has been made by Moor (discussion on Reference 74). This equation leads to a value of 

 + 0.00045 for a ship with an LBP of 500 ft, zero for 700 ft, and negative values for longer 

 lengths, all based on the ITTC line. 



In order that the Series 60 results based upon the ATTC line can be compared with 

 others derived from model tests by the use of the ITTC line, it is desirable to provide a 

 rapid method of conversion from one method to the other. This involves the choice of a 

 correlation allowance C ^. In view of the above discussion, the ATTC allowance of +0.0004 

 would appear too high for modern ships, and moreover it should quite possibly be varied with 

 length of ship, but there is no finality in these matters at present. Since there is little 

 difference in the ship prediction from the Series 60 models whichever line is used for extrapo- 

 lation, the only logical choice would seem to be to use the same allowance of +0.0004 with 

 the ITTC line until such time as a more definite value is recommended by the ITTC. 



A second nomograph has therefore been prepared on the basis of the ITTC line using 

 a correlation allowance of +0.0004; see Figure El. In any individual case, if some other 

 value of C^ is preferred, an appropriate allowance can be made. 



The relative values of the frictional and residuary resistances for a given model total 

 resistance will be different when using the ATTC and ITTC lines, so that it is not sufficient 

 merely to correct the frictional part of the total. 



Using the suffixes t, r, and /for total, residuary and frictional, m and s for model and 

 ship and C and C' for resistance coefficients using ATTC and ITTC lines, respectively, we 

 can write 



^ tm^ ^Ttn + C fm " ^ rm '^ '^ fm 



and 



^'rm - ^rm + ^ fm ~ ^ fm 



also C;, = CV, + C'f^ 



= C + C't + (C ( - C'f ). 



Cj.^ is the residuary resistance coefficient as obtained using the ATTC line, and so the 



R D 



values of — ii can be lifted from the contours and inserted in Column G of Table D3 as 



A 

 before. The frictional resistance coefficient to use with the nomograph for the ITTC line 



will now be 



i.e., ITTC ship coefficient + (ATTC model coefficient-ITTC model coefficient), 



E-4 



