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Old 08-10-2014, 21:26   #16
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Re: Using an Outdated Eldridge Tide and Pilot Book

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Originally Posted by rockDAWG View Post
For academic exercise, does anyone know how to use an outdated version to derive new tide table for the present date. It may be need to use the lunar calendar to do the calculation.

Anyone know?
The tidal cycle is about 19.5 years long. Try that.
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Old 08-10-2014, 22:16   #17
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Re: Using an Outdated Eldridge Tide and Pilot Book

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Originally Posted by rockDAWG View Post
If one wants to predict the magnitude of the tide (how high or low?) it will reach at a particular day, I presume this will involve a complex mathematical model. However, if one simply wants to know when is the high or low tide, it should not be that complicated.
You are of course correct, at least for most (but not all) ports. Tide times in some ports are alarmingly complex.

For most, the concept of 'standard establishment' applies - that's the idea that the peaks and trough of the tide wave arrive at a set lag time behind the moon crossing the meridian of that port.

But the US Navy did not rely on that for the tricky landings at Incheon in the Korean War. Nor for the landings at Normandy beaches in WW2. And even their best predictions were a little wrong in both cases.

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Old 08-10-2014, 22:59   #18
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Re: Using an Outdated Eldridge Tide and Pilot Book

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Originally Posted by Alan Mighty View Post
For most, the concept of 'standard establishment' applies - that's the idea that the peaks and trough of the tide wave arrive at a set lag time behind the moon crossing the meridian of that port.

l
AKA "lunitudinal interval" or "high water interval". It can vary by half an hour or so either side of the mean over a month.

And it's only useful where the semidiurnal component of the tide is dominant.
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Old 08-10-2014, 23:53   #19
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Re: Using an Outdated Eldridge Tide and Pilot Book

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The tidal cycle is about 19.5 years long. Try that.
Do you have the reference by chance?
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Old 09-10-2014, 09:44   #20
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Re: Using an Outdated Eldridge Tide and Pilot Book

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Originally Posted by rockDAWG View Post
Do you have the reference by chance?
NOAA uses 19 years.

"Tidal Datums and Tidal Epochs Obviously nothing is going to prevent sea level from changing in response to these and other factors. However, we can take sea level averages over several years to obtain a tidal datum - a vertical reference based on some phase of the tide - to slow the process if only temporarily. This is a workable idea because, in addition to sinking crusts and melting ice, tidal variations also have their effect on sea level. One such effect is the 18.6-year cycle of the lunar nodes a cycle accompanied by variations in tidal range. Another force for change is the annual variation in solar declination that modulates solar heating and density of ocean waters. To account for both, a 19-year period of water level averaging the National Tidal Datum Epoch (NTDE) has been established by NOAA/NOS in the United States. NTDEs have included the years 1924-1942, 1941-1959, 1960-1978, and most recently, 1983-2001. NTDEs thus are being updated roughly every twenty years."

What is a Tidal Datum

The 19.5 year cycle came up in a conversation with the Canadian Hydrographic Service. It is roughly the period between Lowest Astronomical Tides.
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Old 09-10-2014, 09:47   #21

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Re: Using an Outdated Eldridge Tide and Pilot Book

dawg-
The Wiki says:
Careful Fourier data analysis over a nineteen-year period (the National Tidal Datum Epoch in the U.S.) uses frequencies called the tidal harmonic constituents. Nineteen years is preferred because the Earth, moon and sun's relative positions repeat almost exactly in the Metonic cycle of 19 years, which is long enough to include the 18.613 year lunar nodal tidal constituent.
-- https://en.wikipedia.org/wiki/Tide

But you never know, if you call NOAA you might actually get some academic type who wants to chat about it. I suppose 19 years of Eldridge would only be maybe 18" wide on the shelf. Or the author of some of the tide applications might also have some insight on this, since they must be running algorithms to the same purpose.
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Old 09-10-2014, 09:50   #22
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Re: Using an Outdated Eldridge Tide and Pilot Book

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But you never know, if you call NOAA you might actually get some academic type who wants to chat about it.
A few years ago, I had a 90 minute chat with a hydrographer from the Bedford Institute in Halifax (part of CHS).

It was quite enlightening.

Jack
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Old 09-10-2014, 10:58   #23
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Re: Using an Outdated Eldridge Tide and Pilot Book

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Hell's Gate actually IS a piece of cake. The Army undermined some 11 acres of the river bottom and dynamited it, about a hundred years ago, in what was then the world's largest explosion, in order to drop the river bottom over ten feet deeper and eliminate a couple of pesky rock islands in the process.

Hell's Gate today? Just feels like the water trolls are tugging at your rudder, or holding you in place. No big deal compared to trying not to get run down by commercial traffic that really has limited maneuvering options.
It was a 100yrs. ago I last went through there. It must be a real plus. As I recall figuring slack tide was the problem. I can remember barges on the rocks, may have been one of the islands blown up? Have they done anything to clean up New Town Creek?
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Old 09-10-2014, 11:14   #24
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Re: Using an Outdated Eldridge Tide and Pilot Book

Sailorboy1 only got it half correct. Take his old copy and……. toss it in the water. When it stops sinking, it is low tide and when it stops rising, it is high tide.

This method doesn't depend on any solar/lunar cycles or calculations and is more accurate than even a new copy of Eldridge's.

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Old 09-10-2014, 12:07   #25
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Re: Using an Outdated Eldridge Tide and Pilot Book

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Sailorboy1 only got it half correct. Take his old copy and. toss it in the water. When it stops sinking, it is low tide and when it stops rising, it is high tide.

This method doesn't depend on any solar/lunar cycles or calculations and is more accurate than even a new copy of Eldridge's.

Mark
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Old 09-10-2014, 12:13   #26
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Thumbs up Re: Using an Outdated Eldridge Tide and Pilot Book

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Originally Posted by MooGroc View Post
I use my old outdated Eldridge all the time. There hardly seems to be a reason to get a recent one. What I use it for is planning passages to hit a fair tide - especially when going through NYC/East River.

Their are lots of websites and chart plotters what will tell you what the tides are. Eldridge shows the currents at different offsets from the highs and lows - that's all I'm really interested in when planning. I suspect this relative data never changes much.
This is exactly how I use my outdated Eldridge (although for currents in the Vineyard/Nantucket Sound). I don't see the need to spend $10/year for tide tables that I can get off the web for nothing.
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Old 09-10-2014, 13:42   #27
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Re: Using an Outdated Eldridge Tide and Pilot Book

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Originally Posted by colemj View Post
Sailorboy1 only got it half correct. Take his old copy and……. toss it in the water. When it stops sinking, it is low tide and when it stops rising, it is high tide.

This method doesn't depend on any solar/lunar cycles or calculations and is more accurate than even a new copy of Eldridge's.

Mark
The next of part that is: when it floats it moves in the direction of the tide and the time it takes to move gives you the current speed, very old school right up there with where the sun rises and sets
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