Dissimilar metal question

[antonywardle]

HI

I've recently replaced the the surrounds by the petrol tank filler.

It was an old bit of steel that was rusting and staining the gelcoat.

I found and old disk drive box and used that. Its made of Aluminium

and I've used stainless screws/bolts to put it in place. The fuel cap

is also stainless.

I though I read somewhere here about being careful to keep all the dissimilar metals

from touching each other. Is that right? If so, how do do I keep them apart?

Some gaskets made of rubber?

[Choicebro]

Hi Mate,

Dissimilar metals will create a galvanic reaction with each other in the presence of saltwater or a saltwater environment such as in a boat.

Basically the weaker material will give way before the stronger material.

A simple way to prevent this is to insulate the 2 surfaces with a non permeable surface, most commonly used is sikaflex or a similar product to provide a moisture barrier between the two materials.

Most people forget to insulate their stainless screws when mounting things like rod holders etc and end up with corrosion, and yes it is a pretty easy thing to be blasé about.

Cheers

Choicebro

[Davemmm]

Yeh you are going to struggle a bit with galvanic corrosion.

You can put in rubber washes between the screws and the plate and then put a gasket under the fuel cap. This will reduce it but probably wont stop the corrosion in the long run.

Best bet is to replace the plate with stainless.

dave

[Robroy]

Antony,

Maybe have a look at this :

Duralac - Anti Corrosive Joining Compound.

Regards

Bob & Robbie

[antonywardle]

Thanks guys

I've also got another bollard to put on. Its an alloy type

so i might have to try the sikaflex option.

I guess long term I can replace the plate, but thought the

Aluminium looked ok and I had it lying around.

Of course, if I can't get my engine sorted then its a bit of a moot point!

[pjbink]

Don't use rubber, it can also cause galvanic corrosion. I'd try some Duralac - that's what it is designed for.

That said stainless steel doesn't usually cause too much of a problem with aluminium and the plate is not

part of the boat's structure.

[BWV]

Most rubbers contain carbon, carbon will eat though the stainless and aluminium pretty quickly. If you are going to use rubber you need one that is carbon free. You should use Duralac or Tefgel. It's not perfect but it works well.