What is the appropriate light configuration for a sailing vessel under sail at night?

The appropriate light configuration for a sailing vessel under sail at night includes having a red and green sidelights, as well as a white sternlight. This arrangement allows for clear visibility and identification by other vessels during nighttime navigation. The red light indicates the port side, while the green light signals the starboard side. The addition of the white sternlight helps to communicate the vessel's direction of movement and provides visibility from behind.

This configuration is integral to the International Regulations for Preventing Collisions at Sea (COLREGs), which ensure that all vessels can interpret each other's lights and take necessary actions to avoid collisions. Proper lighting not only aids in navigation but also enhances safety on the water, ensuring that both the sailing vessel and others in the vicinity are aware of its presence and orientation.