98
Th e greatest tides occur in the Bay of Fundy, Nova Scotia, where there
is an extreme range of 57 feet.
—Robert Hendrickson, The Ocean AlmanacIn unfamiliar waters, how can you accurately determine if you have enough
water to enter port, lie alongside a pier, or anchor in a pristine cove? Ahead lies
a narrow passage with strong rip currents. When can you safely transit the pass,
and how much time will you have to make it through?
In Th is Chapter You’ll Learn How To:
D Make an easy graph to predict tidal heights and currents worldwide
D Find the speed of a current without a table or a calculator
D Determine the window of opportunity to transit an inlet
D Learn how to steer an accurate course across the Gulf Stream
D Deal with the mystery of leeway in three simple ways
How to Predict Tides Anywhere in the World
Both the sun and moon exert a gravitational pull on the earth’s waters to pro-
duce tides. The moon, being the closer of the two heavenly bodies, exerts
twice the influence of the sun. The result is a bulge of high water beneath the
moon, and this high-water bulge travels around the globe as the earth spins.
There is a second high-water bulge on the opposite side of the globe from
the fi rst, the result of centrifugal forces in the earth-moon couple. Th us, in the
absence of local eff ects, each spot on the world’s oceans would receive two high
tides and two low tides each day (a semidiurnal tide). But latitude, shoreline
confi guration, and seabed topography also aff ect local tides. While midocean
tides are scarcely noticeable, the tides funneled up the Bay of Fundy, through
the English Channel, and into other mid- and high-latitude constrictions can
achieve truly impressive heights. A big range of tide requires a correspond-
ingly rapid horizontal transport of water, so big tides are associated with
TIDES,
CURRENTS,
AND LEEWAY
5