Question 385General Subjects - 1st Asst/Chief

The correct answer is A) When leaving the navigable waters of the US which is 3 nautical miles from the coast line. The transition from maneuvering watch to at-sea manning on the engine room typically occurs when the vessel departs the navigable waters of the United States, which extend 3 nautical miles from the coastline. This is the point at which the vessel is considered to have left the port area and is now operating in the open ocean, allowing the engine room to be periodically unmanned as per the vessel's classification. The other options are incorrect because they refer to different geographic boundaries (exclusive economic zone, territorial limit) or areas (emission control area) that do not directly determine the transition point for engine room manning.