I don't think "The same ship is at harbour." is a good translation. The correct form is "The same ship is in harbour." or "... in the harbour."
A0lso, in English the words "harbour" and "port" do not mean the same. While harbour is just a sheltered place out of the swing of the sea a port is a haven with docks and buildings and all that. And for example in Spanish "puerto" means port, that is, you can only call a man-built haven "puerto" but not a natural harbour. Therefore I think in Italian it must be quite the same, but I'm not sure though.