 Fairlie's vision was limited by the limitations of the steam locomotive — its thirst for water and the unbalancing forces of its directly driving pistons.A variation of the Fairlie that enjoyed some popularity, especially in the United States, was the single Fairlie, essentially half a double Fairlie, with one boiler, a cab at one end, and a single articulated power bogie combined with an unpowered bogie under the cab, maintaining the ability to negotiate sharp turns.This design abandoned the bidirectional nature of the double Fairlie but gained back the ability to have a large bunker and water tank behind the cab, and the possibility of using a trailing tender if necessary.