 The engines , situated in separate watertight compartments , were each fed by a pair of coal @-@ fired boilers . Each boiler was horizontally mounted and was 9 feet 6 inches ( 2 @.@ 90 m ) in diameter and 17 feet 6 inches ( 5 @.@ 33 m ) in length with a total grate area of 220 square inches ( 1 @,@ 400 cm2 ) . Yorktown 's coal bunkers could carry up to 400 long tons ( 410 t ) of the fuel , and were shielded from " shot and shell " . At a near top @-@ speed of 16 knots , the ship could cover 2 @,@ 800 nautical miles ( 5 @,@ 200 km ) in 6 ½ days ; at the more economical speed of 8 knots ( 15 km / h ) she could cruiser 12 @,@ 000 nautical miles ( 22 @,@ 000 km ) over 62 days . 
