Propeller Design 



r 



.);y)y^>)>>>>>>>>)>>>);;>)>.V.V>>>i>>>>>>>>);;..Vvv;;;;);;;;;^ - V, -. u u ^ u; 



PARTS OF THE AFT BOHY AT 

 WHICH THE INSTANTANEOUS 

 FORCES WILL BE MEASURED 



DYNAMOMETER 

 (PROPELLER THRUST 

 AND TpRQUE ) 



WALL OF CAVITATION TUNNEL OBSERVATION WINDOW /■ 



Fig. 4 - Arrangement in cavitation tunnel for the determination of the effect 

 of propeller cavitation on the vibratory forces on the afterbody of a ship 



Speed ahead, rpm ahead 

 Speed ahead, rpm backing 

 Speed astern, rpm backing 

 Speed astern, rpm ahead 



(a 

 (a 



= 0°- 90°), 

 = 90°- 180°), 

 = 180°- 270°), 

 = 270°- 360°). 



The part for a = 0° to about 30° indicates the "normal" "open-water" screw 

 diagram. From Fig. 6 the effect of the width of blade chord, also of B.A.R., on 

 thrust coefficient and torque coefficient in the ranges where separation of flow 

 occurs is clear. This type of diagram is of importance for the analysis of stop- 

 ping maneuvers of ships. 



A research area of increased interest is that of the behavior of the propeller 

 in a seaway. Besides the dynamic load on the shaft and the afterbody induced by 

 the propeller, the behavior of the propeller in a seaway with respect to cavita- 

 tion plays a role. Diagrams as indicated in Fig. 3 may be of great value, when 

 we analyze the danger of psc and ssc starting from the design condition (known 

 Cf and given cavitation index o^) if we should know the load variations of the 

 propeller in a seaway. From test results with ship models in waves, it has ap- 

 peared that the load variations of the propeller are built up on an average power 

 increase due to seaway. These load variations are the same order of magnitude 



1580 



