To calculate the fall of the tide for 02:45 UTC we now use the “Rule of Twelfths”.

First we have to calculate the time.

02:45 UTC minus 00:45 UTC gives us 2 hours.

As we already know, in the first hour the tide will fall 1/12 of its range, which is 0.33 meters.

For the second hour the tide will fall 2/12 of its range, which is 0.66 meters.

The total fall for the tide in two hours is 0.33 plus 0.66 meters,

which equals 0.99 meters.

Now we can calculate the height of the tide for 02:45 UTC.

Height of the tide for 02:45 UTC is 4.0 meters minus the fall of the tide

– 0.99 meters – equaling 3.01 meters.

The final step is to add the height of the tide to the charted depth on the chart.