Austenitic steel

[model 10]

Originally Posted by Stumble

Going to be replacing those annodes daily. The boat was scrap six weeks after being launched. That's tons of steel and monel turned to powder a week.

They didn't build it right. You can't have other metals touching it in salt water. They probably didn't know that 100 years ago. Even so, I doubt this boat in question is made from monel.

[transmitterdan]

Originally Posted by Guy

They didn't build it right. You can't have other metals touching it in salt water. They probably didn't know that 100 years ago. Even so, I doubt this boat in question is made from monel.

I also doubt the boat in the OP is made from Corten either. Corten needs oxygen to rust and create the protective layer. Under water it would be starved for oxygen. If it is Corten I would be doing a ton of research before buying. If the boat is hauled out every few months and left to rust on the hard then maybe it would work ok.

The galvanic series was known 100 years ago but the boat designer in 1915 probably did not think about it. I see people using monel (and titanium) components on boats today instead of stainless steel in the mistaken belief that these other metals do not partake in galvanic corrosion. The only things more damaging than monel to aluminum and zinc is stainless steel and titanium but not by much. All three (monel, SS and Ti) are highly corrosive to aluminum, mild steel and zinc when immersed in salty water.

[roverhi]

Cotten is billed as a big improvement over mild steel in corrosive environment like the sea. Its big advantage is that it's supposed to build a protectve oxide layer to protect the underlying metal and not exfoliate as readily as mild steel. It is also harder than mild steel so not as easy to bend into the compound shapes of around bilge boat.

Cotten is a big improvement over mild steel for corrosion but still needs to be painted around salty air/water. It was used unpainted to build the stadium in Honolulu and sold as corrugated roofing. It didn't work as well as the hype and proved it needs to be painted in a salty environment. It was still better than anything else for the price.

I'd consider Corten steel in a boat as a big plus. Much less a problem for the small nicks a bumps that are the bane of the typical steel boat.

[model 10]

Almost everyone now agrees that Corten Steel is not the correct material to use, however 20-30 years ago it was popular. Maybe this boat is one of those.

[hpeer]

Took me a bit to find it...Asperid....Monel


Copper Nickel : Asperida 70-30 boat hull

[Pauls]

Some incorrect information in the above posts. Corten is a trade name for one of the HSLA (high strength low alloy) steels. It is absolutely a good boat building material. This is NOT because of its corrosion resistance, because in a salt water environment it is NOT corrosion resistant. It must be painted for marine use. Its advantage is higher strength than the common A36 structural steel. Tom Colvin, enormously experienced naval architect and steel boat designer/builder recommended Corten for its better strength properties, not for any improvement in corrosion resistance.

Bottom line, I'd suggest that what kind of steel used is pretty irrelevant now. The boat has held up for 26 years so whatever was used the builder did an adequate job with his weld joints. If the hull is fair then that is a strong indication he did his job well.

Pay very close attention to how well she is painted, particularly on the inside. As recommended above, do a careful ultrasound. As an ME and occasional boat builder/designer I wouldn't worry about the steel alloy on this one.

[DeepFrz]

Neil, I suggest you check out the the forum at the "Metal Boat Society" web site.

[Cheechako]

The advantage of Corten Steel is it's ability to develop a rust type oxide coating. If you want a big rusty looking boat then go for it. If you want to paint your boat I don't think there is any advantage to Corten. ?
Having worked welding problems on Corten... even in a clean aerospace shop environment... I'm not sure the risk of inferior welding issues is worth the small extra strength of Corten. The very nature of the oxides it develops readily cause weld contamination to a larger degree than clean steel. Just a thought anyway.
If you want a steel boat, then I guess I'm saying Corten is fine, but I wouldn't let the use of Corten influence me either way....

[roverhi]

Originally Posted by Guy

Almost everyone now agrees that Corten Steel is not the correct material to use,

Not the case at all. Don't know where you get the idea that Corten has a problem. When welded properly it's considerably better than mild steel. The problem with mild steel as the inevitable dings that occur, bare metal is exposed which rusts, exfoliates, exposing more bare metal and quickly rusts through when you are talking thin gauge deck plating. Corten will do the same thing but way way slower. It was originally billed as a needing no paint but that was proved too opitimistic in a salt environment. You will still get the nicks and scratches but it won't immediately begin to rust out. Less maintenance needed immediately but you'll still have to seal any ding off with paint for long term solutions.

[gjordan]

In talking to a New Zealand metal boat builder (many years ago), he said he prefered to work with corten, since the added stifness made it easier to get a fair curve to the plating, and it also cut down on the rust. The biggest problem with amature built metal boats is the hungry horse look, where every rib shows. Corten is stiffer, and folds around ribs and stringers in a smoother manner. A fairer hull with less rust makes it a very desirable material. -_____)_Grant.

[Pelagic]

I’ve owned a Dutch built Steel yacht for the last 10 years and it is now 32 years old.
Corten steel was used to build the Hull, House, cockpit and all wet lockers.

Steel boats rust from the inside out, so the quality of its coating and welding on the inside will determine the lifespan regardless of the kind of steel used.
.
Since my boat has circumnavigated twice the hull has obviously worked over the years, but I have yet to find rust even where continuous welds were not possible and in those hidden away places that are all the usual suspects.

This year I removed all the original insulation from the engine room and I was especially concerned about the hull sides where 4 large Air Vents would have allowed salt water inside, in heavy going.

Did find it very salty and dirty, but the original green coating and inside shell was completely rust free.
A good cleaning, light sand and prime of corners before 2 coats of white 2 part poly and I honestly believe it will be good for another 32 years.

In 2010, I sandblasted the hull down to white metal and found it to be completely blemish free, except for a small spot on the stern quarter (size of about 1 inch in diameter) where something had been happening.

Inspection inside revealed that under the aft storage floor, a Zinc ingot had come loose and had scratched thru the interior coating.
I am guessing it had created a hot spot in marinas for galvanic action.
Ultrasound tested that the plating was to original spec and that blemish was simply filled with rod and the inside recoated.

So I don’t know how to convince anyone about the value of Corten steel, but I am very happy with it as I have worked on a lot of other mild steel yachts, that all needed some re-plating work after 20 years.