Is a stainless steel boat possible?

[hansp77]

Just curious,
as I am getting ready to try to weld up my own stainless pushpit
the thought crossed my mind.
Could one make a stainless steel hull?
Or has anyone already done this?
Aside from much higher cost, are there any fundamental reasons why this couldn't be done?

The obvious idea I had to make this more affordable would be to use salvaged stainless, from things like big chemical storage tanks and what not.

Hans.

[Raggi_Thor]

"Stainless" means it doesn't rust in air.
It will still corrode in (salt) water, I think.
At least stainless bolts and screws are no good in wood under water.

[hansp77]

Thanks Raggi,
i do know that stainless still corrodes,
(maybe it should be called something like 'lessstain' or 'lessrust')
but as far as I know, even without air- the rate of corrosion is still a lot 'less' than normal steel.
I am not really picturing a gleaming silver bare metal hull (well ok the thought did briefly cross my mind) but rather some sort of painted, or zinc treated or other protective finish just like a normal steel hull. With the advantage of much slower corrosion (and much higher repair costs!)
I am sure that there must be some reason other than price though.

[antonfourie]

As long as you coat prepare the stainless steel you should not have a problem, i.e. you need to create the protective layer that forms on stainless steel when you have worked with it, i.e. welding / forming, if you used 316 you would be able to leave the hull bare. The rate of corrosion is slower then even painted and cared for mild steel.

If you were able to source the stainless and you paint it then you would be better off than using mild steel even the lower grades of stainless are still way better than mild steel, you would have to make sure that you use the correct electrodes as you might be welding disimilar grades of stainless.

[waikikin]

A couple of years ago we installed a stainless deck onto a self propelled mooring service lighter 40' in length, works well, plating cost was about 4x steel & consumables about 10x. Its worth it if it cuts maintenance costs in high aggression zones like anchor handling on foredecks & cockpits, sponson beltings & the like.Jeff.

[Raggi_Thor]

What about aluminium?
Isn't that more durable than steel?

[hansp77]

Originally Posted by antonfourie

if you used 316 you would be able to leave the hull bare. The rate of corrosion is slower then even painted and cared for mild steel.

So you are saying that a gleaming silver bare metal hull is actually a possibility?
Surely someone with a bare metal fetish and money to burn must have made one.

Another thing, are there any industrial uses of 316, like maybe my afore mentioned storage tanks or something like that, where the correct thickness and relative flatness of metal might be salvaged?

Here I am concieving of a long term project in scrounging and rustiling up enough bargain 316 sheeting to eventually build some big dream rust free gleaming silver round the world cruiser....

Again, probably near imposible.
But wouldn't you just love the safety and ease of repair of a steel hull, without the hassel and hazard of rust..

And just incase anyone who has the figures and calculations easily at hand, what might it cost to build a 316 stainless hull, lets say of around the 40ft length sail-motor-cruiser... (at the very least so that I can extinguish this extravagant idea before it gets too comfortable)

[SeaSpark]

Hutting once (maybe more) build a 40ft all stainless yacht about 10 years ago, something simular to their current 40ft model. Don't know what happened to it http://www.hutting.nl/Hutting40/Gene...aigen4001.html

These days they build in aluminum, with wood/epoxy deckhouse. You could ask them for an opinon.

[antonfourie]

Hans, the most likely source would be old chemical tanks, which may not be that pleasant to work with and may have some chemical corrosion damage. The other thing that you could look for is ex road tankers that have been in a accident. How ever you do it please be carefull as 316 is most used when there are nasty chemicals or acids and there may be harmfull residue.

As for a gleaming hull, yes as this is what handrails are made from, but if not looked after properly i.e. washed and cleaned like any other boat the stainless steel will get brownish surface corrosion or water marks, although this will only ever be a few microns thick

[hansp77]

Thanks SeaSpark and antonfourie,
this is all just theoretical for me at the moment.
I thought it might be an interesting thread,
and as it stands I have my hands full enough with my current boat.
But, for a long term future oriented project, who knows?
At lest it does seem that there could be prospects for obtaining the metal cheap.
Maybe by the time that I am ready to invest (a rather funny word in this context) in a 40-50ft round-the-worlder I may also be ready to just buy the damn thing ready to go.

[Ike]

Can it be done. Yes. Practical? Not very. The Nickel Institute in Canada did a serious study of the effect of salt water on various stainless steels. What they found is that they all corrode if they are wet and stay wet. Stainless like aluminum has a natural oxide on it's surface that prevents corrosion. Water washes the oxide away. With aluminum the oxide doesn't wash away so the aluminum doesn't corrode unles you damage or remove the oxide.

The other problem is the welds. The welds would have to be near perfect. Stainless is very subject to crevice corrosion. Any defect, even the slightest crack or crevice, will breed corrosion which will spread. Plus that, to weld it right you would have to use the TIG process further raising the cost.

Build out of aluminum if you want a bare metal yacht. There are lots of them.

[hansp77]

Ike,
I don't really want a bare metal yacht,
I am quite content at the moment with my lovely warm wooden one,
I was wondering if it were possible with 316, and if so, if it had been done already- or why not?

These reasons you have provided, however, are of the kind that I was looking for.
Cheers.

[gonzo]

Stainless bellow the waterline will get crevice corrosion. It will also interact chemically with antifouling paint. However, Monel metal is corrosion resistant to be used below the waterline and is also naturally antifouling. You can have a shiny boat after all.

[lewisboats]

Being as I am reading about corrosion right now...I would like to point out that stainless has two "levels" for want of a better name. One "level is significantly more noble than the other. The more noble level is the one where the chromium in the steel has oxidized (it needs a constant supply of oxygen to maintain) on the surface and is providing the corrosion inhibiting surface coating and the lesser level is any place that that coating has been penetrated (scratches, any oxygen deprived area (the coating doesn't last without oxy), etc). Add an electrolyte (salt water/contaminated fresh water...it all is to an extent) and the electrical capacity of the metal itself and you have a galvanic cell...a battery. The lesser noble level will sacrifice itself (corrode) to the more noble level (pit corrosion). You will also get corrosion anywhere stagnant water (oxy depleted) sits...the bilge for one, condensation for another. You will also encounter corrosion anywhere where you have biologicals attached to the surface of the metal, cutting it off from oxygen and in contact with moisture. The last type of corrosion you might see is around the welds, where you have altered the diffusion of alloys in the metal. The chromium gets bound up with the carbon leaving the area starved of chromium...the anti rusting agent. Using 316L (lo carbon) would help to alleviate this particular issue. Bare 316/316L needs water moving at a rate of about 3 ft/sec to maintain the coating of oxydized chromium at the required levels to provide corrosion protection.

Steve

[lewisboats]

Originally Posted by gonzo

However, Monel metal is corrosion resistant to be used below the waterline and is also naturally antifouling. You can have a shiny boat after all.

Yep...but I hope you have DEEEEEEP pockets!