Question 1

During your oral exam you are asked: what is meant by the term "parallel indexing" and how is it used during coastal navigation?

Accepted Answer

Parallel indexing is a technique using radar to maintain a planned track by monitoring the range and bearing of a fixed object (such as a headland or charted feature) relative to a parallel line drawn on the display offset from the planned course line, allowing the navigator to continuously monitor cross-track error without relying solely on position fixing Parallel indexing provides a continuous, real-time indication of whether the vessel is maintaining its intended track relative to a charted feature, which is particularly valuable in situations where GPS may be degraded or where an additional independent check on position is desirable, such as transiting a narrow channel. It is a fundamental radar navigation technique that predates GPS and remains relevant precisely because it provides a method of monitoring track that is independent of satellite-based positioning, supporting the principle of using multiple independent methods to verify position.

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.