Rouse tsky 



2 Wp 

 t = 1 +\ 1 + 6 p 



(2) 

 where "Wp is the nominal potential wake factor . 



The thrust deduction factors calculated by formula (2) hold , 

 strictly speaking , for the perfect fluid only , however , the errors 

 due to this assumption are essential but at very small load factors . 

 The interaction factors can be refined through the tests in a cavitation 

 tunnel . During the tests "Z " drive resistance and propeller perfor - 

 mance curves are recorded . Apart from the refinement of the inter- 

 action factors , the tests make it possible to reveal the propeller ca- 

 vitation effect upon the value of these factors . When analysing these 

 experimental results the wake and thrust deduction factors may be 

 determined by the following formulae : 



A p A R 



W = 1 , t = — - — 



where A p - propeller advance ratio , 



A - apparent advance ratio , 



P - propeller thrust , 



AR - gain in resistance of "Z " drive due to the presence of 

 propeller . 



The tests with various types of "Z " drives showed that the 

 wake value was independent of the propeller loading . This gives 

 grounds to consider that the wake value will neither be influenced by 

 the propeller loading changes due to cavitation . 



Therefore the wake value obtained by the comparison of the 

 propeller performance curves for subcavitating regimes maybe used 

 in further calculations . For the agreement of the propeller perfor - 

 mance curves in open water and downstream of "Z " drive under cavi- 

 tation use is made of the correction factors taking into account the 

 effects of the flow nonuniformity and pressure change in the propeller 

 disk upon the propeller thrust and torque . 



The dependence of the thrust deduction factor upon the propel- 

 ler loading and cavitation number for the propulsion system with the 

 pod length-to-diameter ratio —j— = 5 and -H— = 1 . 5 is shown in Fig. 

 3 . As is seen with the development of cavitation the thrust deduction 

 factor decreases . This result is in qualitative agreement with the 

 conclusions of the paper f 3 J 



404 



