If the prop is not marked, take it to a shop and let them tell you what it is. If you don't know what you got, you don't kow what you need and you can guess till the cows come home, throw props at it trying to get it right, and end result is that someone will have made a lot of money selling you props and you will still be trying to get your boat to run at it's optimum.
2015 Seaark 1872 MV CC Etec-90
Helix 12 CHIRP SI, HB 1199, MinnKota Riptide ST80/i-pilot Link, Bob's Hydraulic
Bitter Gun Owner