Whenever different metals are placed in a conductive liquid you create a battery. If you connect these pieces of metal together, current will flow. The current will be removing metal from one of the metal pieces = "electrolysis". If this piece is the zinc in your flashlight battery that is good, but if one of the pieces is your propeller it is bad.
The zincs you use on a boat are called "Sacrificial Anodes". Zinc is used because it has a higher voltage in the water so the current will be more inclined to flow from it than from your propeller. To complete the electrical circuit, the zincs must be connected to the items they are intended to protect. Usually this is no problem because the zinc is bolted right to the shaft or underwater housing. Non metal boats will usually have a copper bonding wire inside that connects all the underwater metal items together so they all share the protection from zinc anodes. Since engines use the metal frame as the negative battery connection and the engine is connected to the prop shaft, the engine and the negative side of your 12 volt system are also part of this bonding connection. This bonding wire is usually connected somewhere to the rigging. This is not for electrolysis protection but for some protection from lightning strikes to conduct it into the water through the items connected together. Periodically the zincs have to be replaced as they "eaten" away by the electrolysis process.
On Sunday, December 4th 2016, divers replaced some of Overfalls' zincs in preparation for the ship being taken to a New Jersey based dry dock in the fall of 2017.
|Getting the Dry Suit On||First Steps|
|Putting on Swim Fins||Looking For Zincs|
|New Zinc||Lowering New Zinc|