Marsich and Merega 



^AV ^AV + ^AD ^AD 

 P = 2 



DL 



where 



D = displacement, 



D^^ = displacement portion lying forward of ship's center of gravity, 



D^jj = displacement portion lying aft of ship's center of gravity, 



x^^ = distance between ship's center of gravity and D^^'s center of 

 gravity, 



X^j, = distance between ship's center of gravity and D^^'s center of 

 gravity, 



L = waterline length. 



Thereafter, the quantity p has been assumed as representing the weight distri- 

 bution along the hull. 



When considering the hull volume distribution and the waterline shape , 

 the following factors were to be assessed: 



(a) the independent effect of the two parameters, each separately 

 considered, and 



(b) the reciprocal influence of the two parameters. 



Some systematic calculations have been carried out, assuming the same hull 

 volume, first maintaining the same waterline shape and systematically modifying 

 the area curve, then maintaining the same area curve and modifying the water- 

 line shape. It has been found that the wave bending moment is much more af- 

 fected by waterline shape modifications than by area curve, in agreement with 

 what had been clearly stated by Swaan (see Sec. 2.2). 



Therefore, the waterline coefficient has been kept as only significant param- 

 eter and as a matter of fact the consequent errors are even more negligible than 

 could be expected at first, owing to the fact that generally a certain correspond- 

 ence exists between block coefficient and waterline fineness coefficient, it being 

 extremely unlikely that full ships have low-fineness waterlines or that fine ships 

 have full waterlines. 



When considering sea spectrum it was decided to adopt Scott's formula, 

 which allows one to write the equation as a function of frequency, when wind 

 speed is known. In Table 1 the above formula is reported, together with the ex- 

 pressions for significant height, peak frequency, and mean wave period. Figure 

 1 shows spectra corresponding to wind speeds of 20, 40, and 60 knots, while in 

 Fig. 2 diagrams are drawn of significant height, peak frequency, and mean wave 

 period, as a function of wind speed. 



818 



