Secondary Port

A location where tidal information is derived by applying corrections to data from a nearby standard port. 

A secondary port is a coastal location where tidal predictions are calculated by referencing a nearby standard port, which has a full set of tidal data. Since not all ports have their own dedicated tidal observations, secondary ports use time and height differences to estimate local tide times and levels based on the data from the standard port. These corrections account for variations in tidal behaviour caused by local geography, seabed contours, and other factors. Secondary port information is commonly found in nautical almanacs and tide tables, allowing mariners to plan safe navigation, berthing, and anchoring. The accuracy of secondary port predictions depends on the quality of the correction factors, which are typically derived from historical tidal observations.