Engines for HMS 'Northumberland', 1868 and HMS 'Minotaur', 1867.
© Science Museum / Science & Society Picture Library
Model of a trunk engine (scale 1:12). The single-trunk engine was patented by James Watt (1736-1819) in 1784, but the double-trunk engine, was patented by John Penn in 1845, and was extensively used in screw propulsion. They were fitted in the 'Northumberland' and a sister-ship, the 'Minotaur' by John Penn and Sons. They had two simple cylinders, 112 inches in diameter, by 52 inches stroke. The engines made 58.4 revs per minute, and indicated 6545 hp, which gave a speed of 14.1 knots.