Machinery density shifts the battlecruiser spectrum

In this classification, battle cruiser, battlecruiser, fast battleship, and battleship occupy different points on a spectrum of capital-ship roles. The two-word battle cruiser is close to a large armoured cruiser intended to range worldwide with battleship-grade guns, with Invincible as the example. Designs intended to fight comparable capital ships sit farther along that spectrum. The boundaries also change with machinery technology because greater power density alters how much hull space propulsion requires. HMS Tiger could generate much more power than Invincible for a given machinery allocation. A hypothetical Tiger devoting the same proportion of hull space to machinery as Invincible is estimated here at about 32 knots; that is a design comparison, not a claim about Tiger's actual service speed.