Bravo One Prop woes

[stinger222]

89 7.4 with perf cam, rectangle heads, 5000lb chaparral 2550 sx, prev owner had a 25 pitch mirage on there, only 4000 rpm WOT, so I swapped out 20p Turbo brand prop, boat screamed 5000rpm WOT, better holeshot, better top end, everything better. So I figured I a 22p prop would be perfect, found Mich wheel 22p....decent holeshot, WOT 4700, but boat feels much slower top end....should I have bought a Turbo 22p. Do the brands really vary that much. The Mich wheel 22p doesn't seem to push as much water as the 20p Turbo, but that shouldn't be!!

 

[Bondo]

Re: Bravo One Prop woes

Do the brands really vary that much.

Ayuh,..... Sure Do.....

 

[45Auto]

Re: Bravo One Prop woes

but boat FEELS much slower top end

You'll have a lot more success if you actually measure performance rather than going on "feel". A motorcycle mag did tests a while back where they changed things to make the bike slower or faster, then asked the rider whether it was faster or slower. Turned out they had to make a difference of more than 10% in performance before the riders (professional riders at that) could be correct more than 50% of the time. So your boat could easily be 10% slower but it will "feel" faster to you because you did something to it or spent some bucks on it. Seen that happen a lot. ONLY way to know for sure is to actually measure the performance.

The Mich wheel 22p doesn't seem to push as much water as the 20p Turbo, but that shouldn't be!!

How do you tell or measure how much water a prop is "pushing"? If you mean it's accelerating slower that would probably be true since it's a higher pitch (22 vs 20).

 

[stinger222]

Re: Bravo One Prop woes

I was referring on the top end. With 20p at 5000 rpm, the boat is at least 5 mph faster than the 22p at 4600 rpm.

 

[lmannyr]

Re: Bravo One Prop woes

Was this by GPS/Speedo?

 

[stinger222]

Re: Bravo One Prop woes

neither....but I have been boating for over 20 yrs...I can tell when I am going faster or slower, ie the water is passing by you faster.

 

[45Auto]

Re: Bravo One Prop woes

Was this by GPS/Speedo?

neither....but I have been boating for over 20 yrs...I can tell when I am going faster or slower, ie the water is passing by you faster.

Not much point in pursuing this any further. Motor RPM, engine sound, vibration, wind, etc. all combine to give you the "feel" of how fast you're going. Stick the prop on that makes you happiest and don't worry about it anymore.

 

[stinger222]

Re: Bravo One Prop woes UPDATE!!!

Re: Bravo One Prop woes UPDATE!!!

Got a brand new working speedo. Here are the stats with both props

22p Michigan wheel SS prop WOT 45 mph @ 4600 rpm

20p Turbo SS prop WOT 48 mph @ 5000 rpm

I knew I was going faster with the 20p prop. This means the mich wheel prop sucks because the extra 2 pitches should be a little faster on the top end, not slower. A 22p Turbo prop might push me over 50 mph or a 23 mirage might be the next to try out. maybe even a 22p 4 blade, extra lift may help.

I know speedos are not accurate but at least I can prove speed differences.

 

[stinger222]

Re: Bravo One Prop woes

just tried out a mirage 23p today. WOT 4400 rpm @ 45mph

so no pickup in top speed with the 23p, just dropped 200 rpm. Anybody have any opinion on 4 blades?

 

[MikDee]

Re: Bravo One Prop woes

IMO, From my experience, a Michigan wheel is more for power then speed, I think a Mirage is better, but not one of the best either.

 

[steelespike]

Re: Bravo One Prop woes

Generally a brand change even going same demension will produce a difference.Then there is the design issue as well.A prop may produce bow lift another stern lift obviously wouldn't produce the same results on a given boat. Also a prop may be wonderful on one boat/engine combinatiopn and awful on the next.Its best to find a brand that seems to work well on your boat and stick with it as you try different types.
4 blades generally will improve low end performance while comprimising top end.

 

[QC]

Re: Bravo One Prop woes

It is quite possible that your particular engine, as built, makes it's peak power at 5000 RPM . . . No way of knowing without an engine dyno . . . Also, three blades are generally faster. Buuuuut, you could have a 4 blade that matches your boat well against a 3 blade that doesn't and prove absolutely nothing. Prop stuff is a lot of voodoo with some hydrodynamics and math thrown in for good measure.

 

[Tail_Gunner]

Re: Bravo One Prop woes

While i do not know the spefics of the Turbo brand of prop i do know there sister company Stilletto and under that brand they make a Bay Pro 2. It provides a tremendous amount of lift. So much so that it can lift the boat far enough out of the water creating less wetted surface which in turn reduces drag and ups the speed almost enough enough to offset the 4 blade drag. In short its one hell of a prop on a I/O, you get the benefit of lower planing speed....noiticeably increased midrange punch....smoother operation...at the cost of about 1mph at top speed...

If you are trying to go to another prop think of that 20 as a 21p ss it will be easier to understand the jumps.. If your running truly at 5000 with a load id say your dead on the money, a 22 would probably drop you to 4600 or more... depends on how much tourqe the motor has at the top of its range

 

[stinger222]

Re: Bravo One Prop woes

Just to clarify, the turbo 20p that I used is a 3 blade.....All the perf oriented boats at my lake all have 4 blades, so I want to try one and see if the "lift effect" helps me out.

 

[Tail_Gunner]

Re: Bravo One Prop woes

............even pitched 3 blades's........:redface: Me bad. Anyway Turbo props have a lot of cupping and will act like 1 pitch higher than a lot of prop's that's some of the confusion. Going to a 4 blade "Precison" will probably result in a loss of some top speed but get you qualities as stated above.

A 22p 3 blade should put you at 4800..Now i need to go Precison and see if they make a 22 3 blade that will fit my volvo drive..