The basic lights: arcs, colours and ranges
1The lesson in plain words
Four kinds of light, each shining over a fixed arc. Together they show other vessels what you are and which way you are heading.
When lights go on
Show your navigation lights from sunset to sunrise (Rule 20). Show them by day too in restricted visibility, such as fog or heavy rain, and whenever you think it helps. At night, show no other light that could be mistaken for them, that hides or dazzles them, or that spoils your look-out. Bright cockpit and deck lights can do all three.
Four basic lights
A masthead light is white, on the centreline, and shines forward over 225°: from right ahead to 22.5° abaft the beam (behind the line square across the boat) on each side. Sidelights are green to starboard (right when facing forward) and red to port (left), each over 112.5°, from right ahead to 22.5° abaft the beam. The sternlight is white and shines aft over 135°: 67.5° each side of right aft. An all-round light shows over 360°.
How the arcs fit
With separate masthead, side and sternlights, both sidelights show from right ahead, one from either side, and the sternlight aft of 22.5° abaft either beam. Neither sidelights nor masthead light show in that aft sector. A small motorboat may instead show an all-round white there; you will learn that option next.
How far they must show
Rule 22 sets minimum ranges in nautical miles (M). Under 12 m: masthead light 2 M, sidelights 1 M, sternlight and all-round lights 2 M. From 12 m to under 50 m: masthead light 5 M, or 3 M under 20 m, and all other lights 2 M. At 50 m or more: masthead light 6 M, all others 3 M. Lanterns must be bright enough for these ranges in clear weather.
What it means for you
A vessel of 50 m or more needs a masthead light visible for 6 M. On a boat under 12 m, sidelights need only reach 1 M. You may therefore see a large ship before she sees you. Buy lanterns made and marked for your boat’s length, keep them clean and switch them on to test before dark. Full text: /colreg/rule-21 and /colreg/rule-22.
2Key data
- Masthead light
- White, 225°: right ahead to 22.5° abaft the beam each side
- Sidelights
- Green starboard, red port; 112.5° each
- Sternlight
- White, 135°: 67.5° each side of right aft
- Under 12 m (Rule 22)
- Masthead 2 M, sidelights 1 M, sternlight and all-round 2 M
- 12 m to under 50 m
- Masthead 5 M (3 M under 20 m); all other lights 2 M
- 50 m or more
- Masthead 6 M; all other lights 3 M
3Key points
- 1
Show navigation lights from sunset to sunrise, and by day in restricted visibility.
- 2
Masthead 225°, each sidelight 112.5°, sternlight 135°, all-round 360°.
- 3
Sidelights and masthead light reach 22.5° abaft the beam; the sternlight covers the rest.
- 4
Under 12 m your sidelights need show only 1 M; a vessel of 50 m or more needs a 6 M masthead light.
4Frequent mistakes
Wrong: Navigation lights are only needed at night.
Right: Show them from sunset to sunrise and also by day in restricted visibility, such as fog or heavy rain.
Wrong: The sidelights shine all the way to the stern.
Right: Each sidelight stops 22.5° abaft the beam. With separate masthead, side and sternlights, only the sternlight shows aft of that line.
Wrong: Bright deck lights make you safer at night underway.
Right: They can hide your navigation lights and blind your look-out. Keep extra lights off or shaded.
5Practice case & exam keys
At dusk on your 9 m motorboat, a friend asks why the sidelights look weak next to the white light and whether you need brighter ones to be seen by ships.
Show the answer
Rule 22 requires only 1 M for sidelights under 12 m, against 2 M for the white masthead or all-round light. Lanterns made and marked for your length meet the rule. Keep them clean and working, but remember a ship may still see you late. Keep a good look-out and act early rather than relying on being seen.
Exam keys
- Lights: sunset to sunrise, and by day in restricted visibility (Rule 20).
- Arcs: masthead 225°, sidelight 112.5°, sternlight 135°, all-round 360° (Rule 21).
- Under 12 m: masthead 2 M, sidelights 1 M, sternlight 2 M (Rule 22).
- 12 m to under 50 m: masthead 5 M (3 M under 20 m), others 2 M; 50 m or more: 6 M and 3 M.
Finish this unit
When you've read it, match the terms, then answer three questions. Get them all right to finish the unit; opening the page alone doesn't count.
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