Back in the 1990s, I used a CAD package to regenerate the charts from a book I found in an Oxfam shop, writes PBO reader Nick Liddle.
The book may have been an early edition of The Glénans Sailing Handbook – my favourite book at the time, which I no longer have. The charts assume a sinusoidal tide and produce intermediate heights and times based on that. The user prints the charts for single use or laminates them for multiple use, and then:
■ Join the height of high water and height of low water on chart 1 with a straight line, and…
■ Join the time of high water and time of low water on chart 2 with a straight line. A percentage can then be read off at the side of a chart for any given height (chart 1) or time (chart 2).
Transfer the percentage to the other chart and, hey presto, intermediate time for any height or height at any time, without calculation, within the limits of a sinusoidal tide height/time chart.
Height markings on chart 1 represent every 10cm, and time markings on chart 2 represent every five minutes.
A top tip sent in by PBO reader Nick Liddle
Click here to download the height of high water chart
Click here to download the time of high water chart
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