A paddle steamer is a steamship or steamboat powered by a steam engine that drives paddle wheels to propel the craft through the water. In antiquity, paddle wheelers followed the development of poles, oars and sails, where the first uses were wheelers driven by animals or humans.
In the early 19th century, paddle wheels were the predominant way of propulsion for steam-powered boats. In the late 19th century, paddle propulsion was largely superseded by the screw propeller and other marine propulsion systems that have a higher efficiency, especially in rough or open water. Paddle wheels continue to be used by small, pedal-powered paddle boats and by some ships that operate tourist voyages. The latter are often powered by diesel engines.
Paddle wheels
The paddle wheel is a large steel framework wheel. The outer edge of the wheel is fitted with numerous, regularly spaced paddle blades (called floats or buckets). The bottom quarter or so of the wheel travels under water. An engine rotates the paddle wheel in the water to produce thrust, forward or backward as required. More advanced paddle-wheel designs feature "feathering" methods that keep each paddle blade closer to vertical while in the water to increase efficiency. The upper part of a paddle wheel is normally enclosed in a paddlebox to minimise splashing.
Types of paddle steamers
The three types of paddle wheel steamer are stern-wheeler, with a single wheel on the rear, a side-wheeler with one on each side, and an inboard with the paddlewheel mounted in a recess amidship. All were used as riverboats in the United States. Some still operate for tourists, for example on the Mississippi River.
Stern-wheeler
Although the first stern-wheelers were invented in Europe, they saw the most service in North America, especially on the Mississippi River. was built at Brownsville, Pennsylvania, in 1814 as an improvement over the less efficient side-wheelers. The second stern-wheeler built, Washington of 1816, had two decks and served as the prototype for all subsequent steamboats of the Mississippi, including those made famous in Mark Twain's book Life on the Mississippi.
Side-wheeler
Side-wheelers are used as riverboats and as coastal craft. Though the side wheels and enclosing sponsons make them wider than stern-wheelers, they may be more maneuverable, since they can sometimes move the paddles at different speeds, and even in opposite directions. This extra maneuverability makes side-wheelers popular on the narrower, winding rivers of the Murray–Darling 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 90 degrees 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.