tssteph

If I can spin bone stock 27 pitch Mirage Plus (used) props at 5000. What will happen if I switch to 28 pitch Bravo 1s? I am told the four blade Bravo 1 prop will setttle the boat down at high speed some. The boat has great cruise speed right now with the 27's, will it change with 28 four blades? Better or worse? What will it do the top end? 5000 is about all I want to run to keep it easy on the motors. I have read that the slip calculators you subtract one from the pitch for a four blade compared to a three blade so I can I assume the slip will be close to the same?

1998 Scarab 29, twin 350 mag mpi's with 5 psi prochargers.
Bravo drives, 6400 lbs dry plus gear and 100 gallons of fuel

throttleup

If you were to run a 28P 4B propeller you will experience and RPM Decrease at WOT. The Miarge Plus has a 14 3/8 diameter and the Bravo I comes in around 14 7/8 ish. Additionally as you said the Bravo I propeller is really one inch less than is stamped on the propeller, so a 27P rather than a 28P. However you have added a blade and this will bring the RPM down as well, additional drag around 150 ish RPM. Typically you can loose 1.5 knots on top when going to a 4B particularly if your sip is low with the 3B. I would also be concerned running your motor at the appropriate RPM at WOT, ensuring that your are running in the torque band of the motor.

Julie

bbladesprops

Expect about a 2-300 rpm loss by going to the 28 Bravo 1's.

Top speed change guesses thoughts more information.

The diameter of a 28 Bravo 1 is advertised at 15 1/4" it is actually closer to 15". It depends on each casting (believe it or not).

Labbing the 28 Bravo 1 would get you back in the 5000 rpm range. The cruise speeds will also increase with the B1.

tssteph

Thanks, good information.

Rocko C

tssteph - I had a Mirage+ 27P on my Procharged 502 25 Outlaw and would hit the rev limiter. I switched to a 28P Bravo I and only reach 4500 RPM @ WOT albeit at 71.8 MPH GPS. It gets up on plane almost instantly, though which is awesome. I'd LOVE to get those 500 RPM's back since the boat/motor are designed for it. bbladesprops - Is labbing the answer for me or is a 24P/26P Bravo I the answer ?

bbladesprops

Definately not the 24 Bravo 1.

Labbing the 28 puts you at 4800 @ aprox. 75mph.

The 26 in box stock will put you at about the same rpm at a slower speed. Labbing the 26 will put you above 5000 rpm and back to the 75 mark.

28 better cruise speeds, 26 better throttle response.