the ss "st. marys challenger" is a freight-carrying vessel operating on the north american great lakes built in 1906. originally an ore boat, she spent most of her career as a cement carrier when much larger ore boats became common. after a 107-year-long working career as a self-propelled boat, she was converted into a barge and paired with the tug "prentiss brown" as an integrated tug-barge. before conversion, she was the oldest operating self-propelled lake freighter on the great lakes, as well as being one of the last freight-carrying vessels on the great lakes to be powered by steam engines.