True pitch of a Bravo 1 prop
 

I want to get my proper slip #'s for my hull. I know that the B1 props are rated higher than they say. so what is the auctual pitch of a 32 B1 prop

My boat ran 86.7 @ 5200 rpm with 1.5 gears

I,m going to try a 30P B1 this week end to get my rpms closer to 5700 where I make more power. What is the true pitch of a 30 B1 so I can run the slip #'s when I'm done.

For all intensive purposes use 31P. This holds pretty true for 22P-32P. But when it comes to 34P and 36P this will not be the case.

Julie

Depending on the cup heights, I'd use 31.2.

What would be the case with 34p and 36p ? Thanks

36's can be quite a bit lower than marked. I have seen some as low as 33.5. Typically they seem to be about 34-34.5. The diameter on the 34's and 36's is a little larger, typically, they seem to be the 15.25" they are marked, unlike most of the other Bravo 1 props.

Winrace Propeller in Norway, they are a highly respected as experts on props.
Delivered a lot of racing propellers for Offshore Class One boats. " The Bblades of Europ"

They told me that Bravo 1 props in most cases are actually much lower pich then claimed on the actual
Prop. They guy let me in to his workshop, and he messured my 24 pich, which actually was 22,5
1,5 pich lower ......

That's explain some of my very high Slipp when I put 24 in the prop calc program

Any comments ??

When a prop is measured it does not take any Cup height into consideration . The cup height is factored in to the overall stamped pitch though

I was told. Once you get close. Try the next size up. Pitch that one back down and the rake works out better for true numbers.

Winrace is indeed a awesome business and group of professionals.
Yes, pitch is determined via the tools you have. Included in this determination is the company's understanding of propeller geometry. I am sure that Winrace used true pitch to determine their pitch quote. Because most of the Bravo family is slightly more than a inch less than the pitch stamping. However, there is much more to the story. Some of which I will not divulge.
Cup is huge. Back in the day when my teachers at Mercury were writing information on pitch, they used a generalization on cupping as a additional inch of pitch when cup was in place. In other words, we published, if the prop is cupped, add a inch of pitch. So in this case, a 22.5 inch pitch prop can act as a 23.5 pitch prop or classified as 24 by Mercury Marine.

Today, we understand the pitch progression as well as the cup heights are specific to the overall prop geometry and pitch. We can adjust prop pitch to various degrees using cup (and bending but, only a certain part of the blade can be bent)). It must be done specific and each propeller design has to be understood.

I use .7" less calculation for most of the Bravo 1 family. Of course there are variations.
Great history behind these propellers. Boy do they work well and Lab and modify better than anyother propeller in history.

Scroll back and you might find a decade of fun history I have written about these propellers.
Thanks for bringing it up!
Brett

Dear Brett

This is what is so fantastic with this forum and specaly BBlades

You have a question about something or a story, and you get so quick respond :-) :-)

If I understand you correct its more to propeller then just the pich ;-)

But in my case will it be correct to use 22,5 pich in a prop calc to find my slip ??

I have a Formula 271 SR1 2009 496 HO Bravo1 XR drive 1.50 Bravo 1 24 pich prop ( real average pich 22,5)
.

My top speed are 61 mph 5100 rpm
46 mph 4000 rpm
40 mph 3500 rpm
34 mph 3000 rpm

I fell that I have a couple of mph on the top speed, and I also hope for a litle more speed at the 3 "crusing speed" levels. I am sure that the Bravo 1 26' is to high
I woul like trying to cup the blades on my 24 ' to get a better grip and a litle more natural bow lift ?? Saying that I am more or lass happy With the result ;-)

Does this sound as a good idea ??

When the transom on the boat was rebuild the former owner, innstaled the drive a bit higer then Formulas original conservative drive setup.
I am not sure how much, I am checking this now, to find out exactly how many inches I am higer then the original set up

I am also consider to have a propp number 2, what will you recomand Brett ??

Br
Rune
Oslo