to the best of my recollection, the only way to tell a ship from a boat is to watch it make a "high" speed turn, ships lean out, boats lean in. But this is probably incorrect, just like all of my education was.
Submarines are considered "boats". The leaning thing is only about the position of the rudder in relation to the center of gravity while moving. Small boats that ride high in the water will lean into turns because the rudder is well below the center of mass. But a hydrofoil "ship" will do the same. Many small sailboats will lean out of turns too, even though they are "boats".
to the best of my recollection, the only way to tell a ship from a boat is to watch it make a "high" speed turn, ships lean out, boats lean in. But this is probably incorrect, just like all of my education was.