Thanks for the advice!

I found the can for the paint I used on the boat. It turns out I was wrong when I said it was oil based. It is an acrylic enamel (water based).

http://www.homedepot.com/p/BEHR-Premium-1-gal-6050-Ultra-Pure-White-Low-Lustre-Porch-and-Patio-Floor-Paint-605001/100162380#specifications

It has some great properties like "resistant to scuffing, fading, cracking and peeling" and it is UV resistant. However, under the section that says "waterproof" it says "No". That is a bit worrying to me. I wonder if there is any point in trying to put another type of finish over this, or should I just keep using it since it lasted a couple of years before it started cracking?