What is a secondary port?
A port without its own daily tide predictions: you work its tides out from a standard port using published differences.
A standard port has full daily high and low water times and heights, plus its own tidal curve. For a secondary port, the almanac gives time and height differences to apply to its standard port. You interpolate them for the day, then use the standard port's curve.
- Work in the standard port's time zone (UT for UK ports), then add an hour for BST at the end.
- Ports between Swanage and Selsey have their own curves, worked from low water.
Source: Standard RYA tidal theory.
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