Deciding what’s a boat and what’s a ship may be easy for those who own a boat (or a ship), but for the rest of us there is a confusing number of definitions to be found online. Size, purpose, sail configuration, and other criteria all seem to play a role, leaving me wondering if Tommy the Tugboat grows up to become Tommy the Tugship.
I found these three definitions the most helpful, and think of them as Logical, Technical and Practical:
Logical You can put a boat on a ship but you can’t put a ship on a boat (or if a ship sinks, you get in a boat, but if a boat sinks, you get in the water).
Technical A boat leans into a turn, while a ship leans out.
Practical The function of a boat happens on its deck. The function of a ship happens inside it.
Just to confuse things, a submarine is always a boat, despite having the characteristics of a ship, and a Viking vessel is usually referred to as a longship, though it fits the description of a boat.
Seaway freighters are easily identifiable as ships, though afficionados might try to classify them as lakers or salties.