Module 12 - Visual Aids to Navigation
Advanced Scenario: Visual Aids
What you will learn
Manage a compound night approach in which a floating light, sector cue, depth and shared electronic position no longer form one reliable navigation picture.
This fictional scenario rehearses evidence control under pressure. It cannot prescribe a course, speed or passing side for a live vessel and does not demonstrate practical Yachtmaster competence.
A yacht is approaching a fictional harbour at night as rain reduces visibility. The plan expects an east cardinal mark followed by a white sector. An intermittent group of three white flashes appears near the predicted bearing, but repeated timing has not established either charted Q(3) 10s or VQ(3) 5s. The white sector is not visible, depth is two metres shallower than the stage model, and the chartplotter and tablet repeat the same GNSS position and chart data.
Do not convert partial agreement into a route instruction. A group of three white flashes is consistent with an east cardinal character, but the incomplete period, missing sector, unexpected depth and common-source displays leave the aid and vessel position unresolved. The mark may be obscured, off station or misidentified; the yacht may also be somewhere other than the electronic picture suggests.
Preserve the briefed open-water option before troubleshooting consumes it. Keep one person conning, one on helm and one maintaining the outside lookout. Review safe speed and engines as the vessel and conditions require, use properly adjusted radar if fitted and operational, and record the light's bearing, complete timing attempts, depth trend and every source dependency.
Reopen the approach only when a repeated light character, current chart and warning status, depth, radar or physical geometry and independent position evidence form a coherent picture with a controllable escape. If that standard is not met at the last safe point, hold, divert or abandon the approach. Port permission or a desired track cannot replace the missing navigation evidence.
Worked example
Give the first five-part command response before the yacht reaches the entrance commitment point.
- 1Decision: keep the entrance gate closed and preserve the open-water hold or abort route.
- 2Control: maintain the con, helm and proper lookout; review safe speed and collision risk for the actual visibility and traffic.
- 3Measure: record several complete light periods from the same repeat point, bearing each attempt and rejecting partial groups hidden by rain or background light.
- 4Corroborate: compare depth, radar, known physical geometry and a position source that does not merely repeat the same GNSS and chart path.
- 5Trigger: reopen only after the aid and vessel position are coherently supported; otherwise hold, divert or abandon at the briefed limit.
Sense check: The response first protects time, sea room and collision awareness. Steering towards the assumed safe side while still naming the mark would spend the margin needed to resolve the error.
| Conflict | What may explain it | Safe response |
|---|---|---|
| Partial triple-white rhythm | Rain, background light, wrong aid or incomplete observation | Measure complete cycles and keep the identity provisional |
| Expected sector not visible | Bearing, range, visibility, obstruction, outage or position error | Do not treat absence as a line; cross-check the whole picture |
| Two displays agree | Shared GNSS, power, chart or configuration | Count the shared displays as one source and seek independent evidence |
| Depth two metres shallower than expected | Position, tide, datum, offset or seabed assumption | Protect clearance and the abort route before diagnosis |
Brief evidence and ownership
The crew ask whether the triple white flashes are enough to continue while rain repeatedly hides part of the sequence.
1. Lookout
Report the observed flashes, eclipses, colour and bearing without naming the aid prematurely; continue the wider traffic lookout.
2. Navigator
Time complete repeat cycles, trace chart and position dependencies, and compare depth, radar and current publications.
3. Helm
Maintain the named safe command and repeat any ordered change; do not steer towards a presumed sector or cardinal side without confirmation.
4. Skipper
State whether the gate is closed, what evidence would reopen it and the exact point at which the approach will be held or abandoned.
Sense check: Separating observation from interpretation makes it easier for another crew member to challenge a false identification before it becomes a helm order.
Common mistake or limitation
- Three visible flashes do not establish the complete cardinal character or its period when rain may have hidden part of the sequence.
- A floating mark can support navigation but should not be treated as an exact fixed position when other evidence conflicts.
- Port permission addresses traffic movement; it does not identify the aid or certify the route as safe for this yacht.
- This scenario cannot supply the live Rule 19, speed or manoeuvring decision; those depend on the actual traffic, vessel and conditions.
Recap
- Protect the open-water option before resolving the identity conflict.
- Record observation separately from interpretation.
- Challenge shared electronic sources with depth, radar and physical evidence.
- Reopen the approach only when the aid, position and escape picture agree.
Optional quick check
Section 10 of 10
A partial triple-white light, missing sector, shallow depth and two shared-source displays conflict near the entrance. What should open the gate?
Sources and factual review
Reviewed 2 September 2026 - Compass Revision editorial review.
Continue studying Visual Aids to Navigation
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