Engineering 101: Steam Engines

Note: the model in the above video is actually of the CSS Virginia, formerly the Union ship Merrimac.

The earliest ships were powered by human muscle or wind, but early in the nineteenth century the Industrial Revolution brought steam power to the world's waterways. Steam has been superseded only within the last century by other types of power. There are still ships at work today that are powered by steam, from small replica paddlewheel riverboats to large cargo ships.

Paddlewheeler steam engine. Image from Twaintimes.

Steam engine systems, or "plants," have many advantages over other types of propulsion. They have relatively low vibration and noise, low weight, can be fit into small engine room spaces, and, despite their sometimes complicated looking appearance, are simple to operate and repair. On the other hand, steam engines tend to burn fuel at a higher rate than other engines. It was this drawback that forced the British Navy to set up coaling stations all over the world in the late nineteenth and early twentieth centuries. The need to maintain and protect these coaling stations was one of the reasons the Britain needed its empire in the first place, for better or worse.

In a basic steam engine, water is heated by burning coal or something else to create steam in a boiler. Sometimes the "something else" is nuclear energy. In modern steam engines the steam is heated up even more, or superheated, to give it even more energy.

A "Parsons"-type steam turbine.
Image from The Leander Project.

The steam is then directed through nozzles to concentrate it, and is then applied to a turbine, a disc or wheel with blades or paddles mounted on its edge. There are usually two turbines, one for both forward propulsion and astern.

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

The steam is then cooled. Inevitably, some steam escapes the system during all this, so it is replaced with fresh liquid.

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.

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