Question 1

In which direction do winds circulate around a Tropical Revolving Storm (TRS) in the Southern Hemisphere, and how does this affect the layout of the dangerous and navigable semicircles relative to the storm's track?

Accepted Answer

Winds circulate clockwise around the low in the Southern Hemisphere (the opposite sense to the Northern Hemisphere), so the dangerous semicircle lies to the left of the storm's direction of travel and the navigable semicircle to the right Due to the Coriolis effect, winds circulate anticlockwise around a tropical revolving storm in the Northern Hemisphere but clockwise around one in the Southern Hemisphere. This reversal also reverses the layout of the dangerous and navigable semicircles relative to the storm's track: in the Northern Hemisphere the dangerous semicircle is to the right of the track (in the direction of movement) and the navigable semicircle to the left, whereas in the Southern Hemisphere the dangerous semicircle is to the left of the track and the navigable semicircle to the right. A mariner determines which semicircle the vessel is in by observing whether the wind is backing or veering and whether the barometric pressure is falling steadily (indicating the storm is approaching or the vessel is in or near its path) — and then applies the appropriate avoiding action (bringing the wind onto a particular bow/quarter and altering course) based on the hemisphere, since applying Northern Hemisphere rules in the Southern Hemisphere would steer the vessel toward, not away from, the dangerous semicircle.

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.