i have a new 9.9 merc 4 stroke on a 12' alumacraft john boat,with a 3x9x9 stock prop.it tops out at about 20 gps mph.the merc prop finder suggest a 11.5 pitch.i think that the motor is under proped now.there is a rev limiter on the merc.i don't know how the motor repsonds when the rev limiter...