 Sully had three propeller shafts , each powered by one vertical triple @-@ expansion steam engine , which were rated at a total of 20 @,@ 500 indicated horsepower ( 15 @,@ 300 kW ) . Twenty @-@ four Belleville water @-@ tube boilers provided steam for her engines . She had a designed speed of 21 @.@ 5 knots ( 39 @.@ 8 km / h ; 24 @.@ 7 mph ) . She carried up to 1 @,@ 590 long tons ( 1 @,@ 620 t ) of coal and could steam for 12 @,@ 000 nautical miles ( 22 @,@ 000 km ; 14 @,@ 000 mi ) at a speed of 10 knots ( 19 km / h ; 12 mph ) . 
