25hp Yamaha 1993 Which prop do you recommend

[theeqguy]

Hello I have a 1993 25hp Yamaha pull start. The motor is stock without any modifications.
Currently it has a 10x10 1/4" prop. I am making a boat and its loaded weight should be around 650 pounds. (including motor and one occupant)
The boat is a custom fiberglass composite boat (Light weight) the Hull has a rather smooth bottom.

I would like to pull this boat at around 38 possibly 40 mph max speed. However the ultimate goal is not to go at the fastest speed but rather to have the most efficient traveling cruise speed with reasonable fuel consumption.
I understand the max speed for this motor was probably around 28-30 mph but this is a rather light boat and should be able to get faster cruise speed.

Your thoughts are greatly appreciated.

 

[steelespike]

Re: 25hp Yamaha 1993 Which prop do you recommend

A 15" pitch could produce about 38 mph.Disregarding the size and weight of the boat.
I don't think a 15" pitch will work well with what will likely be over 650 lbs.
Your gear ratio is 1.85 likely to need less pitch to make rpm
If it truly has a smooth fast bottom ( may need to be flat with a hard chine)
Get us a base line wot rpm and gps speed with your present prop.
I have a 375lb 18ft bare utility with a 50 Evinrude (200)me 200,gas battery oars 100lbs.with a 19" prop 2.42 gear ratio at 5500 it calculates to 38 mph,6000 40, 21" pitch 6000 44. Again disregarding the hull.Don't know if it would make 6000 with a 21 but the gear ratio should make it easier to do.
Unfortunately I never had a gps or tach to check the figures and its my sons now and he's not likely to have the time for a while.
If you check the Yamaha performance bulletins I think you will see typical prop is 12".