NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Map of the "Age of the Tides"
From: Frank Reed CT
Date: 2004 Jan 12, 17:05 EST
From: Frank Reed CT
Date: 2004 Jan 12, 17:05 EST
Well, it took some digging, but I managed to find a set of global tidal harmonics despite the UKHO's diligent efforts to expunge them from the Internet. [Ya see, there are certain old software libraries that can be found on the net but they're not hooked into the WWW, and those libraries include old DOS shareware that has never been indexed on the web so the UKHO never found them and never managed to issue one of their cease-and-desist orders].
As I mentioned back in December, early editions of Bowditch say that the Spring Tides occur about three days after New Moon and Full Moon. I pointed out that this is reasonably accurate in northwest Europe, but it's not accurate in North America and most other parts of the world. I suggested that Bowditch was repeating European (probably English) tidal lore and applying it globally. This statement caused some frustration for some list members, so I've made a map. The lag between the Spring Tides and the moon phase can be calculated by taking the difference in degrees between the phase of the S2 tide and the phase of the M2 tide. By a fortuitous cancellation of factors of two, this difference in degrees is almost exactly equal to the lag of the Spring Tides in hours. There is a roughly five hour variation in this calculation during the course of the 18.6 year nodal cycle of the Moon's motion, but it's the same amount everywhere globally.
The map is here:
http://www.clockwk.com/agetide.gif
The lag is three days along the southern coast of the North Sea and two days in neighboring areas. Notice that the lag is generally one day on the US East Coast and zero to one days on the West Coast.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
As I mentioned back in December, early editions of Bowditch say that the Spring Tides occur about three days after New Moon and Full Moon. I pointed out that this is reasonably accurate in northwest Europe, but it's not accurate in North America and most other parts of the world. I suggested that Bowditch was repeating European (probably English) tidal lore and applying it globally. This statement caused some frustration for some list members, so I've made a map. The lag between the Spring Tides and the moon phase can be calculated by taking the difference in degrees between the phase of the S2 tide and the phase of the M2 tide. By a fortuitous cancellation of factors of two, this difference in degrees is almost exactly equal to the lag of the Spring Tides in hours. There is a roughly five hour variation in this calculation during the course of the 18.6 year nodal cycle of the Moon's motion, but it's the same amount everywhere globally.
The map is here:
http://www.clockwk.com/agetide.gif
The lag is three days along the southern coast of the North Sea and two days in neighboring areas. Notice that the lag is generally one day on the US East Coast and zero to one days on the West Coast.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
