Mates supervise crew members engaged in maintenance and the primary up-keep of the vessel. All mates stand watch for specified periods, usually 4 hours on and 8 hours off. The mate would assume command of the ship if the captain becomes incapacitated. When more than one mate is necessary aboard a ship, they are typically designated Chief Mate or First Mate, Second Mate, and Third Mate. Engineers or marine engineers operate, maintain, and repair propulsion engines, boilers, generators, pumps, and other machinery.
Assistant engineers stand periodic watches, overseeing the safe operation of engines and machinery.
Seamen, also called deckhands, particularly on inland waters, operate the vessel and its deck equipment under the direction of the ship's officers, and keep the non-engineering areas in good condition. They stand watch, looking out for other vessels and obstructions in the ship's path, and aids to navigation. They also steer the ship, measure water depth in shallow water, and maintain and operate deck equipment such as life boats, anchors, and cargo-handling gear. When docking or departing, they handle lines. They also perform routine maintenance chores such as repairing lines, chipping rust, and painting and cleaning decks or other areas.