i have a 84 v20 fisherman. it has 1986 200hp merc. with a 17 pitch four blade the max rpm is 5800 @ 40-41 mph by gps. changed to my spare prop with a 19 pitch three blade & the max rpm went to 6200 @ 39 mph. don't know the exact dia. of each prop but the 19 pitch is said to be for a sterndrive unit & is larger in dia., it barely has clearance on the foot. the 17 pitch is smaller dia.