Walt -
While the "theory" might imply high tide at lunar noon, it doesn't work out that
way in practice.

For instance, in the Gulf of Maine high tide precedes lunar noon by less than an
hour. But then you go down to Block I and the tide is almost 4 hours before
noon. Cape May is also almost 4 hours early. This continues all the way down
the down the coast to the Keys. In fact, there isn't a place on the East Coast
between Cape Cod and Key West where high tide is within two hours of lunar noon.

Rather than randomly sampling tides, try looking at the tables I posted:
http://www.sv-loki.com/NETides.jpg
http://www.sv-loki.com/SETides.jpg





"Walt" wrote in message
...
N1EE wrote:

1 pt to you Wally.

High Tide will be somewhat close to the
mid point between moonrise and moonset.

In theory.

I have not researched many lcoations but I'd
estimate +/- an hour for more locations.

You need to do some more research. Use the following two resources to
compare moonrise/set times and tides for various locations:

http://www2.shore.net/~mcmorran/tide/tideform.html
http://aa.usno.navy.mil/data/docs/RS_OneYear.html
(be sure to correct for daylight savings time)

For instance, try comparing Virginia Beach, VA and Solomon's Island, MD
. Moonrise/set times are within a couple of minutes of each other, but
the tides are six hours out of synch.

Why? Well, obviously it takes some time for the large bulge of water
that is the tide to make its way up the Chesapeake Bay. Since water
doesn't move instantly, moonrise is essentially useless for predicting
tides on large bays.


--
//-Walt
//
// Sigs suck. Oh, the irony.

Jeff Morris wrote:

Walt -
While the "theory" might imply high tide at lunar noon, it doesn't work out that
way in practice.

Yes. I think that's what I was trying to illustrate with my "random"
examples.

Rather than randomly sampling tides, try looking at the tables I posted:
http://www.sv-loki.com/NETides.jpg
http://www.sv-loki.com/SETides.jpg

Good point. While a random sample will disprove the connection between
lunar noon and high tide, these charts give a better idea of the overal
trend. Worth a second look.

--
//-Walt
//
// Sigs suck. Oh, the irony.

Navigator wrote:

No, I'm trying to get people to think about the relationship between
altitude and period between rise and set for a fixed lunar orbital
period.

Not so much a side-step, as a stumble.


--
Wally
www.forthsailing.com
www.wally.myby.co.uk

Jeff Morris wrote:
Are you claiming its broken?

There are a number of factors that determine the time between moonrise and
moonset. However, there is no reason why a 12 hour duration can't occur, and no
reason why it can't happen from 4pm to 4am.


Yes, but is the period from rise to set at a fixed location constant?
And yes I'm trying to get some thinking going.

Cheers

After you've thought about it a bit, you can report back.


"Navigator" wrote in message
...


Jeff Morris wrote:
Are you claiming its broken?

There are a number of factors that determine the time between moonrise and
moonset. However, there is no reason why a 12 hour duration can't occur,
and no
reason why it can't happen from 4pm to 4am.


Yes, but is the period from rise to set at a fixed location constant?
And yes I'm trying to get some thinking going.

Cheers

C'mon you can try better than that.

Cheers

Wally wrote:

Navigator wrote:


No, I'm trying to get people to think about the relationship between
altitude and period between rise and set for a fixed lunar orbital
period.


Not so much a side-step, as a stumble.

So you don't know the answer?

Cheers

Jeff Morris wrote:

After you've thought about it a bit, you can report back.


"Navigator" wrote in message
...


Jeff Morris wrote:

Are you claiming its broken?

There are a number of factors that determine the time between moonrise and
moonset. However, there is no reason why a 12 hour duration can't occur,

and no

reason why it can't happen from 4pm to 4am.


Yes, but is the period from rise to set at a fixed location constant?
And yes I'm trying to get some thinking going.

Cheers

I know the answer, having worked it out (for the nth time) a few minutes after
reading the question. But it seems like you have some difficulty with the
concepts. After all, I had the correct answer to the problem; all you've
offered is nonsense.


"Navigator" wrote in message
...
So you don't know the answer?

Cheers

Jeff Morris wrote:

After you've thought about it a bit, you can report back.


"Navigator" wrote in message
...


Jeff Morris wrote:

Are you claiming its broken?

There are a number of factors that determine the time between moonrise and
moonset. However, there is no reason why a 12 hour duration can't occur,

and no

reason why it can't happen from 4pm to 4am.


Yes, but is the period from rise to set at a fixed location constant?
And yes I'm trying to get some thinking going.

Cheers

So why not answer the question "is the period from rise to set at a
fixed location constant?" Why be so evasive? I'll give you a hint and
then add to it: Is it constant at a fixed location on the same day each
year? If not why?

Cheers


Jeff Morris wrote:

I know the answer, having worked it out (for the nth time) a few minutes after
reading the question. But it seems like you have some difficulty with the
concepts. After all, I had the correct answer to the problem; all you've
offered is nonsense.


"Navigator" wrote in message
...

So you don't know the answer?

Cheers

Jeff Morris wrote:


After you've thought about it a bit, you can report back.


"Navigator" wrote in message
...


Jeff Morris wrote:


Are you claiming its broken?

There are a number of factors that determine the time between moonrise and
moonset. However, there is no reason why a 12 hour duration can't occur,

and no


reason why it can't happen from 4pm to 4am.


Yes, but is the period from rise to set at a fixed location constant?
And yes I'm trying to get some thinking going.

Cheers

N1EE wrote:
1 pt to you Wally.

High Tide will be somewhat close to the
mid point between moonrise and moonset.

I have not researched many lcoations but I'd
estimate +/- an hour for more locations.

In my location High tide occurs about an hour
before that mid point.

Geographical factors will have a big influence.
A body of water might be north-south like the
Bay of Fundy or Gulf or California versus
east-west like Long Island Sound.

Yup, guess the geography is the single biggest factor affecting the
interval between lunar noon and high tide. At least, I'd imagine that a
smooth planet completely covered in water would have a constant interval for
all locations.


I find it handy to be able to judge high tide
by looking at the moon. I can add or subtract
to estimate when the next high or low tide will
be.

That's a habit I might try to develop. That said, I only daysail (club
racing), so I tend to use published tide info and the little program in my
PDA (Tide Tool).


As you can see we have at times nearly a 9
foot swing, so tidal currents coupled with river
current can cause problems with launching if you
are like me, and using a chain hoist. At times
I cannot drop the boat all the way into the river.
I need longer lift straps.

My boat isn't in the water, but the one I crew on has a marina berth, which
is very convenient. We have a similar situation with current - we're at a
narrow on a tidal river a couple of miles across which immediately opens out
to an estuary to the east. On the ebb, the current can get up to 3 knots in
places. There are islands and bridge piers dotted around, a deep channel on
the north side, and shoals to the south, all of which seem to make for a
great variety of water to contend with. Tidal range gets close to 6m at
springs (about 20 feet).



2004-05-04 11:42 PM EDT 8.21 feet High Tide

2004-05-05 5:44 AM EDT Sunrise
2004-05-05 6:06 AM EDT Moonset

You will note that the time of high tide slips
about 50 minutes every day and the interval
between high tides is about 12.5 hours.

A quick scan at my local data suggests slightly less slippage (30-40
minutes), but I'm not sure how reliable the info is. Did you use software to
derive your numbers?


A good sailor will know what these factors are
for his or her location to figure the next
high tide.

Aye, still getting there. :-)


--
Wally
www.forthsailing.com
www.wally.myby.co.uk