Really... really needs more detail.
I won't repeat comments, but the fact that I've already decided I'm not going to like it simply from the screen shot doesn't bode well.
The boats look reasonable, and from experience I know how hard it is to make a convincing boat, but from the looks of things once you jump off of them there's no way back on.
Perhaps you could think of a way to link them up convincingly?
Secondly I understand how difficult it is to stop people swimming off of the map without it looking ugly, but you really need to. It looks much worse when the water carries on to infinity.
Use the height map tool create some natural-looking cliffs, perhaps.
As hero said, drop the boats down a little so that some of the hull is sitting under the water. This will make them look more convincing.
You should also use the heightmap tool with the noise brush on the sea floor to make it look more natural.
In general the map needs a really large amount of effort to look good, but I'm sure it's not beyond you. Use a little imagination and try to make the map look as plausible as possible. Always add features with the thought "How will this improve game play?" rather than "This will look really cool."
It's a mistake that a lot of inexperienced mappers make, myself included.
Hope I've helped!
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