ship v. boat

Boats are small, open watercraft that can be operated by one person or a small crew. Boats are used primarily on rivers or lakes, or close to the coast. Motorboats, rowboats, canoes, kayaks, rafts, catamarans, and tugboats are classified as boats.

Ships are larger vessels found in deeper water or the open ocean, and usually require a considerable crew. Some categories of ships include cruise ships, frigates, container ships, and aircraft carriers. A boat might be carried aboard a ship, but a ship would never fit on a boat.

The Straight Dope on ship v. boat

wiseGEEK on ship v. boat