I have a 1996 Fountain 24cs 502 MPI with a 26 pitch 4 blade prop. 1.5 ratio Bravo. At 5050RPM I'm running 66-68 mph. Based on this information my prop slip is 17.9%. This boat tested new at 77MPH @ 5050RPM with a 27 pitch prop. the slip would have been 10.5% Why so different from then to now?

Sounds like whatever prop you are running now is not the ideal prop for that hull.

Also, No 2 props ever seem to yield exactly the same results.

Should I go back to the same spec prop it was tested with in 1996 14.5 27 pitch 4 blade? Weight an issue? Fuel, persons, gear?