SHIP 



5355 



SHIP 



sion is easier to obtain. In 1917 vessels con- 

 structed of concrete were projected. 



The chief points considered by a designer 

 are stability, capacity, strength and speed. For 

 great speed, narrow, long lines are necessary, 

 but they can be obtained only at a sacrifice of 

 carrying capacity. The first consideration is, 

 of course, safety. The stability of a ship in 

 the water depends upon the proportion of its 

 parts, the weight and disposition of the cargo 



'THE GREAT EASTERN 



This vessel was not typical of boats of its day, 

 for it was constructed for cable laying, and was 

 made so long that people were sure they never 

 would see another vessel of its size. 



and the displacement. The displacement is 

 measured by the weight of water the ship dis- 

 places, and this weight is equal to that of the 

 ship with its cargo and passengers. Steel was 

 introduced under modern conditions of build- 

 ing about 1870, and its use has tended to alter 

 the lines of modern ships. Ships of wood had 

 projecting keels, which increased their stability 

 and rendered them more manageable. The 

 great steel liners and freighters of to-day are 

 built without external keels. The bottom of 

 the ship is a keel plate of steel, extending the 

 length of the vessel and joining the upright 

 framework of the sides. The double-bottom 

 system of building, developed first in the Great 

 Eastern (1852), is now quite common. It has 

 added greatly to the safety of sea travel. 



In ships having a double bottom, the keel 

 proper, which is about two feet deep, connects 

 the central line of the keel plate with the inner 

 bottom. It serves to support the transverse 

 structure of ribs and joins the stem and stern- 

 posts, giving greater rigidity to the framework 

 of the vessel. The ribs, which are of steel, are 

 covered with a sheathing of steel plates of va- 

 rying thickness. In battleships of the first line 

 this sheathing of steel is often a foot thick, to 

 resist the action of heavy shells. The decks 

 are placed one above another and fastened to 

 the framework of the sides. A cross section 

 amidships has the shape of the letter U. The 

 steel used in ships is .known as mild steel; it 

 is tough and pliable and so treated that it is 

 less affected by heat and cold than tool steel. 



The steam turbine engine, by which most 



large ships are driven, was invented by C. A. 

 Parsons, of Sweden, in 1884. It maintains a 

 speed of thousands of revolutions a minute, 

 driving the twin or triple screws at racing 

 speed. The screw was first used on ocean ves- 

 sels in 1839, and has now displaced the old 

 paddle wheels. The screw propeller is less af- 

 fected by the rolling of a ship than are pad- 

 dles, and it acts on a relatively greater volume 

 of water in a given time. 



Experiments which had been conducted dur- 

 ing a considerable period culminated in 1888 

 in the use of petroleum spirit for fuel instead 

 of coal. The naphtha launch and the high- 

 speed racing boat were later developments. 

 They are driven by internal combustion en- 

 gines, the power being applied directly by a 

 succession of small explosions within the en- 

 gine. Large motors burning heavy oil fuels 

 have been installed in vessels of considerable 

 displacement, but their use is still confined 

 chiefly to craft of smaller types. There is a 

 tendency in present-day warship building to in- 

 stall oil-burning engines. 



The use to which the ship is to be put deter- 

 mines the design. Passenger vessels ride high 

 in the water, so as to afford ample light and 

 air for the tiers of cabins. Cargo vessels, on 

 the other hand, ride much lower, especially when 

 laden. These cargo ships, sometimes called sea 



THE SAVANNAH 



The first steaming vessel to cross the Atlantic 

 Ocean. The feat was accomplished in 1819. 



tramps, do a great part of the world's carrying. 

 They maintain an average speed of from ten to 

 eleven knots, being built for capacity rather 

 than for speed. The freighter of the Great 

 Lakes is regarded as a model of adjustment to 

 the ends it serves. Ore carriers like the /. 

 Pierpont Morgan are built 600 feet long and 

 with a 60-foot beam. They carry 12,500 tons 

 of coal or ore, or 450,000 bushels of grain. The 



