wzawart

Hello,
I have a 21ft formula boat and just put in a new 383 stroker crate motor and all new parts on engine. I currently have a 17P stainless quicksilver prop on it I am looking for some help on what size prop to go with. There is sometimes six of us total on the boat and I am looking for the most out of the boat but not to tear up the drive its an alpha 1. The motor has 370hp and a holley double pumper on it. We like to go fast but never holeshot I always bring it up on plane. I was thinking 19p but loking for some input... Thank you all..

sprink58

Sell that 17" to someone that has a heavy boat that needs it.

If you have a 1.5:1 (which is standard) in your Alpha and cary that many people...try a Mirage Plus in 19" pitch. Be carefull with this because with a light load and that much power and torque...you could very easily over speed the engine and drive.
Alphas don't live long at 5500+ RPM for more than a minute or two and I suspect your engine could reach 6000 in that boat with a 19.

If you only occasionally carry that many people...go to a 21" Mirage Plus. I suspect you will push 60~65 MPH with a 21 and with a light load could handle a 23"

I suspect you trailer and with a single I/O it's no big deal to swap props for different conditions...get a 19 and a 21 and swap back and forth based on what you are doing that day.

Let us know how that rig runs...with a 383 in a 21 it's got to be a bullit

wzawart

You said sell my 17" to someone with a heavier boat I thought my formula was heavy it sure seems heavy with a deep hull. I am going to look around for a 19" prop like you said maybe I can find one used. On my gps I was full throttle trimmed out with 6 people with the 17" and could only see 49.5 Mph and my rom was around 4500 to 4800 but bounces around alot i am gonna install a new one that is more Ocean:Ocea​n is alot like our lives.It changes daily,like​ us.It becomes rough at times. But like the tide we ride them out.Like the waves that break sometimes also our heart does the same.But as the water goes back out so does our pain.Just for another wave of love to change everything​.accurate. But i would love to see 55 or more hopefully the 19" will let me see some more speed.. The whole prop thing is very confusing.. Thanks for replying.