Comparison with the later Renown class makes the increase in machinery power density visible. Queen Mary was roughly 400 tons lighter than a Renown but about 94 feet shorter and more than a foot narrower. Renown and Repulse used the same 42-boiler count with geared turbines to produce about 112,000 shaft horsepower, compared with Queen Mary's 75,000. That power drove the later ships to about 32 knots rather than Queen Mary's 28. Their longer, less densely packed design and speed-first priorities reflected Fisher's influence, in contrast with the more solid evolutionary path through Queen Mary.
Notable Point · 30:59-33:17
What Renown's machinery reveals about power density
The same 42-boiler count produced 75,000 shaft horsepower in Queen Mary and 112,000 in the Renown class. Propulsion and design priorities had changed rapidly.