Question 1

As Chief Officer reviewing how the day's weather developed, you note the atmosphere behaved as stable through the morning — hazy, little vertical cloud growth — but by afternoon, cumulus began forming and quickly grew into showers once the air had been lifted enough to cool to saturation. Which condition does this describe?

Accepted Answer

A conditionally unstable atmosphere — the environmental lapse rate sits between the dry and saturated adiabatic lapse rates, so the air behaves stably while unsaturated but can turn unstable once lifted far enough to cool to saturation and condensation begins releasing latent heat This is the conditionally unstable case: below the condensation level the parcel cools at the (faster) dry adiabatic rate and behaves stably against an environmental lapse rate that sits between the two adiabatic rates. Once lifted enough to saturate, it switches to the (slower) saturated adiabatic rate — the latent heat released by condensation keeps it warmer than its surroundings from that point on, so further uplift can produce rapid cloud growth even though the morning looked stable.

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.