Module 12 - Visual Aids to Navigation
Why Visual Aids Matter
What you will learn
Classify an observed aid as identified, provisional or not identified by combining its expected bearing, structure, colour, rhythm, period and independent position evidence.
At Yachtmaster level, a light is not a destination and one attractive match is not a fix. Visual aids are planned observations whose identity must survive cross-checks before they control a close-water decision.
Before a night or low-light approach, predict the order, approximate bearings and charted characters of the lights, sectors, leading marks and lit buoys that should appear. Add a safe limit for each critical cue: what the skipper will do if it is late, absent, obscured or inconsistent with the plan.
Build identification in layers. First check whether the aid lies near the expected bearing and position. Then compare structure or daymark, colour, rhythmic character and full period. Finally compare depth, electronic position, adjacent aids and the sequence already observed. Agreement across independent evidence supports identification; one approximate match remains provisional.
The ADMIRALTY List of Lights and Fog Signals provides official information for more than 90,000 fixed light structures of navigational significance and selected lit floating marks in 15 regional volumes A-Q. It does not claim that every local, temporary or floating light is listed, and weekly corrections, navigational warnings and local information remain part of the passage plan.
| Evidence | What it can support | What it cannot prove alone |
|---|---|---|
| Bearing and sequence | The aid is where the plan predicts | Its identity or the vessel's exact position |
| Colour, rhythm and period | A match to the charted character | That a similar light is not being observed |
| Depth and electronic position | An independent position consistency check | That the visual aid is serviceable or correctly identified |
Keep an attractive sighting provisional
The approach brief predicts a white group-flashing light on the starboard bow. A white flash appears nearly ahead, but the period has not been timed and the preceding buoy was not seen.
1. Hold the name open
Record the bearing and call the light provisional rather than changing the plan to fit it.
2. Measure the complete character
Count the group and time several full periods from the same recognisable point.
3. Cross-check the sequence
Compare depth, electronic position, adjacent marks and the missed buoy before any close-water alteration.
Sense check: If naming the light requires ignoring a missing cue or a bearing mismatch, it is not positively identified.
Common mistake or limitation
- Brightness and colour are weak identifiers on their own; background lighting, haze and another aid on a similar bearing can create a persuasive false match.
- Not seeing an expected light is not a position line. Visibility, geographical range, background contrast, obstruction, serviceability or an error in the vessel's assumed position may explain the absence.
Recap
- Predict the observation and the safe limit before relying on it.
- Require several matching attributes plus independent position evidence.
- Treat an unresolved aid as not yet identified and keep the fallback active.
Optional quick check
Section 1 of 10
A white group-flashing light is near the predicted bearing, but its period and the preceding buoy are unconfirmed. What is the defensible call?
Sources and factual review
Reviewed 2 September 2026 - Compass Revision editorial review.
Continue studying Visual Aids to Navigation
This public lesson is part of Revision Module 12. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.