A 265-psi boiler option is available for the proposed machinery. Lion is 213.4 metres long, 27 metres in beam and 9.9 metres in draught, with forty-two earlier Yarrow boilers and Parsons turbines producing 70,000 shaft horsepower through four shafts. Her boilers occupy six rooms of seven. The class's nominal speed is 27 knots, while Princess Royal reached 28.5 knots on trials. Iron Duke is 189.8 metres long, 27.4 metres in beam and 9.98 metres in draught. Its eighteen Babcock and Wilcox or Yarrow boilers supply four Parsons turbines, producing 29,000 shaft horsepower for about 21.25 knots. These installations show how boiler-room arrangements, pressure and turbine efficiency were changing during the design period.
Notable Point · 37:36-39:49
Lion and Iron Duke as machinery comparisons
Earlier battlecruiser and battleship installations show how rapidly machinery options were changing.