T&T: Tidal Variations

[Robin Brueckner]

JH Ward posted, regarding Maptech tidal charts

".. You can be clever and set the computer clock for the time you  think
you'll be at the
location in question and see which way the tide will  flow..."

On slow summer days I have done just that and it's endlessly interesting.

I've checked tidal current changes on several occasions in the NE. Mostly
Mass, Maine, RI. I use Eldridge  (the yellow reference book) to gauge
tide changes and currents and I've noticed some large variations from
predicted flow directions from time to time...perhaps an hour or
more apparent difference. These were all on days of moderate to calm
winds when I would not have thought wind would be a factor... and I hope
the tables take moon phases into account as those are very predictable.

 I have no way to measure either time of actual tidal change (max or min
height) nor rate of flow with any accuracy, but can determine at some
locations direction of flow relative to predictions. It seems it's
sometimes a lot more variable in shallow than deep water, but that's
anecdotal only. At Tuckernuck Island, off the West end of Nantucket
Island (and formerely part of Nantucket), there are miles and miles of
sand shoals adjacent to the north. ( Ditto for the sand shoals around
Stage Habor, across Nantucket Sound on Cape Cod.) I've tried to time my
arrival through the very shoal Tuckernuck harbor entry (I only have about
a foot or two to spare, one time bumped the sand shoal and could not get
through) and arrived to find the flow opposite to that predicted!!.  Very
unnerving!!!  I assume depths are not all that different from
predictions, but I like to oppose currents when entering shoals, to ease
backing out if necessary, rather than be swept along toward shoals with
currents...

In contrast, in LI Sound where I have boated for many years and currents
are modest, predictions seem to be far less variable...

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