|Paddlewheeler steam engine. Image from Twaintimes.|
|A "Parsons"-type steam turbine. |
Image from The Leander Project.
The exact arrangement of pistons, arms, and gears varies after that, but eventually the steam's energy is used to turn the propeller shafts and thus the propellers themselves. Because modern steam turbines work best at speeds between 4000 and 7000 revolutions per minute, reduction gear must be used to reduced the speed of the shaft and propeller to more practical speeds
Steam engines require more planning and attention than diesel engines. The high temperatures involved (approaching 400 degrees Fahrenheit) and constant presence of water can dangerously stress materials of not handled correctly. It can take four hours or more between the time the order is given to get underway and the time the boiler is up to the needed temperature. The engine itself must be warmed up as well. Similar attention to detail must be observed when cooling down an engine.