T&T: Advantages and Disadvantages of Cold Molded Epoxy Hull vs.

Alan Wagner Wagner.Florida at verizon.net
Sun Apr 22 18:48:22 EDT 2007


I would not so quickly jump to the conclusion that steel beats aluminum on
the issue of strength.  It depends:

http://kastenmarine.com/aluminum.htm :

"It takes over 60,000 pounds per square inch (psi) to tear apart a chunk of
mild steel, and 30,000 psi to deform the same piece, to make it yield. With
aluminum, around 45,000 psi will tear it apart, and around 35,000 psi will
deform it. Yes, you read that correctly: size for size, aluminum has a
higher yield strength. In these facts lie the extreme benefits of metal for
hull construction: The "plastic range" of either metal is quite high, so the
material can take a terrific beating without failure."

"An aluminum bare hull, built to the same strength standard, will weigh
roughly 45% less than the same hull in steel.  As a result, if high strength
is of the highest priority, the aluminum boat can be built to the same
structural weight as the steel vessel, and then be considerably stronger."


http://kastenmarine.com/alumVSsteel.htm

"Again, for the sake of an easy to follow comparison, we might say that "one
inch" of steel plate will yield beyond its ability to recover its original
shape at approximately 36k psi, and will fail at approximately 60k psi.
A "strength-equivalent" aluminum structure, having used deflection
(stiffness) as the design criteria, will have been built using roughly 50%
greater plate thickness. We might then say that this strength-equivalent
one and a half inch" thick aluminum plate will yield at around 51k per
square inch of surface area (around 29% greater yield strength than the
equivalent" region of steel plate), and will fail at around 67.5k psi
(around 12.5% greater ultimate strength than the "equivalent" region of
steel plate)."
Both of the above are pretty good explanations of the steel vs aluminum
issue.

Alan Wagner
Tampa, Florida
Building (Kasten designed) "Passage of Time"  in aluminum
http://kastenmarine.com/valdemar52.htm
http://yachtsmiths.com/valdemar_52_gallery_01.htm





-------Original Message-------

From: Robin
Date: 4/22/2007 5:01:33 PM


I don't think you can beat steel for rugged strength: if you could beat it
easily, then many trawlers,draggers, and other offshore commercial vessels
would be cold molded. Even in Europe and the far east. So steel wins on
strength, durability  and ease of repairs.
                                .      .      .

Aluminum is next in strength with some weight savings, but that's not
significant for most recreational boats. In fact, the strength of steel or
aluminum isn't even necessary for most recreational trawlers of moderate
size..

                                .      .      .

Rob Brueckner
Hatteras YF
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