To assist in the use of the data, calculation forms for the prediction of chp and ©400 



are given in Tables B46 and B47. The tables are largely self-explanatory, but a few points 



call for a little comment. 



^R ^ B 



The contours give and [Q for three \alues of — - 2.5, 3.0, and 3. .5. For any 



particular ship, therefore, it is necessary to interpolate between these to obtain the correct 



n 



value for the actual of the ship in question. This could be done by plotting the three 



'^ B 



values and lifting off the ordinate at the correct — value. In Table B46, it is suggested 



thatthis interpolation be done by assuming a parabola to pass through the three points. This, 



in effect, means that all users will obtain the same \alue of or (Q for the desired — , 



i.e., it removes personal interpretation of the data; moreo\er, experience has shown that the 



B 

 data can thereby be extended to — values of 2.0 and 4.0. 



H 



For comparison purposes, it is sometimes desirable to compute ©and @ for the 

 actual ship under consideration, and this can be done by completing columns 0, P, and Q in 

 Table B46. This value of © will be different from that for the equivalent 400-ft ship, of 

 course, since frictional resistance is a function of length. The value of © for lengths other 

 than 400 ft can be estimated approximately from the differences shown in Table 348, due to 

 Professor L.A. Baier (discussion on Reference 63, page 571). Much of the resistance data 

 published elsewhere refer to a standard ship length of 400 ft and the © contours given in 

 this report are for such a standard length, and for — values of 2.5, 3.0, and 3.5. Table B47 



will enable the value of (£)4oo ft '° ^^ interpolated for any other desired value of — . 

 The nomograph in Figure B127 gives a rapid graphical method of finding the 



o 



frictional resistance per square foot of wetted surface for ships of different lengths operating 



at various speeds. The results apply to a ship in sea water at a temperature of 59°F (15°C), 



which has been adopted as a standard figure by the ITTC. A standard ship correlation allow- 



^F ' 



ance of +0.0004 has been included. — is obtained by passing a straight line through 



appropriate values of VL and V and reading the answer at the intersection of this line with 



f^F 

 the scale which is connected to the F-scale used. Estimates for other than standard 



correlation allowance of +0.0004 can be made by taking the above values and increasing 



o 

 them in the ratio of the total C p- values for the desired allowance and +0.0004, respectively. 



In computing the frictional resistance for estimating power for a proposed vessel, it 

 is recommended that the wetted surface for the proposed vessel be used. If this figure is 

 not known, the wetted surface for the equivalent Series 60 hull can be obtained from the 

 contours in Figures B124 to B126. 



B-2 



