When metals are placed in a conductive liquid, such as salt water, they create a battery. Current flows between the metals in the process of electrolysis and essentially eats away at one of the metals. The goal is to set things up so that electrolysis eats away at a piece of metal that we don’t really need, and doesn’t destroy the prop or the hull or the motor. So sailboats have small pieces of zinc on the hull and on the prop that are designed to crumble and fall apart over time keeping the important bits intact. One of the last things we did before putting our boat back in the water was to replace these zincs or sacrificial anodes. While we were at it, we greased the prop as well.
See how crumbly the old zincs are?
And a nice clean new one!
Mike loves his grease gun.