Tides and Currents Tide times Times of HW and LW are found in “tide tables”. You should know how to read tide tables and find the times of high and low water for your normal boating area.
Tides The gravitational pull of the moon and to a lesser extent, the sun, on the seas and oceans of the earth, causes tides. This pull causes the water of the sea at any particular place to get deeper or shallower in a definite rhythm. The rising tide is called the “flood” tide and the falling tide is called the “ebb” tide.
Tidal currents As well as the rise and fall of the level of the sea due to the tides, there are also horizontal movements called “Tidal streams”. In some places these streams or currents can be quite strong. Strong currents can cause overfalls in some places. You should learn about Tidal currents in your own area and know which way they run at different stages of the tide. The flood stream, when the tide is rising, is usually in the opposite direction to the ebb stream, when the tide is falling.
The time taken by the tide to flood and to ebb varies in different places but around the Irish Coast the average is about 6.25 hours each way. This means about 12.5 hours between two high waters (HW) and 12.5 hours between two low waters (LW). Spring and Neap TIDES At the times of full moon and new moon the high tides are higher and the low tides are lower than average. These are called “Spring tides”. When the moon is at first or third quarter the high tides are not so high and the low tides are not so low. These are called “Neap tides”. Spring tides occur every fortnight. Neap tides also occur at fortnightly intervals between Spring tides.
Effect of wind Wind blowing over the water causes waves; the stronger the wind, the bigger the waves. Wind blowing against the tide can cause bigger and breaking waves, sometimes dangerous for small boats. Find out about local currents in your Troop’s boating area, and what problems may be caused by a change of direction of tide or wind.
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