van Manen, Oosterveld and Witte 



in the case of the nozzle propeller propulsion to pay attention to this problem, 

 and it might be necessary to introduce special braking arrangements in order to 

 reduce the stopping length. 



Finally, a short question. Has the comparison between the Hogner-type and 

 conventional stern given in Tables 5 through 8 been based on experiments with 

 jet tunnels installed in the model, thus actually taking into account the small in- 

 crease of resistance due to the tunnel opening? 



DISCUSSION 



S. Bindel 



Bassin d'Essais des Carehes 



Paris, France 



I am a little skeptical of the elimination of the rudder from such full ships 

 as tankers. In fact, the rudder has two separate functions — the first one is, of 

 course, to make the ship turn but it also constitutes, when amidship, a stabiliz- 

 ing fin to maintain the ship on a straight line. I would like to ask the authors if 

 they have measured the course stability of the tanker without rudder. 



Besides, it may be added that the rudder has a beneficial influence on the 

 propulsive efficiency, in reducing the energy loss due to the rotation of the flow 

 behind the propeller. Have the authors compared the supplementary resistance 

 due to the hull openings of the stern lateral thruster with the effective resist- 

 ance of the rudder ? 



DISCUSSION 



Orvar Bjorheden 



KMW Maine Laboratory 

 Kristinehamn, Sweden 



Let me first compliment the authors for bringing up a most interesting 

 paper within this very important field. Indisputably, a cigar -shaped stern as 

 once suggested by the late Professor Hogner will, to a considerable degree, 

 reduce the problems involved in cavitation erosion and propeller -induced ship 

 hull vibrations. Among the most interesting results from the present N.S.M.B. 

 tests is that such a stern arrangement also seems to give a considerable 



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