What is the civilian equivalent of the Commanding Officer on a merchant vessel?

The civilian equivalent of the Commanding Officer on a merchant vessel is referred to as the Master. The Master is ultimately responsible for the ship's safety, navigation, and overall management, much like a military commanding officer oversees their vessel and crew. This role encompasses all aspects of ship operations, including compliance with maritime regulations, the welfare of the crew, and the security of the cargo.

In this context, the Chief Engineer, Ship's Doctor, and Chief Mate hold important responsibilities on the vessel but do not possess the level of authority and overall command that the Master does. The Chief Engineer is responsible for the engineering and machinery aspects of the ship, the Ship's Doctor provides medical care, and the Chief Mate assists the Master in the overall operation of the ship, often overseeing the deck department. However, none of these positions equate to the comprehensive command that defines the Master’s role.