What are the ranks and hierarchy in the merchant navy?

A merchant ship is organized into departments, each with a clear internal hierarchy of rank, all operating under the overall command and legal authority of the Master, whose authority over the ship, crew and cargo is effectively absolute while at sea, particularly in an emergency, regardless of what any individual department head might otherwise prefer.

The deck department handles navigation, cargo operations, mooring and the general seaworthiness of the ship. Below the Master, the chief officer, also called chief mate, is second in command and carries direct responsibility for cargo planning and stability, deck maintenance and supervising the deck crew; the second officer is typically the navigating officer responsible for passage planning, chart correction and often medical duties; and the third officer commonly holds responsibility for safety equipment, life saving and firefighting appliance maintenance, alongside standing bridge watches like the other two. Trainee deck officers serve as cadets, and the deck ratings, an experienced bosun supervising able seamen and ordinary seamen, carry out watchkeeping, steering, lookout, mooring, cargo work and general maintenance on deck.

The engine department keeps every piece of machinery running, from the main engine to the smallest pump. It is headed by the chief engineer, with full responsibility and legal accountability for the engine department's performance and condition; the second engineer runs the day to day maintenance program and much of the practical direction of the engine room; and the third and fourth engineers serve as watchkeeping officers responsible for assigned machinery and standing engine room or control room watches, supported on many ships by an electro-technical officer responsible for electrical, electronic, automation and control systems, a role that has grown considerably in importance as ships have become more automated. Engine ratings, oilers, motormen or fitters and wipers depending on the ship and company, support maintenance and watchkeeping under the engineers, with engine cadets training alongside them.

The catering or steward's department, headed by a chief cook or chief steward, provides food and domestic services for the whole crew, and while smaller in numbers than the deck or engine departments, is essential to crew welfare on a long contract. Historically ships also carried a dedicated radio officer, but the introduction of the Global Maritime Distress and Safety System largely automated radio watchkeeping duties and folded them into the deck officers' responsibilities, so the standalone radio officer rank has mostly disappeared from modern merchant ships.

Each rank corresponds to a defined level of responsibility and, for officers, to a specific certificate of competency earned through sea time and examination under STCW, so rank on a merchant ship is not just a title but a legally recognized qualification level. This clear structure of departments, ranks and certified competence is what allows a crew, often numbering only around twenty on a modern automated ship, far fewer than ships carried decades ago, to operate a vessel safely around the clock across every ocean and time zone.