Yeah, I think that's right. You must have a clear route with no hostile ships and you have to leave from a port province but you don't have to land in one. Of course, this means if you get into trouble your troops have to survive for a minimum of four turns in control of the captured province (ie. until you can build a port) before you can get them out by sea again!
I'm pretty sure the 'deep' sea areas become navigable after 1172(?) when compasses become available, for ship types that are stated as 'deep water/ocean-going/whatever' on their profiles. It takes a while anyway. Caravels can do it, I know that.
Bookmarks