2.3 Predicting high and low water

We saw in the last section how to use a tide table.

First few rows of a tide table for Plymouth.

Such detailed data is not available everywhere that we would wish to paddle. To overcome this problem, reference books quote tidal constants for other locations. These are either added or subtracted to times of high and low water at standard ports to give local high and low water times. For example, this extract from a paddling guidebook tells us when HW and LW will occur at a location in the Isles of Scilly.

Extract from the excellent Pesda Press (https://www.pesdapress.com) guidebook to South West England. Notice that it tells us that high water at St. Mary’s will occur 55 minutes before high water at Plymouth.

Find times of high and low water at St. Mary’s during the day on June 1st 2020.

Using the tide table, we can find the times of high and low water at Plymouth - ignoring the high water in early morning, and the low water late at night and remembering to add an hour for British Summer Time:

08:28 BST High water Plymouth
14:43 BST Low water Plymouth

We are told that HW and LW occur 55 minutes earlier than they do at Plymouth. Subtracting 55 minutes from the Plymouth times gives:

07:33 BST   HW ST MARYS
13:48 BST   LW ST MARYS