If a vessel is over 50 meters in length, how many mast lights must it display while underway?

For vessels that are over 50 meters in length, the regulations specify that they must display two masthead lights when underway. This requirement is designed to enhance the visibility and recognition of larger vessels, ensuring they are easily identified by other vessels on the water, especially in poor visibility conditions or during night operations. The two masthead lights are typically positioned vertically, which helps to indicate the size of the vessel as well as its orientation and direction of travel.

The presence of two mast lights differentiates larger vessels from smaller ones, which may only require a single mast light. This distinction is critical for navigational safety, as it allows other mariners to assess the size, type and course of a vessel more accurately, reducing the risk of collisions and improving overall situational awareness on the water.