Which of the following vessels is considered "underway" under the Rules?

Answer: B — vessel drifting with the engine off

A vessel is considered "underway" when it is not at anchor, made fast to the shore, or aground. Being "underway" typically means that the vessel is in motion or is capable of being in motion. In this case, the vessel drifting with the engine off still meets the criteria for being underway because it is not anchored, docked, or moored, even though it may not be actively navigating. Anchored vessels are stationary and, therefore, not considered underway. A vessel at dock is secured and also not underway. Similarly, a vessel that is moored is tied to a dock or another vessel and is not capable of independent movement, thereby classifying it as not underway.