They also perform maintenance chores such as repairing lines, chipping rust, and painting and cleaning decks and other areas. Seamen may also load and unload cargo. On vessels handling liquid cargo, they hook up hoses, operate pumps, and clean tanks. Deckhands on tugboats or tow vessels tie barges together into tow units, inspect them periodically, and break them apart when the destination is reached. Larger vessels have a boatswain or head seaman.
Marine oilers work below decks under the direction of the ship's engineers.
They lubricate gears, shafts, bearings, and other moving parts of engines and motors, read pressure and temperature gauges and record data, and may repair and adjust machinery. A typical deep sea merchant ship has a captain, three deck officers or mates, a chief engineer and three assistant engineers, plus six or more seamen and oilers. Depending on their size, vessels operating in harbors, rivers, or along the coast may have a crew comprising only of a captain and one deckhand, or as many as a captain, a mate or pilot, an engineer, and seven or eight seamen. Large vessels also have a full-time cook and helper, while on small ones, a seaman does the cooking. Merchant mariners also have an electrician, machinery mechanics, and a radio officer.