I agree with Sean.
I have used Zaino Z3 on my Jetski for years, and converted my friend for use on his boat. Z3 and a rotary restored and sealed his fiberglass better than any marine products he used. Not only that, but one application takes us through the entire summer here on LI. Easiest cleanup Ive ever had on a saltwater craft.
Definitely try your favorite products on a boat, you'll be pleasantly surprised.
This isnt the greatest pic (the only one I have here though), but this jetski is 10 years old, and has only had 1 coat of Z3 each spring.