Propeller Excitation and Response of 220000 TDW Tankers 



DISCUSSION 



William B. Morgan 



Naval Ship Research and Development Center 

 Bethesda, Maryland, U.S.A. 



The paper presents very interesting comparisons between mo- 

 del and full-scale pressure measurements. The agreements are rea- 

 sonable, which is no doubt due to the carefulness with which the ex- 

 periments were carried out. One would not expect much better agree- 

 ment because of the relative sizes and locations of the transducers 

 and the influence of ship motions on these pressures. 



I was a bit confused by the discussion in the paper concerning 

 the model mean pressures. It appears that the model mean pressures 

 were not in quite as good an agreement with full scale values as the 

 maximum amplitude of the pressures were, but when I read the paper 

 more carefully I found that this was probably the way the data were 

 analyzed. I would like to know whether or not the poor comparison is 

 due to the way the data were analyzed. 



In Section 6 the authors discuss the theoretical calculations 

 and comparisons between theory and experiment, I find this discus- 

 sion very confusing. The comparison between lifting line and lifting 

 surface theory shown in Figure 24 is completely contrary to our ex- 

 perience. We have had generally very good experience with lifting sur- 

 face theory and not too good with lifting line theory, when the propeller 

 does not influence the wake. I would think that the comparison you 

 have made merely indicates the inadequacy of your lifting surface cal- 

 culations, not of lifting surface theory in general. 



The observation that for this type of ship the propeller influ- 

 ences the wake is a very important one, I believe. However, from the 

 description in the paper,- I do not understand how you corrected the 

 wake. Was this an unsteady correction ? If it was not, I do not under- 

 stand why you got an increase in amplitude. If it was, I do not under- 

 stand how you could make the correction by simple momentum theory. 



Also, I do not understand your comment about extending the 

 lifting surface theory to include non-linearity and effects of inter- 

 action with nearby boundaries in light of your results. In the first 



655 



