Naval Architecture and Ship Building 123 



of gravity of every weight in and on the ship running literally to many 

 thousands of items upon a 40,000-ton battleship. Naturally this is very 

 difhcult to estimate with great accuracy during the design stages of a 

 vessel. Howeyer, we can calculate very exactly the position of the meta- 

 center from accurate plans of the lines of a ship and for a coimpleted ship 

 we can determine very accurately the distance of the center of gravity 

 below the metacenter and hence its locatlofi in the ship. This is done 

 by means of the so-called " inclining experiment." With the ship floating 

 freely in still water we moVe a known weight a known distance trans- 

 versely and measure carefully the resulting inclination of the ship. 

 From these results we can calculate by simple formulae the distance 

 of the center of gravity below the metacenter. 



The usual conception is that the stifTer a ship is, or the greater the 

 metacentric height, the greater her safety from the point of view of 

 stability. This is true generally but if a vessel is given too great meta- 

 centric height she is most uncomfortable in a seaway, responding like 

 the chip to every passing wave and her motions may become so abrupt and 

 jerky as to be dangerous. Passenger vessels have often crossed the 

 Atlantic in perfect safety with zero initial stability or even a slightly 

 negative metacentric height, their freeboard afid shape giving them 

 perfect safety through a range of stability of as mu^ch as 90° and their 

 small metacentric height making them unusually comfortable in average 

 weather. 



When the naval architect comes to consider the questioji of the 

 strength of his designs, he is forced to realize that exact scientific methods 

 are not yet applicable to this problem. The designer of a great bridge 

 is able to fix in advance the loads which his bridge must provide for, 

 and then do his designing accordingly. The naval architect cannot do 

 this. The strength of a ship should be such as to enable it tp withstand , 

 under all conditions, the waves of the sea, but the latter are infinite in 

 variety and there must always remain some uncertainty as to just what 

 will be the strains upon the ship due to the action of the sea. However, 

 although we cannot treat this matter by the accurate methods of science, 

 we can make an approxirriation of the most severe conditions, based 

 upon previous accumulated experience and observation, and then apply 

 the usual methods. 



In spite of the many thousands of observations that have been made 

 on waves of the sea, there is yet no complete agreement in regard to their 

 limiting characteristics, such as length and height and the relations 

 existing between these dimensions. We do know that waves have 

 extremely wide ranges of characteristics. We may have, for instance, 

 a wave five hundred feet long, — that is, five hundred feet from crest to 



