I have a 1995 Mariner 115 hp 24 pitch prop that runs between 4200 and 4300 rpm wot. From what I read it should be in the 4800-5250 range. Will a 19 or 20p prop put me where I want to be?

20 or 21 would be a good start

this ^ ^ ^ get a 20 and go from there, one inch pitch equals about 200 rpm.
having a prop "worked" is always a good idea too, they run a lot better.
josh at steves custom props in quitman if you get that done.

thanks gents!

It would always be a good idea to mention what boat and exactly what prop you're running. Some generic aluminum 24 would be a total different wheel than a high end stainless. Better details get better answers.

16' Sprint, 24p Laser 2

might try josh at steves and see if he has a 20 that will work for ya, may be a different name but he will do ya right.