TIDAL CURRENTS 



11 



nearby place for purpose of reference. In figure 6 the average hourly 

 velocity and direction of the tidal current at Nantucket Shoals Light- 

 ship is shown with reference to the times of high and low water at 

 Boston, Mass., H standing for the time of high water, and L for the 

 time of low water. 



In figure 6 the velocity and direction of the current at the begin- 

 ning of°each hour is given by the length and direction of the line from 



Nor+h 



L+3 

 "'^^-^ 



/^ /AH- 2 



<? 



/ 



«-? 



/ 

 I 

 I 

 I 



<^> / 



f 



j>H 



.^/ ■«% 



// 



■^\ 



\ / 





f/ 

 y 



PH+I 



,OH+2 



0-- 



H+3 



Scale of Knots 



I I I I \ L 



0.0 O.Z 0.4 0.6 0.8 1.0 



Figure 6. — Mean current curve, Nantucket Shoals Lightship. 



the center of the ellipse to the hour in question. Thus at the time of 

 high water at Boston the current at Nantucket Shoals Lightship has 

 a velocity averaging 0.7 knot setting N. 85° E. 



With regard to the current curve, or current ellipse as it may be 

 called, which represents the rotary tidal current at any place, the basic 

 features are the relation of the major and minor axes which determine 

 the ellipticity of the curve, the direction of rotation, and the direction 



