Page:Popular Science Monthly Volume 90.djvu/285

 Battle Cruisers in the World

proposed battle cruisers at a speed of 35 knots. Never in our naval history has such a power plant been installed in a ship

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���comparison with New York's Public Library and adjacent Fifth Avenue buildings in this picture. They will cost $16,500,000 each. It will take 180,000 horsepower to drive one at 35 knots

��is not the way ships are built. The Lusitania made twenty-five knots with 70,000 horsepower. To make fifty knots, it might be supposed that it would be necessary merely to double the size of the engines. Battle cruiser building* would be easy if that were all. Each additional knot is purchased at the expenditure of thou- sands of horsepower. Our naval engineers estimate that 180,000 horsepower w'ill be required to develop thirty-five knots in one of the new battle cruisers. Never have marine engines of that power been built. As a result, American shipbuilding companies are loath to bid on the cruisers. The builders say that they will not bid ex- cept with the understanding that they will receive the cost of building plus ten percent. A similar plan of paying for ships was worked out in Germany when the giants Imperator and Vaterland were built. The Naval Appropriation Act of Aug. 29, 1916, permits this method of bidding. Our shipbuilders maintain that even on the ten-percent-plus-cost basis they will prob- ably be losers because the Government will undoubtedly copy their successful models, and build ships in its own yards after the hard work has been done in private yards. To develop a speed of thirty-five knots — forty miles — an hour, turbines must be employed. A steam turbine works on

��the windmill principle. Steam spurts against blades on a long shaft. The old- fashioned steam engine — ''reciprocating en- gine" in engineers' language — is very tall. Its pistons work up and down in the cylinders, as everyone knows. Recipro- cating engines take up much space, so much, in fact, that a ship like the Lusitania, which was driven by them, was practically all engines. The steam turbine requires \ery little head room and very little floor space, so that great economies can thus be effected. Moreover, oil will be used as fuel, which can be carried in the double bottom of the cruiser, thus further releasing space which would otherwise have to be taken up by coal bunkers. Moreover, steam turbines are lighter than recipro- cating engines. They can be heavily overloaded, should emergency arise- On the other hand, the use of steam turbines is not all plain sailing; for turbine engines, unlike reciprocating engines, are non-reversible and special means must be provided for backing. Furthermore, the most efficient speed of revolution of a boat's propeller is very much lower than the most efficient speed of the shaft of a turbine engine. Therefore it is not the most efficient proceeding to couple the turbine directly to the propeller-shaft. Gearing and a novel method of driving

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