Hell's Gate

Hi kids!
There is a river that runs beside Manhattan Island called the East
River. It connects Long Island Sound and the New York Harbor. There is
one spot in the river that is very dangerous for sailors. The tidal
currents run very, very fast. They swirl and boil and can toss a big
ship around and make it impossible to control. They can even make it
crash and sink.
Funny thing about tidal currents, though. Since they come in and go
out twice a day there are four times a day when they stop entirely as
they turn around. (Of course, the astute mathemeticians among you have
already seen this as an example of the theorum that a continuous
function cannot pass from positive to negative quantities without
passing through zero.)
When the tide comes in it 'floods'. When it goes out it 'ebbs'. When
there is no current it's called 'slack water'. It's only safe to go
through Hells Gate at slack water. We looked up when that would happen
in a book then figured out when to start driving the boat to just get
there at that time. It turned out we had to get up at four in the
morning!
So we got up early and drove the boat through the dangerous place in
the pre-dawn darkness, through a hard rain with the wind blowing and
everything. It's REALLY HARD to figure out where you are going in the
dark. Boats don't have headlights like cars. But we used our charts
and figured it out. Here is a picture of one of the huge bridges we
went under, the Triborough Bridge. Man, was it ever hard to see! I
sure was glad to have Angel Jen on board. She's a good navigator and
she REALLY doesn't want any crashes.
Man, was it exciting. The river was pretty quiet at slack water but
still had a lot more current than we ever saw in Maine! And a few
minutes later, when we were past the danger place, the current came
back again. Good thing we got out of there!
Tomorrow, we go see the Statue of Liberty!