In Figure El the V- L and C'f scales have been extended to cover model values, so 

 that C't can be found. For convenience, extended scales of VL and Cf for the ATTC line 



jm J 



are also given at the left-hand side, but these form no part of the nomograph itself. 



As an example, consider a ship 500 ft in waterline length with a speed of 20 knots. 



V =20 knots 

 L^^ = 500 ft 

 V • L = 10,000 

 The Series 60 models have a WL length of 20.388 ft, so that the scale will be 



500 



'^= 20.388 = ^^-^^ 



20 20 20 



For the model, V = —= = = = 4.039 knots 



' ^Jk V24.52 4.952 



and L = 20.388, 



whence VL = 4.039 x 20.388 = 82.34. 



For VL =.82.34, from Figure El 



Cf + 0.0004 = 0.00330 for ATTC line 



and for VL = 10,000 



C'f + 0.0004 = 0.00337 for ITTC line 



C'f + 0.0004 = 0.001879 for the ITTC 



Hence the final value of the resistance coefficient to be used is 



C'f +iCf - C'f ) = 0.001879 + (0.00330 - 0.00337) 



's ' m •'m 



= 0.001879 - 0.00007 

 = 0.001809 



On Figure El, starting with this value of C'y^ for the ITTC line, a straight line 

 through a speed of 20 knots on the V scale will give a value of of 2.069, which wi 



o 



inserted in Column J of Table D3 and the calculation completed in the usual way. 



E-6 



