Module 12 - Visual Aids to Navigation
Lighthouses and Other Structures
What you will learn
Distinguish fixed, floating and paired aids and state the position evidence and failure modes each can contribute to Yachtmaster pilotage.
Structure and daymark help recognition, but different aids carry different positional limits. A lighthouse can be obscured or altered, a floating aid can move or be off station, and an aligned pair supplies one line rather than a fix.
Major fixed lights may be recognised by charted structure, daymark, light character, elevation and sometimes a fog signal. A fixed structure is useful bearing evidence once positively identified, but obscuration, background lighting, sector limits, equipment failure or an outdated publication can still make it unavailable or misleading.
Beacons are fixed and may be lit or unlit. Light vessels and other lit floating marks occupy charted stations but can move within their moorings or be reported off station. Never transfer the surveyed precision of a fixed charted object to a floating aid without checking its condition and role.
Leading marks are a front and rear pair arranged on a charted alignment. When the marks are in transit they provide one leading line or line of position. They can guide an approach within the charted limits, but another independent observation is required to determine distance along the line or create a two-dimensional fix.
| Aid | Useful evidence | Boundary |
|---|---|---|
| Fixed lighthouse or beacon | Bearing, structure, daymark and character | May be obscured, altered or unserviceable |
| Lit floating mark | Mark type, local channel/hazard cue and approximate station | Can swing, drift or be off station |
| Leading pair | One charted alignment/line of position | Needs another observation for distance or a fix |
Resolve a fixed-versus-floating ambiguity
At dawn, a flashing white light and pale structure appear on the expected side, but the bearing is closer to a charted lit buoy than to the lighthouse in the brief.
1. Compare structure and motion
From a safe situation, use binoculars and repeated observations to distinguish fixed structure from a moving mark.
2. Time the character
Compare the complete rhythm and period for both candidates, not the colour alone.
3. Protect the position margin
Do not use either as a fixed point until bearing, structure, character and surrounding evidence agree.
Sense check: A familiar-looking object on the wrong bearing is evidence against the identification, not a reason to adjust the chart mentally.
Common mistake or limitation
- A lit buoy is not a fixed surveyed structure and may not occupy the centre of its charted symbol at the observation instant.
- A leading line controls cross-track position only; it does not give distance along the line or guarantee depth outside the charted plan.
Recap
- Separate fixed structures, floating aids and paired leading marks.
- State the line, bearing or approximate-station evidence each supplies.
- Keep movement, serviceability and single-line limits explicit in the pilotage brief.
Optional quick check
Section 5 of 10
What does a correctly identified pair of leading marks provide when exactly aligned?
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.