2.2 Tide tables

The tide at ports is of significant interest to mariners and data exists on the height of tide going back many years. For example, data at https://www.bodc.ac.uk gives records of the tide at Newlyn in Cornwall going back to 1915. This data enables very accurate forecasts to be made of the times of high and low water at these locations, known as ‘standard ports’. Times of high and low water for standard ports are given in tide tables.

Tide tables are easy to use, but often report times in Greenwich Mean Time (GMT). During summer, when British Summer Time (BST) is in operation, an hour needs to be added to give the correct time. Some tide tables are given with the corrections for BST already applied - so always check if you’re using an unfamiliar tide table!

First few rows of a tide table for Plymouth. The table gives times and heights of high and low water for each day. Note that times are given in GMT – one hour needs to be added to convert to British Summer Time.

Tide tables are available from many sources. I find that the most useful are:

• The National Tide and Sea Level Facility: Accurate data for all major UK ports for the next 28 days.
• Easytide: UKHO site giving predictions 7 days ahead for practically anywhere in the world.
• Visit My Harbour: An impressive array of free tide tables for the whole of the current year.

Tide tables can, of course, be purchased in printed form. They also appear in nautical almanacs that are republished each year. I find it useful to obtain a copy of Reeds Small Craft Almanac each year so that I’m not reliant on an internet connection when I’m doing tidal planning.

Find times of high and low water during the day at Plymouth on June 4th 2020. Also, find the tidal range.

Consult the tide table for Plymouth above. Note that times are given in GMT. Find the entry for June 4.

Big values of tidal height (5.6 m, 5.7 m) must refer to high water (HW). Low values (0.9, 0.9) refer to low water. So, during the day, the times are:

10:31 GMT   0.9 m Low water
16:43 GMT   5.7 m   High water

(we’re ignoring the early morning high tide and the late night low tide)

Being June, British Summer Time (BST) is in operation. To convert to BST, we must add one hour to the times given:

11:31 BST   0.9 m Low water
17:43 BST   5.7 m   High water

The tidal range is the difference in height of tide between high and low water: 5.7 - 0.9 = 4.8 m.