Question 1

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 2

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.

Question 3

You need to enter a marina at a time when the tidal height will give you only 0.4m clearance under the keel at the shallowest point of the approach. The owner wants to arrive earlier than this. What should you do?

Accepted Answer

Advise the Master/owner of the calculated clearance and the risk, and recommend delaying arrival until sufficient rise of tide gives an adequate safety margin A 0.4m margin is minimal and leaves no room for error (swell, draft changes, chart datum inaccuracies). The OOW's duty is to communicate the navigational risk clearly so the Master/owner can make an informed decision — commercial pressure should never override a safety recommendation.

Navigation Practice Questions