I have a maxprop and it is too close to the hull to put a shaft zinc on it. I typically get three to four months on it whether I am at anchor or at the dock. I added a galvanic isolator and have use a zinc fish. Neither of those make any difference and I am pretty sure all the wiring on my boat is correct, but maybe not. from talking to others with my boat and prop, I believe it is just the nature of the beast.