NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Fw: A little off topic _ Ebb and Flow
From: hellos
Date: 2006 Jul 2, 10:57 -0500
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From: hellos
Date: 2006 Jul 2, 10:57 -0500
Guy-
Yes, there is a relationship for every
specific point on the earth, but no, there is no general relationship you can
apply universally.
To oversimplify: Once the "basin" has filled with
water (high tide has come all the way in) there will be no current as the water
stands still for a short time. Then, it will run out of the basin (bay, inlet,
whatever) and there will be a current. The speed of that current and the timing
of it will depend on the local underwater geography, which largely controls how
fast that water can escape wherever it is.
You can stand by an inlet or a jetty and the
local fishermen will gladly tell you (often incorrectly and sometimes that's
intentional<G>) that slack current occurs at that point ## hours before or
after high or low tide. But that number won't apply to any other location except
by coincidence. And the time difference will vary with the height of the tides,
the prevailing winds and fetch (pushing more water) and gravitational tidal
pulls from the moon, etc.
So if you need a universal answer, you get a
list of tide/current differences for tide stations, or software that has the
lists built in, or you stand at the location and write it down as observed. I
suppose you could generalize and say the maximum current MIGHT be halfway
between the tides, but I've never heard of any firm rule to calculate it, versus
measuring it and listing it.
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