Question 1

In IALA Region A (which includes UK waters), what colour and shape typically indicates a port-hand lateral mark, and on which side should it be passed when proceeding in the "conventional direction of buoyage"?

Accepted Answer

Red, can/cylindrical shape (or red light), passed on the port (left) side of the vessel when proceeding in the conventional direction of buoyage IALA Region A (UK, Europe, most of Africa/Asia) uses red can/cylindrical port-hand marks, kept to port (on your left) when proceeding in the conventional direction of buoyage (generally the direction of the main flood stream, or as charted) — Region B (e.g. Americas) reverses the colour scheme.

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.