This is a working model of an inverted vertical triple-expansion steam engine. In the second half of the nineteenth century, this became the commonest form of marine engine. In this engine, the expansion of steam was divided over three cylinders in sequence, making the engine very efficient. The lightweight design featured cylinders raised over a bedplate on columns. This arrangement made the parts accessible and allowed the crankshaft to be positioned low enough to be coupled directly to the propeller shaft. These highly developed engines, together with the steam turbine lasted as long as steam propulsion was in use. The design had a powerful influence on that of the internal combustion engines that eventually replaced them. This working model, not strictly based on full-size practice, is typical of the products of amateur modelling, which was then becoming a popular hobby.