van Manen, Oosterveld and Witte 



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DISCUSSION 



H. Lackenby 



British Ship Research Association 



London, England 



I was very interested to see the statement iii the conclusions that the 9 per- 

 cent improvement in SHP with the Hogner-type stern was of the same magnitude 

 as an extreme bulbous bow which leads to a 15 percent reduction in SHP in the 

 light condition. 



In the first place, I would be glad to have some clarification on this matter, 

 that is, whether the 15 percent is the figure for the bulbous bow alone or 

 whether it refers to the bulbous bow and Hogner- stern together. 



In this connection, I should like to mention an experience we had in carrying 

 out bow and stern variations to a tanker model. First we did the bow variations 

 in conjunction with a conventional stern and obtained a small improvement of 

 the order of 3 percent (this was not a ram bow, by the way). We then tried a 

 cigar-shaped stern in conjunction with a conventional bow and obtained an im- 

 provement, here of about 3 percent also. We then tried the bulbous bow and 

 bulbous stern together, hoping of course that the two improvements would be 

 additive, but this did not turn out to be the case. In fact the improvement was 

 barely significant. In other words, the effect of either the bow or stern bulb 

 alone was slightly better than both together. 



I should like to underline here that the bulbs I am talking about were very 

 much less pronounced than those dealt with by the authors, and to some extent 

 we were probably flapping around in the experimental scatter band. 



270 



