Which of the following vessels has the least maneuverability?

The vessel that has the least maneuverability is the one classified as "Not Under Command." This classification refers to a vessel that is unable to maneuver as required by the Navigation Rules due to circumstances such as a loss of propulsion or steering ability. Because it cannot take required actions to avoid collisions or navigate effectively, it poses significant challenges in terms of maneuverability.

In contrast, fishing vessels, powerboats, and sailing vessels, while they can all have limitations based on their design, operational conditions, or weather, generally retain some degree of maneuverability. For instance, fishing vessels may operate with specific constraints, but they are still capable of traversal and navigation based on their fishing operations. Powerboats, due to their engine-driven nature, are typically quite maneuverable, especially at slower speeds. Sailing vessels rely on wind and may be less maneuverable in certain conditions compared to motorized vessels, but they can still make navigational adjustments.

The key distinction lies in the actual inability for the "Not Under Command" vessel to maneuver due to technical or mechanical failure, which renders it the least maneuverable compared to the others listed.