A screw steamer or screw steamship is an old style term for a steamship or steamboat, powered by a steam engine, using one or more propellors, also known as screws, to propel it through the water. Such a ship was also known as an 'iron screw steam ship'. In the 19th century, this designation was normally used in contradistinction to the paddle steamer, a still earlier form of steamship that was largely, but not entirely, superseded by the screw steamer.