[iCaMpWiThAWP]

Well, i never played a naval battle with ships, but i once made little islands with guns and ammo depots so i would hit the other islands with my howitzers and blow them(ammo dumps go bang)
There are a few scenarios with rivers and river gunboats, you could use the "Wide river" setting at random to get one in a generated map so you could move along them with gunboats to shoot things.