Why did Black Prince need more boilers than Dreadnought?

Did HMS Black Prince's larger boiler count reflect more machinery compartments than Dreadnought required?

Partly, but the vertical triple-expansion layout mattered more, along with the greater power density that turbines allowed Fisher to obtain within Dreadnought's hull.

The viewer notes that Black Prince required 26 boilers for broadly similar stated power while Dreadnought used 18. The answer accepts that compartment division played a part but points more strongly to the arrangement needed around vertical triple-expansion engines. Turbines let designers feed power through a denser and more flexible machinery layout. Fisher pressed for the new machinery despite objections because that internal power density supported the hull, speed, and gun arrangement he wanted. Boiler count alone therefore does not describe the whole engineering advantage.