system in Australia, where a number still operate. European side-wheelers, such as , connect the wheels with solid drive shafts that limit maneuverability and give the craft a wide turning radius. Some were built with paddle clutches that disengage one or both paddles so they can turn independently. However, wisdom gained from early experience with side-wheelers deemed that they be operated with clutches out, or as solid-shaft vessels. Crews noticed that as ships approached the dock, passengers moved to the side of the ship ready to disembark. The shift in weight, added to independent movements of the paddles, could lead to imbalance and potential capsizing. Paddle tugs were frequently operated with clutches in, as the lack of passengers aboard meant that independent paddle movement could be used safely and the added maneuverability exploited to the full. Inboard paddlewheeler Recessed or inboard paddlewheel boats were designed to ply narrow and snag infested backwaters. By recessing the wheel within the hull it was protected somewhat from damage. It was enclosed and could be spun at a high speed to provide acute maneuverability. Most were built with inclined steam cylinders mounted on both sides of the paddleshaft and timed 90Deg apart like a locomotive, making them instantly reversing. Feathering paddle wheel In a simple paddle wheel, where the paddles are fixed around the periphery, power is lost due to churning of the water as the paddles enter and leave the water surface. Ideally, the paddles should remain vertical while under water. This ideal can be approximated by use of levers and linkages connected to a fixed eccentric. The eccentric is fixed slightly forward of the main wheel centre. It is coupled to each paddle by a rod and lever. The geometry is designed such that the paddles are kept almost vertical for the short duration that they are in the water. History Western world The use of a paddle wheel in navigation appears for the first time in the mechanical treatise of the Roman engineer Vitruvius (De architectura, X 9.5–7), where he describes multigeared paddle wheels working as a ship odometer. The first mention of paddle wheels as a means of propulsion comes from the fourth– or fifth-century military treatise De Rebus Bellicis (chapter XVII), where the anonymous Roman author describes an ox-driven paddle-wheel warship: Italian physician Guido da Vigevano (circa 1280–1349), planning for a new crusade, made illustrations for a paddle boat