Module 14 - Passage Planning

Advanced Scenario Check: Gate Failure and Easier Divert

What you will learn

Combine a failed arrival gate, increasing wind against tide, crew fatigue and a closing fallback margin into one timely diversion brief.

A skipper does not earn safety by proving the original plan nearly worked. The defensible decision closes the failed route while the easier option still has margin, then gives the crew a plan they can execute and monitor.

At 0830 in this fictional exercise, the yacht has made 8.0 NM in two hours and now has 16.0 NM remaining to an entrance that must be reached by 1130. The wind is increasing against the stream, one experienced crew member has not slept, and the observed speed made good is 4.0 kn. The easier harbour is 7.5 NM away, is expected to make 5.0 kn on its route and has a fictional latest controlled-entry time of 1030.

Separate the evidence. The gate time and exercise distances are fixed inputs; 4.0 kn is monitored progress; 5.0 kn towards the fallback is an estimate; the wind and crew state increase workload and uncertainty. None of those facts can be repaired by keeping the original planned speed in the passage card.

Test the destination: 16.0 NM at 4.0 kn takes four hours, giving 1230 — one hour after the 1130 gate before any manoeuvring or contingency. The destination plan is closed on the monitored case.

Test the fallback: 7.5 NM at 5.0 kn takes one hour thirty minutes, giving 1000 and only thirty minutes before its fictional 1030 limit. Waiting until 0900 would consume that entire nominal margin before allowing for speed error, entry or manoeuvring. The easier decision exists now, not indefinitely.

Brief the divert, immediate course and sail plan, navigation and lookout roles, support for the unrested crew member, the next position and weather review, plus the condition for further change. Record why the destination closed and the calculations used. This lesson rehearses written judgement; it is not a live route, harbour or weather recommendation.

Worked example

At 0830, compare the original destination and easier harbour using the stated fictional distances, speeds and gate times.

1Destination time: 16.0 NM ÷ 4.0 kn = 4 hours.
2Destination arrival: 0830 + 4 hours = 1230, which is 60 minutes after the 1130 gate.
3Fallback time: 7.5 NM ÷ 5.0 kn = 1.5 hours.
4Fallback arrival: 0830 + 1 hour 30 minutes = 1000, leaving 30 minutes before the fictional 1030 limit.
5A 30-minute delay would move that estimate to 1030 and consume the nominal fallback margin. Divert now, then keep checking speed, conditions and entry evidence.

Sense check: The destination is not marginal: it misses the gate by one hour. The fallback calculation shows a shrinking opportunity, not a guaranteed safe arrival.

Advanced Scenario Check: Gate Failure and Easier Divert
Evidence	What it establishes	What it does not establish
8.0 NM in 2 h	4.0 kn monitored progress for the completed period	A guaranteed speed for either remaining route
16.0 NM at 4.0 kn	1230 monitored arrival, 60 minutes after the 1130 gate	Permission to ignore manoeuvring and contingency
7.5 NM at estimated 5.0 kn	1000 fallback estimate, 30 minutes before its fictional limit	Guaranteed harbour access or shelter
Wind and failed rest	Growing workload and uncertainty that must enter the decision	One universal yacht response without route and vessel context

Give the crew a change-control brief

The crew still believe the destination is the objective and do not yet know that its gate has failed.

1. Facts and uncertainty
State the 0830 position evidence, 4.0 kn monitored progress, both calculations, wind against tide and crew-rest limitation; label the fallback speed as an estimate.
2. Decision and action
Close the destination, name the easier harbour, give the immediate course and sail or engine action, and protect sea room while the turn is made.
3. People
Assign helm, lookout and navigation, support the unrested crew member and name when the skipper must be called.
4. Monitor and record
Record the reason and revised plan, set the next timed position and conditions review, and state the trigger for a further hold or alternative.

Sense check: Every crew member should be able to repeat the destination, immediate action, their role and the next review point.

Common mistake or limitation

Continuing because the destination is only sixteen miles away, without converting distance into a monitored arrival time.
Waiting for certainty even though waiting consumes the fallback's entire nominal margin.
Treating the 5.0-knot fallback estimate as a promise rather than monitoring it with an entry limit and another trigger.
Announcing a new destination without assigning immediate actions, crew roles, a record and the next review point.

Recap

Recalculate from monitored progress; do not defend the original speed model after it fails.
Compare the fallback before waiting consumes its decision margin.
Close the failed route explicitly and make the amended route the crew's working plan.
Brief action, roles, record, review and the next change trigger.

Optional quick check

Section 12 of 12

At 0830, the destination calculation gives 1230 for an 1130 gate; the fallback gives 1000 for a fictional 1030 limit. What is the defensible decision?

Sources and factual review

Reviewed 2 September 2026 - Compass Revision editorial review.

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