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André Langevin André Langevin is offline
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First recorded activity by BoatBanter: Oct 2006
Posts: 25
Default Steel hull and aluminum superstructure

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