You see a single white light. What could it be?

• A. Stern light of a SV of PDV
• B. Vessel <50m at anchor
• C. PDV less than 7m and not capable of 7kts
• D. Sailing vessel under 7m

Answer: (B)

A single white light at night is the telltale sign of an anchored vessel. When a vessel is at anchor, it shows a white light visible in all directions to mark its position and prevent collisions. If the vessel is smaller (less than about 50 meters), this white light is typically the only navigation light you’ll see. Larger anchored vessels may display more than one white light, but the absence of red or green sidelight colors and a forward masthead/galley-type arrangement strongly suggests the vessel is stationary rather than underway.

The other options imply lights that would normally appear in combination with others if the vessel were moving or under specific conditions (for example, stern lights or green/red sidelines associated with underway power or sailing). So, seeing just a single white light most consistently points to a vessel at anchor, especially a smaller one.