Rotary Tidal Current Tables
Rotary Tidal Current Tables
The speeds given in the tables are aver-
Some secondary stations exhibit rotary
age. Current speeds may increase 15 to 20
current patterns, where the current flows
% when the moon is new, full, or in perigee;
continually, with the direction of flow chang-
and up to 40 percent if perigee occurs near
ing through all points of the compass during
at new or full moon. Conversely, speeds may
the tidal period. Such currents are most often
decrease 15 to 20 percent at quarter moons
found offshore where the direction of flow is
or apogee and 40 % when a quarter moon
not restricted by any barriers. The rotation
and apogee coincide. Expect average speeds
has its origin in the Coriolis force and, unless
when apogee occurs at a new/full moon and
modified by local conditions, is clockwise in
when perigee occurs at a quarter moon. Apo-
the northern hemisphere. The speed usually
gees and perigees are listed below.
passes through two maxima in approximately
opposite directions and two minima at approx-
Apogee Perigee
imately 90° to the direction of the maxima.
Jan-10 Jan-22
Two rotary current tables follow. The first
Feb-07 Feb-19
table gives for a number of near-shore sta-
Mar-07 Mar-19
tions the average speed in knots and direction
Apr-03 Apr-17
of the current for each half-hour of the tidal
Apr-30 May-15
cycle with reference to a particular current
May-27 Jun-12
phase at one of the primary reference current
Jun-24 Jul-09
stations found earlier in this chapter. The di-
Jul-22 Aug-04
rection of the current is given in degrees true
Aug-19 Aug-31
s
and is the direction toward which the water is
Sep-15 Sep-28
Oct-13 Oct-26
e
nt
flowing. The second table lists the same infor-
mation in increments of one hour for several
Nov-09 Nov-24
u
r
r
offshore stations and a few stations located in
Dec-06 Dec-22 C
wider indentations or bays. Example
On page 705, the current 3.25nm SW of
Cuttyhunk Island, Massachusetts, is given for
each hour after the time of maximum flood
at Pollock Rip Channel. To determine the
n
c
e
s
current at 1100 on June 1, 2007, check the
re
Pollock Rip Channel table on page 562. The
i
ffe
last max flood prior to 1100 occurs at 0740,
about 3 hours earlier. From page 705, at
about 3 hours after max flood at Pollock Rip,
n
t

D
the current off Cuttyhunk averages 0.3 knot
re
and sets 123° true.
u
r
C
715