The moment you plug your boat into an electric hookup, without a Galvanic isolator, it's at the mercy of Galvanic currents. 

galvanic isolator faq

Galvanic currents are tiny electrical "charges" that flow down the earth wire of your your hookup cable, and as they flow to earth, they take with them fragments of your boats hull, anodes, saildrive or outboard. It's a process very similar to the way a battery works. 

On steel hulled boats, the telltale sign is pitting around the waterline, for outboards and saildrives, it's flaking of the coating on the leg. Galvanic currents can also erode metallic propellers. Sometimes you'll see pitting on the prop, or it may turn a pinkish colour, as the Galvanic currents "suck" the zinc out of the alloy.

The easiest solution to all of the above is a Galvanic isolator, which simply plugs into either end of the hookup cable, and interrupts the flow of Galvanic currents, whilst allowing electricity to flow normally. There's no wiring involved, so you can connect it yourself.

For more info, please...  <Click HERE>

Propeller turned pink due to Galvanic currents.
This prop appears sound, but is seriously weakened  

propeller turned pink galvanic corrosion