Slip Calc.
 

Can someone give me an accurate slip number. 61 mph, 24 bravo, 1.5 gears, 4950 rpm. Thanks. I know the Bravo pitch rating is a bit inflated but not by how much. :rolleyes:

Re: Slip Calc.
 

Prop Calculations are:

(RPM/Gear)x Prop x .000947= Speed (Assumes No Slip)

Divide Actual Speed by Formula Speed = Slip

In your case 61/75=18.7%

Re: Slip Calc.
 

Thats assuming an actual 24 pitch which I'm prtty sure the bravo is not. Anyone know how much to deduct to get a "true" pitch?

Re: Slip Calc.
 

1 inch... slip would be right @ 15% if you use 23...

Re: Slip Calc.
 

According to Throttle up prpellers Bravos are rated at 1.5 greater than their true pitch.

Re: Slip Calc.
 

Dave,
I agree. Bravos have 1" to 2" less pitch than advertised. Some people theorize it's marketing since Mercury has 3 blade Mirages in odd # pitches, and they're just tring to cover every pitch. I think Merc is compensating for the difficulty of turning the additional blade area vs the 3 blades, making it easier for the consumer to understand the actual effect of switching from 3 blades to 4 or the reverse.
For example, if you go from a 27" Mirage to a 28" Bravo, the pitch is actually the same, but the normal effect will be to reduce WOT RPM because of having to turn the additional 4th blade area. You may pick up speed too, in midrage usually, and sometimes top end also, but it's because of a lowering of slip, not an increase in pitch. Just MHO.
The 1st theory is the propeller guys who've actually had them on a pitch block, and the 2nd one is mine.
Regards,
Steve

Re: Slip Calc.
 

Good stuff Steve :D

Something else to ponder and also from the prop gurus (that wouldn't be me :rolleyes: ).

Hydromotives are true pitch; meaning they are what they say. Although many variables apply generally speaking when running a 4 blade Bravo, lets say a 28, you will need to drop to a 26 4 blade Hydro to achieve the same rpm and speed.

Sounds like a Merc marketing strategy thing to me :drink:

Later,
Dave

Re: Slip Calc.
 

Something else,
and I would love to hear from some propeller gurus on this.
My local guy @ Performance Propeller, Old Hickory, TN, says the Bravo 1 blades are often not all the same pitch, and that just evening them out can offer a increase in performance.
I don't know if that's bad castings, bad finishing, or what.
It does make sense, there's nothing worse than having different pitch blades fighting each other.
IE, higher pitch blades hurting acelleration and planing, and lower pitch blades hurting top end...............
Regards,
Steve

Re: Slip Calc.
 

Steve, I received a before and after print out some time ago from Throttle Up when I sent a Bravo 30 to them to lab. The pitches blade to blade had a spread of over an 1.25" :eek:

Re: Slip Calc.
 

Dave,
Gives a whole new perspective on the "variable pitch propeller" doesn't it :rolleyes: ............I bet if you asked Mercury, they would either deny it, say "that is within production tolerances", "that's what our Merc Racing lab dept. is for", or "we know that, we designed it that way" :D !
One thing for sure, it has made for good job security at aftermarket prop shops and the Merc lab.
Regards,
Steve