The interval between the time of meridian passage of the new or the full moon and the time of the following high tide. This interval which is constant for a given port is also known as the High Water Full and Change constant (HWF & C). The average interval is known as the mean high water lunitidal interval. Because the tides are governed largely by the moon, and because the time of meridian passage of the moon is later each day by about 50 minutes, it follows that, if the age of the moon and the establishment of the port are known, the approximate times of high and low water on any day may be found. If, for example, the HWF & C constant for a given port is 3 hours 45 minutes and the age of the moon is three days, the time of morning high water at the port will be approximately 0345 + (3 × 50) min. = 0615.
Subjects: Maritime History.