Archimedes' screw a crank mechanism in his "Bellifortis" (1405). This mechanism quickly replaced the ancient practice of working the pipe by treading. The Archimedes screw consists of a screw (a helical surface surrounding a central cylindrical shaft) inside a hollow pipe. The screw is usually turned by windmill, manual labor, cattle, or by modern means, such as a motor. As the shaft turns the bottom end scoops up a volume of water. This water is then pushed up the tube by the rotating helicoid until it pours out from the top of the tube. The contact surface between the screw and the
SS Archimedes lead to the adoption of screw propulsion by the Navy (see Legacy section below). With the conclusion of the Dover trials, "Archimedes" was placed at the disposal of Captain Chappell for a circumnavigation of Britain, which took place in July 1840. This voyage presented an opportunity to not only conduct further tests, but also to allow inspection of the technology by shipowners, engineers and scientists in ports throughout the country. "Archimedes" completed the 2006-mile voyage at an average speed in excess of 7 mph, and a maximum speed under ideal conditions of 10.9 mph. With the completion of this voyage,