A paddleboat or paddlewheeler is a ship or boat propelled by one or more paddle wheels driven by an engine. Boats with paddle wheels on the sides are also called sidewheelers, while those with a single wheel on the stern are known as sternwheelers.
The paddle wheel is a large wheel, generally built of a steel framework, upon the outer edge of which are fitted numerous paddle blades (called floats or bunkets). In the water, the bottom quarter or so of the wheel is underwater. Rotation of the paddle wheel produces thrust, forward or backward as required. More advanced paddle wheel designs have featured feathering methods that keep each paddle blade oriented closer to vertical while it’s in the water; this increases efficiency.
Sternwheelers have generally been used as riverboats, especially in the United States, where they still operate for tourist use. On a river, the narrowness of a sternwheeler is preferable.