NavList:

Frank wrote:
"Another  approach would be to generate your own tidal constants from a long
run of  predictions from some software that has licensed the official tidal
harmonics . . . About one year of hourly data is sufficient to get values
for the  major tidal harmonics and most of the minor ones, too."

An interesting thought;  but I think I would get better results using the
published data, even if a few years old.  My interest in fiinding an
electronic source is to avoid errors in transcribing (or scanning) published
data.

... and
"Meeus tidal algorithms? Where did you get  them?"

No, the well known astronomical algorithms with which you can calculate the
position (RA and distance) of the Sun and Moon - and can therefore calculate
the tide raising forces which are then mediated by the tidal constants of
the port.

... and
"How many tidal  harmonics have you included?"

The 14 variables specified for the UKHO tidal prediction method

... and
"What sort of  topographical shifts? With rare exceptions, you could use
hundred-year-old tidal  constants (pretending that they exist and are
calculated correctly) and they  should yield very good present-day tide
predictions."

All the ports, for example, of the Irish Sea (particularly Liverpool and
Morcambe Bays), the Bristol Channel, the North Sea coasts of UK, Holland,
Germany and Denmark are affected by shifting sand/mud deposits and by the
changing strategies for dredging key commercial approaches.  I ran my
programme firstly with data now 15 years old and got poor agreement with
published tide tables for certain of these ports:  largely corrected when I
used data published 10 years later.  Frank's assumption is true only for
non-silting locations.

Geoff Butt


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