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