Mixing galvanised and stainless

[Steveandelfrys]

If I were silly enough to attach a stainless bolt to a galvanised plate under the deck - any suggestions on preventing the two reacting - I'm tempted with a nylon sleeve /forums/images/graemlins/laugh.gif if this little man is you reaction I don't blame you - advice welcome

 

[orizaba]

i might be shot down here but i would say you would have no real problem,if it worries you use some duralac on the bolts,i have galvanised turnbuckles to stainless rigging with no real problems. most of the problems with disimilar metals occur when they are constantly submerged in seawater,

 

[goldscoter14]

I would partly agree with orizaba, its the salt water providing an electrolyte that causes the corrosion. My galvanised keel plate is simply bushed using vesconite on a SS pin, with the galvanise etch primed and anitfouled. you could do well to paint your galvanised plate for an extra layer of protection. other than that, you are prob ok. just check it after a while!!

 

[Channel Ribs]

This is a contentious issue, I have even started a study and placed some galvanised items and some stainless items together at the bottom of the sea. I shall report back soon.

 

[Niander]

I had a stainless shackle hanging on a galv chain[connecting angel]

within a week or 2 the 3 nearest links had gone rusty

was under water at high tide....changed it to rope...made a mess of the chain..

 

[Leighb]

I used to make the stainless shackle on my main halyard fast to a galvanised shackle on a mast fitting when I left the boat.

The galvanised shackle rusted so badly I had to replace it every year, but at least the mast fitting survived!

 

[ccscott49]

Simple answer, dont mix the two, have a look at a galvanic table, (very good one on classicmarine site). The zinc will degrade, as it tries to protect the stainless, insulating it will work, but needs to be totally insulated, why not just use galvanised bolts.

 

[Salty John]

We've had this question just recently. It was a discussion of attaching galvanised chain to a stainless shackle in an anchoring system. At the time I posted this:
'You are technically right regarding the galvanic scale and the potential for bi-metal corrosion, but before everyone rushes out and changes their stainless steel shackles for dodgy galvanised ones let me put it into perspective. In researching an article on anchoring I considered this problem and I asked the Association of Galvanisers, or some such august body, for their comments. They referred me to a report which said '....however, when austenitic stainless steels (300 series) are in contact with zinc (galvanising) neither material will suffer additional corrosion, or at the most, slight corrosion. The slight corrosion is usually tolerable when in this bimetallic contact.' They go on to say that where there is a massive amount of s/s and a small amount of zinc, such as a zinc rivit in a s/s plate there will be corrosion of the rivit. In the chain application the contact area is so small that there will be no noticable effect, except if the zinc surface has been eroded away.
I think this is a non-problem and the choice of gavanised or s/s should be made on the basis of other factors.
All IMHO, of course.'
Of course, stainless links being in moving contact with galvanised links can lead to errosion of the galvanising and, thereby, to rusting.