Module 12 - Visual Aids to Navigation
Using Lights for Navigation
What you will learn
Build a night-pilotage observation plan that predicts, identifies, monitors and safely rejects visual cues without allowing one light to become the whole navigation system.
The strongest use of lights is a sequence of expected observations with explicit decision gates. The skipper briefs what should appear, what proves identity, what trend is acceptable and what happens when the visual story breaks.
For each critical light, record the expected bearing window, sector or colour, character, period, detection range and surrounding sequence. Add the charted hazard or channel information that the light supports. This turns recognition from a memory test into an observable passage-plan control.
At first sighting, call the aid provisional. Time several complete periods and compare bearing, colour, structure and adjacent marks. Promote it to identified only when the whole description and independent position evidence agree. A bearing from one identified fixed light supplies one line; a sector boundary or leading line also remains one-dimensional evidence.
Monitor after identification. A sector colour, leading-line displacement or changing bearing can reveal cross-track trend, but the response must come from the charted geometry and brief. If an expected aid is absent, late or contradictory, slow or hold as appropriate, increase margins and use the planned fallback rather than chasing a plausible light.
Use current charts, the applicable A-Q light-list volume, weekly corrections, navigational warnings and local information. The publication is official evidence for listed aids, not permission to ignore temporary changes, unlisted local lights or the limitations of visual observation.
| Stage | Bridge question | Safe output |
|---|---|---|
| Predict | What should appear, where and by when? | Observation window and fallback gate |
| Identify | Which independent attributes agree? | Identified, provisional or not identified |
| Monitor | Is bearing/sector/alignment trend inside the brief? | Continue, correct, hold or abort |
| Challenge | What evidence conflicts or is missing? | Reopen identity and increase margin |
Run the night-approach decision loop
A light matches the expected group and period, but its bearing is eight degrees left of the planned window and the depth is shallower than predicted.
1. Reject confirmation bias
Keep the light provisional because two independent observations conflict with the planned picture.
2. Protect sea room
Use the briefed speed, hold or abort action before investigating the alternative identity or position error.
3. Rebuild the picture
Check electronic position, depth trend, neighbouring marks, warnings and both candidate lights.
Sense check: Matching rhythm cannot outweigh a material bearing and depth disagreement merely because it was the expected answer.
Common mistake or limitation
- Timing several cycles improves period measurement but is not the definitive test of identity; a different light can share a similar rhythm.
- The light list covers listed aids of navigational significance in A-Q volumes, not every temporary, local or floating light worldwide.
Recap
- Use lights as planned observations with measurable decision gates.
- Require agreement across character, bearing, structure, sequence and independent position.
- When the story breaks, protect sea room first and rebuild the navigation picture.
Optional quick check
Section 8 of 8
Rhythm and period match, but bearing and depth disagree materially with the plan. What is the correct status?
Sources and factual review
Reviewed 20 August 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.