Randy - I have a diver do my boat quarterly and my zincs seem to hold up pretty well. Do you have a galvanic isolator? I put one on a couple years ago. They're not cheap, but cheaper that a prop or strut. I was on a real hot slip at Shilshole and lost a prop. If I did it again, I'll probably spend the $500 and put in an isolation transformer.
Thanks for the warning.
Craig