This is really impressive; it feels very realistic, but also pretty easy to understand and interact with. Or well, I'm not sure I completely knew what I was doing, because I couldn't manage to make it to the last, secret island. It just got to a point (pretty early on while the island was still a long ways off) where I would just capsize to the one size despite standing on the edge of the other side (thought probably too late).
I liked the way you split up the gameplay into voyages to each island, rather than just making it one long thing; it gave me things to aim for, and the checkpoints were lifesavers, since I almost always capsized nearly directly after reaching a new island!
Awesome job with this!