A ship is a large vessel built to travel on water, carrying people and goods. Boats are small enough for one person to handle. Ships are big enough to need a crew.
A ship has a hull (the physical structure that floats), a deck (the working surface), holds (enclosed spaces below deck for cargo), and some means of propulsion — sails, engines, oars. The hull keeps the water out. Everything else happens inside or on top of it.
Ships need people to operate. A captain commands. A crew works. The captain’s authority is formal — it starts when they take command and ends when they are relieved. The crew is enrolled for a voyage and dissolved at the end of it. The ship persists across crews. The same ship sails with different people year after year.
Ships have legal identity. A flag state registers the ship and issues an identification number. The IMO number is assigned when the ship is built and follows it until scrapping, regardless of who owns it, who crews it, or what it is named. In admiralty law the ship is a legal person — you can sue a ship. A maritime lien attaches to the vessel itself and travels with it even if the ship is sold. Justice Story, The Brig Malek Adhel (1844): “the vessel… is treated as the offender… without any reference whatsoever to the character or conduct of the owner.”
A charter is the document that gives a ship its purpose for a voyage — where it goes, what it carries, under what terms. A ship without a charter is idle. A ship without registration is stateless. A ship without a crew cannot sail. All three — charter, flag, crew — are required for a ship to operate, but the ship exists as an entity independent of any of them. Sell it, reflag it, hire a new crew: same ship.
The word comes from Old English scip, from Proto-Germanic skipą. Every maritime culture has a word for this because ships are among the oldest complex technologies — large, expensive, dangerous objects that require coordinated human effort to build and operate. A ship is not a metaphor for an organization. It is the original case of one.