get your boson's chair or binocs
my 30 has a kenyon spar. had 4 sheaves, 2 forward 2 aft. but halyards used all as they were run outside mast.with halyard winches mounted on mast. I moved halyards to inside and winches to cabin hesd.now i have 2 jib halyards,main and adj. boom lift. if your winches are mounted on mast and halyards run out side, more than likely there are 4 sheaves.