How could F2 and F3 make 30 knots on two shafts?

How could the F2 and F3 designs reach about 30 knots with only two shafts?

By combining contemporary Brown-Curtis turbines, Admiralty boilers, and an efficient hull; forced draught could add speed, but only by increasing machinery wear.

Brown-Curtis turbines, Admiralty boilers, and a well-designed hull make about 30 knots plausible on two shafts. The shafting is also tentatively assumed to be hollow. Forced draught could raise speed beyond the quoted trial figure, with increased machinery wear. A possible wartime speed of about 26 knots for Rodney illustrates the expected emergency margin when machinery due for replacement could be driven hard enough to accept damage.