The port navigation light is a red light mounted on the port side of a vessel. IRPC regulations dictate minimum visibility, a function of brightness.
Navigation lights are obligatory. When sailing at night, the color of the navigation light visible on another vessel indicates its general heading.
The port navigation light is mounted to port such that it is visible through an angle of 112.5°, from the bow to just abaft midships. The navigation lights of ships above 50 meters in length must have a range of three miles. Between 12 and 50 meters, the light must be visible for two miles and below 12 meters, one mile.
Vessel length will determine minimum brightness and range. Vessels less than 20 meters long may carry their navigation lights in a single housing mounted along the centerline of the boat.
