The pepperpot cap sits on top of the tower , giving the mill an overall height of 45 feet ( 13 @.@ 72 m ) to the finial . It houses the cast @-@ iron windshaft and 7 feet 2 inches ( 2 @.@ 18 m ) diameter wooden brake wheel internally . Externally the four double Patent sails span 64 feet ( 19 @.@ 51 m ) . They are 9 feet ( 2 @.@ 74 m ) wide and can develop 30 horsepower ( 22 kW ) . The eight bladed fantail keeps the mill turned into wind .