Strip Theory 



DISCUSSION . 



G. Aertssen ,-. - . : 



''■■■' ■-' ' University of Ghent ■■ 



Ghent, Belgium \ ■ .. 



This work of Prof. Marsich and Dr, Merega on bending moments is un- 

 doubtedly one of the investigations which should be made. I have, however, 

 two remarks, both related to the sea aspect the authors have selected for their 

 calculations. In their Table 1, they refer to wind speeds of 60, 65, and 70 knots 

 and corresponding wave heights of 13, 14, and 16 m, but nevertheless the calcu- 

 lations are made for a 60-knot wind and the corresponding wave height of 13.23 

 m. However, significant wave heights of 16 m have in fact been reported. I 

 confess that this wave height of 16 m was recorded near Iceland and that the 

 usual track of a 200-m ship is not in this area. 



My second remark concerns energy distribution in waves. The authors 

 assumed what they in Sec. 1.1 called a long- crested confused sea. There was 

 a contradiction in this sea description. If the sea is long-crested the super- 

 position principle fully applies. For a confused sea you have to assume a di- 

 rectional energy spread, and this, according to experiment, gives you a longi- 

 tudinal moment which is 10 to 20% less. Actually, in these extreme seas energy 

 is spread, and so it happens that the 20% loss in bending moments because of a 

 significant wave height taken too low is counterbalanced by the 20% gain made 

 by the authors where they ignored directional spread. There is also the ques- 

 tion of Froude number. For a ship 200 m in length a Froude number 0.1 cor- 

 responds to a speed of 9 knots. I hardly imagine a ship, even one so large as 

 200 m, sailing at a speed of 9 knots ahead in waves Beaufort 11. I would also 

 raise the point of wave frequency, but here again the authors are on the pessi- 

 mistic side. Altogether, it is a satisfactory approach to the problem. 



DISCUSSION 



H. Volpich 



Brown Bros. & Co. Ltd. 



Edinburgh Scotland 



The authors have selected for their important and valuable investigation 

 the Series- 60 Todd hull forms and given for them the appropriate parameters 

 in the paper. Since the modern trend for large bulk-carriers and tankers con- 

 sists of hull forms having large ram bulbs, it is suggested they include in any 

 future study at least one form with a heavy ram bulb, because this may show up 

 in the resulting bending moments and would give some idea of any possible devi- 

 ations from the Todd Series 60, when the calculations are applied to bulbous hull 

 forms. 



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