Final answer:
The principal assistant to the JOOD while underway is the Officer of the Deck (OOD). The OOD is responsible for the safe navigation and overall operation of the ship.
Step-by-step explanation:
The principal assistant to the JOOD while underway is the Officer of the Deck (OOD).
The OOD is responsible for the safe navigation and overall operation of the ship. They work closely with the JOOD to carry out the ship's mission, maintain situational awareness, and make critical decisions.
For example, if the ship encounters a potential hazard, such as another vessel or a navigational challenge, the JOOD and the OOD will collaborate to assess the situation, communicate orders to the crew, and take appropriate action to mitigate any risks or avoid a collision.