Which light(s) is/are required to be shown by a dredge at night to indicate the passing side of an obstruction?

A dredge is a vessel that often operates in areas where it can present a hazard to navigation due to its ongoing operations. To ensure the safety of other vessels traveling in the vicinity, the dredge displays specific lights to indicate its presence and the safest side to pass.

The correct answer involves two green lights positioned vertically. According to the U.S. Coast Guard Rules, a dredge operating at night must show these green lights to indicate the side where other vessels should navigate to avoid obstruction or danger. When these lights are displayed, they signal that this is the clear path for passing, helping to enhance maritime safety.

In contrast, a red light or white light does not provide the same indication for passing. A single red light would signify another type of navigational hazard, while a white light is more often used to indicate general vessel activity or the presence of a vessel at anchor. Therefore, showing two green lights is the standard requirement for dredges at night to guide navigation clearly.