If it's an F115, you should be pulling 6000 rpm WOT with a "normal" load. So you're probably 3 or 4 inches long on pitch to start with. The range is (as I recall) 5000-6000, but optimally you want to be in the higher end with a lightish load (say, one or two people, and say half a tank of fuel.) Going a touch over isn't going to do much, but being low on rpm means you'll never get rated power out of the motor.
If you'll be doing a significant amount of skiing, you might want to have a second, even shorter prop for a better hole shot, but you don't want to use that for long distance running without skiers for risk of overrevving.