Anodes , What type of bolts.

pandos

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Tomorrow I will have to remove the anode for replacement. The existing bolts are mild steel and are rusted. I will have to cut them off. I know that stainless bolts would not conduct as well, but is there any other reason that I should not use stainless bolts when putting on the new one.

Thanks in advance.
 

discovery2

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I think the proper bolts to use are made of galvanised steel, however you do not state to what material the anodes will be attached.

I have two anodes on a (stainless steel) rudder attached with stainless steel bolts, and they certainly do the job very efficiently.

Antifouling the bolts after fixing to reduce rusting is acceptable, providing antifoul does not get on the anode!

David.
 

DickB

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The bolts I purchased for the job are S/S and include a welded square washer plus two nuts and washers. They are sold specifically for anodes and weren't particularly cheap. All works fine but they do rust after a couple of years...
 

boatmike

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Sorry to contradict you but I think if you put a magnet to them you will find they are galvanised carbon steel. Stainless would be subject to crevice corrosion. The normally supplied bolts are galvanised.
 

richardabeattie

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The old bolts may look rusty but before you cut them try a big stilson wrench. I did - one nut came off OK and the other bolt sheared so I only had to replace one bolt. It was sold to me as stainless (with the square washer welded on) but the earlier posts now have me wondering!
 

boatmike

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You appear to be correct! My apologies they appear now to sell both SS and Zinc plated. I still don't like SS below the waterline though although some types are better than others. The "standard" bolts from Mc Duff have in the past all been galvanised. I stand corrected!
Either way try to fit the proper bolts as they are designed so that even if the end of the bolt corrodes away you won't end up with a hole in the hull.
 

boatmike

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Philip... I did not think you were being sarcastic, and if you were I am big enough to take it. No worries! Quite happy to be corrected when I am wrong anyway. I may be a marine engineer (or more correctly a mechanical engineer having worked all his life building boats) but I am retired now. At one time I know MGDuff only supplied galvanised bolts. I note now that the carbon steel ones are not even galvanised anymore, they are zinc plated. Just shows I am getting old thats all!
 

Johnjo

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Arn't we all !
I also, always thought that fixing anodes with stainless was not the done thing.
We live and learn !
 

Micky

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Have to agree with boatmike, stainless steel should not be used under the water. Don't ask me why, but i was told this only last week by a surveyor when i suggested fitting a new rudder.
 

philip_stevens

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Micky,
wasn't there a contentious thread on here a while back about SS under water, and deprived of oxygen?

I think someone (metalurgist (spelling??)) stated that it was OK if there was air - as in normal seawater - that was able to get to the SS to oxidise or do something with the SS surface.

I fitted a SS rudder stock on a previous boat, and a friend is in the process of having his rudder stock changed from mild to stainless steel. Most of his stock will be within the foam filled rudder casing, so what happens to the SS within?

Many years ago, before MGDuff sold SS studs, I had two made up for my anode - before I knew about the problems with SS and oxygen. To my knowledge, they are still there after 14/15 years.
 

Ships_Cat

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I think that the ss underwater thing is taken far too seriously. In fact most of us have ss underwater on our boats in that the propellor shaft and rudder stock is such. One may even find that ones propellor shaft is magnetic if it is a high corrosion/strength alloy which puts another common myth to one side.

Another example of ss use underwater is the use of ss seacocks. While I often see on here that people say they are no good, the fact is that larger commercial vessels built of aluminium (and other materials too, but aluminium is a nice "active" example) are very commonly fitted with ss seacocks, strainers, etc with no issues.

The main chances of difficulty are in the case of welded components (using poor practices, or in the case of steel boats welding to mild steel underwater without taking the coatings for the mild steel well up the ss past the weld), or as has been said in some instances under nuts etc (but a good thread compound will avoid that, should such corrosion ever want to happen).

On our own boat, which is steel, the anodes are fixed using ss studs welded to the hull in two locations. We only use one anode so only one set of studs is used. The boat is in the water continuously and is normally only lifted from the water for a couple of days every 2 years but there is no evidence of any problems with either the used set of studs or the unused set.

John
 
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