Sec. 60.7 



!.0 DWL= 28.00 ft 



SHIP-POWERING DATA 



365 



DWL-28.00ft 



\ X ^. 



s \ \ 

 \ \ s 

 \ \ \ 



0.8 DWL = 2Z.40 ft 



\ \ \ 



/ / / 

 / / / 



^ ^ / 

 / / / 



\ \345\ O^^S / 15 / 



Lentjth on Woterlme, 



J)esigned 444.0 ft 

 Draft, for'd, 13.0 ft 



Draft.oft 20.50 ft 



Displacement 8,268 t 

 Speed for test 17.92 kt 

 To^lor Quotient Tt^, bosed 



0.852 

 Plane of Survey 



is 6.3i3 ft for'd, of AP 

 Third Numerol Represents Moqnitude 



of the Tonqentiol Component of the 



Woke Velocity 



Fig. 60.J Wake-Survey Diagram for Victory Ship, TMB Model 3801, at 8,268 Tons Displacement 



fractions of 18.2 and 14.3 per cent in the vicinity, 

 is only about [100 - 0.5(18.2 + 14.3)] = 83.7 

 per cent of the ship speed. Here the pitot head 

 automatically takes account of the cosine of the 

 angularity of flow. 



The effect of the boundary layer is felt rather 

 noticeably on the tip circle at the 1 o'clock posi- 

 tion, where the wake fraction is 34 per cent. 



Sec. 11.10 points out that no model-basin 

 techniques in current routine use, and no graphic 

 or tabular representations which have so far been 

 developed, take account of variations in wake- 

 velocity magnitudes and direction with time. 

 If such variations exist, the current (1955) 

 observation methods average them out. Unfor- 

 tunately, the propulsion-device blades do not fail 



to take account of them. The result is that periodic 

 forces are exerted on the blades, which when 

 transmitted through the propulsion-device bearing 

 usually produce vibration in the ship structure. 

 The foregoing is what may be termed a qualita- 

 tive inspection and interpretation of wake-survey 

 data. It lacks a set of specific rules, not yet 

 formulated, to be used by the naval architect or 

 marine engineer to discover flow features which 

 need correction, such as those mentioned pre- 

 viously in this section. In the case of the finer 

 Normandie, these features were revealed only by 

 excessive vibration of the structure, which re- 

 quired withdrawing the vessel from service to 

 rebuild the four bossings. In the case of certain 

 large combatant vessels of the U. S. Navy, 



