46 Steamships A Ship-Launch. 



3. The ribs are then covered with thick 

 planks, and those planks which are below the 

 water-line are covered with plates or sheets of 

 copper or other metal. 



4. Steamships are now built wholly of iron 

 and steel. The plates, instead of planks, are 

 secured by bolts and rivets passing through 

 their overlapping edges. Iron ships can carry 

 larger cargoes than wooden ships. 



5. When the body or hull of the ship is 

 ready to be launched, long, slanting timbers are 

 placed under it, reaching down into the water. 

 These timbers or tracks are covered with grease 

 and soap, some of the props removed, and the 

 whole is made to slide down into the water. 

 People take great pleasure in witnessing a launch. 



6. After the ship is launched it receives its 

 masts and sails, and is finished. If intended for 

 a steamship, it is also provided with engines, fur- 

 naces, smoke-pipes, and perhaps paddle-wheels. 



7. Instead of paddle-wheels, which you may 

 see at the sides of steamboats, you will find 

 that now most steamships are driven by a pro- 

 peller, or huge iron screw, at its stern, or hinder 

 part. When this propeller turns round and 

 round very rapidly, its great, wide arms strike 

 the water in such a way as to push the steamer 

 ahead at the rate of about fifteen knots, or miles, 

 every hour. 



