raystuttgart
Civ4Col Modder
Why not simply add a slot for frigates and ships of the line? And if no slots are available then ... tough luck !
The problem is if your city is far away it will seem un-natural to have units appearing !
Or something totally different.
(Which I think is probably even better.)
If pirates would get a leader, the players could get "Bukaneers" in a DLL-Diplo-Event.
(Similar to Native Mercenaries ...)