The tension at the ship, T, is determined from the length of the 

 radius vector T/WY to the point D/WY, L/WY. The tension at the anchor, T , 

 is then given by 



T = T - WY [la] 



WY WY 1 [1b ] 



In using the charts to solve anchor problems it will be necessary 

 frequently to estimate ship drags, to determine the weight per foot and the 

 safe working load of anchor cable of given types, and to compute the current 

 parameter fi and the required holding power. To facilitate the use of the 

 charts, simple approximate expressions for these quantities have been derived 

 and are assembled in the following section. 



ESTIMATE OF SHIP DRAG 



The drag of a ship due to current can be calculated from the approx- 

 imate formula 



D c = 0.12 V 2 VU 



where D c is the drag due to current, in pounds, 



I is the length of the ship at the waterline, in feet, 

 A is the displacement of the ship, in tons, and 

 7 is the current speed in knots. 



The drag due to wind can be calculated from an approximate formula 

 proposed by Captain E.F. Eggert, USN (Retired), 



D a = 0.0022 B 2 V 2 



where D a Is the drag due to wind, in pounds, 



B is the beam of the ship, in feet, and 

 V a is the wind speed in knots. 



The drag of the ship will be greatest when V a and V are in the same direction. 

 In this case the drags will be additive and the total drag D is 



D = D a + D c = 0.0022 B 2 V 2 + 0.12V 2 VTZ [2] 



EVALUATION OF CURRENT PARAMETER 



The parameter n is defined as 



"-# 



