Question 1

In what realistic modern scenario would an OOW actually need to fall back on celestial navigation during a passage?

Accepted Answer

A sustained loss of GNSS on an ocean passage — whether from jamming, spoofing, receiver failure, or a systemic GNSS outage — combined with being beyond reliable radar/visual range of land or charted aids, is exactly the scenario where celestial observations become a genuinely necessary, independent means of position fixing until GNSS or another aid is recovered This ties the syllabus requirement back to genuine operational relevance — celestial navigation is retained precisely because the GNSS-denial scenario, while uncommon, is realistic and has real safety consequences if no fallback method is available.

Question 2

You're preparing a passage plan for a coastal leg in a yacht drawing 3.2m. At one point the chart shows a least depth of 3.8m at chart datum. What MUST you check before finalising this leg?

Accepted Answer

The tidal height at the time of transit to confirm sufficient under-keel clearance Charted depths are referenced to chart datum (often LAT), so you must add the predicted tidal height for your transit time to get the actual depth, then compare to your draft plus a safety margin to confirm UKC.

Question 3

During your watch the ECDIS gives a "safety contour crossing" alarm. What is the correct response?

Accepted Answer

Assess the situation against the planned route and charted depths, take action to maintain safe water, and inform the Master if there is any doubt A safety contour alarm indicates the vessel may be approaching water shallower than the set safety contour. It must be investigated against the route and charted information, with avoiding action taken and the Master informed as appropriate — never simply silenced.