A steamship, often referred to as a steamer, is an ocean faring seaworthy vessel that is propelled by one or more steam engines that typically drive (turn) propellers or paddlewheels. The first steamships came into practical usage during the early 1800s; however, there were exceptions that came before. Steamships usually use the prefix designations of "PS" for paddle steamer or "SS" for screw steamer (using a propeller or screw). As paddle steamers became less common, "SS" is assumed by many to stand for "steam ship". Ships powered by internal combustion engines use a prefix such as "MV" for motor vessel, so it is not correct to use "SS" for most modern vessels.