 Each paired set of Parsons direct @-@ drive steam turbines was housed in a separate engine @-@ room and drove two shafts . The wing shaft was coupled to the high @-@ pressure ahead and astern turbines and the low @-@ pressure turbines to the inner shafts . Each wing shaft drove a propeller 10 feet 10 inches ( 3 @.@ 30 m ) in diameter and the propellers on the inner shafts were 10 feet 3 inches ( 3 @.@ 12 m ) in diameter . The turbines were powered by thirty @-@ one Babcock & Wilcox water @-@ tube boilers in five boiler rooms . Indefatigable 's turbines were designed to produce a total of 43 @,@ 000 shaft horsepower ( 32 @,@ 065 kW ) , but reached over 55 @,@ 000 shp ( 41 @,@ 013 kW ) on forced draught during trials in 1911 . The turbines of Australia and New Zealand were slightly more powerful at 44 @,@ 000 shp ( 32 @,@ 811 kW ) . They were designed for 25 @.@ 8 knots ( 47 @.@ 8 km / h ; 29 @.@ 7 mph ) , but all three bettered 26 knots ( 48 km / h ; 30 mph ) during trials . 
