Copper and Aluminium

[Boathook]

I've got to do a temporary (for the season) 'repair / bodge' on some aluminium. Ideally I hoping to do this in aluminium to reduce the chance of corrosion but the other option is copper.

Is there going to be a risk of corrosion between the copper and aluminium ? Ideally I would do it correctly but time and resources won't allow it before the start of the boating season.

I'm not worried about strength as it is 'protective' and not structural.

 

[lustyd]

I don't know about corrosion but copper will certainly go green and make an awful mess if you don't regularly clean and polish it.

 

[srm]

Oh yes, lots of corrosion potential.
When I bought my last boat I was fortunate in having to take the mast down. Someone who called themselves "A Rigger" (according to the previous owner) had used copper ferrules on the ss cap shrouds to stop the spreaders from drooping. Spreaders had alloy end plugs. The copper ferrules had eaten most of the way in to plugs. Probably the same clown had made up a copper bracket for the VHF antenna screwed in to the alloy masthead casting. This was severely distorted by the build up of white alloy corrosion between the two metals that had stretched the copper sheet.

 

[Daydream believer]

I don't know about corrosion but copper will certainly go green and make an awful mess if you don't regularly clean and polish it.

He did not say if it was above the waterline or below. If below, then copper would keep the barnacles at bay. But as copper antifoul paint is not recommended on aluminium, then one assumes that copper would not be the solution.

 

[srm]

If below, then copper would keep the barnacles at bay.

And turn the alloy hull in to a sacrificial anode (even more effective in fresh water).

 

[Boathook]

He did not say if it was above the waterline or below. If below, then copper would keep the barnacles at bay. But as copper antifoul paint is not recommended on aluminium, then one assumes that copper would not be the solution.

On the waterline so the lightest ripple will wet the area. Not bothered about looks as slightly hidden !

 

[Boathook]

And turn the alloy hull in to a sacrificial anode (even more effective in fresh water).

GRP hull.

 

[Daydream believer]

GRP hull.

Why is it that these Op questions have to turn into "quizzes"? We always have to wring the information out of the Op first to get some idea of what is actually needed. It always starts out with a long winded guessing game. So far all I have gleaned is that it is a bit of aluminium & copper & you spend all your time in 2 pubs in Surrey & Dorset.- Well Isuppose that is a plus, but it does not help much with the repair does it?
Well not, if you spend most of the time in the pub pi..sed

 

[noelex]

If connecting copper to aluminium you have to electrically isolate the two metals if they are in any sort of damp environment. Sticking with all aluminium is much better.

 

[rotrax]

If it is not structural or under high pressure I have had great success with Belzona Metal.

Other two pack repair substances are available too.

I saved an ex Grand Prix racing motorbike cylinder head once that had had the inlet port enlarged until it broke through into the valve chest.

Araldite and a carefully shaped piece of sheet alluminium fixed that.

 

[Boathook]

Why is it that these Op questions have to turn into "quizzes"? We always have to wring the information out of the Op first to get some idea of what is actually needed. It always starts out with a long winded guessing game. So far all I have gleaned is that it is a bit of aluminium & copper & you spend all your time in 2 pubs in Surrey & Dorset.- Well Isuppose that is a plus, but it does not help much with the repair does it?
Well not, if you spend most of the time in the pub pi..sed

I only asked about corrosion between 2 metals. Its just that some people just like to add more. Once I understand the corrosion issues I can sort out my 'repair' for the season.
I tried to Google and got even more confused to what I thought was a simple question.

It's more than 2 pubs ! The Scillies have around 6 or 7 scattered around the Isles.

 

[Boathook]

If connecting copper to aluminium you have to electrically isolate the two metals if they are in any sort of damp environment. Sticking with all aluminium is much better.

Just the type of answer I require. Thank you, unlike the rambling from daydream believer.