Navigation Lights

Navigation lights are governed by COLREGs Rules 20 to 31 and Annex I, which fix the arc, range, and color of each light by vessel type and length. A power-driven vessel underway shows a masthead light (white, 225-degree arc), sidelights (green to starboard, red to port, 112.5 degrees each), and a sternlight (white, 135 degrees). Required ranges scale with length: a vessel of 50 m or more shows a masthead light visible 6 nautical miles. The light pattern lets another vessel read aspect and type at night before the radar picture confirms it.