THE COMPARATIVE SAFETY OF IRON SHIPS. 741 



Iron as a material for ships has some very great and 

 material advantages. It is on the whole lighter, so that an iron 

 phip weighs less, absolutely, than a wooden one of the same 

 size. Then as the knees and other timbers take up less space 

 when made of iron, than when made of wood, and as the thick- 

 ness of the sides is much less, more space is secured in an iron 

 ship than in a wooden one for carrying the cargo. Besides 

 this, a vessel built of iron can be divided into water-tight com- 

 partments, so that an accidental leak will damage only that 

 portion of the cargo contained in that compartment in which 

 it occurs. 



This method of construction is also another factor of safety 

 in case of accident by collision or in any other way. One com- 

 partment may be injured so as to fill with water, while the 

 others, being uninjured, their buoyancy will still keep the ship 

 afloat. An objection, however, to the use of compartments 

 lies in the fact that, as they must be riveted to the sides, the 

 rows of holes for the rivets necessarily weaken the strength of 

 the sides, so that a ship with compartments, which touches on a 

 rock or other obstacle, at one end, is more apt to break apart 

 than one without compartments, as the sides, unsupported by 

 the buoyancy of the water, have the less strength to support 

 her weight in the length. Still, all things considered, iron has 

 come so much in favor for the construction of large ships, that 

 it is in much more general use for that purpose than wood. 



In the construction of an iron ship, the naval architect draws 

 his plans, and sends his construction drawings to the iron roll- 

 ing mill, where each plate is made of the exact curve and di- 

 mensions. The holes for the rivets are punched by machinery, 

 and the plates are then ready to be put together. The hull of 

 the vessel is made of iron bars riveted together, and the plates 

 are riveted to the iron upright ribs, each plate overlapping the 

 preceding. The ribs are placed from ten to eighteen inches 

 Hpart, and the whole structure is of iron. The simplicity of 



