Donal,

Any ideas

How about the Increase of Tidal Flow and height during Hurricanes?

Ole Thom

"Donal" wrote in message
...

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

Right you are! Tell Donal to mark you up for One Point.

The Tides use the Moon Calender:^)
That is also the reason that Tide rides are possible.

I'm afraid that I can only award Marty 0.75 of a point.

I'm about to dissappear for a couple of days, so I'll explain when I get
back.

[hint] The sun has a much greater gravitational effect on the Earth than
the moon. So why does the moon seem to have a greater impact on the tides?



Regards


Donal
--

"Donal" wrote in message
...

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

Right you are! Tell Donal to mark you up for One Point.

The Tides use the Moon Calender:^)
That is also the reason that Tide rides are possible.

I'm afraid that I can only award Marty 0.75 of a point.

I'm about to dissappear for a couple of days, so I'll explain when I get
back.

[hint] The sun has a much greater gravitational effect on the Earth than
the moon. So why does the moon seem to have a greater impact on the tides?

The tides are not created by what is normally called the "Gravitational Force."
(Of course, the tides are caused by gravitational forces, but they are not
calculated the same way as the "inverse square" rule that is used for
calculating orbits.)

I leave the rest as an exercise for the reader.

Sure. There was I thinking you would discuss a scientific subject
intelligently. Silly me.

Cheers


Jeff Morris wrote:
Sorry Nav, that was obviously meant for Booby.

Your backpedal was pretty pathetic, also. You most pathetic since claiming to
be a charter member of the "Save the Constitution" committee!





"Jeff Morris" wrote in message
...

You mean a line parted and it wasn't even chafing on the boat or dock???

Good

Grief!!!

This is the most pathetic confession since jaxie admitted he didn't know how

to

use a compass!



"Nav" wrote in message
...

That's not a backpedal. Tidal current is discrete from hydraulic current
and the two sum as I said.

Cheers

Jeff Morris wrote:


Holy Backpedal, Nav!

Of course the total current is the sum of a variety of effects. However,

these

are certain places where the hydraulic current dominates the flow. Snow's

Cut,

I suspect, is one. There are others, and they tend to be very

significant

for

sailors.

Most simple tidal currents around here max at under 2 knots, while the
hydraulics are frequently over 4, sometimes 6 or more. For simple

currents,

the

"50-90" rule, which approximates a sine curve, can be used. This says

that

the

current reaches half strength in the first third between slack and max,

and

90%

in the second third.

However, when a hydraulic current dominates, the current changes very

quickly,

often with virtually no slack. Cape Cod Canal this morning went from a .9

knot

ebb to a 1 knot flood in 10 minutes. It went from 50% ebb to 50% flood

strength

in less than an hour, or twice as fast as a sine wave would predict. Hell

Gate

changes even faster than that.

This is a very significant effect for the sailor, who often wishes to

transit

such areas at slack. Perhaps they are not common where you are, Nav, but

I'm

rather surprised you heard of it.

jeff





"Nav" wrote in message
...


I just looked up Bowditch because I was surprised at the generality you
implied. Bowditch is clearly talking about hydraulic current which
_adds_ to the tidal current. The overall effect is as I described in my
other response.


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.

Nav wrote:
Constellation actually, little man.

Are you sure?

For how many posts & how many days did you rant and rave about the
Consitution, not noticing (or just as likely, not knowing) the
difference, little boy?

DSK

Sorry Nav, I missed that. Perhaps you should have a special annotation for when
you're trying to be intelligent.



"Nav" wrote in message
...
Sure. There was I thinking you would discuss a scientific subject
intelligently. Silly me.

Cheers


Jeff Morris wrote:
Sorry Nav, that was obviously meant for Booby.

Your backpedal was pretty pathetic, also. You most pathetic since claiming
to
be a charter member of the "Save the Constitution" committee!





"Jeff Morris" wrote in message
...

You mean a line parted and it wasn't even chafing on the boat or dock???

Good

Grief!!!

This is the most pathetic confession since jaxie admitted he didn't know how

to

use a compass!



"Nav" wrote in message
...

That's not a backpedal. Tidal current is discrete from hydraulic current
and the two sum as I said.

Cheers

Jeff Morris wrote:


Holy Backpedal, Nav!

Of course the total current is the sum of a variety of effects. However,

these

are certain places where the hydraulic current dominates the flow. Snow's

Cut,

I suspect, is one. There are others, and they tend to be very

significant

for

sailors.

Most simple tidal currents around here max at under 2 knots, while the
hydraulics are frequently over 4, sometimes 6 or more. For simple

currents,

the

"50-90" rule, which approximates a sine curve, can be used. This says

that

the

current reaches half strength in the first third between slack and max,

and

90%

in the second third.

However, when a hydraulic current dominates, the current changes very

quickly,

often with virtually no slack. Cape Cod Canal this morning went from a .9

knot

ebb to a 1 knot flood in 10 minutes. It went from 50% ebb to 50% flood

strength

in less than an hour, or twice as fast as a sine wave would predict. Hell

Gate

changes even faster than that.

This is a very significant effect for the sailor, who often wishes to

transit

such areas at slack. Perhaps they are not common where you are, Nav, but

I'm

rather surprised you heard of it.

jeff





"Nav" wrote in message
...


I just looked up Bowditch because I was surprised at the generality you
implied. Bowditch is clearly talking about hydraulic current which
_adds_ to the tidal current. The overall effect is as I described in my
other response.


