How to read a Tide Table

TIDE TABLES

Tides are caused by the gravitational effect of the Moon and the Sun.  As it is possible to predict the position of both the Moon and Sun many years into the future the time and heights of the tide can also be predicted.

The UKHO (United Kingdom Hydrographic Office) are the main publishers of Tidal Data and they print four volumes of Tide Tables which cover the whole world.  They also sell the data to many other publishers such as Reeds and Imray who reprint the Tide Tables in various almanacs.

The image below shows a page of tide tables from a typical almanac.


Tide Tables example
 

 

Admiralty Tide Tables and most almanacs present the information in a similar style so if you can become familiar with this layout you should be able read any tide table.

Main features are as follows:

Name of Port at top of page, with Latitude & Longitude.

Time Zone - (UT - Universal Time = GMT - Grenwich Mean Time)         Tide times are given in the official standard time at the place (with no adjustment for any Summer Time kept).  So a Tide Table for Plymouth as above would be printed in GMT (UT).  If you looked at Tide Tables for Quebec the Time Zone would be +0500, meaning that adding 5 hours to the tabulated times would give you GMT (UT).

For each day we have date and a letter indicating a day, you then have time in the 24hr clock and a height in metres.

 

 

Tide Tables and how to read them

Spring Tides occur about every 14 days near the Full and New Moon, these are the times of highest high tides and lowest low tides.  Neap Tides occur about 7 days after Springs around the First and Last Quarter phases of the Moon.

The Range of the tide is worked out by deducting the height of a Low Water from the Height of a subsequent or Preceding High Water.

 

Effect of Barometric Pressure and Wind on Tide

Tide Tables are predictions but it is worth bearing in mind that both Barometric Pressure and Wind have an influence on both Time and Heights.

Unusually high pressure will depress heights and unusually low pressure has the reverse effect.  A difference from the average of 34mm can cause differences in height of up to 0.3m.

Strong wind will also have an effect with raised sea levels on a lee shore and lower levels on a weather shore, winds under about force 5 will have little effect.  These effects are very variable and depend on the topography of the area.