Navigation Lights, Explained
At night, a vessel can't wave at you — it talks entirely through its lights. Learn to read them and you can tell, at a glance, what a vessel is, roughly how big it is, and what it's doing. Here's the plain-English guide every watchkeeper needs.
The lights a power-driven vessel shows
Start with a standard power-driven vessel underway. It carries a masthead (steaming) light — a white light over the bow; sidelights — red on port and green on starboard; and a sternlight — white, facing aft. Larger vessels carry a second, higher masthead light aft of the first, which helps you judge their size and heading.
The arcs: who sees which light
Each light only shows over a fixed arc, and those arcs are the key to reading a vessel's aspect — which way it's pointing relative to you:
- Masthead light: white, 225° — covers the bow and round to just abaft the beam on each side.
- Sidelights: 112.5° each — from dead ahead to just abaft the beam on their own side. See green and you're looking at her starboard side; see red and you're seeing her port side.
- Sternlight: white, 135° — covers the arc across the stern.
- All-round light: 360° — visible from every direction, used for anchor lights and many special signals.
Add the sidelights and sternlight together (112.5 + 112.5 + 135) and you get the full 360° — which is why the combination tells you exactly how a vessel is oriented.
All-round light combinations
Vessels that are restricted in some way add vertical all-round lights to say so. A few of the common ones: two red lights in a line mean not under command; red-white-red means restricted in ability to manoeuvre; three red lights mean constrained by draught; and a single all-round white light is a vessel at anchor.
The rhymes that make it stick
Generations of crew have learned the trickier combinations with mnemonics — and they genuinely work in the moment:
How to read a vessel in the dark
Put it together in order: first work out what she is from the lights, then what she's doing and which way she's heading, then what that means for you under the rules. That's the exact thinking the COLREGs are built on — and the exact thing examiners test. Go deeper in our plain-English COLREGs guide, and see how lights come up in the OOW oral exam.
Drill the lights by ear — free
The full Collision Regulations, including the lights and shapes, read aloud and free to download. Perfect for learning them on repeat.
Download freeMake the rules second nature
COLREGs Explained unpacks the lights, shapes and signals in plain language and shows you how to apply them — ideal for OOW candidates.
Get COLREGs ExplainedFrequently asked questions
What are the navigation lights on a boat?
A standard power-driven vessel shows a white masthead (steaming) light over the bow, a red sidelight on port and a green sidelight on starboard, and a white sternlight facing aft.
What are the arcs of navigation lights?
The masthead light shows over 225 degrees, each sidelight over 112.5 degrees, and the sternlight over 135 degrees. An all-round light shows over the full 360 degrees.
What does red over white mean at sea?
Red over white means a vessel engaged in fishing — remembered by the rhyme 'red over white, fishing at night'. Green over white is a trawler, and white over red is a pilot vessel.
Which side is the red navigation light on?
The red sidelight is on the port (left) side and the green sidelight is on the starboard (right) side. If you see a vessel's green light you are looking at her starboard side.
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This article is general guidance for aspiring and serving yacht crew. Qualification rules change — always confirm current requirements with the MCA (MSN 1858) and an approved training provider before committing time or money.