I'm not an expert when it comes to "boats", but on my web site you will find a list of the 20 largest cruise ships: Visit http://english.ruderhaus.de/ and choose one of the three "TOP 20 Cruise Ships" lists (by gross tonnage, length or passenger capacity).
Well, when I hear "boat" I think "submarine," as my Dad was working at Electric Boat when I was born. Obviously, most people mean motorboat. is it like nails on a blackboard to me? No. I think as long as you know what what the poster is referring to you are all set.
Yes, it is like nails on a chalk board. Many, Many, post on this site use the term "boat" when they are talking about a certain ship. Sorry, its my pet peeve, just as you have yours. Hope you have fun on the NCL Spirit.
I was invited to the Captain's table on the Adventure in February and someone at the table used the expression "boat" when asking the Captain a question about his SHIP. He was cool with it, but I did detect a smerk on his face.