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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

Hi Roger,

Here is the quote i've received. Indeed quite costly for an amateur. My
Roberts 43 would need at least 100 feet of this so about 6000 $ of material.

Item Qty Thickness Width Unit Price USD /lin ft Total Price USD
/item
1 12' 0.75 * 2" $62.13 $706.56


The more i think to your proposal the more it make sense. And it would but
my Roberts 43 to a very high level of stability given that i would save me
about 2000 pounds and the equivalent lever-arm since it is farm from the CG.
Another advantage is that it is so easy to keep the rust out of the hull but
much less on the decks since there is a lot of holes, fixtures and contact
with items like anchor, spi pole and so on.

It definitely need more reflection !

Thanks !


"Roger Long" wrote in message
...
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