When is a vessel required to display sidelights?

A vessel is required to display sidelights when navigating at night, which is essential for ensuring visibility and safety on the water. Sidelights consist of a green light on the starboard side and a red light on the port side, which help other vessels determine the direction a vessel is facing and its intended movement. This is crucial for preventing collisions in low visibility conditions.

Displaying sidelights during the night allows mariners to assess the position and heading of other vessels, contributing to safe navigation. Vessel operators must understand that the use of sidelights is specifically mandated by maritime regulations to enhance situational awareness for all vessels operating after sunset and before sunrise, which is why this option is correct.

In contrast, when a vessel is at anchor or in a harbor, it does not necessarily need to display sidelights; other lighting requirements apply. Similarly, vessels engaged in fishing may have different lighting requirements based on their activity and the time of day. Understanding these nuances helps mariners comply with regulations and maintain safety on the water.