Using the tide tables.
Tidal information is given in the form of tide tables listing the times and heights of High Water and Low Water for each day.
The following animation is based on the port of Dover in the UK, however the representation is standardised all over the world to help make navigation easier when moving between countries.
The animation also makes reference to obtaining tidal information from an Almanac. In many locations around the world, local navigational information and tide data are published together in an almanac providing all the key information for you to safely enter a harbour. While many other locations prefer to publish this information separately to save costs.
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​This lesson explains how to use the various tide tables found in the almanac.
There are number of tide tables throughout the almanac, each one providing tidal information for the port that the table relates to.​
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This one relates to Dover in the UK and gives the times and heights for low
water (low tide) and of high water (high tide) for the months June, July, August and September.​
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Note. This table has been cut short at the bottom and some of the days are missing to facilitate fitting the graphic on screen.​
In the highlighted box at the top of the table the time zone is given as UT (GMT) which stands for Universal Time or Greenwich Mean Time.​
The times of the high and low water in this table are based on universal time or UT. All times are given in 24 hour format and labelled UT for universal time.
Time to look at how to use the table. We can enlarge one of the days.​
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For instance we wish to find the times and heights of HW and LW on the 4th of August.​
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Find the correct month, August and the correct day which is the Tuesday the 4th.​
The dates and days are listed down the left hand side of each block of information.
​The table gives both the day and the date. This is good for a double check that the correct day and date is being used.
This is an example of what a shaded area looks like in the almanac and any times given in these areas should not have an hour added for DST.​
In the same box are the words "Add one hour in non shaded areas for DST". This refers to Daylight Saving Time.​
In the summer we put our watches and clocks forward but the tide tables are based on UT for the whole year.When the clocks go forward an hour for DST, we need to add an hour to the times
The tidal information is taken horizontally the first one being 0236 hours 2.0m.​
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In this case the first row is the Low Water (LW) time and height. The morning LW on the 4th of August is at the time of 0236 UT (or 0336 DST) and a height of 2.0m.​
The second row is the first HW of the day.​
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August 4th morning HW is at 0803 UT. height 5.5m or 0903 DST 5.5m​.
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The range is the difference between HW and LW which gives a morning range of: 5.5 - 2.0 = 3.5m.​
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The third row is the second LW of the day.​
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August 4th afternoon LW 1509 UT 1.9m or 1609 DST 1.9m​
​Midday range 5.5m - 1.9m = range 3.6m.
The final row is the afternoon HW for the day. HW 2022 UT 6.3m or 2122 DST 6.3m. The evening range 6.3 -1.9 = Range 4.4m​.
​Make sure, when using the tables, that you use the correct HW and LW for the sailing period. E.g. sailing period 1000 DST to 1200 DST.
​The correct tides to use for HW, LW and range are 0903 DST to 1609 DST.
Occasionally there is a day when a row of data appears to be missing. Look at the 1st of August on this table. This is due to the time of the tide advancing by around 40 minutes per day. This means that two HWs and two LWs take around 24 hours and 40 minutes. Logically there must be a day when the times are such that two HWs and two LWs will not fit in to one day.
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Tidal height information can be found on tidal height gauges at the entrances to some ports and marinas.