Expert Help please Prop 21 foot Boat
 

Have project boat(1989 scarab excel) that is almost done, came with fresh alpha drive and 19 pitch 3 blade ss prop. Motor was cracked, so got short block 383 , with BM MOTOWN 23° ALUMINUM HEADS, demon 650 , stock merc dist. , thru hull corsa exhaust. Just need advise on prop size, I run the local river , with myself and one other person. Would like to see top end in the 64-66 range. Thanks in advance. I have a 4 blade ss set off my Formula 24 pitch.....too much for an alpha?

I think a 3 blade high rake SS prop will serve you best. Try the one you have and let us know if you wish to test any others.

Brett

test run results
 

boat ran 53 mph on gps with 3/4 tank of fuel, 650 lbs of people , looks like I need to go to a 23 pitch. Still plenty of power left in the stick

Let us know if you need some test props.

Brett

you have a PM

go up in prop size? 21 foot with 383cu 23 pitch mirage
 

ran yesterday on the bay, WOT is 55 on the gps, 3/4 tank and two guys , can't trim too much at all, loosing bite at higher rpm's. can I run a 4 blade? maybe 24 on the alpha? Thanks

What is your RPM at WOT?

5000k thanks

So you are at 5000 rpm with a 23" pitch prop and 55 mph gps?

What is your drive ratio?

CRG,
did you send me a PM?

Sorry, I was at Desert storm for the last week and I want to make sure I didn't miss anything.

Brett