The Tidal Curve Method

Start with the relevant high-water time and height and the bracketing low-water height. Calculate range = HW height - LW height. Express the required time as hours before or after high water, then use the curve supplied for that port and exercise to read the corresponding fraction of range.

Calculate height at time = LW height + (range × curve factor). The factor describes how far the water has risen above low water for the selected point on this curve. Some port diagrams or training exercises use a different construction, so follow the published method rather than forcing every tide into a smooth curve or a rule-of-twelfths approximation.

Write units and intermediate values. Check that the answer lies between the bracketing low and high waters and that it moves in the expected direction. The result is still a prediction and needs a prudent allowance for meteorological effects and the vessel's required clearance.