When sidelights are out on a vessel less than 39.4 feet, what light serves as the anchor light?

In vessels that are less than 39.4 feet, when sidelights are out, the all-around white light serves as the anchor light. The purpose of the all-around white light is to provide visibility from all angles, which is essential for safety when a vessel is anchored. This light signals to other vessels that the boat is not underway and helps prevent collisions.

Sidelights, which are typically green and red, indicate the sides of the vessel while underway. If these lights are malfunctioning, relying on the all-around white light ensures that the vessel remains visible to others nearby, maintaining safety. The all-around white light is also used in various situations, including at anchor, providing a clear indication of a vessel's position even in low visibility conditions.

The masthead light is primarily for when the vessel is underway and doesn't serve the same purpose as an anchor light. The stern light provides indication of the vessel's rear position but is not sufficient when at anchor. A deck light is typically used for illumination on the working or living areas of the deck and is not intended for signaling purposes to other vessels. Thus, the all-around white light is the correct choice in this scenario.