Frequently Asked Questions
- What are Spring and Neap Tides?
Spring tides occur approximately twice a month when the range between low and high tide is at its maximum. They occur around the times of a Full Moon and New Moon when the Sun, Moon and Earth form a line known as ‘syzygy’. When this happens, the tidal forces exerted by the Sun reinforce the tidal forces exerted by the Moon to produce a welling up of the tidal waters, or a ‘spring’.
Neap tides occur when the range between low and high tide is at its least. Again, these occur approximately twice a month. A neap tide occurs around the times when the Sun and Moon are at right angles to the Earth; this results in the gravitational pull on the Earth’s water being weakened as it comes from two different directions. There is approximately 7 days between a spring and a neap tide.
- How reliable is your tide data?
We publish data that has been generated by the United Kingdom Hydrographic Office, a world leader in the supply of digital hydrographic information.
- Why do some days have five tides and others only three?
In general, most locations will have two high and two low tides in any one 24 hour period. However, the actual tidal period is a little more than 24 hours (24 hours and 50 minutes), with each tidal event occurring just over every six hours. In situations where the first high or low tide occurs close to 6am, the third tidal event will take place just after midnight of the same day. These situations usually occur in March when the clocks are adjusted at the start of British Summer Time, resulting in a 23 hour day. Conversely, when the clocks go back in October at the end of British Summer Time, the resultant 25 hour day means that 5 tides are possible within one day.
- What do the Heights represent at each Tide Time?
These numbers are the tidal heights, or water heights that are reached at each high and low tide. For example, if the height at high tide is 5.00m, this is the highest predicted height that the high tide water level will reach over Chart Datum. In simple terms, this can be regarded as the lowest predicted water level for the whole of the UK and Ireland. For a more detailed explanation, read on.
Chart Datum is a tidal level that is defined so low that the actual tide level will rarely fall below this point. It is the level to which all tidal levels and predictions are measured, and is the same as the zero of the tidal predictions. In other words, Chart Datum approximates to the Lowest Astronomical Tide, or the lowest level that can be predicted to occur under average meteorological conditions and under any combination of astrological conditions.