1862.] and its Resistance to Projectiles at High Velocities. 493 



These proportions apply with great force to vessels requiring close 

 rivetting, such as ships and boilers that must be water-tight, and in 

 calculation it is necessary to make allowances in that ratio. 



Strength of Ships. — Of late years it has been found convenient to 

 increase the length of steamers and sailing vessels to as much as eight 

 or nine times their breadth of beam, and this for two reasons ; first, to 

 obtain an increase of speed by giving fine sharp lines to the bow and 

 stern ; and second, to secure an increase of capacity for the same mid- 

 ship section, by which the carrying powers of the ship are greatly 

 augmented. Now, there is no serious objection to this increase of length, 

 which may or may not have reached the maximum. But, unfortunately, 

 it has hitherto been accomplished at a great sacrifice to the strength of 

 the ship. Vessels floating on water and subjected to the swell of a 

 rolling sea, — to say nothing of their being stranded or beaten upon the 

 rocks or sand banks of a lee shore, — are governed by the same laws of 

 transverse strain as simple hollow beams, like the tubes of the Conway 

 and Britannia tubular bridges. Assuming this to be true, and indeed 

 it scarcely requires demonstration, it follows that we cannot lengthen a 

 ship with impunity without adding to her depth or to the sectional area 

 of the plates in the middle along the line of the upper deck. 



If we take a vessel of the ordinary construction, or what some 

 years ago was considered the best — 300 feet long, 41 feet 6 inches 

 beam, and 26 feet 6 inches deep — we shall be able to show how in- 

 adequately she is designed to resist the strains to which she would be 

 subjected. To arrive at these facts we shall approximate nearly to the 

 truth by treating it as a simple beam ; and this is actually the case, to 

 some extent, when a vessel is supported at each end by two waves, or 

 when rising on the crest of another, supported at the centre with the 

 stem and stern partially suspended. Now in these positions the ship 

 undergoes, alternately, a strain of compression and of tension along the 

 whole section of the deck, corresponding with equal strains of tension 

 and compression along the section of the keel, the strains being reversed 

 according as the vessel is supported at the ends or the centre. These 

 are, in fact, the alternate strains to which every long vessel is exposed, 

 particularly in seas where the distance between th^ crests of the waves 

 does not exceed the length of the ship. 



It is true that a ves^sel may continue for a number of voyages to 

 resist the continuous strains to which she is subjected whilst resting on 

 water. But supposing in stress of weather, or from some other cause, 

 she is driven on rocks, with her bow and stern suspended, the proba- 

 bility is that she would break in two, separating from the insufficiency 

 of the deck on the one hand, and the weakness of the hull on the other. 

 This is the great source of weakness in wrought-iron vessels of this 

 construction, as well as of wooden ones, when placed in similar trying 

 circumstances.* 



* See Vol. I. of the * Transactions of the Institution of Naval Architects,' on the 

 Strength of Iron Ships. 



