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Working with tidal streams

Never give up, for that is just the place and time that the tide will turn!

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Tidal Stream Calculations

I often get asked “how do we calculate the best time to depart” based on the tide being favourable or which hour to use when working out an EP or course to steer.

To the newbie, if you get this one wrong then your passage could linger longer, and you may miss last orders at the destination! Or worse still you could be a long way out with your EP or your course to steer and possibly not know that you could be in a dangerous position or even sail off in a dangerous direction because you got the tide wrong

There are two basic ways to do this

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  • Use a Tidal Stream Atlas
  • Using Tidal Diamonds on a chart.

Tidal gates can be checked to ensure you get through them, nothing worse than sitting off Alderney for 6 hours waiting for the tide to turn in favour because you didn’t check the tide streams.

So, what’s the best way to ensure you get this correct?

So how is it done?

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For an overall picture and to assist with planning I use the tidal stream atlas, for more precise and accurate work (EP’s and Course to Steer) I tend to use the tidal diamonds.

Always use the tide stream atlas to check which direction the tide is going and what time it turns. I literally look through the pages and determine when the arrows change direction.

From that point you can see how many hours before/after HW you need to plan for.

It is always a good idea to write the time of HW at the reference port on the HW page of the tide stream atlas and then fill in the times for +1 hour, + 2 hour etc (and the minus hours). That way when you are on passage and you want to see what the tide stream is doing at a given time it will be easy to find. Remember the page you look at is valid for 1 hour, ie 30 minutes either side of the time you have written on that page.

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Pitfalls and common mistakes

Use the correct port of reference. Tide stream atlases always say to where they refer. The reference port may not be on the chart so be aware of this. For example, the tide stream atlas for the Alderney race refers to HW Dover as a reference port and time.

Allow for DST and possible time zone difference if applicable when looking up the time of HW at the reference port. Some French coast charts use Dover as a reference and if you are in French time (local time) you need to account for this in your plans.

Click to expand this chart

I have produced a tidal hour calculation sheet to assist which tide hour to use when working out an EP or Course to Steer. This is self-explanatory and there is an example of how to use it on the page. Feel free to email me if you have any questions about this.

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