Why rebuilding an old battleship cannot be reduced to horsepower

Could an upgraded Queen Elizabeth-class battleship have reached 28 knots while retaining its basic hull, armour, and armament?

A rebuild had to account for an aged hull and the use of machinery weight savings elsewhere. Better original machinery is argued to have made 25 knots certain and 28 knots possible, but that design-potential argument does not establish the speed achievable by an old rebuilt ship.

British rebuilds used machinery weight savings for other purposes while retaining broadly similar power. Their hulls had already endured decades of hard service, which limited what further strengthening could achieve. Matching horsepower and length-to-beam ratios therefore cannot establish equivalent speed, because the detailed hull shape also matters. Comparisons with the Revenge, Iron Duke, Nelson, Tiger, and Renown designs illustrate that distinction. The Queen Elizabeth class's original boilers worked near their limits to supply the high steam pressures its turbines required. More efficient original machinery is argued to have made 25 knots certain, with 28 knots a further contention about the hull's potential given enough power. These estimates concern unrealised design potential and do not establish what an aged hull could achieve after rebuilding.