Hi guys

I just bought the game and am happily playing La Serenissima. This is only slightly curbed by the fact that I cannot figurte out how to get a unit onto a ship. I have tried the "control every piece of Sea in between" thing but that doesn't seem to work either. Feeling slightly daft here :( What am i missing? I cannot rightclick a unit onto a fleet and if I tell it to go across a piece of water that i control I tells me "no can do" :(

any help appreciated.