October 16, 2008 13:07
mm, well, ok I added the harmonics and tested them. Confusion reigns :crazy:
From the UKHO website, Plymouth on 10/16 gives
1:15 0.7, 7:23 5.5, 13:35 0.7, 19:42 5.6
Using only the 4 harmonics in the book, I get
1:24 1.07, 7:32 5.51, 13:41 1.11, 19:47 5.55
Close in time I guess, but way off on the heights of the low tides. High tides seems ok.
There's a method to calculate additional harmonics from limited data, but when I use this method I get:
12:58 0.68, 7:06 5.9, 13:15 0.67, 19:23 5.97
Ouch, times are worse and the high tides are too high, but low tides are close.
Finally, I found an old harmonics file with Plymouth in it, and that one gives me
1:08 0.52, 7:02 5.66, 13:27 0.51, 19:17 5.71
Lows are off, but close. Times for the highs are wrong, though, off by 20-30 minutes. Not good.
So nothing comes close the UKHO's predictions. I would have been happy with only being off by a few minutes or a few tenth's of a metre, but I can't get that close. Unfortunately, mixing and matching doesn't work
I'm not sure how to proceed. I'll have to ponder this and think about what to do.
From the UKHO website, Plymouth on 10/16 gives
1:15 0.7, 7:23 5.5, 13:35 0.7, 19:42 5.6
Using only the 4 harmonics in the book, I get
1:24 1.07, 7:32 5.51, 13:41 1.11, 19:47 5.55
Close in time I guess, but way off on the heights of the low tides. High tides seems ok.
There's a method to calculate additional harmonics from limited data, but when I use this method I get:
12:58 0.68, 7:06 5.9, 13:15 0.67, 19:23 5.97
Ouch, times are worse and the high tides are too high, but low tides are close.
Finally, I found an old harmonics file with Plymouth in it, and that one gives me
1:08 0.52, 7:02 5.66, 13:27 0.51, 19:17 5.71
Lows are off, but close. Times for the highs are wrong, though, off by 20-30 minutes. Not good.
So nothing comes close the UKHO's predictions. I would have been happy with only being off by a few minutes or a few tenth's of a metre, but I can't get that close. Unfortunately, mixing and matching doesn't work
I'm not sure how to proceed. I'll have to ponder this and think about what to do.