Which Prop?

[RustyGoat]

I've been trying to figure out why my boat is so slow and just discovered the prop is way off. Current prop is a 4 blade 10" 7 pitch and the boat tops out at 7 mph. I'll probably stick with the 10" size but what pitch? 3 or 4 blade?

Boat is a 14' Polar Kraft deep v with a 2007 4 stroke Mercury 9.9 Bigfoot.

 

[Andrew04]

I would think a 9x9 3 blade would let it spool up enough to make some power, while. Sing realistic about output.