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Old 14-10-2013, 09:33   #1
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Protecting Mild steel in the water

Hi,

I have my boat out of the water at the moment and am doling some maintenance to the wet metal fittings. I have a rudder-heel fitting, rudder stock and stern tube all in mild steel.

I am interested in people's experience protecting them from rusting. I have them all bonded into sacrificial anodes. What I am not sure about, is painting.

I intend to get the parts galvanised. But what to paint on next? Usually I would epoxy anything like this - but I worry that if a tiny it of rust occurs then the epoxy will be cracked and pushed off. So perhaps an inhibitor like red-oxide followed by epoxy...

My thoughts:
Is red-oxide paint any use in salt water?
Have you tried the zinc-doped epoxy paints? - was it good?
Is there some obvious product/method that I don't know about?

Thanks in advance,

Duncan
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Old 14-10-2013, 09:45   #2
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Re: Protecting Mild steel in the water

I am rather surprised that any underwater metal is mild steel, much less critical stuff like a rudder stock and stern tube.

But if so, then galvanize the $#%@ out of them and don't paint. The galvanizing protects the steel and paint just covers it up. There are paint systems that could work- cold tar epoxy I think, instead of galvanizing, but they have to be perfect and not a single nick for them to work well. Find a yard that maintains steel boat hulls and ask them what to do.

Galvanizing will last a few years, maybe 2 or three, but just like cruisers who anchor out full time or with mooring chain, the galvanizing gets eaten away and has to be redone every few years.

David
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Old 14-10-2013, 09:54   #3
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Re: Protecting Mild steel in the water

djmarchand,

Thanks for posting. When you say not to paint the galvanised metal - is that because the paint won't keep the water off the zinc?

Can mild steel be that bad? Plenty of yachts are made entirely form mild steel.

I am getting some work done by a yard and will gewt their view, I wanted to widen my research as much as possible
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Old 14-10-2013, 16:31   #4
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Re: Protecting Mild steel in the water

My boat is mild steel, and lots of it is under water. The stern tube is unpainted steel hollow bar (unpainted on the inside) and has been there for 25 years no problems. I would not consider galvanising the parts as the gal will act as an anode and blow all of the paint off the fitting and then the gal will disappear pretty quickly and you will have an unprotected mild steel fitting.
Better to abrasive blast and epoxy coat the fitting.
Make provision for some metal tabs that you can tack weld a small anode onto and all should be fine. I don't like bolting anodes on , as you need a resistance free coupling.
I would not like stainless in this fitting as it may suffer crevice corrosion where it is bolted on.

Regards,
Richard.
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Old 14-10-2013, 16:46   #5
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Re: Protecting Mild steel in the water

If your boat is not steel, then you should not be using mild steel below the water... I mean really.... what is the cost savings? If your boat is steel then it makes perfect sense....
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Old 14-10-2013, 17:11   #6
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Re: Protecting Mild steel in the water

You will have constant trouble with this Remove parts and have them fabricated in quality s/s then have them electro polished. If the budget wont go that far then boden36 is right on track. Don't gal as you are just making an other anode. Good luck Jacko
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Old 19-10-2013, 13:13   #7
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Re: Protecting Mild steel in the water

Amerlock 2/400. Blast the steel, or chip or sand or whatever, get rid of as much rust as you can, then paint with Amerlock. Stuff will cure down to -6C, and was developed to use on oil rigs, mid Atlantic. If you can pull the shaft paint the tube inside by cutting a roller open and forming it to fit the interior diameter.
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