380 HYDRODYNAMICS IN SHIP DESIGN Sec. 60.13 



TABLE 60.C — Propulsion Factor-s for Ship and Model for Various Types of Naval and Commercial Vessels 



identity it follows that the ship hull eflBciencies 

 are also higher than the model values 



(iv) The resistances used were those of the 

 model when fitted with all appendages but 

 without appendage scale-effect correction 



(v) The roughness allowance figures given were 

 obtained from the model-ship comparison, using 

 the 1947 ATTC friction coefficients on the model 

 and ship 



(vi) On the average, the overall propulsive 

 efficiency for the ship appears to be less than for 

 the model. 



(3) With the e.xception of the commercial vessels 

 and Carrier C the ship-roughness values are in 

 general relatively high; in these cases the wake 

 fractions are also rather high for the ship. Closer 

 agreement would be expected for new, clean, 

 merchant vessels. Had thrustmeters been fitted 

 to the merchant vessels and the wake fractions 



been computed for thrust identity, some differ- 

 ences would undoubtedly have been found but 

 the general trends would have been about the 

 same. 



60.13 Merit Factors for Predicting Shaft 

 Power. For making quick predictions of shaft 

 power from a background of reference data, 

 and for comparisons of ship performance, the 

 Telfer merit factor described in Sec. 34.10 of 

 Volume I is available in two forms, both producing 

 the same 0-diml numerical values for a given set 

 of basic data. These are, as hsted under Eq. 

 (34.xxiv), 



M 



LP., 



and 



gLPs 



Sec. 34.10 discusses a possible relationship 

 between the Telfer merit factor M and the fatness 

 ratio V/{0.lOLy, which when plotted for mer- 



