5-Blades
 

Wondering how the 5-blades will work on my application. Running a 1.36 Imco Extreme SC with a standoff box, 103 @ 5700 on a lab 30 Brovo 1. You can check out picks of the drive height.

http://community.webshots.com/album/83701358qOJGlb

I thought you sold that bad boy?? I bet it will work well, I've got a P5X coming for the Pantera, will advise

Couldn't do it - Runs too well.

LOVE my 5 blade hering.

Hell my setup is coservative and kinda slow by all means but the herring really really helped picked up soem speed and my slip numbers dropped significantly.

Hey John,
Draw a line across side to side from the inside corner of the sponsons and then see where the prop centerline fall relative to it, that is inches above the line or inches below. I was running 100 at 5100 with 30" so your slip is up a bit.

John,

The 5 blade would help bring the slip down and maybe even pick up some top end speed as well but; Your WOT rpm should be running around 6500 with the cam in that motor. One reason for the high slip number is due to your WOT rpm being too low.

Your dyno sheet shows the motor still making hp beyond 5700. The max torque is at 5300, your WOT should be about 1200 rpm above max torque. Since your WOT is only 400 above max torque the drive train is "torque loaded" which tends to lift the stern, bringing the prop higher out of the water and increasing the slip.

If you are interested in trying a 5 blade let us know and we can send one out to you. Ideally your slip should be in the 6-8% range in your application.

Matt

It looks like the max TQ is about 4200rpm at 750+ and I would NOT turn that motor over 5500 rpm max 5700. I bet the way it is proped it is a rocket in the acceleration.

Matt, I have been staying half in tune with the 5 blades available. Herring, Mercury and Hydromotive are the brands I am familiar with. My rev limiter is set at 5850 and I would like to prop as close to it as possible. I cruise at 3500 at 65 mph as it hits the hardest from about 60-90. The last 5-7 mph takes some distance to hit, but it will run consistantly at 100 with 3 people 3/4 tanks and a full cooler. It pops right onto plane with ease and I do not blow out at all.

Let me know what you recommend.

John

They are a hell of a performance boat for the money aren't they- I miss mine already:(

Cobramarty, you are dead on, my mistake. I went right past those low numbers.

John, your rev limiter is set just right. In your case I think a P5X 28 or 29 would put you at about the same WOT rpm you are now. Acceleration will improve and your cruise speed should improve about 7 or 8 mph compared to the Bravo 1 lab you have now. The nice thing about the P5X is the way it runs right out of the box. A stock P5X should get you at about the same top end, if not better, than your lab Bravo 1 but with all the advantages of a 5 blade.

If you are interested in trying one give us a call.

Matt

Marty, My prop CL is dead even with the bottom of the sponson.

Ken, You are soo right with the performance. On a lake, you cannot beat them. We ran the north Dallas lakes for the last three years, I just moved to Austin - Lake Travis is a decent size lake and we shock people with the performance and sound - (dry tailpipes), as long as no one shows up with a twin engine cat.

Matt, are the P5X propellors lab finished, or is there a need. Since I have a light weight cat on a lake and I do air it out, I would think that I can go pretty thin on the blades to get the most out of it. From a goal perspective, I am looking for 1. accelleration from 50-90, 2. top end, 3. mid range cruise speed.

If I reduced my slip from 16% to 6 percent, that should be close to 10 mph - worth paying big $$$ for. I am at a point that I believe the setup is as good as it is going to get - hull is blueprinted, can't go any higher with the x-dim without drastic changes, and I have an extension box. The alternative is to throw lots of HP at it and overpower the problem.

Matt, I meant I do not air it out - If the prop airs once a season it is a lot.

John,

I think you should try the P5X stock and then see how it runs on your boat. If you like it and it performs well then you can consider lab finishing.

What I have been so pleased with, is that the P5X runs outstanding right out of the box. We have seen very impressive top speeds with the P5X and it holds it's own against lab finished Bravo 1's.

John, What lower do you have? Is it 2" shorter?

Dang,

Looks like it could use higher X.

