Sec. 45.7 



FRICTION-RESISTANCE CALCULATIONS 



101 



Using the ATTC procedure, the friction resist- 

 ance of the wetted area of a ship is calculated by 

 the general formula given as Eq. (22. iv) in Sec. 

 22.15, based on specific friction-resistance co- 

 efficients: 



Rf = qSlCp for fully turbulent flow on a flat, 

 smooth plate having the same S as the 

 ship 



+ AiCp due to the increment of relative 

 water velocity for longitudinal curva- 

 ture 



-FAzCf due to the increment of drag for 

 transverse curvature 



+ ApCp for plate or planking roughness 



+ AsCf for structural roughness 



+ AcCf for coating roughness 



-f-ApCp for fouling roughness] 



= qS{CF + 2ACf) (45.ii) 



where the ram pressure q = 0.5pV^, S is the ship 

 wetted area, and V is the ship speed. 



Methods of estimating the curvature allow- 

 ances are described subsequently in Sec. 45.14. 

 Tentative values for the four listed roughness 

 allowances are given in Sees. 45.18 and 45.20. 



In many of the published reports quoting 

 SACp values [Todd, F. H., TMB Rep. 663, 1949; 

 TMB Rep. 729, 1950; SNAME, 1951, pp. 327-345] 

 this term embraces not only all the roughness 

 allowances listed in Eq. (45.ii) preceding but the 

 equivalent resistance of condenser-coohng scoops 

 and discharges and miscellaneous sea chests, as 

 well as the forces involved in driving cooling 

 water through the condensers and in overcoming 

 the effects of forcing water out of and drawing it 

 into certain hull openings. 



In towed and self-propelled tests of ship models 

 it is customary to omit the lips, projections, 

 openings, and internal ducts belonging to these 

 systems. Not all ships have them, and in any case 

 they partake of the nature of appendages rather 

 than of structural or other roughnesses. Unfor- 

 tunately, no suitable procedures have been worked 

 out as yet whereby the true additions to ship 

 resistance occasioned by the devices proper and 



TABLE 45.C— Sample Table of ff„ and Cf for the ATTC 1947 Meanline in the MODEL RANGE 



This table is adapted from the upper portion of the table on page 8 of SNAME Technical and Research Bulletin 1-2, 

 pubUshed in Aug 1948. The listings of fl„ in the extreme left-hand column are in terms of (10») or millions. Those in all 

 other columns are Cp(lO'). 



