What is the minimum visibility of a masthead light on a vessel of 15m in length?

For a vessel that is 15 meters in length, the International Regulations for Preventing Collisions at Sea (COLREGs) specify the minimum visibility distance for the masthead light. According to Rule 21, which details the visibility of lights and shapes, a power-driven vessel of less than 20 meters in length is required to exhibit a masthead light that must be visible for at least 1 nautical mile.

Given this requirement, the choice indicating a visibility of 1 nautical mile for a masthead light on a vessel of 15 meters is accurate. Larger vessels, such as those over 20 meters in length, are subject to different requirements with higher visibility distances. It's important to understand these regulations as they are designed to ensure safe navigation by allowing vessels to be seen from a distance, thus preventing collisions, especially in poor visibility conditions.