A type of steam propulsion engine developed in the USA from the early pumping engines installed by James Watt in many Cornish mines, in which a beam is pivoted in the centre above a vertical cylinder and transmits the motion of the piston down a crankshaft by a long connecting rod. This type of engine, used at first on land in mills and factories, was adapted in the USA for river paddle steamers from about 1830. It was to be seen on almost all the side-wheelers on the Mississippi, Ohio, and other western rivers, as well as on New York ferries and eastern seaboard coastal steamers.
To make local manufacture simple and to save top weight, the A-frames or entablature on which the beam was mounted in the vessel were almost entirely of wood, and the beam itself was made rigid by means of iron truss rods in the form of a flattened diamond. Owing to the height of these frames, the beam stood in full view above the upper deck of even the largest steamboats, and its movement as it rocked up and down turning the paddle wheels earned it the Native Americans' description ‘mill walkee on river’.
Because of the weight of this lofty structure and its effect on the vessel's stability, it was seldom fitted to ocean-going ships. It was entirely American in conception and ideal for its purpose in smooth waters, but not to be found in quite the same form anywhere else in the world. In Europe its counterpart was the side lever engine.
Subjects: Maritime History.