The basic lights and their arcs
- Masthead light: white, 225 degrees, from right ahead to 22.5 degrees abaft the beam on each side.
- Sidelights: green to starboard and red to port, 112.5 degrees each, from right ahead to 22.5 degrees abaft the beam.
- Sternlight: white, the remaining 135 degrees astern.
- Towing light: yellow, with the same arc as the sternlight.
- All-round light: 360 degrees.
A useful consequence: if you can see only a vessel's sternlight, you're overtaking her, because you're more than 22.5 degrees abaft her beam.
- Power-driven, 50m or more
- Restricted in ability to manoeuvre
- Constrained by draught
Minimum ranges (Rule 22)
| Vessel length | Masthead | Sidelights | Stern, towing, all-round |
|---|---|---|---|
| 50m or more | 6 miles | 3 miles | 3 miles |
| 12m to under 50m | 5 miles (3 if under 20m) | 2 miles | 2 miles |
| Under 12m | 2 miles | 1 mile | 2 miles |
Vessel by vessel
Power-driven, underway · Rule 23
Night: Masthead light, sidelights and sternlight. A second masthead light, aft and higher, if 50m or more.
Day: Nothing. Under sail and motor together, a cone point down.
Sailing, underway · Rule 25
Night: Sidelights and sternlight. Under 20m these may be combined in a masthead tricolour. Optional all-round red over green at the masthead, never with a tricolour.
Day: Nothing.
Towing · Rule 24
Night: Two masthead lights in a vertical line (three if the tow is over 200m), sidelights, sternlight, and a yellow towing light above the sternlight.
Day: A diamond on both vessels if the tow is over 200m.
Trawling · Rule 26
Night: All-round green over white, plus sidelights and sternlight when making way. Green over white, trawling at night.
Day: Two cones, points together.
Fishing, other than trawling · Rule 26
Night: All-round red over white, plus sidelights and sternlight when making way. Red over white, fishing at night.
Day: Two cones, points together, plus a cone point up towards gear extending more than 150m.
Not under command · Rule 27
Night: Two all-round reds in a vertical line, plus sidelights and sternlight when making way. Red over red, the captain is dead.
Day: Two balls.
Restricted in ability to manoeuvre · Rule 27
Night: All-round red, white, red in a vertical line, plus the normal lights when making way, or anchor lights at anchor.
Day: Ball, diamond, ball.
Constrained by draught · Rule 28
Night: Normal power-driven lights, and may add three all-round reds in a vertical line.
Day: A cylinder.
Pilot vessel on duty · Rule 29
Night: All-round white over red, plus sidelights and sternlight underway, or anchor lights at anchor. White over red, pilot ahead.
Day: Usually flag H (the rules themselves set no shape).
At anchor · Rule 30
Night: All-round white forward, and a second, lower one aft if 50m or more. Under 50m, one all-round white where it can best be seen.
Day: One ball forward.
Aground · Rule 30
Night: Anchor lights plus two all-round reds in a vertical line.
Day: Three balls in a vertical line.
Which lights mean keep clear?
Rule 18 sets the pecking order. A power-driven vessel underway keeps clear of vessels not under command, restricted in their ability to manoeuvre, engaged in fishing, and sailing. A sailing vessel keeps clear of the first three. Any vessel other than one not under command or restricted in her ability to manoeuvre should avoid impeding a vessel constrained by her draught.