I am getting close to a launch date for my project and would like to get as close as possible to an accurate prop selection instead of " throw on a pair of what ever you've got and figure it out trial and error".

All of the prop calculators I have seen take into account weight, horsepower, hull type and prop slippage. I have not seen mention of single engine vs. twin as a factor.

My boat is a '79 Formula 255 Liberator that has a 24* dead rise and weighs in at 5600# dry. Let's add another 900# for fuel, equipment and driver....so we are working with 6500#.

The power is twin SBC Vortecs that dyno tested at 400 horse @ 5200 through headers and 435 ft lbs @ 3200...400 ft lbs @ 2000. I am using thru prop exhaust so I predict a 25 horse loss at the top leaving us with 750 horsepower in the water. The drives are Bravo I with 1.5:1 gearing.

This boat is heavy for it's length (typical Formula) and handles rough water like a champ. It will however get up on the back 1/4 of the hull and move across the top of the water once she's trimmed out.

My goal is to run long distances at 50+ with snappy low and mid range performance/throttle response. Running 65~70 on the top for a short time to out run weather would be an added bonus.

I'm thinking a Revolution 4 21" or 23" or a Bravo I Labbed for the boat.

Thoughts and suggestions welcomed.

The intriguing question is...if this boat had a single 502 Blower motor putting out 750 horsepower and 850 ft lbs of torque through a Bravo XR or what ever drive that handles that kind of power...would we use a different method to calculate the prop and if so why?

I would try a Merc Mirage Plus 23'. I used a pair of 25s on my Formula with 2x500 hp. Bill

What size 'bird and weight was yours?