Question 1

During a night passage, the radar shows a target that is not displaying on AIS, on a steady bearing with decreasing range — a classic constant-bearing, decreasing-range (CBDR) indication. What should the OOW/Master do?

Accepted Answer

Treat CBDR as an indication of risk of collision under Rule 7 regardless of AIS status — many vessels (small craft, fishing vessels, some military/government vessels) do not transmit AIS — and take early action per Rules 8 and 19 (or the appropriate rule for the situation) to avoid a close-quarters situation AIS is a useful aid but not a substitute for radar/visual observation — Rule 7 (risk of collision) explicitly notes that radar plotting (including CBDR) should be used to determine risk, and absence from AIS does not mean absence of risk.

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.