Establishment of a port is the technical expression for the time that elapses between the moon's transit across the local

meridian Meridian or a meridian line (from Latin ''meridies'' via Old French ''meridiane'', meaning “midday”) may refer to Science * Meridian (astronomy), imaginary circle in a plane perpendicular to the planes of the celestial equator and horizon * ...

at new or full moon at a given place and the time of the next high water at that place. As an example in the UK, the interval (constant at any one place) may vary from 6 minutes (

Harwich Harwich is a town in Essex, England, and one of the Haven ports on the North Sea coast. It is in the Tendring district. Nearby places include Felixstowe to the north-east, Ipswich to the north-west, Colchester to the south-west and Clacton-on- ...

) to 11 hours 45 minutes (

North Foreland North Foreland is a chalk headland on the Kent coast of southeast England, specifically in Broadstairs. With the rest of Broadstairs and part of Ramsgate it is the eastern side of Kent's largest peninsula, the Isle of Thanet. It presents a bo ...

) meaning that the time difference of high water between those two places is 21 minutes. At

London Bridge Several bridges named London Bridge have spanned the River Thames between the City of London and Southwark, in central London. The current crossing, which opened to traffic in 1973, is a box girder bridge built from concrete and steel. It r ...

it is 1 hour 58 minutes. The term ''establishment of the port'' is identical to the obsolescent term High Water Full and Change (HWF&C) ''Full'' referring to the full moon and ''change'' referring to the new moon. Before the creation of modern tide tables, it was a quick way of predicting the time of local high water. The moon’s passage at the local meridian is about 50 minutes later each day. If it is HWF&C 1 hour 30 minutes and we are three days after the full moon, then the morning high water is 1h 30 + 150 minutes = 0400.

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{{DEFAULTSORT:Establishment Of A port Time in astronomy Durations