Putting this stuff under boats or watercraft is a largely debated topic right now. I've seen a ton of surfboard builders saying a lot of stuff about it. Sanded bottoms made craft faster way back when. From what I know, it's about controlling and enabling laminar flow and not creating turbulence, not repelling water.
That being said, somebody try it. Gotta think of some things that would be way more fun if they were water/chocolate syrup proof.