The MV Royal Iris is a twin screw, diesel-electric, Mersey Ferry. The vessel was built by William Denny & Brothers of Dumbarton (Yard No. 1448) and launched in December 1950, costing £256,000. The engines were produced by Ruston & Hornsby Metropolitan-Vickers. Propulsion: 4 oil 4SA, each six cylinders driving four generators, each 300 kW/300v DC-connected to two electric motors, each 730shp and 2 shafts. The maximum speed is 12 knots. The ship measured 1,234 GT. Length is 159 feet long and 48 feet wide, with a draught of 9 feet. At least during the first decade of its life, the ship's diesel-electric propulsion made it more economical to run than the other vessels in the fleet.