question for the propellor heads...
 

so I tried the magic mach sterndriver... lost over 500 rpm speed is the same though.. way too much prop and slip is 9%

So with 310 hp swinging it to 4000 rpm at 60 mph.. how much hp and I going to need to swing it about 5200 rpm?? and what would speed be?

Boat Avanti 22 3500ish pounds

Current motor 7.4 mpi 310 hp

Prop mach stern driver 24x14 4 blade (labbed, cup added cut down from 14.5 to 14

1.36 ratio drive? thats the only way i am getting 9% slip @ 24p, 4000rpm, 60mph

My guess with above numbers is high 70's @ 5200 rpm and around 270 more hp, (@ 15hp per mph), My "guess" is based on previous forum conversations and theoretical calculations.

What's your rpm at wot with that prop now? Not sure if you meant you can only spin it to 4000rpm

With the new prop Rome max out at 4000 rpm but speed is the same as the 23 3 blade at 4600

Id guess about 500-550hp

I'd go back down on pitch to get the motor where it likes to be. The problem with props. If you like the way it handles. But at the wrong RPM. when you re pitch the prop or go to the same prop with different pitch the handling could change. I had a 87 22 avanti with a 450hp SB 1:50 Alpha. Spun a 21 3 blade at 6000rpm to 72mph.