A watercraft is any vessel that is designed to travel through water. This category will include boats, ships, personal watercraft (PWC), canoes, and so on. The term is a broad definition, while the individual types of craft serve a more specific definition; a ship, for example, is a large vessel that is prepared for use on the ocean, while a boat is a smaller craft intended for use on still water, oceans, or other bodies of water. Boats are small enough to fit on a ship.
The smallest watercraft category is the PWC, which may include jet skis and waverunners, or any other type of vessel intended for use by one person. A PWC is usually powered by an engine, and rather than sitting inside the vessel as in a boat, a person will stand or sit on top of the PWC. Local or regional laws may address the proper use and ownership of a personal watercraft, and safety procedures must be taken when using a PWC. Life vests should be used at all times when riding on a PWC, and a person should be familiar with proper operation of the craft.
Ships are the largest category of watercraft, and perhaps one of the broadest. Large, ocean-going vessels may be propelled through a variety of means: some are wind-driven with sails, while others are propeller-driven with different types of engines turning the propeller. The purposes of these ships can vary significantly as well: some are cargo ships designed for hauling goods over long distances, while others are for recreation, such as cruise ships. Military vessels include aircraft carriers, battleships, and so on. It may be difficult to tell the difference between a ship and a boat, and in some cases it is impossible, though in some regions of the world, laws will dictate the difference between the two as well as the activities that are approved for each type of watercraft.
Submarines are perhaps the most difficult watercraft to categorize. Small, early models were called boats because of their size, while larger, nuclear-powered subs are large enough to be classified as ships. The definitive label can vary by country or region, and laws do exist to regulate the use of such vessels. Submarines can float on the water and they can operate while submerged beneath the water; the vessel is entirely enclosed, with all passengers and crew working within the ship.