Could new boilers have made the Nelson class much faster?

How fast might Nelson and Rodney have become with modern high-pressure boilers?

Boilers alone were not the main limit. A third shaft and its machinery might have raised them toward roughly twenty-eight to thirty knots if designed in from the start.

Nelson and Rodney were unusual Royal Navy battleships because they transmitted all propulsion power through only two shafts. More boiler output could help, but the existing shafts limited how effectively additional power could be used. A third shaft and the associated engines might have produced a ship in the high twenties, perhaps approaching thirty knots. The proposed estimate assumes that the additional shaft and engines were included when the ships were built. The shaft arrangement limited what higher-pressure boilers alone could achieve.