Propeller

 Archimedes (287-212 BC) is credited with the invention of the propeller, which for many years was referred to as the “Archimedes screw”.  His was actually an inclined plane spiraled around a shaft, used primarily for lifting water for irrigation purposes.  In the late eighteenth century, developers started installing the Archimedes screw on boats.  These boats were invariably powered by humans and had little or no advantage over the traditional oar propulsion.  The submarine Turtle, invented by David Bushnell during the American Revolution, used hand-cranked Archimedes screws for both propulsion and for depth control.  Invention and improvement of the steam engine was a game changer.  The first steam-powered vessels utilized side wheels.  Advantages of the screw propeller were recognized, but the engineering proved daunting.  In 1827, the first patent for a practicable screw propeller was granted to Josef Ressel in Bohemia.  John Ericsson of Sweden failed to convince the Royal Navy of the value of screw propulsion.  He promptly moved to the United States, where the US Navy funded construction of the USS Princeton, the world’s first warship with screw propulsion.  The Royal Navy quickly got on board and built the HMS Rattler with screw propulsion of a slightly different design.  The technological race was on and few new steam-powered vessels were built thereafter with side wheels (although stern-wheelers remained common on US inland waterways for many years).  Once the maritime world settled on the screw propeller as the primary means of propulsion, the challenge was to design the most efficient propeller.  The Archimedes screw was quickly discarded as inefficient at the rotation speeds needed for a ship.  Early propellers generally had two blades, but the blade number rapidly increased to four or five.  The original blades were generally flat surfaces placed at an angle on the shaft.  Later, blades were given a shape resembling what is commonly called an airfoil.  Variations have been adopted to address cavitation and other issues.  Nowadays, many ships are equipped with controllable pitch propellers, counter-rotating propellers, or azimuthing propellers.  Regardless, they all are derived from the original work of Archimedes coupled with mechanical power.