Question 1

You are the OOW on a yacht approaching a busy anchorage at night. The echo sounder shows decreasing depth faster than the chart suggests for your plotted position. What is the most appropriate immediate action?

Accepted Answer

Reduce speed, stop or alter course away from danger as necessary, and re-check your position using all available means (GPS, visual fixes, radar) before proceeding A discrepancy between the echo sounder and the charted depth is a classic early warning sign of either a charting error, a positioning error, or an uncharted hazard, and has been a contributing factor in numerous yacht groundings. The correct response prioritises immediate safety — reducing speed and gaining sea room — over continuing on a plan that may no longer be valid, followed by a thorough position check using independent methods.

Question 2

When taking a visual position fix using two compass bearings of charted objects, why is a third bearing often taken if a suitable object is available?

Accepted Answer

Two bearings give a position at their intersection, but a third bearing forms a small triangle ("cocked hat") where the three position lines meet — the size of this triangle gives a visual indication of the likely accuracy of the fix and any compass error, helping the navigator judge how much to trust the result A two-bearing fix gives a single intersection point with no indication of error; a third bearing reveals a "cocked hat" whose size is a practical, visual guide to the fix's reliability.

Question 3

Using the "rule of twelfths" to estimate the height of tide between low water and high water, what fraction of the total tidal range is gained during the first hour after low water?

Accepted Answer

1/12 of the range The rule of twelfths approximates the rise/fall over each hour of a (roughly) 6-hour tide as 1, 2, 3, 3, 2, 1 twelfths — so the first hour accounts for 1/12 of the total range, the slowest rate of change near the turn of the tide.