A separate time difference is tabulated for high and low water. Each time difference is added to or subtracted from the time of the respective high or low water at the reference station in with its sign. A navigator must be alert to changes of date, either forward or backwards, when the time difference is applied. Example, if a high water occurs at a reference station at 2200 on 23 March and the tide at the subordinate station occurs 3 hours later, then high water will occur at 0100 on 24 March at the subordinate station. If a high water at a reference station occurs at 0200 on 29 March, and the tide at the subordinate station occurs 5 hours earlier, the high water at the subordinate station will occur at 2100 on 28 March.
The height of the tide is found in several ways, depending on local conditions. If the difference for height of high water is given, with 0.0 feet tabulated as the low-water difference, apply the high-water difference with its sign to the height of high water at the reference station. The height of low water will be the same as that at the reference station. If a difference for height of low as well as high water is given, each must be applied in accordance with its sign to the height of the corresponding tide at the reference station, adding the difference if its sign is plus (+) and subtracting if its sign is minus (-). If a ratio of ranges is given, the heights of the tides at the subordinate station can be obtained by multiplying the heights of both high and low tides at the reference station by the respective ratios.
Any unusual conditions pertaining to a subordinate station, or any complex calculations required, are explained in keyed footnotes on the appropriate page of Table 2.
The mean tide level and the ranges of tide (mean, plus spring, diurnal, or tropic) are listed in Table 2, but are seldom used by a navigator except as items of interest. An explanation of them is given in the Tide Tables.
The height of the tide at a specific time other than those tabulated in Table 1 or computed using Table 2 can be found by means of Table 3, which is normally used without interpolation. This table is easy to use and the instructions given below the table are explicit. Note that interpolation is not done when using Table 3. The predictions of times and heights of tide are influenced by local conditions to the extent that they are not exact enough to make meaningful any interpolation for more precise values. Table 4 gives the local mean time of sunrise and sunset. Table 5 provides local mean time to standard time when the difference in longitude is known. Table 6 list the time of moonrise and moonset for some locations. I like to use a format when doing Tides and Currents which I hope to have on here later. It will help your calculations and help with accuracy.
In cases of doubt in working with Table 3 in the Tide Tables, and Tables 3 and 4 in the Current Tables, reference to the explanatory notes accompanying the tables will clarify the method of solution.
The most common errors in the completion of a tide table for a subordinate station are: applying the high-water difference to the height of low water at the reference station as well as to the height of high water; not being alert to a change in date at the subordinate station after applying the high-water or low-water time difference to the reference station; and failure to apply the difference factor from Table 3 (with the proper sign) to a rising or a falling tide at the station in question. When the nearest tide is high water, subtract the correction factor of Table 3 from nearest high tide; when the nearest tide is low water, add the correction to nearest low tide.
