Well THERE'S yer problem! As fstbttms said,
anti-fouling paint is not no fouling paint.
It will never totally prevent all growth, no matter what an advertisement may tell you, and no matter what paint you use in what conditions. I paint my bottom every two years, but my divers are on a regular 3 month schedule. They pop by every 3 months and do the zincs, clean the running
gear, check thru-hulls, and once or twice a year clean the bottom. Just part of owning a
boat, unless you dive on it yourself, IMHO. Develop a good relationship with a good diver, and you'll find the regular schedule is much cheaper than dive-on-demand. Our's do everyone on the
dock who use them at one time, makes it much easier for them. They like this and charge much less as a result. It's just common sense, what if you suddenly have a stray
current problem from a new neighbor or something? Your zincs could be gone in weeks and your running
gear at risk. Regular
diving is a no-brainer, and as long as they're down there they might as well clean the gear or bottom if it needs it. This means a clean bottom at all times, safe running gear, and less frequent bottom painting. It pays for itself really...