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Roger Long Roger Long is offline
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First recorded activity by BoatBanter: Jul 2006
Posts: 172
Default Steel hull and aluminum superstructure

You would have plenty of electrical connection through the bolts.
They could be isolated but there would be little need to since they
would be inside and dry. You would probably want to use stainless
bolts anyway.

Even if you had the house isolated, lightning current would jump over
the small gap at the gasket like it wasn't even there.

The people wringing their hands over dissimilar metals forget that
stainless and aluminum are quite far apart but the millions of highly
stressed and critical stainless rigging fittings attached to the
millions of sailboat masts out there function for years and decades
without a problem.

--

Roger Long



"André Langevin" wrote in message
...
Roger,

I'm still discussing with people at SPURIND and another company. I
thought of using a joint and it would work but what if lightning
strike and i don't have electrical connectivity between the
superstructure and the hull ? The mast could still be
interconnected to the hull but it is a risk....

Better have electrical bonding between the two. i'm currently
discussing price, i'll post the findings.

cheers

"Roger Long" wrote in message
...
That is the stuff.

For homebuilding, I would just build a flatbar flange at the base
of the superstructure. Bolt and aluminum flatbar to it and then
build the aluminum superstructure on top. Unbolt after it's done,
lift, and insert a suitable gasket material. Then bolt it back on.

Being able to remove the superstructure would have a lot of
advantages if you had to do major repair on the interior.

Actually, I would build the whole boat out of aluminum. Stronger
at the same weight, more likely to deform in a way that stays
watertight in event of major damage, and easier to drill for
temporary patches with hand or battery powered tools. I'd much
rather go up on a reef in a far away place in an aluminum boat than
a steel on unless the latter was large enough to carry a full
welding outfit.

Also, less compass issues with an aluminum boat.

--

Roger Long



"André Langevin" wrote in message
...
Very interesting Roger what you bring. As you said, i've searched
also in internet but there is not much reference. I will talk
with a local machinist also and keep you posted.

There is this company though: www.spurind.com but it might turn
out very costly since it seems to be a specialty.

André

"Roger Long" wrote in message
...
Sorry, but the following is completely wrong. The explosively
jointed bimetallic strips have a long and successful history.
The aluminum is welded to the aluminum side and the steel to the
steel side. The strips simply seem to have become hard to locate,
at least via the web.

Regular steel and stainless steel are often joined. Problems can
occur, especially if submerged in salt water but you'll see mild
steel / stainless joints on fishing vessels that have been going
for years and years.

True, you can't weld aluminum directly to either.

How do I know about aluminum superstructure on a steel hull?

I did it on this boat:

http://www.bbsr.edu/About_BBSR/Facil...herbird_ii.htm

--

Roger Long



wrote in message
...
I have just double check with my friend who worked as a welder
for 35 years in a shipyard that build commercial, coast guard
vessels, battleships and drilling platforms.
If you have an aluminums structure welding steel plates on or
doing the reverse was not in practice. Aluminums and mild steel
or cold rolled steel are not compatible. The same thing applies
to welding stainless steel. What takes place is a white inter
granular corrosion that is hardly visible to the naked eyes.
Given time the white corrosion will cause a structural failure.
Not to mention the saline atmosphere at sea that will accelerate
the process.

"André Langevin" wrote in message
...
Hi to all,

I am a newcomer on this newsgroup and you'll see me around as
i'm starting the construction of a new boat. I currently have
a 34 feet powerboat in aluminum and my nest boat will be a 44
or 45 steel sailboat. I'm looking at building a Bruce Roberts
design and i would like the deck superstructure to be in
aluminum. I've seen many commercial boat done this way and
even old Coast Guard patrol boat of 30+ years old without any
corrosion problem so it is something i'd like to do. But i
can't find any industry that carries the special strip that
isolate both metals but still permit to weld them both.

Does someone ever see this ?

André