Module 14 - Passage Planning
Monitor
What you will learn
Compare position, time, depth, weather, tide, traffic, vessel and crew state with the accepted plan, then use a trigger before the safe alternative closes.
Monitoring asks whether the whole safety case still holds. Being on the route line cannot compensate for a closing gate, deteriorating crew or unusable refuge.
Monitor position and progress closely against the plan using the named primary and independent evidence, safe-water limits, depth, cross-track error, speed and ETA at critical points. Match method and frequency to risk: open water and a narrow tide-constrained approach do not justify the same interval or evidence.
Also monitor the conditions that made the passage acceptable: forecast versus observed weather, tide, visibility, traffic, equipment, usable fuel, crew alertness or seasickness, and continuing suitability of destination and alternative. One accurate position does not prove that the arrival remains inside its weather, daylight or crew margin.
Use decision points and observable triggers set during planning. If progress is late, position sources disagree, visibility deteriorates or crew capacity falls, decide while holding, returning, shortening or diverting remains feasible. After a change, update and monitor the revised plan instead of continuing to compare with the obsolete one.
| Observed change | Question | Possible trigger response |
|---|---|---|
| Position evidence conflicts | Is safe water assured and which source is independent? | Create sea room, slow or stop as appropriate, then verify |
| ETA slips | Does the gate, darkness or refuge margin still hold? | Recalculate, hold, shorten or divert |
| Weather differs | Which exposed leg or arrival assumption changes? | Reef, update, reroute or return |
| Crew capacity falls | Can critical navigation and handling roles still be covered? | Rest, redistribute, shorten or seek refuge |
| Equipment degrades | Does the remaining method retain adequate independence? | Change method, route, destination or passage |
Protect the remaining choice
At the planned decision point, ETA is 0640 for a 0700 gate. The plan required a one-hour margin, visibility is worsening and the refuge remains reachable for another 25 minutes.
1. Compare
The current 20-minute margin is 40 minutes below the accepted contingency.
2. Add conditions
Worsening visibility increases arrival workload and uncertainty rather than restoring the margin.
3. Use the trigger
Apply the briefed hold, divert or return decision while the refuge is still reachable.
4. Reset the plan
Record and brief the action, then monitor the revised route, ETA and crew state.
Sense check: Arriving before 0700 is not the same as satisfying a plan that deliberately required arrival by 0600.
Common mistake or limitation
- Monitoring only position while ignoring time, conditions, equipment and crew assumptions that can invalidate the passage.
- Waiting until a limit is crossed, even though the alternative had to be chosen earlier to remain usable.
- Editing the ETA in the log and treating that record as if it restored the lost margin.
Recap
- Monitor the complete set of accepted assumptions, not position alone.
- Match evidence and frequency to the consequences of error on each leg.
- Act at the decision point while a safer alternative remains a real choice.
Optional quick check
Section 6 of 10
ETA is before the gate, but the planned one-hour margin has fallen to 20 minutes. What is the sound interpretation?
Sources and factual review
Reviewed 2 September 2026 - Compass Revision editorial review.
Continue studying Passage Planning
This public lesson is part of Revision Module 14. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.