Electrical Corrosion on Prop Shaft

[ato]

Hi, my boat is suffering from an electrical corrosion problem. So far it is not clear whether it is caused by some wiring on the boat or by stray currents inside my marina berth.
Pulling the prop shaft and replacing the cutlass bearing next week.
Some photos attached, so you can see how electrical corrosion can destroy your prop shaft despite a working zinc on the shaft and propeller.

[vintageray]

I just replaced my shaft after finding it eaten about halfway through. My prop was fine. Someone else on here had a boat with about as much time in the water between haulouts as mine and his prop was eaten, but his shaft was good. It was suggested that if the current is from inside the boat, the shaft will be attacked and if the current is from the water the prop will be attacked. Personally, I don't understand why there would be a difference.

[fstbttms]

Caused by a bare wire on a bilge pump-

[Ike]

You need to give your electrical system a good going through.