Advanced Scenario Check: Tides

A yacht is approaching a fictional harbour after a machinery delay. The plan uses a direct digital secondary-port prediction of 2.4 m at 0815. A harbour gauge panel copied into both navigation apps shows 2.1 m, but its datum is not displayed and the timestamp is twelve minutes old. The echo-sounder trend is 0.4 m shallower than the passage plan expected, and the cross-stream measured from track error is stronger than the atlas estimate.

Do not average the 2.4 m prediction and the 2.1 m display. The first is a modelled value; the second is not comparable until station, datum, timestamp, variable and quality are verified. The shallower depth trend and stronger cross-stream are operational observations that challenge the plan even though they do not by themselves diagnose one cause.

Keep the entrance gate closed and preserve the briefed holding or diversion option. Assign one person to the con, one to helm and lookout as the vessel requires, and one to rebuild the navigation picture. Confirm the electronic data paths, obtain current authoritative harbour or gauge information if available, recheck tide, depth, stream, squat and clearance assumptions, and compare the result with a route that retains sea room.

Reopen only when the revised calculation, applicable observation and independent navigation evidence agree with the minimum clearance, time window and fallback. If the discrepancy remains at the last safe point, hold, divert or abandon the approach. Harbour permission or pressure to berth does not replace the missing tidal and position evidence.