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

On Thu, 10 Nov 2005 17:08:29 +0000, Peter Wiley
wrote:



Notwithstanding, I like aluminium for boats myself and if I ever get
the urge, would weigh carefully the first cost vs maintenance issues
WRT steel and aluminium.

If I recall, Ted Brewer wrote an article on this very subject (and he
should know). Overall, he saw it as about a 50/50 situation as
regarding ease of building (easier with Al, but trickier to weld),
strength vs. weight, cost of materials, corrosion and electrolysis,
etc.

If you go into it understanding the materials fully, it's pretty
straightforward. One point, however, to note is that while the vast
majority of under 60 foot/under 19 metre yachts are built in various
types of fibreglass, the majority of high-latitude boats are in metal,
and a strong minority of passagemakers are also in metal.

The Europeans and the South Africans make some lovely...and
fast...boats in steel and aluminum, and they are not as widely
appreciated in North America as is GRP, etc. But if it was good enough
for Moitessier...

R.

rhys wrote:
On Thu, 10 Nov 2005 17:08:29 +0000, Peter Wiley
wrote:



Notwithstanding, I like aluminium for boats myself and if I ever get
the urge, would weigh carefully the first cost vs maintenance issues
WRT steel and aluminium.


If I recall, Ted Brewer wrote an article on this very subject (and he
should know). Overall, he saw it as about a 50/50 situation as
regarding ease of building (easier with Al, but trickier to weld),
strength vs. weight, cost of materials, corrosion and electrolysis,
etc.

If you go into it understanding the materials fully, it's pretty
straightforward. One point, however, to note is that while the vast
majority of under 60 foot/under 19 metre yachts are built in various
types of fibreglass, the majority of high-latitude boats are in metal,
and a strong minority of passagemakers are also in metal.

The Europeans and the South Africans make some lovely...and
fast...boats in steel and aluminum, and they are not as widely
appreciated in North America as is GRP, etc. But if it was good enough
for Moitessier...

R.
I think that generally steel boats are best above a certain size. But
they are too inefficient or heavy below that threshold. Once you are up
into the steel size range, all the other annoying things about steel
boats become bearable.

I just discovered that the steel boat that I Captain has areas 50%
corroded due to stray current over the past three years. That just
doesn't happen in fiberglass and happens faster in aluminum.

Welding new plates on is a bigger job than grinding out blisters and no
boat ever sank from blisters!

Gaz

Roger Long wrote:

And people ask me why I am considering steel for an offshore
boat...G

Go with aluminum if you can. No compass problems and you can make
emergency repairs with hand tools and sheet metal screws.

I saw a 60 foot sailboat that had gone ashore on a rocky island and
had it's keel torn off. One side was pushed in three feet for about
half the length. Still, it could have been made watertight and
floated off with about five feet of duct tape. A steel hull, although
stronger according to some measures, would have been in pieces after
that treatment.


The sailboat dosent look anything like the pictures , people have been
going there taking stuff off of it steady there is nothing left mast's
sails everythings gone.


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