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4 Blade Propellor Question

R

rbjscott

Well-known member
Prop. RPMs will be from 2200 to 2300. Does any one know which 4 Blade will make the most thrust at these rpms. I am trying to decide on which one to buy.
 
Allegedly, the big dogs say the thrust is so close from the top manufacturers, they have to stop the machine to see which blade they are turning.

Patty says the 4 blade falcon will make more thrust than a 3 blade maximus all things being equal power wise.

I have ran many different blades from the 3 top manufacturers and they are all nice.

Personally, I choose Water Walker. The Sirius will be on my redrive hopefully by summer.

Which one do you think looks the sexiest??
 
Their all pretty close in thrust but they all act differently! It depends on what or how you want your boat to run! You can take two props that generate the same peak thrust and one will be a beast on the hill and the other will be a stone unless of coarse you run around all day wide open! Props are more preference then about any thing else on a boat, out of all of them only one I consider a terd because it doesn't do anything well all the rest can make about the same peak thrust!
 
Dave's absolutely right. Given an optimized pitch setting and equal TQ at that particular RPM things kinda even out once the engine has met it's match. Now having the torque curve to break into where it needs to be, with a very aggressive prop and how you need the thrust curve to function for you are where the "magic" comes in.

Now before anyone gets giddy....This graph isn't actual data from my thrust machine. I would be a fool for doing that, but I wanted to offer some good food for thought as to what I mean by thrust curve, and how to possibly get better performance out of your combination. It's a BS one I drew up real quick in ACAD to show an example of different blade designs and how they function across the RPM range (At the prop hub)

Once again..Food for thought, so please think twice when looking too far into the data as any form of an absolute.

curvetheoreticalgz0.png


Felber
 
Good post now look at the thrust curve on the left and look at the one on the right. They will act completely different on a boat even though they make the same peak thrust. Around a year ago several people on this site were arguing all that mattered was peak thrust. As you can see by this sample thrust curve cruise RPM's will also be different even though the props may make the same peak thrust! To me the hull design and it's intended use in my opinion are some of the largest factors of prop choice
 
Now let's take it to the next level. Now copy the graph I made and change thrust to TQ and make it an example of different engine's thrust curves. We see people here with TQ curves from the left matched with thrust curves from the right and vice versa. An engine that makes it's steam too low and runs outta gas before the prop does anything, and high HP/RPM engines that the prop strangles before it gets a chance to make any power. And for those of you out there with stuff that don't run.....Think about it.

Felber
 
And to think If I could read the propeller names (in fine print) across the board, left to right, and actual propeller RPM'S, I sure enough could pick me a prop.

Even broke out the magnifying glass. Still can't read the fine print :?: :) :)
 
flying fish":22y2eugj said:
And to think If I could read the propeller names (in fine print) across the board, left to right, and actual propeller RPM'S, I sure enough could pick me a prop.

Even broke out the magnifying glass. Still can't read the fine print :?: :) :)
Click to expand...

Well Chris like I said, the graph is just a hypothetical one with some planned misinformation. But I think it does a good job of gettin the point across.

And that graph is only showing the story from one angle. Now what if you could see the graph of acceleration rate in relation to thrust with a particular camshaft/engine combination. Ahh times they are a changin. ;)

Felber
 
Realize too, different needs and boats require different props. This is why I got worn out when people use to say oh ya this prop made the most thrust hooked to my pick up truck with a scale. And they would say (All that matters is peak thrust) Whats so funny is the prop that always made the most peak thrust while sitting stationary is the worst performing prop of all! About 6 years ago I ran a Sensenich, Power Shift, Warp Drive, Whirl Wind and a Terminator on a 2.38. 2.68 and then a 3.23 Rotator each prop shined somewhere better then the others accept for one it was always a terd! Kinda the same Principal as Mike's thrust tester (on the basis of finding scientific data) Me and a customer of mine mounted an accelerometer on his boat after testing so many props and gear ratios we came down to the two that showed the best ET's and tested those two props with two ratios. If you had the balls to run the boat long enough pretty much all the props but one would make the boat run the same MPH accept for the one terd prop! Now after settling down on two props and one ratio it was neat to see how different the acceleration curves were while running nearly the same ET It's all a combo and getting the setup that will do what you want most!
 
Yeah, if you would go ahead and print the info, I would not have to spend as much money learning what works best for my (newly) chosen test mule. A dynamic beast with a hi- manifold vacuum reading, at a very low RPM (400ish), would be very acceptable.
I reckon that would take the fun out of it for me anyways. :)

Also, if I had bought and paid for a camshaft, and then was sent a camshaft that had the numbers buffed off, and no cam card, before I would install that piece on my engine, off to the Cam Doctor she would go. Walla-- 259/259@.050 106LSA- BAP :wink:-- Almost forgot. Shotty idle. Long ago.--
 
I quit doing that long ago now I have numbers on my cam's. I can see in some cases how that grind you posted would be a great cam!
 
The mentioned grind I got rid of mid summer one year. Guess I got tired of everyone griping at me for blowing their hats off and hitting them with sand and stuff idling around at 1000RPM. She sure would swing a lot of pitch. Big experiment.

I sold the piece to a Modified driver.

I guess in the perfect world there would be no trade offs.

Maybe it is in the 15 degree stuff? Might get there someday. Guess I am a little behind times.
 
Very good points. Another thing I've learned about stationary testing I seriously doubt the prop they claimed made the best thrust really did in any sense that was relevant to anyone other than those guys with that engine and gearbox on that boat on that day..That prop just complimented that engine/gearbox combo more

This is the most common question I get. "What prop makes the most thrust?" And the answer is All of them! Yeah I know...I don't know what I'm talkin about. Gimme a infinitely adjustable redrive system to set engine RPM where it needs to be, on damn near any adjustable-pitch prop and I'll get peak thrust so close you'll call me a liar. If a prop makes it’s peak thrust at 3000RPM and requires 300HP to maintain it there, I don’t care if it’s an DD A/C engine making 525#s of TQ at 3000 or a 2:1 redrive engine making ~290#s (Using a 10% loss factor) of TQ at 6000. As long as the engine is “allowed” to operate where it needs to be, and the pitch is set properly the engine’s HP will dictate the thrust, more than the prop choice. Everyone with me here?

For those that aren’t….Thrust tells me more about the POWER than the prop! I consider my thrust tester a prop dyno from the engine's perspective. It records infinite data about prop performance, and excellent data to make real-world decisions about setup and combination based on the curve of both the prop and engine. But the one black and white thing it does do, is show me if my engine/gearbox combo has the balls or not in a true measurement/calculation. And I ain't talkin about “I swing a so and so prop on #2 200 more RPM than you, so I must be makin more power” crap. That in itself is 10 times more flawed than trailer testing, but I ain’t up to that much typin tonight! LOL

It's having to make concessions based on only so many ratios available, and a fixed pitch that makes it a science within itself.

Two perfect examples are Dave’s engines and mine. My job is to move big boats with the biggest amount of reliable power and props available for a boat that can take it...I need peak thrust and to be able to build the engine that can handle that. Dave needs to build all-around packages on smaller boats that perform above and beyond in their arena. He needs smaller diameter props and more critical blade designs to optimize a more sensitive torque curve and boat. So yeah….It’s pretty simple when you think about it. LOL

Yeah...Long thread...Been drinkin, so don't correct me for typos or jibberish. ;)

Felber
 
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