Munk and Prohaska 



Dr. Strjz^m-Tejsen points out that the new systems should also be an alterna- 

 tive to the contrarotating propeller system. This is also the opinion of the 

 authors, as the reduction of required horsepower for the rather simple over- 

 lapping or interlocking propeller systems in relation to the other propulsion 

 systems was of the same order as the reduction which might be expected for 

 contrarotating propellers, where the technical difficulties are unpredictable. 



Finally, Dr. Str^m-Tejsen mentions the correction of the wake for scale 

 effect. This correction is used to reproduce the conditions of the trial trip, 

 and the test results in this paper are therefore only valid for this case. If no 

 correction had been used, the wake and consequently the other results found by 

 the tests would correspond to some undefined service condition for the ship a 

 year or two out of dock. 



The wake correction is largest for the single- screw propulsion system. 

 Part of the gain in total efficiency obtained by using overlapping or interlocking 

 propellers instead of a single screw is therefore due to this correction. This 

 part is, in the present case, about one-fourth of the total gain. 



The difference in the wake correction for the three different distances 

 between the shafts of the interlocking propellers is small, and only of minor 

 importance for the comparison. The optimum distance between the shafts, as 

 mentioned in the paper, is determined by the propeller loading and the strength 

 of the tangential wake component, rather than by the use of the wake correction. 

 It is therefore difficult to give a general optimum distance between the shafts. 



1546 



