BASED ON AN ARTICLE By Tim Murphy
Knowing how to read a tide table can mean the difference between a good day and a bad one.
If you've ever waited anxiously for the twing of your antenna against the underside of a highway bridge, you know that playing with tides can be a game of inches. To pass safely under that bridge or over the bar that lies between here and home, we need to understand all the components of the tides. Along most of the coast, tides rise twice and fall twice each day. These are called semidiurnal tides. In some places, the tides cycle only once per day; these are called diurnal tides. And in still other places, one daily high tide is much higher than the day's second high tide; these are called mixed tides. Tide tables, provided by the U.S. National Oceanic and Atmospheric Administration (NOAA) at tidesandcurrents.noaa.gov, tell you three important things for any given place: the time of high tide, the time of low tide, and the heights of each. But what about the times in between? For that, you'll need the Rule of Twelfths (see chart ).