Module 5 - COLREGs
Navigation Lights
What you will learn
Identify a vessel from the complete visible light pattern, aspect and making-way clues, then keep recognition separate from collision-avoidance judgement.
One coloured light is rarely enough. Build the whole pattern, infer aspect and movement, then return to risk and the applicable encounter rule.
A masthead light is white over 225°, sidelights are red to port and green to starboard over 112.5° each, and a sternlight is white over 135°. Their sectors create aspect clues: both sidelights with a masthead light suggest a near head-on view; one sidelight with masthead light suggests a bow-quarter view; a sternlight alone suggests the after sector.
An ordinary power-driven vessel underway displays masthead light or lights, sidelights and a sternlight. A vessel 50 metres or more shows two masthead lights, the aft one higher. A vessel under 50 metres is not obliged to show the second masthead light but may do so, so two masthead lights do not by themselves prove a vessel is at least 50 metres.
A sailing vessel under sail shows sidelights and a sternlight, subject to permitted alternatives. If machinery propels it, it is power-driven and shows power-driven lights. Status patterns such as NUC red-red, RAM red-white-red, fishing red-white and trawling green-white must be combined with sidelights and sternlight when making way as prescribed. Recognition starts—not finishes—the risk assessment.
Read the complete visible pattern and aspect; a single green light does not identify the whole encounter.
Move from pattern to safe inference
At night you see red over red with a green sidelight below, but no sternlight from your present aspect.
1. Name the status
Red over red indicates a vessel not under command.
2. Add movement and aspect
The green sidelight shows she is making way and you see her starboard side or bow quarter.
3. Return to risk
Use repeated bearings, range and applicable rules; the status signal does not state safe passing distance.
Sense check: A correct mnemonic without aspect, movement or range trend is recognition practice, not yet a collision plan.
Common mistake or limitation
- Two masthead lights can be shown by a power-driven vessel under 50 metres as well as being required at 50 metres or more.
- Status lights do not replace sidelights and sternlight when the Rule requires them for a vessel making way.
Recap
- Build identification from complete visible sectors, not one isolated colour.
- An under-50-metre power-driven vessel may display a second masthead light.
- Use status, aspect and making-way clues to inform—never replace—the risk decision.
Optional quick check
Section 10 of 12
Red over red with a green sidelight visible below most strongly indicates which observation?
Sources and factual review
Reviewed 2 September 2026 - Coastal Skipper Revision.
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.