Props blowing out, need advice on 5 blades?

[eichhoma]

If a guy had a pair of 26P B1's and wanted to go to 5 Blades, would you stay with the same pitch or do you have to increase or decrease the pitch size? I have a pair of 26P B1's that are labbed and cupped.... they aerate like crazy coming on plane, around 2800-3000 RPM, you hear the motors rev up from the props blowing out and finally catches up with itself as the bow is coming back down. Would a 5 blade help with that? What pitch should I look at in a 5 blade from what I have? maximus or hydro? dia.? Whats the difference?
Thanks in advance for any input. Mark

 

[ThrottleUp Props]

Mark ,

If you 26P Bravo I is running at the appropriate RPOM at WOT then you will need 24P Hydro P5-X props. Keep in mind that your 26P props are really 25P. The rule of thumb is that you will reduce one inch of pitch to compensate for the drag of the addiditonal blade.

Julie

If you go this route I have a NEW 24P P5-X LH on the shelf. I give you a screaming deal on it. You could get a RH from Teague or Hydro direct.

 

[eichhoma]

Thanks Julie, I appreciate the info.
The B1 26's I have - have been cupped and labbed.... so the rpm's are about right.... I would like to see maybe 200 more rpm come out out of them. Am I understanding that a 5th blade will help with the blowing out? Are the 5 blades harder on drives? I have newly rebuilt XZ's.... thanks....

 

[jwurl]

I have the same problem with my Formula fastech with the props blowing out coming up on plane. I tested 5 blade maximus props and it still did the same thing....Jeff Wurl

 

[eichhoma]

Really? Thats actually very discouraging. I dont know what to do now then. I thought another blade in the water would be the answer. I know I am making considerably more torque now down around 2800-3500 than my stock 525sc's did.... but there has to be an answer and a prop solution that the boat will like... Anyone?

 

[ThrottleUp Props]

If a guy had a pair of 26P B1's and wanted to go to 5 Blades, would you stay with the same pitch or do you have to increase or decrease the pitch size? I have a pair of 26P B1's that are labbed and cupped.... they aerate like crazy coming on plane, around 2800-3000 RPM, you hear the motors rev up from the props blowing out and finally catches up with itself as the bow is coming back down. Would a 5 blade help with that? What pitch should I look at in a 5 blade from what I have? maximus or hydro? dia.? Whats the difference?
Thanks in advance for any input. Mark

SOME of what you have described is the behavior of an OFFSHORE performance boat. Remeber Offshore boats do not jump on plane. Ski boats are good for that goal. I really am not sure if a 5B is the correct answer for your application. It could help you get on plane with high drives. Now as for the stress of the additional blade it is indeed true that you have another blade in the water connecting the power so the stress is a little greater. HOWEVER.....everytime you add a blade the harmonics are reduced greatly! Rememer harmonics occur from the moment you turn the key on until you turn it off. So the topic of debate clearly exsists...... ALMOST all Spec Class Race Teams run 5B or 6B props and drive failures are not that prominate. It really has more to do with your skill set!

Julie

 

[eichhoma]

Thanks Julie, thats great information on harmonics. While I am not opposed to the idea of going to a 5 blade, I do not want to do that and have the same result. I am not trying to jump on plane quickly either - I baby the sticks coming on plane. But when the motors hit 2800 they blow out up to about 3500... every time.

The part I am having problems with, and not really getting any answers on is WHY are my props blowing out like crazy now, and they did not at all before. I KNOW I have increased power; about 150 HP per side, and a considerable increase in torque from the stock 525sc's as well.... So am I understanding that this increase here now is preventing me from finding the right props that wont blow out, wont tear up my drives, etc? I will be the first to say I am not up on all this "prop science" just cant believe I increased power and now I have to live with props that blow out like crazy getting on plane???

 

[ThrottleUp Props]

You have increased the power at the prop shaft. The props cavitating and revving up to 3500 is no big deal.....think about any race / poker run boat you have seen ....they all do the same thing. If you have tabs drop them down and as the bow starts to drop then pull the tabs up and that is typically what it takes for a performance boat to get on plane. Your not going to blow up your drive because you hit 3500 RPM or 4000 for that fact.

Julie

 

[eichhoma]

I usually always start off with the tabs down pretty far... mostly so I can see out in front of me. As I speed up I start raising them up so that they are at neutral position at cruising speed... unless its pretty rough, I leave them down just a little.

