A tidal atlas or a tidal stream atlas is used to predict the direction and speed of
tidal currents.
A tidal atlas usually consists of a set of 12 or 13 diagrams, one for each hour of the tidal cycle, for a coastal region. Each diagram uses arrows to indicate the direction of the flow at that time. The speed of the flow may be indicated by numbers on each arrow or by the length of the arrow. Areas of
slack water
Slack water is a short period in a body of tidal water when the water is completely unstressed, and there is no movement either way in the tidal stream, and which occurs before the direction of the tidal stream reverses. Slack water can be esti ...
may be indicated by no arrows or the words "slack water". UK Admiralty Tidal Atlases show speed in units of tenth of a knot.
An alternative to a tidal atlas is a
nautical chart
A nautical chart is a graphic representation of a sea area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land (topographic map), natural features of the seabed, details of the coa ...
that provides
tidal diamonds.
Tides
Navigation
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