Reply To: Tidal rates in World War 1

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Brian D. H

    Thank you for this response. As part of a personal research project I am interested in certain things that happened in WW1 which may have been subject to tidal influences, both height and range, particularly near the Jade River.
    I am attempting to bring some conditions possibly experienced then, into the modern format with which I am more familiar. Older charts (1916) have tidal positions marked (pre-diamond), unfortunately not within 20 miles, and the only German chart I possess (Nr 49 from 1965, large scale of the Jade and Elbe) has no tidal info at all.
    All the older tidal information is in mean rate. I was curious as to how that related to the modern Spring and Neap categories on present charts. The tidal height information at ports is given in HW F&C – High Water Full and Change (of the Moon) – so the tidal height can be obtained and the range extracted.1
    If the calculation of 1/72r is relevant to the mean rates given in the tidal atlas or on the chart info then the approximate rate for the time can be extracted.
    It’s the matter of asking someone who may be familiar with that method of tidal calculation. I assumed that as tides have been flowing before navigators used them the Tidal Atlas would at least give me an idea.

    1. High Water, Full and Change of the Moon, also called the Lunitidal interval or ‘Vulgar Establishment’, is effectively the interval between High Tide and the time of the Moon’s Meridian passage at the port in question at Full and New moon. It was the way that tides were calculated before the Harmonic method used today.
    It is the interval between the Moon’s Southing and the next high water at that port. Generally expressed as, e.g.: Gravesend, Ih 30m (one hour 30 minutes); Milford Haven Vh 15m (Five hours 15 minutes) etc.
    The complete calculation involves finding the Moon’s Southing on the particular day (a function of its age and epact), adding the HW F&C constant and working out local time. This can have similar accuracy to modern methods. The charts I have c.1916 are marked with the HW F&C constants for a number of ports around the North Sea. Apart from a computer programme or a list of tide tables for the period, this is a reasonably well-tried method of computing HW times and was certainly used in the 18th C. (Greenville Collins Pilot 1753) and the early 20thC. (UKHO charts refer).