So, are you saying that the blowing out is normal and I should just not worry about it?
I hear what you are saying about normal behavior for an offshore raceboat.... this is a flatbottom cig, I didnt think the slight increase in power I made would have this much effect on the props, but If I am hearing that I dont need to worry about it and no harm or major loss in efficiency, or increase in stress is taking place... I can leave it alone?

 

[ThrottleUp Props]

Yes for all intesive purposes I am not reading anything alarming here. Post your performance data , we can then run thru your slip and see if there is any room for improvement. And to answer your question did you not say:

"I KNOW I have increased power; about 150 HP per side, and a considerable increase in torque from the stock 525sc's as well.... "

This answers your question for you.

Julie

 

[FastDonzi]

Did the props NOT Slip Before they where Labbed???? When did they Not Slip? before the motor upgrade? or was the motor upgrade and Props labbed at the same time? I don't see anything alarming as long as your not goosing the throttle while it's cavitating. We had a boat that (with dual #4 drives) took 5Krpm to get on plane then ran wot at 4800...

 

[ThrottleUp Props]

Agreed FastDonzi....I was of course thinknig about the cup removal during the labbing as well. But he said it is since the re-power the blow out occurs...not the labbing. If I were eichhoma I would try to find a set of 5B props to test with. It may indeed improve the planning issue to a point that he is happy with them. But there is only one way to find out.....TEST!!!!!!!

Julie

 

[eichhoma]

The props were labbed 26's before the repower. then after the repower I was cavitating real bad and hitting the rev limiter without even getting into any trim. Brett cupped them and took some of the rpm's out, still would like to see another 200 rpm come out of them though. but the cavitating is still happening.

 

[Magic Medicine]

Sounds like a trying a stock set of 28's might be the answer and go from there.

 

[bbladesprops]

I wrote a big story and lost it. Maybe for the best. You guys have already covered the fact that ventilation of propellers on sport boats planning is a common occurrence. The set ups over the last 10 years (high X dimensions and stepped bottoms) have enhanced the issues. This situation is a little different.

If you can manage the ability to plane with trim and tab while still getting some blow out, it might be best to leave it alone. Otherwise, adding cup, changing prop depth, changing blade geometry can help prevent the blow out issue. However, these changes can also have negative effects. Typically the negative is a slower top speed. I believe the 4 blade props are the best choice here unless mid range is the most important issue and then 5 blades could have a place.

In this case the slip # at WOT is acceptable for the vintage hull.

 

[Tinkerer]

This sounds like what is happening with my boat.

Because of excessive trim I want to raise the X 1 to 2 more inches.
If I can get the boat on plane easily without tabs now with 4 blade Bravos.
Will I have the same planing with the drives 1 or 2 inches higher with the 5 blade Maximus props?

Prop shafts now are 4 inches below the hull.

 

[Let 'Er Rip Cig]

I have a flat bottom cig. I ran 600's last year with 26 4b bravo's with little blowout. This year I'm running 725's. With the 26's it was a fight to get it up on plane. I'm running 30's now. I drop the tabs to 7 and run it up to 3500 and keep it there till it's builds some speed then bring up the tabs as the speed increases. If the rpm's get to 4000 I back off till I'm up to speed. I'n my case HP does change the way I have to drive....Oh yeah once the tabs are up I push the thottles to the dash!:driving:

 

[PARADOX]

Just for FYI guys.
My boat have no steps and pretty "ole' school" design. I planed just about any boat you can think of.. They are ALL different. Even the same hulls.
So FYI.. DOn't try to get on plane to fast. Let the engine do the work and give the hull time to react and start planing. Especially on older standard "V" bottems.
Feel the motor. Ease into the sticks and as soon as you feel the props loosing grip, give a small and short "jerk" on the sticks, this will allow the props to bite again. I don't think it's a proping problem. It's the nature of the beast. I see a lot of "poker runners" want to get on plane ASAP. Then the props bust loose. Remember these HP "V" 's push a lot of water before they get enaugh speed to get on top. Having the tabs "TOO" low actually creates drag and slows your planning.
Take your time and be patient.

IMHO.

(Side note) the best way to "learn" getting on plane is learning to get water skiiers up behind the boat. And for what it's worth. I pulled up EVERY body so far on slalom. on 16' hustler and 19" prop. One guy over 275 LB. (Great dude, now I should call him, didn't talk to him for 15 years))

 

[OBNOXUS]

What is your slip %,,,,,,, may also want to try a spacer if you cant find a pair to try without buying.