Lights and shapes tell other vessels what you are, how big you are and what you are doing. This first part sets out the core definitions and the standard configuration for power-driven vessels.
Rule 20 - Application
This Part's rules apply in all weathers. Lights are shown from sunset to sunrise, and during that time no other lights are shown that could be mistaken for those prescribed, impair their visibility, or interfere with a proper look-out. Lights may also be shown in restricted visibility by day, and in any other circumstance deemed necessary. Shapes are complied with by day.
Rule 21 - Definitions
- Masthead light: a white light over the fore-and-aft centreline, showing an unbroken arc of 225 degrees, fixed to show from right ahead to 22.5 degrees abaft the beam on either side.
- Sidelights: green to starboard, red to port, each showing an unbroken arc of 112.5 degrees, from right ahead to 22.5 degrees abaft the beam on its own side. In vessels under 20 metres, they may be combined in one lantern on the centreline.
- Sternlight: a white light as near the stern as practicable, showing an unbroken arc of 135 degrees, 67.5 degrees from right aft on each side.
- Towing light: a yellow light with the same characteristics as the sternlight.
- All-round light: a light showing an unbroken arc of 360 degrees.
- Flashing light: a light flashing at 120 or more flashes per minute.
Rule 22 - Visibility of lights
- Vessels 50 metres or more in length: masthead light 6 miles; sidelight 3 miles; towing light 3 miles; white/red/green/yellow all-round light 3 miles.
- Vessels 12 to under 50 metres: masthead light 5 miles (3 miles if under 20 metres); sidelight 2 miles; sternlight 2 miles; towing light 2 miles; all-round light 2 miles.
- Vessels under 12 metres: masthead light 2 miles; sidelight 1 mile; towing light 2 miles; all-round light 2 miles.
- Inconspicuous, partly submerged vessels or objects under tow: white all-round light, 3 miles.
Rule 23 - Power-driven vessels underway
A power-driven vessel underway shall exhibit: a masthead light forward; a second masthead light abaft of and higher than the first (not obligatory under 50 metres, but permitted); sidelights; a sternlight. An air-cushion vessel in non-displacement mode adds an all-round flashing yellow light. A power-driven vessel under 12 metres may instead show an all-round white light and sidelights; one under 7 metres with a maximum speed under 7 knots may show a single all-round white light alone, adding sidelights if practicable. On vessels under 12 metres, the masthead/all-round light may be off-centre if centreline fitting is impracticable, provided the sidelights are combined and carried as close as possible to the same line.
These four rules are the "alphabet" of the lighting system - every following rule "spells out" a vessel type using it.
