User:Gatoclass/SB/Geared beam

With the introduction of screw propulsion to steamships in the 1840s, engineers were presented with the problem of finding a way to increase crankshaft speed, as a propeller needs to rotate at least three times faster than a paddlewheel in order to produce the same thrust. Two solutions were developed: the first, to invent engines and boilers capable of producing a higher rpm; the second, to simply add a gear between the existing slow-rpm engines and the crankshaft, so that the crankshaft ran at a higher speed than the engine itself.

The second solution led to the invention of the geared beam engine, also known as the beam and geared or beam-propeller engine. This solution married the old, slow-rpm beam engine to the screw propeller by attaching one end of the connecting rod to a large spur wheel, which in turn rotated a smaller pinion fixed to the crankshaft which operated at an rpm three to five times higher than that of the engine itself.

The geared beam engine had the advantage of being readily adapted to existing engine and boiler technology. Slower engine rpm also meant less wear and tear on engine parts. There were a number of significant disadvantages however, including the added size and weight to the engine of the spurwheel, and the unpleasant "rumbling" noise typically accompanying the operation of the gears. Another problem was the breaking of gear teeth due to flexing of the ship's hull. In spite of these disadvantages, geared beam engines were quite popular on British screw steamships in the 1850s, and were sometimes also used in the United States. They fell out of favour due to advances made in the various types of high-rpm direct-acting engines.

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