Lindgren, Johnsson and Dyne 



# *tl/2 



Ducted prop- arr. 



#0 

 Contrarot. prop. arr. 



*tni2 



#2 



#0 

 Conv. prop. arr. 



Fig. 17 - Tanker project. Stern arrangements. 



6.2. Tanker Project 



The results of the self-propulsion tests, carried out with the tanker model 

 are given in Table 7 and in Fig. 19. A certain caution is recommended when 

 examining the results for two reasons: 



(1) From earlier studies the optimum diameter of a conventional pro- 

 peller in behind condition was known approximately, and the diameters of the 

 two conventional propellers were determined with this in mind. It is difficult to 

 judge, however, if the diameters of the contrarotating and ducted propellers 

 tested were optimum. 



(2) Due to the large scale factor, the advance velocity of the propel- 

 lers is low and thus the thrust and torque values recorded are small. This may 

 influence the accuracy of the measurements, particularly in the case of the 

 torque of the contrarotating propellers. 



Bearing this in mind the following conclusions can be drawn from Fig. 19 

 and Table 7: 



(1) The gain in efficiency for the best set of contrarotating propellers 

 P1250-P1251 is about 6% compared to a conventional propeller at the same 

 number of revs. 



1288 



