Navigation Lights Guide for Sailors – COLREGS 20–31

Why Navigation Lights Matter

Navigation lights are required by the International Regulations for Preventing Collisions at Sea (IRPCAS / COLREGs). They must be displayed between sunset and sunrise, and in any conditions of restricted visibility.

Lights serve three critical purposes:

Visibility — making your vessel visible to others in the dark
Identification — telling other vessels what type of craft you are (sailing, power, fishing, etc.)
Heading — showing which direction you are travelling, so other vessels can determine if there is risk of collision

The rules define minimum visibility ranges for lights based on vessel size:

Vessel length	Masthead light	Sidelights	Sternlight
Under 12m	2 NM	1 NM	2 NM
12m to under 20m	3 NM	1 NM	2 NM
20m to under 50m	5 NM	2 NM	2 NM

Navigation lights are a legal requirement, not optional. Failure to display correct lights is both dangerous and an offence. Even small dinghies must carry a torch or lantern to display in time to prevent collision.

Key concepts — tap to reveal

When must lights be shown?

Between sunset and sunrise, and in any conditions of restricted visibility

What rules govern nav lights?

IRPCAS / COLREGs (International Regulations for Preventing Collisions at Sea)

Three purposes of nav lights

1. Visibility 2. Identification (vessel type) 3. Heading (direction of travel)

Vessel under 12m — sidelight range?

1 nautical mile minimum visibility

Tap a card to flip it

All cards revealed!

Sidelights & Sternlight

The three most fundamental navigation lights are the sidelights and sternlight. Together they show other vessels which way you are heading.

Light	Colour	Sector	Arc
Port sidelight	Red	From dead ahead to 22.5° abaft the beam on the port side	112.5°
Starboard sidelight	Green	From dead ahead to 22.5° abaft the beam on the starboard side	112.5°
Sternlight	White	From dead astern, 67.5° either side	135°

Together, the three arcs cover a full 360°. Vessels under 20m may combine both sidelights into a single bicolour light (red/green) at the bow. Vessels under 7m may show an all-round white light instead of separate lights.

If you see a red light, you are looking at the vessel's port side — it is crossing from left to right. If you see green, you see its starboard — it crosses right to left. Both red and green together means it is heading towards you.

Match the light to its sector

Light

Port sidelight

Starboard sidelight

Sternlight

Masthead light

Colour & arc

Drop here

Section complete!

Masthead & All-round Lights

The masthead light (also called a steaming light) is a white light shown over the forward arc of a vessel. It is carried by power-driven vessels underway.

Light	Colour	Arc	Notes
Masthead light	White	225° (from dead ahead to 22.5° abaft beam, both sides)	Power-driven vessels only. Vessels over 50m carry two.
All-round light	Various	360°	Visible from all directions. Used for anchoring, special vessel types.

Key vessel configurations:

Power-driven vessel underway — masthead light + sidelights + sternlight
Sailing vessel underway — sidelights + sternlight (NO masthead light). May optionally show red-over-green all-round lights at the masthead.
Vessel under oars or under 7m — may show only an all-round white light, or have a torch ready
Motor-sailing — when using both sails and engine, you are a power-driven vessel and MUST show a masthead light

Sailing vessel trick: A sailing vessel may optionally display red over green all-round lights at the masthead. Memory aid: "Red over green — sailing machine." This is in addition to (not instead of) sidelights and sternlight.

Fill in the blanks

A power-driven vessel underway shows coloured ___, a white ___, and a white ___ light. A sailing vessel does NOT show a ___ light, but may optionally show ___ all-round lights.

Sidelights

Sternlight

Masthead

Red over green

Green over red

Section complete!

Special Vessel Lights

Certain vessels display additional or different lights to indicate their status or activity. These lights are typically all-round lights displayed vertically.

Vessel / Status	Lights (vertical display)	Meaning
Not Under Command (NUC)	Red over Red	Unable to manoeuvre as required by the rules (e.g. engine failure, steering broken)
Restricted in Ability to Manoeuvre (RAM)	Red, White, Red	Engaged in work that restricts ability to keep clear (e.g. dredging, laying cable)
Constrained by Draught (CBD)	Three Red (vertical)	Deep-draught vessel in a narrow channel — other vessels must keep clear
Fishing (not trawling)	Red over White	Vessel engaged in fishing with nets, lines, or gear extending >150m
Trawling	Green over White	Vessel dragging a trawl or dredge through the water
At Anchor	White all-round (fore), White all-round (aft, lower)	Vessel at anchor. Under 50m: one all-round white light is sufficient.
Aground	Anchor lights + Red over Red	Vessel is aground — shows normal anchor lights plus two red all-round lights vertically

Memory aids: "Red over Red — the captain is dead" (Not Under Command). "Red White Red — restricted in what's ahead" (RAM). "Green over White — trawling tonight."

Match the vessel type to its lights

Vessel type

Not Under Command

Restricted Ability

Trawling

Fishing (not trawling)

At Anchor

Lights

Drop here

Section complete!

Identifying Vessels at Night

At night, you build a picture of other vessels by combining the lights you can see. Here is the systematic approach:

Look for coloured lights first — red and green sidelights tell you which way the vessel is heading relative to you
Count the white lights — one white light above sidelights = power vessel (masthead). No masthead = sailing vessel.
Check for vertical coloured lights — stacked red/white/green all-round lights indicate special vessel types
Assess relative bearing — is the bearing changing? If not, you may be on a collision course

What you see and what it means:

Lights visible	What it tells you
Red + green + white (high)	Power vessel heading towards you (head-on)
Red only + white (high)	Power vessel crossing from left to right (you see its port side)
Green only + white (high)	Power vessel crossing right to left (you see its starboard side)
White only (low)	Vessel moving away from you (sternlight) — or anchored vessel
Red + green, NO masthead	Sailing vessel heading towards you
Red over red	Vessel not under command — keep clear
Red, white, red	Vessel restricted in ability to manoeuvre — keep clear

Head-on situation test: If you can see both sidelights (red AND green) of a power vessel, plus its masthead light, you are likely in a head-on situation. Both vessels should alter course to starboard.

What vessel do you see? — tap to reveal

Red + green sidelights, white masthead light above

Power-driven vessel heading towards you (head-on situation)

Red sidelight only, white masthead above

Power vessel crossing L to R — you see its port side. You are the give-way vessel.

Red + green sidelights, NO masthead

Sailing vessel heading towards you

Single white light, low

Sternlight — vessel moving away from you, or small vessel at anchor

Two red all-round lights, vertical

Not Under Command — vessel unable to manoeuvre. Keep well clear.

Green over white all-round lights

Vessel engaged in trawling

Tap a card to flip it

All cards revealed!