A second mate (2nd Mate) or second officer (2/O) is a licensed member of the deck department of a merchant ship holding a Second Mates Certificate of Competency, which is issued by the administration[clarification needed]. The second mate is the third in command (or on some ocean liners fourth) and a watchkeeping officer, customarily the ship's navigator. Other duties vary, but the second mate is often the medical officer and in charge of maintaining distress signaling equipment. On oil tankers, the second mate usually assists the chief mate with the cargo operations.
The navigator's role focuses on creating the ship's passage plans. A passage plan is a comprehensive, step by step description of how the voyage is to proceed from berth to berth or one port to another. The plan includes undocking, departure, the en route portion of a voyage, approach, and mooring at the destination.
