SECONDARY PORTS EXPLAINED
Secondary Port information is provided in Nautical Almanacs such as Reeds’ and also in the Admiralty Tide Tables. These publications can’t possibly give complete Tide Tables for all of the hundreds of small ‘Secondary Ports’ around the coast. Instead they give complete Tide Tables for all of the larger ‘Standard Ports’ like Dover and Devonport (Plymouth). They then also provide ‘Secondary Port Differences’ so that times and heights for any Secondary Port can be easily worked out.
LAYOUT OF SECONDARY PORT INFORMATION
Secondary Port Time and Height Differences are always presented in a uniform and logical way. Have a look at the diagram below. The top part shows us the presentation of the information in the Almanac or the Admiralty Tide Tables. Underneath we take a look at what that information means.
How are we going to use that information? Look at the example below. We want to find out the time of High Water at Starcross on the afternoon of the 13th. The Standard Port is Plymouth (Devonport).
This diagram will show us how we use the same process to find the Height of the evening Low Water at Starcross.
It is also helpful to have our handy encapsulated Secondary Port Calculation Sheet reminder with the explanation and the angles ready drawn on.