What's so special about anode fixing studs?

[VicS]

I beleive MG Duff, and presumably other anode suppliers, offer stainless steel fixing studs.

It won't rust but its use below the waterline is always suspect. As a fixing for an anode maybe the usual objections are negated.

 

[gandy]

I think the zinc plating is only to protect the bolts while they are out of the water or maybe just to make them look nice
Once in the water the zinc plating will go at the same rate as the anode, so a few μ won't last long, but from then on in the anode should protect the bolts from serious corrosion. If it doesn't then they cannot be in good electrical contact and if they are not then the bonding wire on the inside will not be effectively connected to the anode either.

I think all our other underwater metalwork is bronze - propeller, prop shaft, through hulls, P bracket. Most of that is bonded to the anode. I wonder whether the steel studs are actually sacrificed in the same way as the zinc. Or doesn't it work that way?

 

[VicS]

I think all our other underwater metalwork is bronze - propeller, prop shaft, through hulls, P bracket. Most of that is bonded to the anode. I wonder whether the steel studs are actually sacrificed in the same way as the zinc. Or doesn't it work that way?

The anode should protect the steel studs.

Bronze or DZR items should not need to be connected to anodes and should definitely not be connected to the same anodes as any ferrous items.

 

[gandy]

The anode should protect the steel studs.

Bronze or DZR items should not need to be connected to anodes and should definitely not be connected to the same anodes as any ferrous items.

Cheers. Does that mean I needn't have any electrical connection to the anode? That would make the installation simpler. Currently the anode is wired to the cooling intake and to the engine earth. Regarding the second point, with steel anode studs the anode is by definition connected to ferrous items.

I suppose the correct solution would be bronze studs.

 

[VicS]

If the only things connected to the anode are bronze through hulls then its proabaly doing nothing useful as they should be resistant to corrosion and are best left unconnected to anything.

I assume your anode is wired to the engine block and that the flexible coupling is bridged to provide protection to the stern gear. Even that may well be unnecessary because a prop made of manganese brass (aka manganese bronze) should not need the protection of an anode.

People like to fit anodes to protect the props as a precautionary measure but in the majority of cases probably unnecessary.

Bronze studs for the anodes would not be a good idea as that would increase the rate at which the anodes are consumed!