Stainless to Carbon Steel Mating?

[DouglasEagleson]

I like the idea of trying a metal boat build. But cost is an issue. My question is about welding stainless to carbon steel. The goal is to use stainless for the bilges and carbon steel for everything above. Sitting water in a bilge is a primary route to rusting.

SO can I weld the two together? Do I use stainless welding rod or carbon rod to weld with?

My design is to have a form of hull with clear suitability. Like a Scow design. or maybe a small tugboat.

 

[CatrigCat]

I dont know about stainless boats but there is a clad joint for stainless to carbon steel.

The clad joint has stainless on one side and carbon steel on the other so you can weld the two metals.

Clad joints are made using explosion welding to join different metals together, steel to aluminium etc.
The clad joint different metals do not rust.

 

[gonzo]

Stainless below the waterline is a really bad idea. Look up crevice corrosion in stainless steel.

 

[JSL]

Gonzo's right, really bad idea
Stainless will corrode as fast as steel and in a more devious manner. Ive seen intergranular corrosion on type 304 used for frames on crab traps. Really neat.... all looks good from the outside but the inside looked like swiss cheese. One fellow lit a cigarette and blew smoke lengthwise through a 9" section of a 3/8" rod. The trap was 9 months old!

 

[DouglasEagleson]

thanks for the replies. I will go back to the study concept stage. Corrosion is a problem!

maybe there is some kind of fault tolerant design to define. Corrosion should not sink the vessel if cracking occurs? An interior double hull to limit cracking events like leaks. A plywood formed inner hull is possible. Chasing crevices/cracks with a welder is better than????

Access to the bilges would require movable cabin walls and floors. I guess my first vessel will have a double hull sufficient to float the boat if swamped?

 

[waikikin]

There is no great issue with the connection, as stated the vessel bottom is the worst place for it, much better in the deck and cockpit and especially for edges that commonly rub.
Jeff.

 

[Stumble]

If anything I would flip them and put the stainless on top, but this is just a silly idea. If you want a steel boat go all steel. If you want to reduce weight then a steel hull with an aluminium superstructure is an option. But personally I would rather have an all aluminium boat than a blend.

 

[DouglasEagleson]

yeah. I will "can" the whole idea.

there is also intergrain corrosion in aluminum. Reynolds is not necessarily honest with the actual rate. Exterior galvanic corrosion can trash an aluminum hull, also.

 

[Barry]

yeah. I will "can" the whole idea.

there is also intergrain corrosion in aluminum. , also.

But not relevant. There are thousands of boats if not 100's of thousands of boats in the world without paint with decades of service behind them and decades of service ahead of them

Most not painted at all.

Certainly you would not ground electrical back through the hull but proper anodes and construction processes and you would have a boat that would out live you and carry a strong resale value if you want to move on

You said that you want to build cheap but then introduce stainless into the mix???

Stumble has it right, no blends, all aluminum preferred if you are wanting a metal boat

Overall when you compare aluminum unpainted to steel with a strict paint regime, inside and outside, perpetual corrosion control in difficult to access areas and maintenance cost, the hull cost between the two are negligible.

 

[JSL]

By "intergrain" you mean intergranular?
Yes it can happen on non-marine grade aluminum where the alloy may be same number (marine or industrial) but the alloying process is different. Google faulty aluminum plate of around 2001- 5083-H321 (I think). About US$250 million worth of boats in the Pacific Northwest (Washington, BC, Alaska) where affected.
Done properly, except for antifouling, painting is not needed. There are many aluminum boats left unpainted and they have been in service for many (15+) years.

 

[Barry]

By "intergrain" you mean intergranular?
Yes it can happen on non-marine grade aluminum where the alloy may be same number (marine or industrial) but the alloying process is different. Google faulty aluminum plate of around 2001- 5083-H321 (I think). About US$250 million worth of boats in the Pacific Northwest (Washington, BC, Alaska) where affected.
Done properly, except for antifouling, painting is not needed. There are many aluminum boats left unpainted and they have been in service for many (15+) years.

This was an issue where the foundry changed the alloy composition or hardening process and did not inform the buyers. Exfoliation, if I remember, was the issue. An expensive lesson for the factory and the boat builders.

As we had just made the switch to 5086, we escaped the problem that others experienced

 

[JSL]

Yes, cold rather than hot alloying. We here in BC had little of this plate deal with. My preference is 5086- not quite as strong as 5083 but more malleable & not as brittle.