In article , Roger Long
wrote:

"Peter Wiley" wrote

No it wouldn't and saying that demonstrates that you don't know the
characteristics of materials. Steel is more ductile than aluminium -
it
will deform more before reaching its plastic limit and tearing. It
is
also less susceptible to work hardening and notch sensitivity, and
welds can be 100% the strength of the parent material, which is not
the
case with al. Steel is also far more resistant to abrasion.

True, (except for the first line), but we are talking about the
behavior of an entire structure not a test specimen. The aluminum
hull behaves sort of like a rubber inflatable boat and the steel hull
like a fiberglass one. The glass hull is "stronger" but may be more
likely to puncture in many situations.

How does this work? The aluminium has a lower elastic limit (amount of
flex before permanent deformation), lower plastic limit (deformation
before rupture) and lower resistance to abrasion than steel does. It is
structurally an inferior material. It compensates somewhat due to its
lighter weight enabling thicker sections to be used, regaining some of
the difference, and in shipbuilding due to its better corrosion
resistance.

The steel hull would have been in pieces not because it is weaker but
because it would have flooded and been rolled around on the rocks full
of water instead of retaining enough buoyancy to get up above the surf
line.

Oh, come ON. That boat (SG) is ballasted to a displacement of 14400
lbs. The steel version is ballasted to a displacement of 14400 lbs.
Both versions have all inside ballast. The keel shoes are 1" thick
plate in both cases. The chine bars are 3/4" thick rod. The frames are
2 1/2" by 1/4" flat bar. Can you explain to me how this ballast
mysteriously changes between a steel hull and an aluminium hull? How
the aluminium hull managed to keep water out that a steel hull would
have allowed in?

Why would a 4mm thick steel hull plate be ruptured, allowing water
ingress, when a 6mm aluminium plate hull kept the water out?

This argument has no credibility.

BTW, I have a full set of blueprints for a Colvin Witch hull so I do
know how they're built.

Obviously, anything can happen in any accident but I've seen enough
damaged boats to have great respect for aluminum.

I have enough understanding of the materials characteristics to design
boats like this one:

http://home.maine.rr.com/rlma/WHOIrv.htm

Nice boat. I have 2 30', 6 tonne alum boats, 4 jet barges and a number
of other small craft. However I also have steel vessels up to 6500
tonnes. Any impact that an aluminium boat will withstand, a steel boat
will also withstand, and likely with considerably less structural
deformation.

PDW