Paddle-wheel boats, which are typified by 19th-century paddle-powered steamships, are a unique historical form of marine transportation.
Their method of propulsion is what makes them stand out, with momentum provided by a rotating drum fitted with paddleboards. As the drum spins – with rotation powered by an engine (steam/diesel) or motor (electric/ hydraulic) – the mounted boards act as oars, perpetually pushing against the water in a forward or backward cycle. Paddle wheels therefore act in a reversed manner to stationary, mounted water wheels, rotating in order to provide a motive force (thrust).
Paddle wheels are attached to vessels either at the rear (large single units) or at the sides (smaller pairs). The wheels, while sometimes exposed, are more often housed within a container called a paddlebox. The paddlebox both helps protect the marine environment (eg animals can’t get caught up in the wheel assembly as easily) and also reduces the amount of splash while in operation.
The speed at which a paddle wheel spins is dictated by a large industrial gearbox, which allows for a selection of drum rotation speeds in addition to a single speed reverse. Certain paddle-wheel systems also come fitted with adjustable paddles. These work by separating each unit from the drum on axle-like rods – a mechanical layout that enables individual paddles to alter their angle upon contact with the water to be closer to vertical. By doing this, each paddle generates a greater amount of thrust, increasing overall efficiency and power.
Historically, paddle-wheel vessels were used as both ocean-going ships as well as riverboats. However, after the development of the modern screw propeller the paddle wheel was largely superseded due to its poorer efficiency in rough waters. Despite this, a number of paddle-wheel ships still operate today, where they are typically used to transport tourists.
Paddling into history
There is no surviving source that reveals precisely when the first paddle wheel was used to propel a boat, however records do indicate that the Romans were using ox-driven variants by the 4th century and that the Chinese were using them as early as the 5th century. Indeed, writings in the 7th-century History Of The Southern Dynasties -a historical compendium of China dating from 420-589 CE – state that Admiral Wang Zhene used paddle-wheeled ships in his 418 military campaign and that mathematician-astronomer Zu Chongzhi operated a paddle-wheel ship on the Xinting River in the late-5th century.