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The Steam Engine

The Power to Speed

When launched in 1843 Brunel’s SS Great Britain was the world’s largest and fastest ship. Isambard Kingdom Brunel used the leading technologies of the day and the massive 12-knot 1,000 horse power engine was its beating heart.

Designed by Thomas Guppy, in collaboration with Brunel, the engine was a development of the triangle engine, the first ‘Vee’ engine, invented by Brunel’s father Marc.

The engine seen today is a full-scale working model constructed using modern lightweight materials.

A full scale working model of the engine

The engine in numbers

  • The three-storey high steam engine weighs 340 tons
  • It produced 1,000 horsepower (745kw). The Victorian equivalent to today’s 70,000 horse power (52,000kw) Rolls-Royce Olympus engine
  • The four 88 inch diameter cylinders were arranged in a V-formation, two on either side at 33 degrees to the vertical
  • The cylinders drove a crankshaft (at the time the world’s largest forged object) with an 18’ 3” diameter wooden toothed chain wheel. The chain wheel used four chains weighing seven tons to turn the propeller shaft
  •  The engine turned the crankshaft at 18 rpm, the propeller shaft turned at 53 rpm (a gear ratio of 2.95:1)
  • This pushed the ship forward at 12 knots (around 22 kph)
  • The engine’s steam was produced from 200 tons of sea water held in the boiler (the largest in the world at the time)
  • The ship could carry 1,200 tons of coal. Enough to take her from Bristol to New York
  • Furnaces under the boiler were stoked round the clock through 24 stoke holes.


How it worked

Although the engine does not run at full speed today, turning at a lower rate than the original, it shows us some key technologies and engineering principles. We can see how a steamship is driven, the expansion working of steam engines, the significance of steam pressure and boiler efficiency and the transfer of linear motion to rotary motion.

The boiler turned the salt water into steam which then pushed through the ‘steam pipe’ into the ‘slide case’, which controlled the inlet and exhaust of steam from the cylinders. The crew regulated the steam entering the cylinders by adjusting the ‘expansion gear’ in the slide case. This helped fuel consumption.

Steam then fed into the cylinders, pushing the pistons up. At the same time water was injected into the steam in the ‘condenser’ which then cooled, shrank and formed a vacuum. This vacuum worked in opposition to the steam pressure on the other side of the piston, and helped draw the pistons up and down.


A moment in time

The 1845 engine gives a snapshot of a moment in engineering history. Boiler design developed rapidly during the 1840s, with engines soon able to operate at much higher pressures than the ss Great Britain’s 5lbs/sq inch.  So the 1845 engine soon became obsolete and was soon replaced. The SS Great Britain was converted from a steam ship with auxiliary sails, to a sailing ship with auxiliary steam power, carrying enough coal for the long voyage to Australia. This smaller more efficient engine design served the ship between 1852 and 1876 when the SS Great Britain was converted to a sailing ship.

Visitors today can see the engine turning, hear the sounds of stokers shovelling coal, and also smell the engine room and its oil and coal.