Tidal Streams and the Tidal Stream Atlas: A Study Guide
- Reece Smith-ward
- Jul 21
- 3 min read
Anyone beginning to study coastal navigation soon meets the tides, and quickly learns that the tide does more than raise and lower the water. It also moves the water sideways. That sideways motion is the tidal stream, and getting to grips with it is one of the more rewarding parts of shorebased study. Becoming comfortable with the idea early makes later topics, from course to steer to passage planning, easier to follow.
This guide sets out the core ideas in plain terms: what a tidal stream is, how it differs from tidal height, how streams change through the day, and what a tidal stream atlas is for. It is written as study material to help you revise the concepts, not as a source of navigational information for any actual passage.
What Is a Tidal Stream
A tidal stream is the horizontal movement of water that comes with the rising and falling tide. As the tide floods and ebbs, large volumes of water shift from place to place, and near the coast this creates a flow that has both a direction and a rate. Learning to picture the water moving along, rather than simply rising, is the first step towards understanding how tides affect a boat's progress across the ground.
Height Rises, Streams Flow
It helps to keep two separate ideas clear. Tidal height is the vertical measurement, the rise and fall that decides how much water lies beneath a hull. The tidal stream is the horizontal flow, the water moving from one area to another. The two are linked, because both are driven by the same tidal cycle, but they are not the same thing. A useful study habit is to think of height as up and down, and stream as along and across.
How Streams Change
Tidal streams are not constant. Through the tidal cycle they tend to strengthen, ease, and change direction, following a broadly repeating pattern. There are periods when the flow is stronger and periods when it is gentler, and there are times when the direction turns. Because the pattern repeats with the tide, students can learn to reason about how a stream is likely to behave over the course of a day, which is exactly the kind of thinking that shorebased courses aim to build.
The Tidal Stream Atlas
A tidal stream atlas is a study reference that shows the pattern of streams across an area at different states of the tide. Rather than describing a single moment, it presents a sequence, so you can see how the flow across a region shifts as the tide progresses. For a learner, an atlas is a helpful way to visualise streams as a moving, changing picture rather than a set of isolated figures, and to connect the idea of the tidal cycle with water actually moving on the chart.
Studying Streams With Skipper
The Maritime Master Skipper app is a free day skipper theory companion, available on the Apple App Store for iPhone and iPad, and it is a convenient place to study these ideas. It includes material on tidal streams and a tidal stream atlas to work through, alongside tidal heights, so you can revise the vertical and horizontal sides of the tide together. It also covers position fixing, course to steer, and passage planning, and it works offline, so you can study wherever you happen to be. Skipper is designed to support a shorebased course rather than replace one.
Tidal Calculators in CalcDeck
For practising the calculation side, the Maritime Master CalcDeck app offers a large library of maritime calculators, including a set of tidal tools. It is free to download with an optional one-time CalcDeck Pro upgrade, and it is available on the Apple App Store for iPhone and iPad. Its tidal calculators cover topics such as the rule of twelfths, secondary ports, and under-keel clearance, giving you a way to rehearse the methods behind tidal work. As with all such tools, the results are for training and reference and should be verified against approved tables and instruments before any operational use.
For Study, Not Navigation
A closing reminder. Skipper and CalcDeck are study, learning, and revision aids only. They are not for real-world navigation, and they are not a substitute for approved training or proper equipment. Nothing here, and nothing in the apps, should be used in place of official tidal information for a real passage. Real navigation is governed by official charts, publications, and tidal data, together with sound seamanship and proper training. Use these apps to build your understanding on shore, and always rely on official sources and qualified instruction when you go afloat.
