Re: Electrollosis
Electrolysis is the term for what happens to metal--in our case in the presence of water.
When ANY two different metals are in close proximity with each other and there is a conducting medium (fresh or salt water) then a voltage potential is set up. This is very similar to a battery, and depending upon which two metals are involved, electrons flow from one to the other. The net effect is eventual disintegration of the metal. We can preferentially USE electrolysis to protect our engine.
For a simplistic example: In salt water, the salt being a very good conductor, any metal in the area of the boat will set up the galvanic reaction and since aluminum is usually more active than dock metal or anchor chain, or even the dissolved metals in the water, it will be sacrificed first. NOW: Since pure zinc is much more active electrically than aluminum, if we solidly attach a piece of zinc to the engine below the water, it will corrode first, protecting the aluminum. ---MAYBE! Nothing is foolproof.
There are electrical systems that "impress" a reverse current over the galvanic battery and purport to stop electrolysis. I don't know; I have no experience with these systems, but the logic is sound.