Ducted and Contrarotating Propellers on Merchant Ships 



Q _ 



Kn = —^ — = torque coefficient 



T 



= thrust coefficient 



pD'n' 



1 = length of blade section 



L = length of duct . .: 



L = length of hull between perpendiculars 



n = number of revolutions 



p = static pressure at propeller shaft 



p^ = vapour pressure • 



P = propeller pitch 



Q = torque 



r = radius 



R = 2~ propeller radius 



Rj = total resistance 



T — R 



t = — =r-^ = thrust deduction factor 



>= total thrust 



Tjj = duct thrust 

 T = draught of hull 



'^ [_ ^ ~ ^A _ Taylor wake fraction determined from torque and 

 jy I V ~ thrust identity, respectively 



V = speed of model 



V^ = speed of advance of propulsion system 



X = r/R 



Xff = nondimensional hub radius 



1301 



