The determining factors that distinguish boats from ships has evolved over time. In modern times, however, a ship is usually a vessel of more than 500 tons of displacement.
Displacement tonnage is a way to measure a ship's capacity.
The number, expressed in tons, is the weight of a vessel as she floats, or the weight of the water she displaces. By a common definition, a boat is small enough to be carried by a ship. And FYI all submarines are called boats. Inc. All Rights Reserved.