Thanks, Peter, yet again for explaining something complex so clearly. This, together with your manifest enthusiasm(s), would have made you a brilliant science teacher - perhaps you were, in years now past? Anyway, you are a big asset to this forum, and I for one am very grateful!
I understood most of it, and I was aware it was complicated. Did all that calculating really go on, at least to any useful effect, in the days before computers? - amazing!
Just one or two relatively trivial points. The tide times I listed came from the Met Office detailed forecast: I don't know where they get them from. I take your point that those with the 'biggest' computers are likely to have the best forecasts, and vice versa.
Your suggestion that low water times (perhaps especially along the 'two highs' south coast) are easier to define is a useful practical point.
With regard to the two highs phenomenon, the graphs I referred to are in the 'Tidal Planner', produced by Crest Publications, for Poole (Town Quay) 2017. The tide curves for the days in question (May 22 - 25) all show the 'first high' as higher than any later surge. So, for inside Poole Harbour at least, the suggestion in your last paragraph doesn't really stand up. And therefore I STILL don't understand why those highs at Studland stacked up the way they did!
I did actually go sailing on Monday 22nd. I got afloat after the predicted morning high, and sailed into Poole Harbour on a dead run past Sandbanks with a southerly breeze. This was wind against a fairish ebb which produced interesting sea conditions - 1 metre waves to surf down even with a mere upper F3 breeze. The critical thing there is enough speed over the ground to get past the chain ferry, which has a very loud horn it uses to make small craft feel even smaller if it thinks they might impede its imperious 200 metre voyages. We made it! Then, as mentioned elsewhere, I had fun chasing BC26 006 for a while. Then, visiting the waters south of Brownsea Island, I was reminded of what I already knew - that huge areas of sparklingly inviting water there are, at lowish tide, covered by about 9 inches of water, and that at least some of the stakes marking channels are nowhere near the channels in question. So I anchored and had a snooze, which was very pleasant and lasted long enough for me to find the tide flooding nicely when I came to. Then it was out past the ferry again, this time against both wind and tide - flattish, gurgly-type water, and bow waves round all the channel buoys. It took quite a while, but we made it, again without incurring the ire of the ferry skipper. A long beat up along the Training Bank (which seemed extra long that afternoon), and round the end beacon into Studland Bay, and home. To borrow from a well-known personality, 'SUCH fun!!"