First time out with new outboard need prop change

[Tex60]

I have a 24' Monark pontoon with three adults on most outings, I just put a 2000 Mercury 90 HP tracker 2 stroke, I purchased with a 12 3/4 X 21 Michigan wheel Vortex aluminum prop it would run 20mph at 4300 to 4500 on tach, range for the motor should be 5000 - 5500 I would like to see some more speed from the boat if it's there and I would like the WOT to get it just past 5500 so that if I add people or drag my son on a tube it has the power and I generally keep a close eye on the tach to prevent over rev.... So what suggestion on prop?

 

[steelespike]

I think a 13" pitch is a good start. If anything it may b e a little light but your better off too light than too heavy.
The 13 will feel peppier and should hold rpm better as you add weight.,

 

[SkiDad]

Something is up. At that rpm you should be in the 30's - and there is no way that boat will do 30. A 13 or 15 pitch would be more normal.

 

[Tex60]

I'm going to check with a place and see if they have any used ones around that I can test with and then when I get zeroed in buy a new one....I did some calculations and if the gains 400 rpm with each 2" change I'm thinking I will probably wind up with a 15p but the trick will be deciding on how big a diameter

 

[steelespike]

I think that a 24 ft. pontoon with a 21" prop would experience some odd numbers.
Is the speed by gps?

 

[Tex60]

yes