Below is a brief description of various positions on a typical - larger vessel. This is given as an overall view there may be more or less people depending on the type of vessel and companies.......
Master (Captain) - In command of vessel and all of its departments, in most cases a pencil pushing job doing the payroll, ships paperwork, only on bridge for entry and departure of ports and to check on navigational watches. Almost always a day worker.
Chief Mate - Directly supervises Bosun, 2nd and 3rd Mates during all deck evolutions (cargo/maintenance/repairs/drills), on most ships also stands a navigation watch. Traditionally the Chief Mate was a day worker, but more recently a watch standee as more and more positions are eliminated from ships he has been made into a watch standee.
Second Mate - Responsible for all aspects navigation (voyage planning, chart/publication correction, navigation equipment maintenance, and recently added GMDSS Communications responsibilities as well) while at sea, in charge of cargo watch while in port for the safe and efficient transfer of cargo. Usually a watch standee.
Third Mate - Responsible for all safety inspections, usually designated as medical officer, maintains navigation watch while at sea, in charge of cargo watch while in port. Usually a watch standee.
Deck Cadet - A student from one of the Maritime Academies doing a sea apprenticeship to become a Third Mate. Entry Level
Bosun / Boatswain - Highest unlicensed rating that supervises all A/B's during deck maintenance and repair. Usually a day worker.
Able Bodied Seaman (A/B) / Leading Seaman / Quartermaster - While on navigation watch under the supervision of the mate on watch, responsible for keeping a lookout (for other vessels, land masses, etc.) and steering the vessel in and out of port. Deck maintenance primarily include chipping rust, painting, lubricating fittings, cleaning various areas, and splicing line. Usually a watch standee.
Ordinary Seaman (O/S) - Same as A/B with no steering, and heavier concentration on cleaning. If a vessel carries O/S's they are usually watch standees. Entry Level
Chief Engineer - In charge of the Engine Department, responsible for most paperwork, ordering, maintaining spare parts inventory, and directly supervises critical engine repairs. Almost always a day worker.
1st Assistant Engineer - Is in charge of all engine room repairs and maintenance. Maintains overtime records. Can either be a watch standee or day worker for the same reasons as a Chief Mate.
2nd Assistant Engineer - Maintains an engine room watch and is responsible for the smooth operation of all engine room system. Also performs system checks on engine room systems. Usually a watch standee
3rd Assistant Engineer - Maintains an engine room watch and is responsible for the smooth operation of all engine room system. Usually a watch standee
4th Assistant Engineer - Maintains an engine room watch and is responsible for the smooth operation of all engine room system. Usually a watch standee
Engine Cadet - A student from one of the Maritime Academies doing a sea apprenticeship to become a Third Assistant Engineer. Entry Level
Electrician - Responsible for anything on ship's electrical system. Usually a day worker.
Mechanic - Responsible for the taking apart of machinery and their repairs, usually under the supervision of the day engineer. Normally the most senior rating.
DEMAC / QMED / Motorman - Make Rounds in Engine Room and report to Engineer on watch, assist as directed. Can either be a watch standee or day worker.
Oiler / UJE (Unlicensed Jr. Engineer) - Make rounds, clean, assist as directed. Usually a watch standee. Can either be a watch standee or day worker.
Wiper - Responsible for cleaning various engine spaces, and to assist as directed. Can either be a watch standee or day worker. Entry Level
Chief Steward/Baker - In charge of steward department, creates daily menus, orders and stock sufficient amounts of food for voyage, cooks, bakes, and prepares food.
Chief Cook - Cooks, bakes and prepare food.
Assistant Cook - Cooks, bakes and prepare food.
GSU/BR (General Steward Utility/Bedroom) - Responsible for cleaning officer's staterooms, and also cleaning of galley areas around meal hours. Entry Level.