Stainless steel Hull Yacht

[davptt]

I recently purchased a 42 foot steel yacht. Yesterday, I got it hauled out of the water. Under high speed water jet wash, to my horror, all the antifoul paint washed out leaving bare silverish metal. Under close inspection, we all quite surprised that underwater line cover by stainless steel.

My question is: Does anyone know of any other stainless steel hull?. and should i applied antifoul over stainless steel... I don't think the antifould would stick to stainless steel..

Thanks.
Davd

[whitepointer23]

the q e 2, i think that had a stainless hull.

[gonzo]

There are several alloys that fall under the "stainless steel" category. Monel is also silver colored. It may take a metalurgist to figure it out.

[davptt]

Originally Posted by gonzo

There are several alloys that fall under the "stainless steel" category. Monel is also silver colored. It may take a metalurgist to figure it out.

I think, you are probably correct...monel is more likely metal. Since any other paint would simply scrap off... I thinking using a product callled POR-15 and applied antifoul over it... it is quite expensive but from what i research.. that it is quite tough and water resistant.

[gonzo]

If it in Monel, you don't need any antifouling. Nothing will grow on it.

[Stumble]

Davptt,

I would highly recomend hiring a metallurgist to determine exacally what you have. It shouldn't cost that much, and knowing for sure could make a huge difference in how to properly care for the boat.

[welder/fitter]

Monel doesn't have chromium in it, so if you polish a small bit of it, it will have a duller appearance than stainless.

[gonzo]

Nickel and copper are the main components of Monel. However, like stainless steels, there are many different alloys. It is a family and not a specific alloy.

[welder/fitter]

Originally Posted by gonzo

Nickel and copper are the main components of Monel. However, like stainless steels, there are many different alloys. It is a family and not a specific alloy.

Not sure if you're referring to my post or another, gonzo, but I agree with everything you've said. None of the Monel alloys have chromium, as I've mentioned.

[brian eiland]

Originally Posted by Stumble

Davptt,

I would highly recomend hiring a metallurgist to determine exacally what you have. It shouldn't cost that much, and knowing for sure could make a huge difference in how to properly care for the boat.

I believe this is good advice. I was recently looking at a 'houseboat' that had been built on stainless tubular hulls. The question arose as to the proper coating of stainless steel totally immersed in water??

Stainless Steel Oxygen Deprivation
http://www.inoxgrp.co.uk/pdf%20files/Tech%20sheets/PhysChem.pdf

[davptt]

I have not able to get a metal expert to examine yet. After stripping remaining antifoul, I am even more puzzling than before.... inside of the hull is completely mild steel cause there are surface rust... outside below waterline as I mentioned before stainless steel (pretty sure stainless it is absolute no rust and it magnetized).. above the waterline mild steel. So it is obvious that underwater line the yacht has two layer stainless and mild steel...
the question is if stainless and mild steel are in contact.. would it cause galvanic corrosion....? Also there are several circular indent from 5mm-10mm in diameter, 1mm-3mm deep underwater line.. I will weld to fill to those hose later after I find out exactly what type of metal underwater line.
Does all this make sense to you?.... Has anyone come across this type of construction?.. The yacht built from Boden Seamist plan....

[welder/fitter]

I'd suggest speaking to the builder of the boat, or even the designer. It won't be easy to determine the exact composition without a spectrographic analysis, which is a destructive testing method. Then again, I've been away from inspection for a number of years so, perhaps, there is newer NDT technology that can be utilized.

[welder/fitter]

Was the magnetic pull very little? Monel is slightly magnetic at room temperature. So far, it does sound like a Monel cladding, but the builder will know.

[Wynand N]

Originally Posted by davptt

I am even more puzzling than before.... inside of the hull is completely mild steel cause there are surface rust... outside below waterline as I mentioned before stainless steel (pretty sure stainless it is absolute no rust and it magnetized).. above the waterline mild steel. So it is obvious that underwater line the yacht has two layer stainless and mild steel...
the question is if stainless and mild steel are in contact.. Boden Seamist plan....

For starters, real stainless steel is non magnetic although 302 grade may be a very slight magnetic.

However, during the eighties there were a few 40 -42ft "stainless steel" boats built in South Africa, but I cannot remember the name of the yard. One boat was actually active on the racing circuit named 3CR12....

3CR12 is a brand name for a stainless steel plate produced in SA by Columbus in Middelburg and is also known as poor man's stainless steel.
This material looks like stainless steel, act as stainless steel, cost about a third of SS and IS magnetic. But, its Achilles heel is rust under extreme conditions such as in the mines it was once considered the "wonder" steel but is still rusted under the damp conditions and acidly water, although it did take much longer. Water tanks also had a bad habit having surface rust on them (outsides) after long exposure to moist conditions
I believe in seawater it would be quite OK while submerged like the outside of a hull, but on the inside it may show rust due to the oxygen present to help along oxidation over time.

Many food industries uses 3CR12 and it will stay shiny and clean because these are usually clean places and the equipment gets cleaned regularly....

I have a suspicion your hull may be built from 3CR12

[davptt]

Originally Posted by Wynand N

For starters, real stainless steel is non magnetic although 302 grade may be a very slight magnetic.

However, during the eighties there were a few 40 -42ft "stainless steel" boats built in South Africa, but I cannot remember the name of the yard. One boat was actually active on the racing circuit named 3CR12....

3CR12 is a brand name for a stainless steel plate produced in SA by Columbus in Middelburg and is also known as poor man's stainless steel.
This material looks like stainless steel, act as stainless steel, cost about a third of SS and IS magnetic. But, its Achilles heel is rust under extreme conditions such as in the mines it was once considered the "wonder" steel but is still rusted under the damp conditions and acidly water, although it did take much longer. Water tanks also had a bad habit having surface rust on them (outsides) after long exposure to moist conditions
I believe in seawater it would be quite OK while submerged like the outside of a hull, but on the inside it may show rust due to the oxygen present to help along oxidation over time.

Many food industries uses 3CR12 and it will stay shiny and clean because these are usually clean places and the equipment gets cleaned regularly....

I have a suspicion your hull may be built from 3CR12

Thank you for that information, it all make sense now... even metal under antifoul that are just above the sea, most of area are silver color but some show sigh of rust.. you corrected pointed out that present of 02 will lead to rust.... inside the hull some area I have sanded to bare shinning metal, for couple days now it is still shinning, if they are mild steel color would change . There are few pieces of spare stainless steel metal about 5mm left in the yacht...

Thank you all for the advice... every one being very helpful.!