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Tidal Currents, Continued
Nontidal Currents. There are known and charted currents in all three
of the major oceans that are classified as major currents. In the Pacific,
the more important ones to note are the North Equatorial, South
Equatorial, Equatorial Counter, Japan Stream, Oyashiwo, Californian,
Australian, and Peruvian. In the Atlantic Ocean, the Gulf Stream is the
most notable because of its clear definition as an ocean current and its
effect on shipping and weather. Another type of tidal current you might
encounter is called a ROTARY current. A rotary current is basically
one that flows continually with the direction of flow changing through
all points of the compass during the tidal period. Rotary currents are
usually found offshore where the direction of flow is not restricted by
any barriers.
The Basics
Tidal currents are most pronounced in the entrances to large tidal
basins that have restricted openings to the sea. Helmsmen should keep
this fact in mind because they often experience difficulty in steering
ships in tidal basins. Tide rips caused by swift tidal currents flowing
over an irregular bottom often set up rips and eddies that are nearly
always deceptive in appearance and will sometimes change a ship’s
course as much as 30°. One characteristic of a tide rip is in the coloring
of the water. The line it caused may not always be straight, but it can
usually be seen. You may also observe small wavelets caused by the
wind. The water outside the current will often have many small
wavelets, whereas the swift running current may be barren of wavelets;
again, a quite visible line may be detected, giving the helmsman a clue
to what may lie ahead as the ship passes from one side of the line to the
other. Another clue for the helmsman is to observe the current trail
streaming from a buoy.
In rivers or straits, or where the direction of flow is more or less
restricted to certain channels, the tidal current is reversing; that is, it
flows alternately in approximately opposite directions with an instant or
short period of slack water at each reversal of the current. During the
flow in each direction, the speed varies from zero, or near zero at the
time of slack water to a maximum, either flood or ebb, about midway
between the slacks.
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