I have a 1970 searay, and it is restored. It is a light boat, 17' long, and the new engine is a 1992 yamaha 115. I had a 1974 johnson 85, and I got a new hub to reuse the prop. It is a 13.25 x 15. I also noticed that the gearcase on the new yamaha is slightly bigger.
Anyway, the 15 pitch prop...