GearPort
Navigation light rules, and how to buy lights that meet them
Navigation lights are the one purchase on a boat where the specification is written down by somebody else. The Navigation Rules set what each light covers, how far it must be seen, and which combinations are allowed, and a fitting either meets that or it does not.
The figures below come from the US Coast Guard Navigation Rules, Rules 21 to 23. They are the arcs and ranges the rules themselves state, not a manufacturer's summary.
The four lights and what each one covers
A masthead light is a white light showing over an arc of 225 degrees, centred on straight ahead so it covers 112.5 degrees to each side. Despite the name it does not need to be on a mast.
Sidelights are red to port and green to starboard, each showing over 112.5 degrees, from straight ahead to just behind the beam on its own side. On smaller boats the pair is often combined into one fitting at the bow, sold as a combination or bi-color light.
A sternlight is white and shows over 135 degrees, centred on straight astern.
An all-round light shows white over 360 degrees. It is what you display at anchor, and on small powerboats it is also the light that can replace two others.
Read together, those arcs are how another skipper works out your heading in the dark. Red and green together means you are coming toward them. A single red means you are showing your port side. White alone means they are looking at your stern.
How far each light must be visible
For a vessel of less than 12 metres, which is under about 39 feet and covers most of what we sell lights for, the rules require: masthead light 2 nautical miles, sidelights 1 nautical mile, sternlight 2 nautical miles, all-round light 2 nautical miles.
This is why fittings are marketed as 2NM or 2-mile lights, and why that marking is worth looking for rather than guessing from how bright something appears on a bench.
Vessels of 12 metres and over face longer required ranges, and the requirements step up again with size. If your boat is over that mark, read the rules for your length rather than assuming a small-boat fitting is enough.
What a boat under 12 metres may substitute
Rule 23 allows a power-driven vessel of less than 12 metres, in place of the full masthead and sternlight arrangement, to display an all-round white light and sidelights.
That is the arrangement on a great many small boats: a combination red and green light at the bow, and a white all-round light on a pole aft, high enough to be seen right around the boat.
The pole height is not decoration. An all-round light blocked by a T-top, a bimini, a raised motor or a person standing in the cockpit is not showing 360 degrees, whatever the box said.
At anchor
A vessel at anchor displays an all-round white light where it can best be seen. This is the same fitting many small boats already carry on a pole for running at night, which is why fold-down and removable pole lights are popular.
There are size and location qualifications in the rules around anchored vessels, so if you routinely anchor a very small boat away from channels and anchorages, read Rule 30 for your situation rather than taking a general summary as the answer.
Buying and installing so it still complies in three years
Buy for the range, marked. A 2NM rating on a fitting for a boat under 12 metres is the specification, not a marketing number.
Get port and starboard the right way round. Red is port, green is starboard. It sounds impossible to get wrong and it is a genuinely common error on rebuilt boats, and it tells every other vessel the opposite of your actual heading.
Watch for lens fade. Years of ultraviolet turn red and green lenses pale. A faded lens is dimmer and no longer clearly the color the rules call for, which makes it a replacement item rather than a cosmetic one.
Check the arcs after installation, not before. Sit in the dark and walk around the boat, or have somebody else do it. Structure added since the lights were fitted is the usual reason a compliant light is no longer compliant.
Mind the sockets and connections. Nav lights live in spray. Corroded pins and a poor ground cause more failures than the lamps do, and an LED fitting that flickers is usually a connection rather than an LED.
Navigation, all-round and anchor lights
Bi-color bow lights, inset and surface-mount sidelights, fold-down and fixed all-round pole lights, and anchor lights from Lumitec, Perko, Attwood, Hella Marine and Sea-Dog.
Common questions
- What navigation lights does a boat need at night?
- A power-driven vessel under way shows sidelights, red to port and green to starboard, plus white lights covering ahead and astern. A vessel of less than 12 metres may show an all-round white light together with sidelights instead of a separate masthead light and sternlight.
- How far must boat navigation lights be visible?
- For a vessel under 12 metres the rules require the masthead light, sternlight and all-round light to be visible at 2 nautical miles and the sidelights at 1 nautical mile. Larger vessels have longer requirements.
- What arc does each navigation light cover?
- A masthead light covers 225 degrees, each sidelight covers 112.5 degrees, a sternlight covers 135 degrees, and an all-round light covers 360 degrees.
- Which side is red and which is green?
- Red marks the port side and green marks the starboard side. Fitted the wrong way round, the lights tell other vessels the opposite of the direction you are actually heading.
- What light do I show at anchor?
- An all-round white light where it can best be seen. The rules include qualifications by vessel size and location, so check Rule 30 for a very small boat anchored well away from channels and anchorages.