Old weak mind

[Bill1565]

Help. I have about +0.5 v potential between my boat and the brackish water it sits in. When the boat across the canal is here potential rises to +0.6v. When I disconnect the shore power cord, It rises to +0.8 v.

I have disconnected all positive leads, with no effect. Any thoughts??Anyone??

 

[heart of gold]

Are your through hulls etc bonded to the negative of the battery in anyway? like to the engine block etc. You have a circuit somewhere. Make sure that anything metallic that extends through the hull, other than the propshaft and cutlass bearing is isolated from negative bat terminal. Sometimes a worn out bilge pump can cause this as well by leaking voltage to the surrounding bilge water....but you did disconnect the positive terminal. This is where I would start.

 

[Bill1565]

No bonding on this boat. Bought one where bronze and zincs were tied together. Ate the copper paint off the bottom in big circles . PO had a captain's licence. Ran charters to the Bahamas. Amazing!!

Busy tomorrow, gonna clean up the contacts for shore power cord on Sunday see if that lowers the voltage more. Bought a shrimp boat zinc today at ACE. Gonna rig up a home made zinc fish. so I don't eat up shaft zinc at the dock. Soon as the windlass is finished, gonna pull out into the harbor, drop the silver chloride cell overboard in saltier water and see what the voltage is there.

 

[Bill Roosa]

sounds like you have a couple. Zinc and something else. you could look at the "table of metal nobility" to determine what would produce a 0.8+ cell in a weak electrolite to determin the other metal. might help track it down if you knew you where looking for iron vs bronze or whatever it turns out to be.