The distinction between a ship and a boat varies depending on regional definitions, but as a general rule, a boat can fit onto a ship. A ship, in other words, is a very large ocean-going vessel, while a boat tends to be much smaller. Additionally, a ship usually is defined as having a displacement larger than 500 tons. During the age of sailing, a craft with three or more rigged masts was considered to be a ship, but this definition has been superseded, as different methods of power generation are used on modern ships.
Watercraft that we typically associate with the category of “ship” include cruise ships, container ships, aircraft carriers, destroyers, tall ships, and frigates. All of these ships are extremely large, and designed to endure potentially long ocean voyages. Traditionally, they required a very large crew of skilled sailors to manage them, although some, especially container ships, are growing increasingly easier to run with only a small crew. This is thanks to the development of sophisticated computer systems and improved mechanization, among other things. They are also capable of carrying a large volume of cargo, people, or a combination of both.
Submarines are technically classified as boats, because early submarines could be hoisted on board a ship. Several specially outfitted submarine rescue ships are also capable of lifting and towing distressed modern submarines, although they cannot lift them on board. More typical examples of of boats include powerboats, rowboats, canoes, kayaks, umiaks, catamarans, and tugboats. They tend to be easier to maneuver than ships, but they are not capable of carrying nearly as much cargo. Boats are also not equipped for long voyage, and some will not fare well on the open ocean.
A ship requires a crew of people to run smoothly, while a boat can often be handled by one person alone. The system of authority on board the larger vessel is also very clear-cut, with crew members organized into ranks. When a boat is large enough to have a crew, the members of the crew often work together under the captain in a much more casual fashion. Ships also usually carry boats on board, in the form of life rafts and rescue boats. These smaller watercraft are also sometimes used to ferry people and supplies between the vessel and the shore, since very large ships cannot fit into some harbors, due to their draft or inability to fit under a bridge.