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:

Nav wrote:

Constellation actually, little man.


Are you sure?


Yes, and with each snipe you get smaller.

Cheers

Good idea -then you can kill file it. I have yet to have a good
scientific discussion about nautical matters with anyone here (except
Gilligan).


Cheers

Jeff Morris wrote:

Sorry Nav, I missed that. Perhaps you should have a special annotation for when
you're trying to be intelligent.



"Nav" wrote in message
...

Sure. There was I thinking you would discuss a scientific subject
intelligently. Silly me.

Cheers


Jeff Morris wrote:

Sorry Nav, that was obviously meant for Booby.

Your backpedal was pretty pathetic, also. You most pathetic since claiming

to

be a charter member of the "Save the Constitution" committee!





"Jeff Morris" wrote in message
...


You mean a line parted and it wasn't even chafing on the boat or dock???

Good


Grief!!!

This is the most pathetic confession since jaxie admitted he didn't know how

to


use a compass!



"Nav" wrote in message
...


That's not a backpedal. Tidal current is discrete from hydraulic current
and the two sum as I said.

Cheers

Jeff Morris wrote:



Holy Backpedal, Nav!

Of course the total current is the sum of a variety of effects. However,

these


are certain places where the hydraulic current dominates the flow. Snow's

Cut,


I suspect, is one. There are others, and they tend to be very

significant


for


sailors.

Most simple tidal currents around here max at under 2 knots, while the
hydraulics are frequently over 4, sometimes 6 or more. For simple

currents,


the


"50-90" rule, which approximates a sine curve, can be used. This says

that


the


current reaches half strength in the first third between slack and max,

and


90%


in the second third.

However, when a hydraulic current dominates, the current changes very

quickly,


often with virtually no slack. Cape Cod Canal this morning went from a .9

knot


ebb to a 1 knot flood in 10 minutes. It went from 50% ebb to 50% flood

strength


in less than an hour, or twice as fast as a sine wave would predict. Hell

Gate


changes even faster than that.

This is a very significant effect for the sailor, who often wishes to

transit


such areas at slack. Perhaps they are not common where you are, Nav, but

I'm


rather surprised you heard of it.

jeff





"Nav" wrote in message
...



I just looked up Bowditch because I was surprised at the generality you
implied. Bowditch is clearly talking about hydraulic current which
_adds_ to the tidal current. The overall effect is as I described in my
other response.


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.

The moon are a lot closer than the sun. Therefore the gravitational
force of the moon varies more over the earth's surface. It is the
variation in the gravitational force and not the force in itself that
creates the tides.

The moons pull on a water-molecule directly under the moon is larger
than
on a molecule on the far side of the earth, actually it is larger than
"the average pull on the whole earth", and here the moon pulls away
from the earth.
On the far side of the earth (seen from the moon) the gravitation from
the moon is less than average and at this point the moon pulls toward
the earth. In the middle (when the moon is in the horizon) the moons
pulls with the same as on the earth as a whole, and there is no
vertical component, so here the water-molecule is "unaffected" by the
moon.

On both sides the change in gravitational pull from the moon reduces
or counteracts the gravitational force of the earth on the
water-molecule(making it lighter, so to speak).
This should explain why there is to tides a day, one when the moon is
culminating and one when it is on the other side.

Peter S/Y Anicula

"Donal" skrev i en meddelelse
...

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

Right you are! Tell Donal to mark you up for One Point.

The Tides use the Moon Calender:^)
That is also the reason that Tide rides are possible.

I'm afraid that I can only award Marty 0.75 of a point.

I'm about to dissappear for a couple of days, so I'll explain when I
get
back.

[hint] The sun has a much greater gravitational effect on the Earth
than
the moon. So why does the moon seem to have a greater impact on the
tides?



Regards


Donal
--

If you look at a curve of the "tidal streams" of a given location, or
at the ATSA, (Admirallity Tidal Stream Atlas), it incorporates the
effect of landmasses and sea-bottom topography on the water-flow.
Doesn't it ?
Otherwise it wouldn't be very useful !

Peter S/Y Anicula

"Nav" skrev i en meddelelse
...
That's not a backpedal. Tidal current is discrete from hydraulic
current
and the two sum as I said.

Cheers

Jeff Morris wrote:

Holy Backpedal, Nav!

Of course the total current is the sum of a variety of effects.
However, these
are certain places where the hydraulic current dominates the flow.
Snow's Cut,
I suspect, is one. There are others, and they tend to be very
significant for
sailors.

Most simple tidal currents around here max at under 2 knots, while
the
hydraulics are frequently over 4, sometimes 6 or more. For simple
currents, the
"50-90" rule, which approximates a sine curve, can be used. This
says that the
current reaches half strength in the first third between slack and
max, and 90%
in the second third.

However, when a hydraulic current dominates, the current changes
very quickly,
often with virtually no slack. Cape Cod Canal this morning went
from a .9 knot
ebb to a 1 knot flood in 10 minutes. It went from 50% ebb to 50%
flood strength
in less than an hour, or twice as fast as a sine wave would
predict. Hell Gate
changes even faster than that.

This is a very significant effect for the sailor, who often wishes
to transit
such areas at slack. Perhaps they are not common where you are,
Nav, but I'm
rather surprised you heard of it.

jeff





"Nav" wrote in message
...

I just looked up Bowditch because I was surprised at the
generality you
implied. Bowditch is clearly talking about hydraulic current which
_adds_ to the tidal current. The overall effect is as I described
in my
other response.


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.