Module 5 - COLREGs
Navigation Lights
What you will learn
Build a night-time vessel picture from light colour, vertical pattern and visible sectors, then use that picture as one part of the continuing collision assessment.
Navigation lights describe a vessel's type, status, approximate length and aspect. Read the whole pattern and its movement over time; a memorised colour rhyme is not a substitute for lookout, bearings and range.
An ordinary power-driven vessel underway shows a forward masthead light, sidelights and a sternlight. A vessel 50 metres or more also shows a second masthead light abaft and higher than the forward one. A power-driven vessel under 50 metres is not obliged to show that second masthead light, although Rule 23 permits it to do so.
A sailing vessel underway under sail shows sidelights and a sternlight. A vessel under 20 metres may combine those three sectors in one lantern at or near the masthead. It may instead add the optional all-round red-over-green pair, but that pair must not be shown with the combined lantern. A yacht using propelling machinery is treated as power-driven even if sails remain set.
Status patterns are read with any prescribed underway lights. Not under command is red over red; restricted in ability to manoeuvre is red-white-red; fishing other than trawling is red over white; and trawling is green over white. NUC, RAM and fishing vessels making way through the water also show sidelights and a sternlight, so the complete picture can reveal both status and aspect.
A vessel under 50 metres at anchor may show one all-round white light where it can best be seen. An aground vessel shows the anchor light or lights plus two all-round red lights vertically. Visibility, background lighting, sector cut-off and aspect can hide part of a pattern, so keep observing rather than treating one glimpse as a complete identification.
| Observed pattern | Initial interpretation | What to check next |
|---|---|---|
| Red over red | Not under command | Making way lights, aspect, range and relative movement |
| Red-white-red | Restricted in ability to manoeuvre | Nature of work, obstruction side and safe passing room |
| Red over white | Fishing other than trawling | Making way lights, gear indication and risk of collision |
| Green over white | Trawling | Making way lights, gear indication and risk of collision |
| Anchor light(s) plus red over red | Aground | Position, charted hazards and a safe passing distance |
Turn a pattern into a usable night picture
Ahead to starboard you see two all-round red lights vertically, then a green sidelight and a sternlight become visible as the bearing remains nearly steady.
1. Identify status
Red over red identifies a vessel not under command.
2. Read aspect and movement
The sidelight and sternlight show that she is making way through the water and help establish the relative aspect.
3. Assess the encounter
Retake bearings and range, choose a safe speed and apply the relevant rule; the light identity alone does not prescribe one automatic manoeuvre.
Sense check: If the answer stops at 'NUC' without considering making way, aspect or collision risk, the observation has not yet become a safe plan.
Common mistake or limitation
- Red over green is an optional addition for a sailing vessel, not a replacement for every prescribed light, and it must not be shown with the combined lantern.
- A missing or temporarily obscured light does not prove a vessel is a particular type; sector limits and viewing aspect can change the visible picture.
Recap
- Read colour, vertical order, sector and movement as one developing picture.
- Distinguish vessel status from whether it is underway or making way through the water.
- Keep assessing risk after identification; navigation lights do not create an absolute right of way.
Optional quick check
Section 9 of 9
What does red over red plus a visible sidelight and sternlight indicate?
Continue studying COLREGs
This public lesson is part of Revision Module 5. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.