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

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

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

Roger,

I'm a fan of aluminum. My current boat is made of. I did a lot of work on
it to change the gas engine to a diesel one. You can see it at the
following adress if interested: www.langevin.biz/marinette34/repowering.htm

I just finished today the bill of material for the Roberts 43 and here are
the important numbers;

Current prices: Aluminum about 2.50 CAN / pound Steel about .050 CAN
/pound

Since there is less aluminum than steel, but not that much, the cost of
material for a Roberts 43 with ballast is the following:

-Steel 29000 CAN including ballast, sandblasted inside+outside, isolated
with foam for a 28500 pounds hull
-Aluminum 57000 including ballast, no paint inside but only under waterline,
isolated with foam for a 25000 pounds hull


All in all, when the boat will be done there will still be a difference of
30 % in price even if you take into account that the gear is smaller, the
engine works less and so on. I compared the resale value of several boats of
43-44 feet worldwide, and there is no significant difference in the future
price of resale either. A good boat is a well designed and maintained boat
and this is what ultimately command the price. Current median price for
either aluminum or steel sailboat is around 197 000 for 43-44 feet.

One of my friend hit a low floating container on his way to Europe ... it
was a glass boat but the aluminum on my boat is so easily teared apart that
i would have had the same problem - big hole and water in ... abandon ship.
Since my plan is to circumnavigate, i want to sleep in peace, protected by
5/32 inches of steel at 40 000 pounds/ square inches of resistance and
welded at 60 000 pounds/square inches. Every weld on aluminum diminishes
the local strenght and this is the problem. Unless they decide to make
containers in aluminum

But i'll truly miss the low maintenance of aluminum. This is why, if
feasible, i would like to have the superstructure built of aluminum. Your
trick is very interesting, i will think on how to apply it to the design.

Thanks very much !



"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

I once saw a 40 something sailboat that had gone aground on an
offshore island. The keel was torn off and one side pushed in about
three feet. There was only about 18 inches of the hull that wasn't
watertight.

It often isn't the numbers strength of the material but the way that
the entire structure deforms under load that determines how it fails.
(Think of your rubber boat.) If I knew I was going to hit something
like a container, I would as soon do it in an aluminum boat of similar
structure weight as a steel one. Of course, that would be an
expensive boat as you point out.

--

Roger Long



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

I'm a fan of aluminum. My current boat is made of. I did a lot of
work on it to change the gas engine to a diesel one. You can see it
at the following adress if interested:
www.langevin.biz/marinette34/repowering.htm

I just finished today the bill of material for the Roberts 43 and
here are the important numbers;

Current prices: Aluminum about 2.50 CAN / pound Steel about .050
CAN /pound

Since there is less aluminum than steel, but not that much, the cost
of material for a Roberts 43 with ballast is the following:

-Steel 29000 CAN including ballast, sandblasted inside+outside,
isolated with foam for a 28500 pounds hull
-Aluminum 57000 including ballast, no paint inside but only under
waterline, isolated with foam for a 25000 pounds hull


All in all, when the boat will be done there will still be a
difference of 30 % in price even if you take into account that the
gear is smaller, the engine works less and so on. I compared the
resale value of several boats of 43-44 feet worldwide, and there is
no significant difference in the future price of resale either. A
good boat is a well designed and maintained boat and this is what
ultimately command the price. Current median price for either
aluminum or steel sailboat is around 197 000 for 43-44 feet.

One of my friend hit a low floating container on his way to Europe
... it was a glass boat but the aluminum on my boat is so easily
teared apart that i would have had the same problem - big hole and
water in ... abandon ship. Since my plan is to circumnavigate, i
want to sleep in peace, protected by 5/32 inches of steel at 40 000
pounds/ square inches of resistance and welded at 60 000
pounds/square inches. Every weld on aluminum diminishes the local
strenght and this is the problem. Unless they decide to make
containers in aluminum

But i'll truly miss the low maintenance of aluminum. This is why,
if feasible, i would like to have the superstructure built of
aluminum. Your trick is very interesting, i will think on how to
apply it to the design.

Thanks very much !



"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

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

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

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

If you are worried about rust, I would suggest making the deck of
aluminum as well as the cabin trunk and having the flange arranged at
the deck edge like a fiberglass boat. Any leaks that did develop
would then be out where they would most likely just run down the side
of the hull. The area under the cabin edge would be very clean and
easy to finish off. A bedded guard rail would protect the edge of the
gasket and keep water away from the area where two kinds of metal are
in close proximity.

The best thing of all would be the fact that sandblasted aluminum
plate without paint is an excellent non-skid surface.

--

Roger Long



"André Langevin" wrote in message
...
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