A ship usually has enough size to carry its own boats, such as lifeboats, dinghies, or runabouts. A rule of thumb used 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 small enough to be carried aboard a ship in transit to distant waters (even though modern submarines could probably fit small boats aboard, tradition dictates they are always referred to as "boat"). Other types of large vessels which are traditionally called boats are the Great Lakes freighter, the riverboat, and the ferryboat. Though large 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 exact size (or the number of masts) which a boat requires to become a ship. Nautical means related to sailors, particularly customs and practices at sea. Naval is the adjective pertaining to ships, though in common usage it has come to be more particularly associated with the noun "navy."