighter than
aluminum, for that matter. Ever hear of the Russian Alfa class subs?
Titanium. They didn't build many of them. Where you really want the
lightest construction is in canoes that are destined to be portaged.
Early fiberglass canoes were way heavier than aluminum, and the
wooden ones were heavy. While metal and wood haven't changed, the
plastic is a lot better than it used to be.

Casady