Module 12 - Visual Aids to Navigation
Why Visual Aids Matter
What you will learn
Use charted position, structure, colour, rhythm and surrounding evidence to identify an aid without treating one sighting as an exact fix.
Lights, daymarks, beacons and lit floating marks are expected observations in a pilotage plan. They help confirm where the vessel may be, but identification is strongest when several independent details agree.
Before a night or low-light approach, mark the lights, leading marks and sectors you expect to see, the sequence in which they should appear, and what you will do if an expected cue is absent or ambiguous. A light by itself is a line-of-sight observation, not proof of an exact position.
Match position and bearing first, then structure or daymark, colour, rhythmic character, period and nearby aids. Background lighting, poor visibility, an obscured sector, an unlit or unreliable aid, or a different mark on a similar bearing can make one cue misleading.
Use the current chart and applicable publications. The ADMIRALTY List of Lights and Fog Signals covers fixed lights and fog signals of navigational significance plus selected lit floating marks; it is not a claim that every temporary or local light is listed. Check corrections, warnings and local information.
Challenge an attractive night sighting
The plan predicts a white group-flashing light to starboard, but the only visible white flash lies nearly ahead and its period has not been timed.
1. Hold the identification open
Record the bearing and do not name the light from colour alone.
2. Measure the full character
Time repeated complete cycles and compare group, period and expected sector.
3. Cross-check independently
Compare depth, electronic position, adjacent marks and the planned safe limit before altering course.
Sense check: If the aid's bearing, period or surrounding sequence disagrees with the plan, the safe conclusion is 'not yet identified'.
Common mistake or limitation
- A powerful or distinctive light can still be the wrong aid when viewed on a similar bearing.
- Failure to see a light is not proof that the vessel is outside its charted range; visibility, background light, height and serviceability also matter.
Recap
- Plan what should appear and where before the approach.
- Combine bearing, structure, colour, rhythm, period and surrounding evidence.
- Keep a safe alternative when identification remains uncertain.
Optional quick check
Section 1 of 6
What is the safest response to a white flash on roughly the expected bearing before its period is confirmed?
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.