Anode Reaction with Stainless Screws

[dreamon]

The large ring anode on one of my sail drive legs is coming lose after about 3 months. I have Volvo sail drives and the anode is attached to the leg with 2 stainless screws. It stays attached but becomes lose and moves around.

I have just hauled out and expected to see the screws missing, they were both still in place but the anode had warn or been eaten away around the screws. The anode on the other leg is always perfectly attached.
Any idea why this is happening on one leg?

[senormechanico]

I'm not an expert, but have recently found my own boat's reason for excessive zinc use.
BAD GROUND CONNECTIONS.
Take every one of them apart, make SURE they are not corroded in any way and are in fact, seriously a good connection. Make sure ALL your negative connections have a CONTINUOUS good path to a saltwater ground.

I used to go through a decent sized zinc about 3 times a year.
I finally fixed all my negative return wiring which was factory.
1/4" spade lug terminals which were in various states of decay.
I replaced ALL of them with crimped and soldered ring terminals on ss screw terminals.
Now the same sized zinc after 3 months looks almost new, due to cutting off positive voltage leakage to ground.
All I can say is,
"Why did I wait so long to finally do this relatively easy job?"

[dreamon]

Thanks. I think you may be onto something there. I think it may be a current in the leg. However the main anodes are on the end of the props and they are wearing at the same normal rate on both sides. Only the one ring anode ( which is fixed directly to the leg ) has the problem of wearing around the fixing holes.