Mixing mild steel, galvanised and stainless ?

[sarabande]

Attached to the mild steel (rusty) ring on each of the two mooring buoys, I have two shackles leading to the mooring pennants.

One shackle is galvanised, the other stainless.

They don't emit great beams of light in the dark, nor is there evidence of pitting, so am I right in thinking that there is so much conductivity between the buoy, the shackles and the oggin, that there is little danger of corrosion/electrolysis, please ?

 

[Neil_Y]

I would think (without checking the actual figures) that they are so close on the galvanic scale of reactivity that there is virtually no activity or galvanic action possible. It's also only when they are all immersed and in good contact that anything happens.

 

[rogerthebodger]

Attached to the mild steel (rusty) ring on each of the two mooring buoys, I have two shackles leading to the mooring pennants.

One shackle is galvanised, the other stainless.

They don't emit great beams of light in the dark, nor is there evidence of pitting, so am I right in thinking that there is so much conductivity between the buoy, the shackles and the oggin, that there is little danger of corrosion/electrolysis, please ?

In our marina there has been several chain moorings that have parted perpetually when stainless steel shackles have been used to attach underwater to galvanized chain.

This is permanently underwater and I think it due to the galvanizing wasting away when in contact to stainless. It does not seem to happen with anchor chain attachment that is not permanently underwater.

 

[NormanS]

Attached to the mild steel (rusty) ring on each of the two mooring buoys, I have two shackles leading to the mooring pennants.

One shackle is galvanised, the other stainless.

They don't emit great beams of light in the dark, nor is there evidence of pitting, so am I right in thinking that there is so much conductivity between the buoy, the shackles and the oggin, that there is little danger of corrosion/electrolysis, please ?

If the shackles in question are on the tops of the buoys, ie out of the water, then that's OK.
If however, the shackles are under the buoys, ie permanently in sea water, don't mix stainless with galvanised.

 

[whiteoaks7]

The galvanic series will tell you that steel will sacrificially protect stainless and zinc, of course, will fizz away and protect both. Although the fittings are not underwater there must be enough electrolyte around to get a cell going so I would expect the zinc to disappear fairly rapidly and that shackle to get rusty at least in the contact area. Corrosion in stainless actually is different - usually you get corrosion when there is no oxygen present so observe and report on that one Why not rescue the stainless one and replace with a galvanised one - then all will be in harmony.