The chief mate is the head of the deck department. This involves administrative tasks such as scheduling work, quality control, coordinating with other departments, and conflict resolution. The Chief Mate also compiles supply, overtime, and cost control records, and requisitions or purchases stores and equipment. Depending on the number of officers carried, he may or may not be a watch officer. If the ship carries a Second Mate and two Third Mates, he will be a dayworker, with a duty day from 0800 to 1700 ship's time. If only one Third Mate is carried, he will stand the 4 to 8 watch in addition to handling his executive duties.
The ship's other deck officers, generally a Second Mate and Third Mate, are also members of the Deck Department. Each watchstanding officer is responsible for the unlicensed crewmen on his watch.
In a four mate ship where the Chief Mate is a dayworker, the Second Mate will stand the 4 to 8 watch, because sunrise and sunset usually fall on that watch. In the days before satellite navigation systems, the Second Mate shot morning and evening star fixes to determine the ship's position. The Second Mate is also responsible for maintaining the ship's charts and navigational publications, the ship's gyrocompass, and all navigational gear. He also keeps the log extract for each voyage used by company management as a short form "howgozit" sheet, covering time at sea, time under pilotage, time in port, and types and tonnages of cargoes moved.
The two Third Mates are often called the Senior Third and the Junior Third. The Senior Third Mate stands the 12 to 4 watch, the Junior Third the 8 to 12 watch. While on duty, they are responsible for handling the ship and fixing its position by shooting sun lines, taking hourly fixes from the satellite navigation gear, and piloting the ship in coastal waters; and the Senior Third will prepare the noon position slip for the use of the Captain and Chief Engineer.
In a three mate ship, the Chief Mate stands the 4 to 8 watch; the Second Mate, the 12 to 4 watch, and the Third Mate, the 8 to 12 watch.
On a fully manned ship, each deck watch consists to two Able-Bodied Seamen and one Ordinary Seaman. The two ABs will alternate between two hour tricks on the wheel in good weather by day. At night, the ABs will divide their time between the helm station, standing lookout on the bow, and standing by in the crew mess or the crew lounge for any duties that may arise. The ordinary seaman will work as directed by the Chief Mate and the Bosun during the day in fair weather, and at night alternates between standing lookout on the bow and standing by in the crew mess or crew lounge for any duties that may arise, such as calling the next watch and making sure fresh coffee is brewed. The OS, with the permission of the Chief Mate and the watch officer, may take a trick on the wheel by day to develop the proficiency required to upgrade to AB.
In the military, the deck department comprises sailors who perform a variety of functions depending on ship type and size.
Examples include maintenance and upkeep of the ship, handling of the ship's rigging and ground tackle, coordination of underway replenishment operations, conductance of minesweeping operations, maintenance and operation of the ship's boats, supervision of diving and salvage operations (including towing), and serving as shipboard seamanship specialists. Undesignated seamen, or those who have not selected a rating (e.g. job or vocation), are normally the most junior sailors onboard and are usually sent to the Deck Department for their first assignment.