Fully Cavitating Propeller for a Hydrofoil Ship 



Fig. Zl - Moderately loaded, fully cavitating propeller 



The development of fully cavitating propellers is being continued, and pro- 

 posals for additional design studies and tunnel testing have been made. An im- 

 mediate objective is to produce a propeller with an efficiency comparable to that 

 of screw W264 mentioned earlier, but in which the structural integrity is in- 

 creased by thickening the blades. For this purpose an additional model with 

 thickened blades has been made and partially tested. However, these results 

 indicate that wetting of the back surfaces occurs, and therefore a modification 

 is necessary. 



Further testing is required to establish the optimum camber and the opti- 

 mum relationship between camber and incidence or pitch, and to this end it is 

 hoped that a further test series of a family of fully cavitating propellers can be 

 initiated in the near future. 



STRUCTURAL CONSIDERATIONS 



The hydrodynamic requirement for relatively thin leading edges in fully 

 cavitating screws, together with the high powers that are transmitted and the 

 difficult operating environment, give rise to severe structural problems which 

 must be considered in the design stage. The blades must be made sufficiently 

 strong to withstand the maximum steady stresses likely to be experienced, in 

 addition to the fluctuating stresses that will occur when operating in the wakes 

 of the pod attachments. Further, the deflections of the blades under load should 

 be as small as possible. 



In order to combat these onerous operating conditions it is necessary to 

 employ a strong propeller material possessing high resistance to erosion and 

 cavitation damage, combined with high values of fatigue strength and elastic 



987 



