good question. i just sold my 76. heres the difference. 1st you know sanger drag hulls by on the deck, mainly called 5 rib youll see 5 ribs on the deck for streanghth. second youll have outboard steering and usually a single seater. now jack davidson owner of sanger sold drag bottoms with ski tops also , mostly were special order. the ski hydros had a 42 inch wide seating area for bench or 2 buckets. also the ski had inboard steering. check yours if you have a outboard steer with 42 in wide seating area its a drag bottom with ski top if inboard steer you got a ski hydro. the hin numbers on a 76 are on rt rear , pass rear side about 8 in from rear and 2 in from bottom. like mine some glass over it. why ill never know. shoot me a pic ill be able to tell you bu looking at it. the forst letters are the maker the last two numbers are the year for the hull. in 77 two versions of the hydro were made. the classic jr witch is the 18 ft and the banana bottom wich was a 19 ft. the hull dont look alike, older classics look good wide sponsons the banana were narrower. and longer . mainly because of the way they dropped back in the water at high speeds they god squirley. if you never drivin a hydro dont plan on making fast turns and it is the opposit of a flat when you get little rough water nail it it will fly over it. i love them wont buy anything but sangers. fyi get on performanceboats.com "better site hot boat burned alot of people". speak with billy b who worked for sanger and others who know them. call precision craft marine in fairfield , cal. speak to joe shelfo. nicest on earth and the greatest setting up hydros. if set ur right they are safe if not your dancing with the devil hope i helped