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.