Just bought 2005 Ranger Reatta 210 with Merc Optimax 225. It has 23 pitch 5 blade. Only been on the water with boat empty - basically no gear. Prop seems to cavitate at high RPM's almost as if motor is outpowering the prop. Ranger suggests 23 pitch regardless of 3, 4, or 5 blade. Mercury suggests 25 pitch 5 blade. Confused!!!!