Tidal Current Tables have a format similar to the Tide Tables.
For a number of principal locations, called reference stations, Table 1 of these tables lists the predicted times of slack water in chronological order in the left-hand column, and the predicted times and velocities of maximum flood (F) and ebb (E) currents, also in chronological order, in the center and right-hand columns for each day of the year. Flood and ebb current directions appear at the top of each page.
All times in the Tidal Current Tables are standard times; each page of Table 1 indicates the central meridian of the time zone used. Adjustments must be made for the use of daylight time or any other deviation from standard time.
Due to the length of the lunar day, approximately 24h 50m, all days in Table 1 will not have a full set of four maximum currents and four slack waters.
Table 2 contains a list of secondary or subordinate stations, arranged in geographic order. Given for each station is its position in terms of latitude and longitude to the nearest minute, its reference station, the difference in time of slack water and time ( maximum current in hours and minutes to its reference station, the maximum flood and maximum ebb velocity ratios with respect to similar current at the reference station, and the direction and average velocities of the maximum flood and ebb currents.
The factors for any subordinate station are applied to the predictions of the reference station whose name is printed next above the subordinate station's listing in Table 2.
The time differences are added to or subtracted from according to their signs, the time of slack water and strength of current (maximum flood or ebb) at the reference station to obtain the times of occurrence of the respective events in the current cycle at the subordinate station. The velocity of the maximum currents at the sub- ordinate station is found by multiplying the velocity of either the flood or ebb current at the reference station by the respective velocity rat listed for the subordinate station.
Note that the time differences for slack water and maximum current are usually not the same; only one time difference given for maximum current and it is used for both flood and ebb where unusual conditions exist, keyed footnotes, applicable to special subordinate stations, appear at the bottom of the page. The average flood velocity is the mean of all the maximum flood currents, and the average ebb velocity is the mean of all the maximum ebb currents
Table 3, is used to determine the velocity of a current at any intermediate time between slack and maximum current. The instructions on its use appear beneath the tabulated factors. This table is in two parts, A and B. Table A is for use at nearly all locations. Table B is used for a limited number of places where there are "hydraulic" currents. These locations for each volume of the Tidal Current Tables are listed beneath Table 3.
Table 4 is used to find the duration of slack, although slack water, or the time of zero velocity, lasts but an instant there is a period each side of slack during which the current is so weak that for practical purposes it can be considered as being negligible From Table 4, the period (half on each side of slack) during which the current does not exceed a given velocity (0.1 to 0.5 knot) is tabulated for various maximum currents.
Table 5 (Atlantic tables only) gives information on rotary tidal currents, or currents which change their direction continually and never come to a slack, so that in a tidal cycle of about 12 1/2 hours they set in all directions. These currents occur offshore and in some wide indentations of the coast. The values given are average velocities due to tidal action only. When a steady wind is blowing, the effect of the current due to wind should be added to the current due to tidal action. This table is seldom used instructions for the use of this table as well as for Tables 1 through 4 are given in the publications themselves.
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