The senior person responsible for personnel assignments on a ship is usually the:

The captain of a ship holds the ultimate authority and responsibility for all operations onboard, which includes personnel assignments. This role is integral to the efficient functioning of the vessel, as the captain must ensure that the right personnel are assigned to the appropriate duties based on their skills, qualifications, and the needs of the ship. The captain's extensive training and experience enable them to make informed decisions that affect the safety and well-being of the crew and the successful operation of the ship.

While the senior officer may have significant responsibilities and the navigator and crew leader also play crucial roles within their specific areas, they typically report to the captain and do not hold the overarching authority to make comprehensive personnel assignments. The captain’s leadership is essential for coordinating all crew activities and making strategic decisions that align with the ship's mission and safety protocols.