Good start! It's an interesting concept, and I can see that it will make for some brutal gameplay (those guided rockets are extremely accurate). In my opinion, it needs:
a) More interesting boats, maybe even more realistic ones. The current boats are pretty boring.
b) More ways to get from one boat to the other
c) A rethink of how the map works. This is a tough call, but I think it would be more interesting if the boats were closer together, so you could actually fire from one to the other without the Nex, and if the middle section were removed entirely. In this map, very little time can be spent on the boats themselves- you are either flying over the water, or inside the hull of the boat. If the boats were made more interesting/complex, that is, set-pieces unto themselves, I think it would be much more fun. The middle area doesn't serve much purpose, aside from making crossing the water almost impossible without the Strength powerup.
I'm kind of envisioning a setup where the two boats would be positioned as if they were locked in combat.
Lots of stuff could be done with this, especially with the turrets (turrets could be used instead of cannons, for example.
You have a really neat base concept here, and it could potentially turn into something really epic. All depends on how much effort you want to put in.
d) some way to make the water end less abruptly. This water + reflections looks pretty good, but it ends in a really ugly way. Could be done with fog. Also, the skybox isn't really appropriate. This isn't a space map.
e) why are there force fields under the water?