I know its been beaten to death but I have also read that people dont have any problems using auto paint below the waterline of a boat. Some people swear it wont last but most do not actually own the boat they speak of.
Will it actually cause issues with flaking despite proper prep work?

I have painted a boat all over and it has lasted fine. The guy that owns it works right next to our shop. But the problem that you run into is the fact that auto paint was never designed to withstand the abuse that it receives below the waterline. So why chance it. You can get colored gelcoat and high gloss clear gelcoat to accomplish the same thing and its really not that much harder to spray. Google Fiberglast or look them up on Facebook. I was really surprised to see some of the things you can do with gelcoat, and I found out that its fairly easy to spray and buff.

Chuck

It's much better to use a marine paint on boats. Bottompaints will have antifoulants
and anti-slime additives mixed into the paint. Use the right paint for the job...

Auto paint will hold up just fine below the water line as long as the boat doesn't
stay in the water all the time.
I painted my boat with urethane and it's held up great, but I
trailer my boat so it doesn't stay in the water more than a day or so.

I have a 1994 Mastercraft Prostar 205 that was originally pink and teal. The boat lives on its trailer in my driveway with a cover over it. I've had it for about 9 years, and it has definitely gotten worse in appearance since I've had it. It appears that there was "minor" hull damage that was a couple feet in on the bottom and ran almost to the top rail of the boat. Below the water line was repaired with gellcoat, above was painted a "medium" metallic Blue with an unknown type of paint with a rather thick clear coat. Much of the clear has flaked off, the rest is very cloudy. The Blue has oxidized badly. I will have to take a picture of it. Oh, they also painted the accent colors on all of the vinyl upholstery, including welting beads. They did a tremendous job which is still holding up very well. I have heard that gellcoat is easy to work with, and I definitely agree that it should be used.


-Seth