General questions bravo 3 drive

[simulatedjim]

HI Julie,

I have a couple of questions about bravo 3 drive and prop selection.
1) Is their a prop calculator for bravo 3 drives? Can I use regular prop calculator?
2) What is a good slip # for bravo 3?
3) How much rpm drop should be expected with each 2 inch pitch change?(i.e. 20p to 22p to 24p)

Thanks, JIM

[who knows]

No good info on B3's

What are you trying to do ?

[simulatedjim]

Info on what I'm trying to do. Boat 2001 Maxum 2700 SCR 6.2L Bravo 3. Not a performance boat but I shouldn't have to cruise at 4000 rpm just to stay on plane. Also the WOT is 5400 which is 200 rpm over max rpm.

[who knows]

Mines a 454 mon mag on a 23 Rinker turning 28" props and I cannot get over 4200 rpm If that means anything. I can get on plane at 2000 rpm, no problem. Not sure what gear ratio it is turning, i think the sticker is stilll on the side though

who knows

[tommynitro]

seems to me like you two need to switch props with each other....... [smilie=061.gif] [smilie=061.gif] [smilie=061.gif] [smilie=061.gif] [smilie=061.gif] [smilie=061.gif] [smilie=061.gif] [smilie=061.gif]

The Bravo 3 typically runs a 2:00 to 1 gear ratio....... and should turn in the 4400- 4800 rpm range....some bigger boats should run a 22 to 24 pitch to get on plane and keep the engine in the proper rpmn range.....

Jim, do you know what pitch your props are now?

[simulatedjim]

Well I did some testing with different props and found a couple of things. My 6.2 came with a 2.2 ratio B3 and 20P props with WOT of 5400rpm. Tried 22P and lowered the WOT to 5200 rpm which is the upper limit of range 4800-5200. Tried 24P props and WOT dropped to 4600 rpm. Why such a big drop from 22 to 24 and a little drop from 20 to 22?

[Throttle Up]

Sorry for the delay guys. Just got back from the Sarasota Races. Bravo III props are available in two versions....cupped and un-cupped. This may account for the different changes seen between the different pitches. Additionally if you might also have the speeds from you testing I can take a look at your slip.

Julie

[simulatedjim]

Hi Julie, Glad to see your back safely!!!!
Speeds for props are gps and tach from dash verified by digital tach. (dash tach reads about 25 rpm more)
20P 5400 rpm 37.7 mph
22P 5200 rpm 43.1 mph
24P 4600 rpm 41.3 mph
I do have one suspect 24P prop. It is not labled as an "L" cupped prop but it looks as if it has been worked on. It is the larger inner prop. Where is cup added to props? Is it at the tip of the blade? Thanks, Jim

[Throttle Up]

Jim,

I have run the slip numbers on your props .

24P has 16% slip
22P has 14% slip
20P has 30% slip

This is using a gear ratio of 2.2 with the 6.2 motor.

The 22P prop is running where it should be at 5200 RPM at WOT with a reasonable amount of slip. The 20P prop is running to high of an RPM, exceed the torque band of the motor, which is evident with the decrease in your speed. The 24P is running to low of an RPM at WOT and has a great amount of slip at 30%. I would say the 22P is the best prop. Maybe clean it up a bit.

Julie

[simulatedjim]

Thanks, Julie I am currently runnin the 22P. Since this is a "cruiser" I'm looking for the most efficient props while running 3400-3600 rpms. I'm new to the changing props thing and trying to learn as much as possible. Could a mis-matched set of props cause the extra slip I have with the 24P? ie. the inner 24P prop maybe cupped.

[Throttle Up]

Yes having the props matched is quite important. Check the cup on both props and compare them. Follow the cup along the trailing edge and see that it is uniform.

Julie