Module 14 - Passage Planning
Monitor
What you will learn
Compare position, progress, depth, weather, tide, traffic, vessel and crew state with the plan, then act at a pre-decided trigger before options close.
Monitoring turns observations into decisions. The question is not only where the boat is, but whether the passage remains inside its safe assumptions and margins.
Monitor the vessel's position and progress closely and continuously against the plan. Use the planned primary and independent position evidence, safe-water limits, depth, cross-track error, speed and ETA at critical points. The frequency and method should match the risk: open water and a constrained approach do not justify the same interval or evidence.
Also monitor the conditions that made the plan acceptable: forecast versus observed weather, tide, visibility, traffic, equipment, usable fuel, crew fatigue or seasickness, and the continuing suitability of the destination and alternative. A single on-track position cannot compensate for a closing tidal gate, deteriorating crew or an exposed arrival that has moved outside its limit.
Use decision points and triggers written during planning. If progress is late, visibility deteriorates, independent positions disagree or the crew loses capacity, decide while waiting, turning back, shortening or diverting is still feasible. After any accepted change, update the plan, log and brief, then monitor the new plan rather than continuing to compare against the obsolete one.
| Observed change | Question | Possible trigger response |
|---|---|---|
| Position evidence conflicts | Is safe water still assured and which source is independent? | Create sea room, slow or stop as appropriate, then verify |
| ETA slips | Does the gate, daylight or refuge margin still hold? | Recalculate, hold, shorten or divert |
| Weather differs from forecast | Which exposed leg or arrival assumption changes? | Reef, update, change route or return |
| Crew capacity falls | Can critical navigation and handling roles still be performed? | Rest, redistribute, shorten or seek refuge |
| Equipment degrades | Does the remaining navigation method retain adequate independence? | Change method, route, destination or passage |
Protect the remaining choice
At a planned decision point, ETA is now 1545 for a gate that closes at 1600. The plan required 45 minutes of contingency, visibility is worsening and the alternative remains reachable for another 20 minutes.
1. Compare
The current 15-minute margin is 30 minutes below the planned contingency.
2. Add conditions
Worsening visibility increases arrival workload and uncertainty rather than restoring the missing margin.
3. Use the trigger
Apply the pre-briefed hold, divert or return decision while the alternative is still reachable.
4. Reset the plan
Record and brief the chosen action, then monitor the revised route and ETA.
Sense check: Being technically before the 1600 gate is not the same as satisfying a plan that deliberately required 45 minutes of contingency.
Common mistake or limitation
- Monitoring only position while ignoring time, weather, depth, equipment and crew assumptions that can invalidate the passage.
- Waiting for a limit to be crossed before deciding, when the safe alternative had to be chosen earlier.
- Treating a new ETA as a solution instead of checking what margin was lost and what action that loss requires.
Recap
- Monitor the complete set of plan assumptions, not position alone.
- Match the method and frequency of checks to the navigational risk.
- Act at the decision point while the safe alternative remains a real choice.
Optional quick check
Section 5 of 6
ETA is before the gate, but the planned 45-minute margin has fallen to 15 minutes. What is the sound interpretation?
Sources and factual review
Reviewed 19 August 2026 - Day Skipper Revision.
Continue studying Passage Planning
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