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Post by Gnat on May 10, 2006 10:14:39 GMT -5
Got a present of a Casio watch with moontime/tide graph facilities. In order to set these 2 features to work correctly, I need to set the lunitidal interval. Having done a search on google, I can retrieve this data for most cities and well known locations etc, but does anyone know how to calculate this for the not so well known areas ?
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Post by Cothi on May 10, 2006 10:16:53 GMT -5
"What is the moon, what is the moon?
Och, that's a daarlin question, a daarlin question".
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Post by oncorhynchusmykis on May 11, 2006 2:17:53 GMT -5
A tide table book should give you the plus/minus time and water difference from (almost) any major port/bay. The book will give you the actual info for some well known area, you just add/subtract the adjustment(s) for your local area.
Google 'tide tables+UK.'
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Post by Gnat on May 11, 2006 8:22:34 GMT -5
A daarlin question indeed.
Thanks, Onchurhynchusmykis, but I'm not sure if it's in the tide tables I have. I don't think it's a question of just setting the watch at a high tide. The GMT time has to be set along with your location in degrees and then the lunitidal interval. I have the first 2 but the lunitidal interval alludes me.
This is what I've got from google and it may be what you are saying but I'm not so bright with these things and I often need it spelled out.
The Lunitidal Interval is the average time difference between when the moon passes over a time meridian and the following high or low tide. If the time meridian referenced is the local time meridian, then the lunitidal intervals are called the "Local Intervals". If the time meridian referenced is the Greenwich meridian, the lunitidal intervals are called the "Greenwich Intervals". Generally, the manufacturers of such items use the Local Intervals for their calculations. Our office does not track or maintain the Local Intervals, we calculate and track the Greenwich Intervals for various locations. This information can be found in the "Water Level Observations" section of our web site under the Accepted Datums heading.
The Greenwich Intervals we provide can be converted to the Local Interval using the following formula:
Local Interval = GI - (0.069 * L)
Where L is the longitude for the location in degrees. West longitudes are positive; East longitudes are negative. Example: 122 degrees 23.7 minutes West would be 122.395 degrees. (23.7 / 60 = 0.395) Longitude for a station is available from the Accepted Datums page by using the link provided for further station information. Where GI is the Greenwich Interval. To calculate the High Tide Local Interval, use the Greenwich Mean High Water Interval in Hours from the Accepted Datums page. To calculate the Low Tide Local Interval, use the Greenwich Mean Low Water Interval in Hours. Some products will require the Local Interval to be a positive number. You can convert a negative interval to a positive by adding 12.42 to the result. For example, if your interval calculated to be -4.11; you could also use 8.31 (-4.11 + 12.42 = 8.31)
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Post by mantog on May 11, 2006 10:16:28 GMT -5
Jesus wept
My watch tells me the time, I couldn't cope with anything else
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Post by oncorhynchusmykis on May 11, 2006 11:07:54 GMT -5
Assuming you're not launching ballistic missiles, take the GMT figure (plus/minus depending upon where you are) and add 30 seconds to 1 minute, per degree. You won't be off by more that a fraction from the tide tables.
Only thing to keep in mind (don't know how your watch works) is high/low tide changes every day due to the earths rotation around the sun. Moon doesn't 'move' in relationship to the earth, but the earth does 'move' in relation to the sun. Most of that mumbo-jumbo means is the moons gravity is 'pulling' the ocean behind it as it changes it's relative position over the surface of the earth (tide follows behind the moons movement not directly below it).
122 degrees 23.7 minutes West ... odd 'they' would choose this number. Roughly equates to Interstate I-5 running north/south through Washington, Oregon and California in the western US.
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Post by Gnat on May 12, 2006 4:35:53 GMT -5
Still a bit baffled with that, Onchurhynchusmykis.
Heres what I have at present.
The watch needs to be set at GMT difference, so for me in Dublin, that's +1 It also needs Longitude (rounded off) so again for me here in Dublin, that's 6degsW. Now the current Lunitidal interval, I have put in is 1 found on the internet (http://www.pol.ac.uk/ntslf/lunitidal.php)and it's 11.16.
Now if I move down to Cobh in Co.Cork, the Longitude changes to 8degsW and the Lunitidal interval (again form the web) is 5.09.
Unfortunately, I don't fish too much in Dublin or Cobh and there isn't any other intervals available for any other part of Ireland on the web.
Soooo, how is this lunitidal figure arrived at and what do I need to perform the calculations?
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Post by oncorhynchusmykis on May 12, 2006 7:42:54 GMT -5
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Post by Gnat on May 12, 2006 7:47:08 GMT -5
It's no good - it only has set locations.
I need the calculation method.
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Post by fredaevans on May 12, 2006 8:27:59 GMT -5
Saw this thread in passing.
Google Lunitidal Interval; you'll get TMI (too much information). See you back in a couple of days. ;D Kidding aside, there are several 'hits' that deal with your specific question.
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Post by Gnat on May 12, 2006 8:37:19 GMT -5
Fred, Got through 3 pages of google with a lot of folk looking for this info aswell, but nobody appears to have any definitive info.
There was even 1 website that would sell it to you for $2.99 !!
All I want to know is how do they arrive at the lunitdal interval figures.
I can get all the moon times, tide times etc but just need the equation.
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Post by AlanB on May 12, 2006 9:20:17 GMT -5
Mantog Mine tells you the date as well but more often than not it isn't set right!
Cheers Alan
p.s. Why John 11:35?
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Post by fredaevans on May 13, 2006 9:16:29 GMT -5
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Post by Gnat on May 13, 2006 13:53:06 GMT -5
Same make, but not that model, Fred, but I believe they would be all set up the same.
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