Question 1

As Master, why does atmospheric stability — not just isobar spacing and forecast wind speed — matter when you assess a forecast for an ocean passage?

Accepted Answer

Stability determines how vigorously convection develops: an unstable air mass forecast along the route signals a higher risk of squalls, thunderstorms, and sudden reductions in visibility from showers, which should influence route timing and safety margins alongside the wind/sea-state forecast, not instead of it A wind and sea-state forecast describes the large-scale pressure pattern, but stability describes what the air within that pattern will actually do vertically — whether it stays quiet or builds convective weather. An unstable air mass along the route raises the real risk of squalls, thunderstorms and sudden visibility loss that a synoptic-only forecast reading can miss, so it belongs in the Master's route-timing and margin decisions, not just the OOW's watchkeeping notes.

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.