Thread: Alumimium corrosion - tinnie

Ask a boat shop where to get sacrifical anodes, should do the trick, they attatch to the boat and corrode themselves rather than the boat...no idea how, they just do.

Thanks for that advice - it had sort of crossed my mind to explore that option, but never got past that stage. I know they do that on the motors, lobster pots etc.

Was cleaning to boat up again yesterday afternoon after a stint on the river and it was on my mind I suppose. The spots individually are still quite smal, and none have ruptured through the paint yet.

Anyway, I will check it up with the local dealer when he opens again after New Year.

Somehow, I had managed to get it in my mind that stainless steel and aluminium are less of a problem than aluminium and lead or brass. However, there is a small spot starting to form in the aluminium panel around one of the ski rope attachments that I had understood to be stainless steel at the time that I fitted them - ex BCF. I was sure that ithey were not plated brass?

Cheers,

When Northside Marine set up my Sportfish they used Duralac on all the stainless screws this stopped the electrolysis. make sure when you buy new zinc anodes for the outboard you buy the purest zinc you can get, people complain that they get eaten away too quickly, better that than the outboard. Also check the logbook in case there are some inside the powerhead and replace them when they are two thirds gone, don't wait until they are all gone.

Thanks for that advice - genuinely appreciated.

I will follow up on the Duralac option (also the anodes) - most of the problem spots are around tonneau buttons held in place with small stainless steel screws.

These would have been fitted as an aftermarket option by the previous owner and possibly were not treated at the time - maybe 7-8 years ago.

Not too late to nip the problem in the bud.

Cheers,

You need to make sure the studs and fittings are high quality 316 stainless , if you wire brush use a stainless brush only. if you sand or grind use proper discs for alloy, any contamination will cause corrosion.
some fitting also contain metal elements not compatable.

To stop bimetalic corrosion you must exclude the electrolyte (moisture) from the joint. If it is in a solution it needs to be connected electricaly to a lower order metal in the solution (zinc) as an annode.

Do not use the hull as a conductor for lights etc, run two conductors. Any bleed of oxides of higher order metals on to bare alloy will lead to corrosion. Not sure how Flouride and chlorine in the water adds to corrosion but any moisture dispersal spray must assist.

Watch your paints - you must use etching primers and paint for alloy without other metals or use a rubber based undercoat. Not to do so will also cause corrosion.

rub it back, apply brown vinegar and seal with "Penetrol".

Thanks for the suggestions - genuinely appreciate the time and insights provided.

Cheers,

Originally Posted by Roverray

You need to make sure the studs and fittings are high quality 316 stainless , if you wire brush use a stainless brush only. if you sand or grind use proper discs for alloy, any contamination will cause corrosion.
some fitting also contain metal elements not compatable.

To stop bimetalic corrosion you must exclude the electrolyte (moisture) from the joint. If it is in a solution it needs to be connected electricaly to a lower order metal in the solution (zinc) as an annode.

Do not use the hull as a conductor for lights etc, run two conductors. Any bleed of oxides of higher order metals on to bare alloy will lead to corrosion. Not sure how Flouride and chlorine in the water adds to corrosion but any moisture dispersal spray must assist.

Watch your paints - you must use etching primers and paint for alloy without other metals or use a rubber based undercoat. Not to do so will also cause corrosion.

Thanks for taking the time to offer some useful advice - genuinely appreciated.

Cheers,

Originally Posted by crump

rub it back, apply brown vinegar and seal with "Penetrol".