How to set up a Tidal Curve

Any sailor exploring tidal waters should be aware of the immense power the tide can have. In this blog I go through how to set up your tidal curve on board and my top tips for using one.

The Tidal Curve

What is a Tidal Curve?

A tidal curve is a graph found in your almanac specific to each port. Taking the appropriate published time and height of high water (or time of low water for a low water curve) and the height of low water you are able to fill in you curve for the day. Once set up the curve allows you to quickly find out the height of tide at any given time or used in reverse, at what time you will have a precise height of tide.

How do I set up a Tidal Curve?

A step by step guide to setting up your tidal curve:

  1. Locate the tide times for the day in question. Making sure to select the tides most appropriate to you (the times you are out sailing).
  2. Calculate the range for the day (high water height minus low water height).
  3. Locate the correct curve in your almanac. This is usually found just after the printed tide tables.
  4. Start by filling in the time of high water (or low water if the port has a low water curve) and count back and forward filling in the boxes on the time scale
  5. Plot the height of low water on the low water scale
  6. Plot the height of high water on the high water scale
  7. Join these two points up with a straight diagonal line

Your curve is now set up and ready to use. Check out the video animation below to see how to read the completed curve.


Top Tips for using a Tidal Curve

My top tips for using your tidal curve:

  • For your most regularly visited ports its a good idea to photocopy and enlarge the tidal curve from the almanac. Not only will this be easier to complete, it will also save your almanac from having the most used pages rubbed out!
  • Once you have an enlarged curve (A4 works well) its a great idea to laminate this. Again, not only will it save the paper from getting wet it will also allow to use a chino-graph pencil to complete it which then can be rubbed out and reused.
  • Always set up your curve for the day before you leave harbour. It may be necessary to complete one for a few different ports depending on your intended passage. Whilst out in the Solent I always have the Portsmouth Curve set up on my chart table ready for easy reference.

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