What is the visibility arc of a stern white light?

• A. Dead ahead to 90 degrees on either side.
• B. 360° around the horizon.
• C. Dead astern to 67.5 degrees on either side, total 135°.
• D. Visible 180° behind the vessel.

Answer: (C)

The concept tested is how a stern white light is visible relative to the vessel’s rear. The stern light is placed at the back and is intended to be seen from directly behind and out to the rear quarters. It has an arc of visibility from dead astern to 67.5 degrees on either side, totaling 135 degrees. This specific coverage lets other vessels behind or to the rear quarters detect the vessel and gauge its heading, without the light appearing forward of the beam and risking confusion with forward navigation lights. Options that describe a full 360° arc, or a frontward or purely rearward 180° arc, don’t match the regulatory stern-light visibility.