Sail in company with the North West Venturers

Phil Orr's Tides spreadsheet

Click here to read the usage intructions and disclaimer           Download the spreadsheet

Whilst every effort has been made to use valid source data and ensure calculations are correct, no such warranty is made. Use of the tide tables is at your own risk.

It must be understood that Standard Port predictions are approximations, and that differences used to calculate times and heights at secondary ports are averages, and precision is not possible. Actual height and time of tides are affected by barometric pressure and other weather effects.


'Tides' contains the times and heights for Holyhead, and secondary ports around Anglesey and the west coast of the Lleyn Peninsula based upon Holyhead.
The secondary port time differences are applied using interpolation between diffences for spring and neap tides, based on the time of HW and LW at Holyhead. Where only a simple average diffence is available, this has been assumed for spring and neap high and low water.
The secondary port heights are calculated by interpolating between (or extrapolating from) the appropriate mean spring and neap heights, using a factor obtained from the Holyhead mean hights and the actual tidal height, treating HW and LW separately.

Liverpool and Dover times are shown, but please be aware that these are only approximate, being based on the predicted Holyhead times with the average approximate time differences of +01:00 and +00:45 respectively

Data sources:
These Tide Tables are based upon:

- - WTides (Holyhead Standard Port predictions)
- - Reeds Nautical Almanack (Standard mean heights and ranges, Secondary Port time and mean height differences)
- - Cruising Anglesey and Adjoining Waters (other HW, LW and Slack Water differnces)

You may wish to replace the predictions, the mean heights and/or the time differences with figures of your own. The secondary port predictions will then update accordingly.

These tables must not be further distributed nor used for commercial purposes

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