A place without published harmonic constants, listed in tide tables with offsets from a reference station: differences in time for high and low water and either height differences or height ratios. Users apply the offsets to the reference predictions to get local times and heights. The method works well where the tide shape is similar to the reference and poorly where shallow water or a different tide type distorts it.
Subordinate station offsets are plus 42 minutes and a ratio of 0.88 on the highs, apply that to the entrance times.
Also heard as
- secondary port
- secondary station
Related terms
Reference station
A tide or current station with its own harmonic constants, for which full daily predictions are published.
Tidal prediction
A forecast of tide heights or currents computed from harmonic constants and astronomy, with no weather included.
Lunitidal interval
How long a place waits after the Moon crosses its meridian before the next high or low water arrives.
Tidal range
The vertical difference between a high water and the neighbouring low water.