Off doody said:
It depends on where you keep the boat and product used but I would say at least two years. I have used Interlux Micron CSC on my boat for several years and have been able to get at 2-3 years out of the paint. Last year I touched up the paint before it went in the water in May and the boat came out with a clean bottom in October. It's pricey but it works very well.
I also did 2 - 2 season stints using CSC. On the second season, I would scrub, sand any chipped spots (there are always a few) and touch up those spots, repaint the water lines and chines and paint one coat just to use up the paint remaining from the previous season. The CSC worked very well for me and it was with much trepidation that this year I switched to Petit Hydrocoat water based paint. It was a little more challenging to apply. It has to be stirred frequently and thoroughly. It dries quickly and the roller doesn't seem to hold as much paint as the CSC did. The Petit looks good but it doesn't cover chips as well as CSC did, so feathering with sandpaper is needed. I applied two coats to the bottom and three to the waterline and transom. I will see how it works out.
The really big advantage is that you can clean up with soap and water as long as your roller and brushes don't dry. I was able to use the same roller for the second coat a day later. It doesn't smell bad at all either.
I expect that in the near future, my state will join the list of states banning copper paints and then I will need to find another product.