What is the minimum visibility of a sternlight on a vessel of 20m in length?

For a vessel of 20 meters in length, the minimum visibility requirement for a sternlight, as per the COLREGs, is indeed 1 nautical mile. The regulations stipulate specific visibility ranges for different types of lights based on vessel size. For vessels less than 50 meters, such as the one in question, the sternlight must be visible at least 1 nautical mile. This is important for ensuring safe navigation and collision avoidance, as it allows other vessels to see the sternlight from a sufficient distance in order to determine the presence, position, and direction of the vessel.

In contrast, larger vessels have increased visibility requirements due to their size and the potential risks they pose to smaller craft. For example, vessels that are longer than 50 meters must have a sternlight visible for 2 nautical miles. Understanding these regulations is critical for mariners, as adherence to light visibility standards is a fundamental aspect of safe navigation in various weather conditions and times of day.