Navigation lights: how to identify vessels at night

COLREG navigation lights use prescribed combinations of colour, position and arc of visibility. Read together, they help you work out which way another vessel is facing (her aspect) and what kind of vessel she is, or what she is doing, at night.

Recognising lights is one input. On its own it does not tell you whether a risk of collision exists or what action to take; that still depends on the rules that apply, the circumstances and a proper lookout by all available means.

What the basic lights tell you

Sidelights: Red to port, green to starboard. Each shows from dead ahead to 22.5° abaft the beam (112.5°). (Rule 21(b))
Sternlight: White, at the stern. Shows over 135°, 67.5° either side of right aft. (Rule 21(c))
Masthead light: White, on the centreline. Shows over 225°, from dead ahead to 22.5° abaft the beam each side. (Rule 21(a))
All-round lights: Show over 360°. Combinations, often in a vertical line, signal status or activity. (Rule 21(e))

Diagram showing the horizontal visibility arcs of a 225-degree masthead light, 112.5-degree port and starboard sidelights, and a 135-degree sternlight. — Horizontal arcs of visibility for the basic navigation lights.

Lights are shown from sunset to sunrise and, if carried, in restricted visibility during daylight (Rule 20).

Read the pattern, not a single light

A single light rarely tells the whole story. A repeatable sequence helps:

Note every light you can see, its colour and its position relative to the others.
Use sidelights and masthead lights to judge aspect: which side, or end, faces you.
Look for all-round lights in a vertical line that signal status or activity.
Match the whole combination to a vessel category, then check it again as the picture changes.

Common vessel categories to recognise

These are summaries of common patterns, not a complete statement of each rule. Size thresholds and exceptions apply.

Power-driven vessel underway

Look for: Masthead light + sidelights + sternlight.
Important: 50 metres or more: a second masthead light, abaft of and higher than the forward one. Under 50 metres may show one.
COLREG reference: Rule 23(a)

Sailing vessel underway (under sail alone)

Look for

Sidelights + sternlight. No masthead light.

Optional: red over green all-round lights at or near the top of the mast. Under 20 metres, the sidelights and sternlight may instead be combined in one lantern at or near the masthead.

Important

Red over green must not be shown together with the combined lantern.
Under sail and also propelled by machinery = a power-driven vessel. She shows power-driven lights, not sailing lights. By day: a cone, apex downwards, forward where it can best be seen (Rule 25(e)).

COLREG reference

Rule 3(c); Rule 25(a), (b), (c) and (e)

Vessel engaged in fishing

Look for

Trawling: green over white.

Fishing other than trawling: red over white.

Both are all-round lights. Making way through the water: add sidelights + sternlight.

Important

Trawler 50 metres or more: also a masthead light, abaft of and higher than the green light. Under 50 metres may show one.
Fishing other than trawling, with outlying gear extending more than 150 metres horizontally: an all-round white light (by day, a cone apex upwards) in the direction of the gear.
Summary only. See the rule for full detail.

COLREG reference

Rule 26(b)(i)–(iii) and 26(c)(i)–(iii)

Vessel not under command (NUC)

Look for

Red over red (all-round, in a vertical line).

Making way through the water: add sidelights + sternlight.

COLREG reference

Rule 27(a)

Vessel restricted in her ability to manoeuvre (RAM)

Look for

Red-white-red (all-round, in a vertical line).

Making way through the water: add masthead light(s), sidelights + sternlight.

COLREG reference

Rule 27(b)

Pilot vessel on duty

Look for

White over red (all-round, at or near the masthead).

Underway: add sidelights + sternlight. At anchor: add anchor lights.

COLREG reference

Rule 29(a)

Vessel at anchor

Look for: All-round white forward + a second, lower all-round white at or near the stern.
Important: Under 50 metres: may show a single all-round white light where it can best be seen.
COLREG reference: Rule 30(a) and 30(b)

Vessel aground

Look for

Anchor lights + red over red (all-round, in a vertical line).

The red lights are shown where they can best be seen.

Important

Under 12 metres: not required to show the additional aground lights or shapes.

COLREG reference

Rule 30(d) and 30(f)

StandOn revision card illustration of a vessel at night showing masthead lights, red-white-red all-round lights and sidelights. — Advanced recognition example: a power-driven vessel towing with a tow over 200 m, also restricted in her ability to manoeuvre (RAM).

What navigation lights do not tell you on their own

Whether a risk of collision exists. That needs bearings, ranges and observation over time.
Exactly what the other vessel intends to do next.
Which vessel should give way, without considering the rules that apply to the situation.
Everything about a vessel when lights are obscured, confused by background lighting or not shown correctly.

By day, many of the same statuses are shown with day shapes.

Practise recognition from memory

Reading a light pattern once is not the same as recognising it quickly in the dark. StandOn Practice asks you to identify light combinations from memory, again and again over time, so weak areas show up early.

Navigation Lights is live in beta in StandOn. See the live question bank.

A revision reference, not a substitute for training

This page is a revision reference, not a complete guide to the COLREGs. It does not replace recognised training, official material, professional instruction or practical experience.

StandOn is an independent sailing revision platform and is not affiliated with or endorsed by the Royal Yachting Association.