-3 lower - I had a blackhawk at one time with a 3" rise extension box - it was much too high. The blackhawk ran the best mounted to the transom w/ out the box

New Props
 

John,
Yesterday my Cat received a big box from Washington and inside were a pair of Hering 6 blades. I, like you was having too much slip and this is supose to be the answer to that .. The only thing is that they are so damn pretty that I'm sorta of afraid to put them on. They come labbed right out of the box.Im told that this will cut my slippage down to around 6 to 7 percent.
Big power,130 ratio B-maxs with ext. boxes. Only time will tell, will let you know whenever summer gets up here to Yankee land:D :D
Best of luck which ever way you go!!
eliminator219

Les, try them out - they are supposed to be the best. Did you get the forged or cast wheels?

BTW, I am a native New Yorker who could not take the cold.

Matt, I just calculated my slip:
Top speed - 16% 1.36 / 30 / 5750 rpm / 103 mph
Cruise - 12% 1.36 / 30 / 3500 rpm / 65 mph

At 8% that would be a dramatic increase
Top speed - 110 mph
Cruise speed - 67 mph

Is this correct by your calculations? Keep in mind 103 is the best I get out of the boat with the good wind, conditions, etc. 101 is typical on any given day, wind, water, people, etc.

Just a thought,
I think Matt will have you use different numbers for slip calculation rather than the 30 for the Bravos; maybe 28.5.
Also less slip uses more hp/trq. In other words if you drop to 8% you wont turn as many rpm and you'll have to drop in pitch.
I'm sure Matt can explain this better.
I'm anxiously awaiting my new P5-X :D
Dave

John,
Dave is right. A more accurate pitch for your 30 lab Bravo's is 28.5. So your slip is more like 11% at WOT and 6% at cruise. The 6% number seems a little low but the 11% seems about right.

You should expect about a 4% decrease in slip with a 5 blade. That does necessarily mean you will gain 7 mph. The prop will be more efficient but it still takes a certain amount of power to move a boat through the water at a certain speed and if the power is not there then the speed won't be there.

You would have nothing to lose by trying a 5 blade. If it works and it gives you the results you are looking for then great. If it doesn't then you haven't lost anything. Everyone I have talked to who has tried the P5X has been impressed with it's performance. I think you should expect the same.

Matt

Matt,
I have a question regarding your reason for selection of 28.5 instead of 30 for the Bravo prop. I understand that the true measurement of the blade is 28.5. However, this does not account for the cup that is added. Doesn't cup add into the equation since that effectively adds to the pitch, in this case about 1.5". It seems to me that the dynamic movement of the blade through water including cup should be figured on the efficiency calculation.

What am I missing????

Thanks,
Rick

Rick,

Thanks for the question.

I have measured many Bravo 1's. I measure them with the Hale MRI Computer measuring system. They are measured on 5 different radii, 50%, 60%, 70%, 80% and 90%. The measurement is from the very edge of the trailing edge to the very edge of the leading edge, which takes the cup into consideration.

A lab finished Bravo 1 typically has the cup reduced which effectively reduces the pitch even more.

For example, I just scanned a set of 36 Bravo 1's lab finished by Mercury, they had cup added and they measured only 34.5" of pitch. Without the additional cup they would be closer to a 34" pitch.

That's why we always have to go down in pitch when going to another manufacturer other than Mercury.

Matt

OK with the 3" shorter lower you are even with the bottom of the sponsons. If you put the blackhawk on, just bolt it to your gimble, where will that put the propshaft relative to the bottom of the sponsons?

Interesting enough on my Cobra the propshaft is 5" above the bottom of the sponson but I have a true tunnel with no center pod.

Marty,I have a BH drive on my 25 daytona. The prop shaft is about 3 inches above the bottom inside edge of the sponsons. It makes for a major lack of trimability below 60 mph until it starts packing but it has run 91.1 gps with a 500efi thru 1.5 gears and 31 BH props at 5100rpm.

Thanks Matt for the reply, I understand now. The cup really is taken into account when you measure the pitch with your scan tool.

Rick