Secondary Ports


Almanacs such as Reeds and the Admiralty Tide Tables can't give full Tide Tables for all of the hundreds of small so called 'Secondary' ports around the coast.  Instead they give full Tide Tables for a number of 'Standard' ports such as Dover and Devonport (Plymouth) and provide Secondary Port Differences so that times and heights for any Secondary Port can be worked out.

People get very worked up about Secondary Ports and they need fear not.  Secondary Port Differences are always presented in a logical way.  Have a look at the diagram below, the top part shows how the information is typically presented and below shows what it means.

Secodary Port layout explained

Now lets look at how we use that information.  In this case we need to find out the time of High Water at Starcross on the afternoon of the 13th.

Secodary Port Calculations explained 

We can now have a look at an example of using the same Secondary Port process to find out the Height of the evening Low Water at Starcross. 

Secondary Port height example 

Secondary Port calculations are nothing to be feared but unless they are used frequently it it easy to forget.  It is helpful to have our encapsulated reminder with the angles ready drawn on.

secondary port calculation sheet