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In many parts of the world the tides approximate to a semi-diurnal sine curve, that is there are two high- and two low- tides per day. As an estimate then each period equates to 1 hour, with the tide rising by 1, 2, 3, 3, 2, finally 1 twelfths of its total range in each hour, from low tide to high tide in about 6 hours, then the tide is ...
Tide tables, sometimes called tide charts, are used for tidal prediction and show the daily times and levels of high and low tides, usually for a particular location. [1] Tide heights at intermediate times (between high and low water) can be approximated by using the rule of twelfths or more accurately calculated by using a published tidal ...
For instance the chart for 3 hours after high water is valid from HW+2½ to HW+3½, not from HW+3 to HW+4. [2] Tidal atlases may provide additional information for areas such as estuaries where it important to calculate tides away from the ports. Such information may include co-tidal range information [3] and time differences. [4]
The largest annual tidal range can be expected around the time of the equinox if it coincides with a spring tide. Spring tides occur at the second and fourth (last) quarters of the lunar phases . By contrast, during neap tides , when the Moon and Sun's gravitational force vectors act in quadrature (making a right angle to the Earth's orbit ...
Tidal flow timings and velocities appear in tide charts or a tidal stream atlas. Tide charts come in sets. Each chart covers a single hour between one high water and another (they ignore the leftover 24 minutes) and show the average tidal flow for that hour. An arrow on the tidal chart indicates the direction and the average flow speed (usually ...
Tide range is the vertical distance between the highest high tide and lowest low tide. The size of the lunar tide compared to the solar tide (which comes once every 12 hours) is generally about 2 to 1, but the actual proportion along any particular shore depends on the location, orientation, and shape of the local bay or estuary.
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A Standard port is a port whose tidal predictions are directly given in the Tide tables. [1] Tide predictions for standard ports are based on continuous observation of tide over a period of at least one year. These predictions are given in feet or meters, with respect to the chart datum for average meteorological conditions. [2]