SS GREAT BRITAIN WAS A QUANTUM LEAP
BY R LEA CLOUGH
Lea Clough continues to look for historic and interesting ships while on holiday in Britain. T
he 98m SS Great Britain, on display in her permanent dock in Bristol, was by far the longest and largest ship of her time and the first screw-propelled iron liner. She pioneered many developments, such as her balanced
rudder, double bottom, watertight bulkheads and wire rope rigging.
She followed her designer, Isambard Kingdom Brunel's first ship, the SS Great Western and was, in turn, followed by his magnum opus, the 20,000 ton SS Great Eastern, built in 1858 and destined not to be surpassed in size for 43 years. The dock in which the Great Britain now rests was built in the autumn of 1839 for her construction, and the end earth wall was dug away to float her out shortly before her christening by Prince Albert, the consort of Queen Victoria. After being modified over the years and suffering damage by bombs during the Second World War the dock was abandoned, only to be resurrected to house its original ship. The Great Britain's design called for frames spaced at about
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450mm, to which plates 1.8m long and 600mm high were riveted. Plating thickness varied from 22mm near the keel to 9mm at deck level.
Her design required 1400 tons of wrought iron and 370 tons of wood, and more iron and wood was used in later modifications. Brunel designed her as a paddle-steamer, but the new technology so impressed him he redesigned her for screw propulsion. Two inverted V two-cylinder engines were installed with a common crankshaft at the top, above the waterline. This carried the sprocket of a chain drive system, which connected to the tail shaft, geared up on a 3:1 ratio.
Full power of 500hp and full speed of about 10 knots was achieved at 18rpm on the engines, hence a shaft speed of 54rpm. Three coal-fired low-pressure (5psi) boilers used seawater. This was the practice at the time, but it sounds incredible to those of us who served in high-performance steam turbine ships, in which the slightest trace of salt in the feed water caused enormous problems.
