Ships are generally larger than boats, but there is no universally accepted distinction between the two. Ships generally can remain at sea for longer periods of time than boats.
 A legal definition of ship from
case law is a vessel that carries goods by sea.
 A common notion is that a ship can carry a boat, but not vice versa.
 A US Navy rule of thumb is that ships heel towards the outside of a sharp turn, whereas boats heel towards the inside
 because of the relative location of the
center of mass versus the
center of buoyancy.
 American and British 19th Century maritime law distinguished "vessels" from other craft; ships and boats fall in one legal category, whereas open boats and rafts are not considered vessels.
Age of Sail, a
full-rigged ship was a sailing vessel with at least three square-rigged masts and a full
bowsprit; other types of vessel were also defined by their
A number of large vessels are usually referred to as boats.
Submarines are a prime example.
 Other types of large vessel which are traditionally called boats are
Great Lakes freighters,
 Though large enough to carry their own boats and heavy cargoes, these vessels are designed for operation on inland or protected coastal waters.
In most maritime traditions ships have
individual names, and modern ships may belong to a
ship class often named after its first ship. In the northern parts of Europe and America a ship is traditionally referred to with a female
grammatical gender, represented in English with the
pronoun "she", even if named after a man. This is not universal usage and some journalistic
style guides advise using "it" as referring to ships with female pronouns can be seen as offensive and outdated.
 In many documents the ship name is introduced with a
ship prefix being an abbreviation of the ship class, for example "MS" (motor ship) or "SV" (sailing vessel), making it easier to distinguish a ship name from other individual names in a text.