What is the difference between a “Boat” and a “Ship”?
In modern parlance, a ship is a large boat. Ships are some times called boats, but boats are not called ships. The rule of thumb is that a ship is a boat that can carry another boat or boats.
Having said that, as a former crew member on a square rigged ship, I feel compelled to offer the arcane, traditional, age of sail definition: A ship is a sailing vessel with more than one mast and square rigged sails on all masts. A ship may have fore and aft sails as well, but must carry yards (Poles that hang crosswise on the mast from which the sails are hung) on all masts.
I was married aboard the Falls of Clyde, a four masted, full rigged ship.
Traditionally, submarines are boats. They don't carry their own boats the way surface ships do.
WWG1WGA
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
any craft that can be carried on another craft is a boat.