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 became 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. Marine or ship 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.
They stand watch, looking out for other vessels and obstructions in the ship's path and navigational aids such as buoys and lighthouses. They also steer the ship, measure water depth in shallow water, and maintain and operate deck equipment such as lifeboats, 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. Seamen may also load and unload cargo, if necessary.