It’s been a while but I’ve now sorted times and amplitudes for three months’ tides at Aberystwyth. If I use the height of the low tide, the lower curve, as a guide to excitement/volume then the piece will start at modest volume, end on a crescendo and have three main peaks:
Next step is to work out the exact ‘phasing’ of these low tides – further apart as they get lower, I believe.
The graph below is the result of alignment to a 25-beat norm of 12 and a half hours between low tides, selecting start (3 tides skipped) and end to complete at zero but with a phase advancement of a single 25-beat bar through the piece as a whole. The blue bars are the beat phasing and the red bars which will be interpreted as ‘excitement’/volume are 25 minus ten times low tide height in metres. This a proxy for high tide height and has the result that amplitude is greatest where the tides are accelerating – i.e. the phase is advancing (getting earlier faster)
An additional 24-beat rhythm within the 25-pulse metre will correspond to half-hours on the sidereal clock and starts with a change in the same direction as the tides, but then diverges. At the end, 175 half-days, this rhythm will also return to the bar line.
The original file with tide tables is attached here for reference as an Excel 2007 set of pages: