Three double Fairlies at Porthmadog, 2 May 2005. From left, Earl of Merioneth, Livingston Thompson and Merddin Emrys. The double engine was invented by engineer Robert Fairlie and engines of this type have been used on the Ffestiniog since 1870. It uses one rigid double ended boiler with two central fireboxes and is carried on two powered bogies, giving it the power of two engines and the ability to go round tight curves. Fairlies are also very useful to photographers as they have a “front” view at each end!