what is a ship

A ship is a large watercraft that travels the worlds oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished from boats based on size, shape, load capacity, and purpose. They have supported exploration, trade, warfare, migration, colonization, and science. Ships are typically larger than boats and can remain at sea for longer periods of time. There is no universally accepted distinction between ships and boats, but a common notion is that a ship can carry a boat, but not vice versa. Ships are likely to have a full-time crew assigned to them. The term "ship" is generally applied to vessels of more than 500 tons of displacement, and submersible ships are generally called boats regardless of their size. The measurements of ships are given in terms of length, breadth, and depth. The length between perpendiculars is the distance on the summer (maximum) load waterline, from the forward side of the stem at the extreme forward part of the vessel to the after side of the rudder post at the extreme rear, or to the center of the rudder stock, if there is no rudder post. The beam is the greatest breadth of the ship, and the depth is measured at the middle of the length, from the top of the keel to the top of the deck beam at the side of the uppermost continuous deck.