About tides – Tide clocks and watches

Tide clocks and watches are practical ways of indicating the state of the tide, in addition to consulting local tide tables.

Tide clocks

Most tide clocks work by using a 12 hour 25 minute cycle. Generally in the UK and Ireland they vary in accuracy between plus or minus 30 minutes over a 30-day period. Therefore it is necessary to reset them using local tide tables every month or so.

Tide watches

Some watches with a moon/tide mode require lunitidal intervals so that they can indicate high and low waters. There are two definitions for this interval, which depends on whether adjacent high waters, or the mean of high waters over a lunar month are being considered.

High water lunitidal interval
The high water lunitidal interval (or high water interval) is the time interval between the moon's transit and the next high water. The interval may be taken from the local time of moon's transit to the local time of high water, or it may be taken from the Greenwich time of the moon's transit to the standard time of high water.

Mean lunitidal interval
Also referred to as the mean high water interval, this is the mean value of all the high water intervals throughout at least a lunation of 29 days, and this is what is given below.

Lunitidal interval

The mean lunitidal intervals (mean high water intervals) are calculated using this equation:

Interval (hrs) = M₂ phase (degrees) x M₂ period (hrs) / 360 (degrees)

Use the values from the table to set the moon/tide mode of your watch. These values should be sufficient information for watches that use the lunitidal interval to indicate high and low waters. Click on the column headings to sort the values – the default order of the following list is by adjacent locations around the coast.

Please note:
If your location in the UK or Ireland is not mentioned, try using the nearest one or average between the two nearest places on either side – however, this is not guaranteed to work. Check your watch against local tide tables to confirm your setting. The usual NERC disclaimer applies to any information given.