Steam arrives on the water
By the late eighteenth century, steam engines were already pumping water and driving machinery, and several inventors saw that they might also drive a boat. The question was how to turn an engine’s motion into thrust on water. The first widely used answer was the paddle wheel, a large wheel with flat blades, mounted on the sides or at the stern of a hull.
Priority in steamboats is contested, and several people worked at the same time. In France, Claude de Jouffroy ran a steam-driven boat on the Saône in 1783. In the United States, John Fitch operated steamboats on the Delaware River in the late 1780s and 1790s, and James Rumsey also built experimental craft. In Scotland, William Symington’s Charlotte Dundas, tested on the Forth and Clyde Canal in 1802, was a practical stern-wheel tug. None of these became lasting commercial successes, partly because of cost, engine reliability and, in some cases, limited backing.
Fulton and the paddle steamers
The breakthrough in business terms is usually linked to Robert Fulton, an American engineer, and his partner Robert Livingston. Fulton’s North River Steamboat, later called Clermont, began regular service on the Hudson River between New York and Albany in 1807. The engine was a Boulton and Watt type, a development of the engines with a separate condenser. Fulton did not invent the steamboat, but his service was reliable enough to attract paying passengers.
Paddle steamers spread quickly on rivers, lakes and sheltered coasts. On the Mississippi and other American rivers, they carried people and freight upstream against the current, which sailing vessels could not easily do. In Britain, paddle steamers served estuaries and coastal routes, and in 1819 the American ship Savannah crossed the Atlantic partly under steam, though she used her engine only for part of the voyage. In 1838, the paddle steamers Sirius and Great Western crossed the Atlantic under steam power, and regular steam service began soon after.
Limits of the paddle wheel
Paddle wheels worked well on calm water but had drawbacks at sea.
- Uneven immersion. In waves or when the ship rolled, one wheel might lift out of the water while the other stayed deep, reducing efficiency and making steering harder.
- Changing draft. As coal was burned and the ship became lighter, the wheels sat higher in the water and lost bite.
- Exposed machinery. The wheels and their housings took up space along the sides, interfered with sails, and in warships were vulnerable to gunfire.
- Drag under sail. The wheels created drag when a ship was sailing without steam, a problem for vessels that still depended on sails for much of a voyage.
The screw propeller
The screw propeller is a set of angled blades on a shaft, turning under water at the stern. It is placed below the waterline, so it stays submerged and is protected, and it provides thrust whether the ship is heavily loaded or light. The idea has a long history. Ideas related to screw-shaped devices go back to antiquity, and inventors proposed propeller-like devices for boats from the eighteenth century. Practical development came in the 1830s.
Two names are most often cited. In England, Francis Pettit Smith patented a wooden screw in 1836 and tested it on a small boat. In the same year, the Swedish-born engineer John Ericsson, working in Britain, patented a different propeller design. Others, such as Josef Ressel in Austria, also experimented, and in many accounts credit is shared or disputed. Early screws were often long, with spiraling forms, and engineers refined the shape and number of blades for efficiency. The principles are related to those later used in airplane propellers, although water and air behave differently.
Proving the propeller
The first major oceangoing demonstration was the SS Archimedes, a screw-driven steamer launched in 1839, which made voyages that helped convince the British Admiralty and other observers. Isambard Kingdom Brunel was impressed and changed his plans for the SS Great Britain, which was launched in 1843. It was an iron-hulled, screw-driven ocean liner, a combination that would become standard; iron hulls depended on the blast furnace as an affordable source of metal.
A frequently told story is the 1845 trial between the Royal Navy ships HMS Rattler, screw-driven, and HMS Alecto, paddle-driven, which were roped together and set to pull against each other. Rattler is said to have towed Alecto backward. The tale is often repeated as decisive, though the trial was one of several tests and the transition was also driven by many other practical considerations.
The transition
Paddle wheels did not disappear. They remained common on river and excursion steamers for many decades, where their shallow draft and maneuverability were useful, and some paddle liners were built for ocean service into the second half of the nineteenth century. But for warships and oceangoing merchant ships, the screw became the norm in the mid-to-late nineteenth century. Combined with better boilers, compound engines, and iron and steel hulls, it pushed sail aside, as the story of the clipper ships shows. Modern ships still use propellers, though often with advanced shapes and sometimes in ducts or as pods.