COASTAL CURRENTS; ATLANTIC COAST 21 



velocity of flood strength, and the duration of flood. These are 

 followed by similar values for the ebb, and in the last column is the 

 mean current hour. 



All times are expressed in solar hours and hundredths. The times 

 of slack water, the times of flood and ebb strengths, and the mean 

 current hours are referred to the Greenwich transit of the moon. 

 The true directions of the current at the times of flood and ebb- 

 strengths are reckoned from the true north (0°), through east (90°), 

 south (180°), and west (270°). The velocities are given in knots 

 (nautical miles per hour) and hundredths. The mean current hour 

 is the mean interval of time between the Greenwich transit of the 

 moon and the time of the strength of the flood current as modified 

 by the times of slack water and strength of ebb. It is computed by 

 taking an average of the Greenwich intervals of the following m.odi- 

 fied phases: Flood strength, slack before flood increased by 3.10 

 hours, slack before ebb decreased by 3.10 hours, and ebb strength 

 increased or decreased by 6.21 hours. Before taking the average, the 

 four phases must be made comparable by such addition or rejection 

 of the tidal period of 12.42 hours as may be necessary. The values 

 given in table 2 are direct averages of observed currents. They in- 

 clude the average nontidal current for the period of the observations. 



In table 3 are given results for stations where the current, although 

 essentially of the reversing type, was too weak to admit of a satis- 

 factory tabulation and reduction of the individual slacks and strengths. 

 The observations were therefore treated as explained for rotary tidal 

 currents. The results given represent the tidal current only, the non- 

 tidal current having been eliminated by the reduction process. Other- 

 wise the values are on the same basis as those given in table 2. 



The results given in table 4 are for stations at which the current is 

 more or less rotary in character. The results are similar to those 

 given in tables 2 and 3 except that the times, directions, and velocities 

 of the minimums before flood and ebb take the places of the times of 

 the slack waters given in those tables. It will be noted that Pollock 

 Rip Slue and Brunswick lightships appear in both table 2 and table 

 4, one set of results having been obtained by plotting and tabulating 

 the observations on a reversing current basis and the other set by 

 resolving the velocities and carrying them through the process 

 usually employed for rotary currents. As in table 3, the results apply 

 to the tidal portion of the observed current, the nontidal current 

 having been eliminated. 



The hourly velocities and true directions of the tidal current at all 

 the lightship current stations are given in table 5. This table includes 

 data for some stations that do not appear in the tables showing the 

 phases of current because the nature of the movement is such that no 

 weU-defined times of strength or minimum current can be selected. 

 At some of these stations, of which Winter Quarter Shoal Lightship is 

 a good example, the current ellipse is practically a circle, the velocity 

 being very nearly the same throughout the cycle and the direction 

 shifting continuously in a clockwise direction. 



In tables 2 to 5, inclusive, the times of current given are reckoned 

 from the Greenwich transit of the moon. They may be referred to 

 times of high or low water at any one of the tide stations listed in table 

 6 through the use of the time relations, of high and low waters to the 



429061—42 4 



