Or you could be able to build the encampment in water tiles too, being able to fire both on land and sea. Granted, that's not a huge improvement, especially since you can already build encampments in coastal tiles (?) and working that way, and also the fact that it would require a rare coastal tile adjacent to land.
So I think Harbors able of firing could be ok, although i find it a little bit odd that they could shot only at water tiles.
A nice thing though would be fortresses that you could build in the middle of the ocean/coast, without requiring adjacent land. In the same maneer Petra is "creating" a rock and other similar wonders. It could even maybe be a wonder with shooting capacity ?