I have found the zinc Yamaha sacrificial anode will last a couple years in fresh water, less than that in salt water. In fresh water a magnesium anode should be used but Yamaha doesn't make them unfortunatelyso I have to be certain to keep the lower unide and propellor painted so the aluminum doesn't become the sacrificial anode. I only use TriOx bottom paint as it doesn't react with the aluminum andis slime/algae resistant.