ship

Usually a ship has enough size to carry its own boats, such as lifeboats, dinghies, or runabouts. A rule of thumb is "a boat can fit on a ship, but a ship can't fit on a boat". Consequently submarines are referred to as "boats", because early submarines were little enough to be carried aboard a ship in transit to distant waters. Other types of big vessels which are traditionally called boats are the Great Lakes freighter, the riverboat, and the ferryboat. Though big enough to carry their own boats and/or heavy cargoes, these examples are designed for operation on inland or protected coastal waters. Often local law and regulation will define the correct size (or the number of masts) which a boat requires to become a ship. Nautical meaning is related to sailors, particularly customs and practices at sea. Naval is the adjective pertaining to ships, step by step in common usage it has come to be more particularly associated with the noun "navy".