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Chapter 16: Mastering the Tides
In a motorized sailboat or low-powered diesel trawler, you might have no choice but to
take advantage of the push of the current to get you outside on the outflow.
Spring Tides
Spring tides are the tides around new and full moons each month when highs are highest
and the lows are lowest. Spring tides come in summer, fall, and winter as well as spring.
Confusing, isn’t it? Around the new and full moon periods in most areas there is one
major high and one major low daily, and the magnitude is much greater than at other
times of the month. These are designated spring tides.
Neap Tides
Neap (pronounced neep) tides are the tides around the quarter-moon periods each month
when tidal variation is minimal. During the “quarter” periods of the moon, in many areas
there are two nearly equal highs and two lows each 24-hour period. Less water is moving
on each tide, and both highs and lows vary less from mean low water. Remember that the
tides repeat themselves on two-week cycles, following the waxing and waning of the
moon. And the tides also pretty much repeat themselves each year on a given moon cycle,
so if there’s a 4.90 high tide in your home port on this year’s December full moon, it will
be about the same next December. (Remember that the full moon won’t come on exactly
the same date, though, if you’re planning a trip far in advance.)
Tide Sense
Watch natural tidal indicators to get a feel for the movement. The way a stick or a buoy
carves the surface can tell you volumes about the flow, and will be much more accurate for
your particular location than any forecast printed in a book. Take what the water gives
you—many days, you’ll find that the published tide tables and nature don’t agree.
Learn to read the real-time clues. In general,
current speeds are controlled by the difference
between the highs and lows, and the time from
the high to the low—lots of water moving over a
short period of time—means strong currents.
However, it also pays to understand how the
geography of an estuary affects current speeds.
Anywhere that lots of water has to fit through a
narrow gap between islands or bars there will be a
strong flow, even on moderate tidal periods. Some
229
Look Out!
Points along a shoreline
can also cause increased tidal
speeds as the water stacks up
and hurries around the obstruction.
Take care when passing
close, particularly in a sailboat
under sail or in a boat with minimal
power.