Archimedes' screw screws of decreasing pitch are used for the compaction of waste material. If water is fed into the top of an Archimedes screw, it will force the screw to rotate. The rotating shaft can then be used to drive an electric generator. Such an installation has the same benefits as using the screw for pumping: the ability to handle very dirty water and widely varying rates of flow at high efficiency. Settle Hydro and Torrs Hydro are two reverse screw micro hydro schemes operating in England. The screw works well as a generator at low heads, commonly found in English
SS Archimedes fitted with Smith's patented propeller, "Princess Royal", was built in the north of England, and in 1842, several more screw-propelled vessels were built or launched in Britain, including "Bedlington", built at South Shields, "Bee", launched at Chatham, and the largest ship built to that date in Ireland, "Great Northern", launched at Derry. From this point, screw-propelled merchant ships grew rapidly in number. By the time the Cunard Line built the paddle steamer "Persia" for transatlantic service in 1856, the paddlewheel was already becoming an anachronism. Though Smith's "Archimedes" had played an important role in the introduction of screw propulsion, Smith