Doug,

Pardon me if I sound argumentative. I'm not trying to be.

7/12 isn't the way I figure the Tides. I use the RMS and the 12 hour
cycle. I round the 707 to 70%. This leaves 30% for the curve at the top
and bottom and since we are only thinking of a 1/2 sine wave 15% on the
top and 15% on the bottom. So, .15x12=1.8 hours from the middle of
Slack Tide, 8.4 hours max flow, 1.8 to Slack again (1.8+8.4+1.8=12 hour
Tide Run)

That leaves only (g) the problem of Mid Slack.This I think is where we
start to lay the blame on the Tide Tables. There can be HW by sight for
at least an hour. I really don't know how to find this mid point and an
hour difference at a inlet can be the difference of passage or no.

Allow time and be early. I let my boat "Lady Bug" until the right time.

Ole Thom

"Nav" wrote in message
...
How do you think it related to the change in tide height that day?

I've no idea.

Our destination, Cherebourg, is a deep water port with 24 hour access to the
marina. We had all done the trip many times, so we weren't watching the
charts too closely. With hindsight, it would have been interesting to check
the depth.


Regards

Donal
--

"Nav" wrote in message
...
No, not in the context of Dougs ideas about max stream lagging
behind
height changes. Max stream is most often at the maximaum rate of
change
of height. Look it up.

Where?

lady bug?


"Thom Stewart" wrote in message
...
Doug,

Pardon me if I sound argumentative. I'm not trying to be.

7/12 isn't the way I figure the Tides. I use the RMS and the 12 hour
cycle. I round the 707 to 70%. This leaves 30% for the curve at the
top
and bottom and since we are only thinking of a 1/2 sine wave 15% on
the
top and 15% on the bottom. So, .15x12=1.8 hours from the middle of
Slack Tide, 8.4 hours max flow, 1.8 to Slack again (1.8+8.4+1.8=12
hour
Tide Run)

That leaves only (g) the problem of Mid Slack.This I think is where
we
start to lay the blame on the Tide Tables. There can be HW by sight
for
at least an hour. I really don't know how to find this mid point and
an
hour difference at a inlet can be the difference of passage or no.

Allow time and be early. I let my boat "Lady Bug" until the right
time.

Ole Thom

yep the lady bug
you know: while waiting for the tide to turn, the rum gets broken out from
stowage, the crew gets naked and a regular party ensues.
once the tide changes, everythings back to normal.
hell you gotta do something while bouncing around out there.

we usually leave 2-3 hours early ;)
gf.



"Scott Vernon" wrote in message
...
lady bug?

I think you are confusing a single example with a generality. While that
may be the case in Hell's gate it would be unlikely to apply to all
bodies of water -for the energetic reason I explained. I suggest that a
form that depends on the square root of the difference of a pair of
curves is hardly a "small departure" from a sine.

Consider this: A pair of tidal basins connected by a straight where the
basin tides are out of phase and a current exists that flows through the
straight. The flow through the straight would not be predictable without
knowlege of the magnitude of the current -and it would not be
proportional to the square root of the difference. OK?

Cheers

Jeff Morris wrote:

Then you're disagreeing with Bowditch:

"A slight departure from the sine form is exhibited by
the reversing current in a strait, such as East River, New
York, that connects two tidal basins. The tides at the two
ends of a strait are seldom in phase or equal in range, and
the current, called hydraulic current, is generated largely
by the continuously changing difference in height of water
at the two ends. The speed of a hydraulic current varies
nearly as the square root of the difference in height. The
speed reaches a maximum more quickly and remains at
strength for a longer period than shown in Figure 914b, and
the period of weak current near the time of slack is considerably
shortened."


"Nav" wrote in message
...

That sounds like an estimate based on an energy argument. However, I
don't think that case could be considered to be a closed system so such
energy balance need not apply.

Cheers

Jeff Morris wrote:


"Thom Stewart" wrote in message
...


Scott,

You've seem to have forgotten "The Gulf Stream Master" Jax. I'm sure he
can help you ride the eddies:^) Maybe even find you a stray current
heading south (g)


Jax also insisted that the time of high water and slack current must be the
same, to be otherwise would violate the laws of physics (on his planet).






Now, for what's it worth. The Tide Flow is a sine wave. Us common folk
understand that slack water is at the top and bottom of the wave. So
slack is, roughly about a hour and it is roughly in the upper 30%
counting the end of the rising tide and the beginning of the Ebb. 15% to
the HW and 15% roughly to the Max Flow. That means about two hours to
max flow, 8 hours of max flow and then another couple of hour of
diminishing flow to LW.


While the current flow in "simple harbors" may follow a sine curve, in cuts
between two bodies of water the flow is different. The curve is more
"squarish," that is, the flow ramps up quicker and stays high longer. The
duration of slack is reduced. The best example is Hell Gate in New York.

IIRC, the flow rate is proportional to the square root of the different of
height of the two bodies.

DSK wrote:

Hmm... Navvie, Bowditch... Bowditch or Navvie...

A tough call but I'd have to say Bowditch has the slightly greater
weight of authority. I'd agree that Bowditch is nowhere near as pompous
nor as self-seeking.


What a sad little man you are. So bound up in jealousy.

Cheers

The reason I ask is that wind and air pressure affect the tide height
and I would expect that that effect could alter time of peak tide and
stream. The question, would such an effect also alter time of slack
water differently from time of high water? I suspect not much.

Cheers

Donal wrote:

"Nav" wrote in message
...

How do you think it related to the change in tide height that day?


I've no idea.

Our destination, Cherebourg, is a deep water port with 24 hour access to the
marina. We had all done the trip many times, so we weren't watching the
charts too closely. With hindsight, it would have been interesting to check
the depth.


Regards

Donal
--

Don't worry, Doug was just BSing. Being a rather poor engineer he
assumed it would be compliant system and would lag.

Cheers

Thom Stewart wrote:

Doug,

Pardon me if I sound argumentative. I'm not trying to be.

7/12 isn't the way I figure the Tides. I use the RMS and the 12 hour
cycle. I round the 707 to 70%. This leaves 30% for the curve at the top
and bottom and since we are only thinking of a 1/2 sine wave 15% on the
top and 15% on the bottom. So, .15x12=1.8 hours from the middle of
Slack Tide, 8.4 hours max flow, 1.8 to Slack again (1.8+8.4+1.8=12 hour
Tide Run)

That leaves only (g) the problem of Mid Slack.This I think is where we
start to lay the blame on the Tide Tables. There can be HW by sight for
at least an hour. I really don't know how to find this mid point and an
hour difference at a inlet can be the difference of passage or no.

Allow time and be early. I let my boat "Lady Bug" until the right time.

Ole Thom

Bowditch? How about Google?

This is basic seamanship on tides. The most likely time of max stream is
when tide height changes most rapidly.

Cheers


Scott Vernon wrote:

"Nav" wrote in message
...

No, not in the context of Dougs ideas about max stream lagging

behind

height changes. Max stream is most often at the maximaum rate of

change

of height. Look it up.


Where?