prop zincs
are small in comparison to shaft zincs, which we (I have a 331)can't use. I also go through zincs inside of three months but they only last that long because I use a "grouper" zinc attached to my main ground on the engine. I now get three months on my prop zinc and replace the grouper every 6-8 months. I know the alternate would be to install an isolation transformer which I have no doubt would help, but I like the idea of seeing the state of the zinc and replacing it as needed. By the way, don't forget your exchanger zinc. That needs changing out every two months. Also check your battery charging levels, when my batteries got older and weak, the charger ran hotter and ate the zincs really fast.
I wish Beneteau had a place for a larger zinc on the shaft rather than the shot glass size prop zinc.
Good luck, its just a factor of marina and your usage.
Mac