How is a sailing vessel under 20 meters at anchor required to show light?

A sailing vessel under 20 meters at anchor is required to show an all-round white light and side lights. The all-round white light indicates that the vessel is at anchor and makes it visible to other vessels in the surrounding area, providing a clear signal that it is not underway. The side lights serve to denote the vessel's orientation when observed from the side, indicating its position and helping to prevent collisions.

This requirement aligns with the International Regulations for Preventing Collisions at Sea (COLREGs), where specific lighting rules are established for vessels at different lengths and under various conditions. These lights ensure safety on the water by helping other vessels understand the status and direction of the anchored vessel.