What is a sternlight used for in boating?

A sternlight is specifically designed to be visible only from behind the vessel. Its primary purpose is to indicate the presence and orientation of the boat to other vessels approaching from the rear, thereby enhancing safety and navigation during nighttime and low-light conditions. It typically emits a white light and is positioned at the stern (rear) of the boat.

The other options refer to different types of navigation lights: lights that shine forward and to both sides are generally referred to as masthead and sidelights, which serve distinct purposes in indicating a vessel's heading and activity; a combination of masthead and sidelights refers to an arrangement used on larger vessels for greater visibility; and a sternlight does not indicate a sailing vessel. Therefore, the unique role of the sternlight is crucial for safe boating practices, particularly in preventing collisions.