AT impeller matching?

[LVjetboy]

"Where does one start when trying to decide what impeller is going to be properly matched to a given pump/hull/motor combination."
Well, start with what can be and already is known in theory (physics) and testing (experimentation), then further that through more experimentation and accurate recording of results and objective reasoning. Trust me. If you understand more power (not torque) to the impeller is good? And efficiency (power out/power in) determines how much input power is converted to output thrust? Then maybe you'll understand where to start.
You think pump curves are bogus? Some may not be accurate, but pump curves are a starting point for understanding how pump impellers give performance. If you have an accurate pump curve you can predict pump performance. That's why pump mfgs (not jet pump mfgs but irrigation and other high market mfgs) understand performance and understand how to use pump performance curves. In fact they publish their curves. Us typical dumb sh*t jetters don't understand either and compensate by saying...just run what you brung and see what happens.
Simple minded bs.
"Seems there's a lot of variables here, and a lot more info than before. Is there going to be an optimum impeller for a particular hull/pump combo which the engine will have to be built around, or will the operating parameters of the engine dictate impeller choice?"
Yes there are a lot of variables, some more important than others, some easier to predict than others. Not all can be known. In that situation, you prioritize and consider what you can test and measure. As well as what can know without testing. No, there's not an optimum impeller combination for a certain hull and engine/pump combo retardless of application. Simple minded. Start with an understanding of the basics, then expand...at some point you'll reach the limit. At least by then, you'll understand the basics and the limit.
Mixed flow pumps have been around for awhile. Pump curves many times tested and shown to follow a cubic relationship between rpm and power. Basics. Berkeley, AT, Dominator, Legend, are you going to ignore pump curves and wonder if there's an optimum impeller without understanding the basics?
If so then simple minded. Test and retest and invent the wheel all over again. Or go study what is already known about pump technology then ask the question about, "where does one start" again.
jer

[drysumpjet]

In these pumps, how much of the impellor's output sneaks past the wear ring back into the impellor's eye? A small amount of water sneaking past the wear ring may not be a big deal in itself but does it significantly disturb the incoming water from the suction piece? With that being said, I wonder if the larger impellor gained higher top speed (with the relatively same bowl pressure) due to less water sneaking past the wear ring? Note the water leaving a larger impellor enters the bowl at a deeper point (greater distance from the wear ring).
Maybe it's not sneaking past the wear ring... perhaps the location of the impellor's output in the bowl is the critical factor. To expand on this observation, with the larger impellors, the water has a shorter distance to travel as it is "pushed" by the back side of the impellor's vein to where it enters the stationary vein of the bowl.
I'm probably way off base, what do you all think?

[OkieDave]

In these pumps, how much of the impellor's output sneaks past the wear ring back into the impellor's eye? A small amount of water sneaking past the wear ring may not be a big deal in itself but does it significantly disturb the incoming water from the suction piece? With that being said, I wonder if the larger impellor gained higher top speed (with the relatively same bowl pressure) due to less water sneaking past the wear ring? Note the water leaving a larger impellor enters the bowl at a deeper point (greater distance from the wear ring).
Maybe it's not sneaking past the wear ring... perhaps the location of the impellor's output in the bowl is the critical factor. To expand on this observation, with the larger impellors, the water has a shorter distance to travel as it is "pushed" by the back side of the impellor's vein to where it enters the stationary vein of the bowl.
I'm probably way off base, what do you all think?
That is something I have been wondering about too. With the 9.5" impellor, there is very little clearance between the bowl and the impellor at the large part of the impellor. I am installing a smaller (AA) impellor and there is like a 1/4" gap all the way around. But I got to thinking, with an A or a B, there'd be more gap and they seem to do pretty good. There's supposed to be about a 600 rpm difference between the 9.5" and the AA. I will find out if my setup benefits from the additional RPM. Not that I mind leaving a little on the table, I just had a SS AA laying around when I discovered the aluminum 9.5 was broken.

[steelcomp]

Touchet!
"Where does one start when trying to decide what impeller is going to be properly matched to a given pump/hull/motor combination."
Well, start with what can be and already is known in theory (physics) and testing (experimentation), then further that through more experimentation and accurate recording of results and objective reasoning. Trust me. If you understand more power (not torque) to the impeller is good? And efficiency (power out/power in) determines how much input power is converted to output thrust? Then maybe you'll understand where to start.
You think pump curves are bogus? Some may not be accurate, but pump curves are a starting point for understanding how pump impellers give performance. If you have an accurate pump curve you can predict pump performance. That's why pump mfgs (not jet pump mfgs but irrigation and other high market mfgs) understand performance and understand how to use pump performance curves. In fact they publish their curves. Us typical dumb sh*t jetters don't understand either and compensate by saying...just run what you brung and see what happens.
Simple minded bs.
"Seems there's a lot of variables here, and a lot more info than before. Is there going to be an optimum impeller for a particular hull/pump combo which the engine will have to be built around, or will the operating parameters of the engine dictate impeller choice?"
Yes there are a lot of variables, some more important than others, some easier to predict than others. Not all can be known. In that situation, you prioritize and consider what you can test and measure. As well as what can know without testing. No, there's not an optimum impeller combination for a certain hull and engine/pump combo retardless of application. Simple minded. Start with an understanding of the basics, then expand...at some point you'll reach the limit. At least by then, you'll understand the basics and the limit.
Mixed flow pumps have been around for awhile. Pump curves many times tested and shown to follow a cubic relationship between rpm and power. Basics. Berkeley, AT, Dominator, Legend, are you going to ignore pump curves and wonder if there's an optimum impeller without understanding the basics?
If so then simple minded. Test and retest and invent the wheel all over again. Or go study what is already known about pump technology then ask the question about, "where does one start" again.
jer

[LVjetboy]

"Maybe it's not sneaking past the wear ring... perhaps the location of the impellor's output in the bowl is the critical factor. To expand on this observation, with the larger impellors, the water has a shorter distance to travel as it is "pushed" by the back side of the impellor's vein to where it enters the stationary vein of the bowl.
I'm probably way off base, what do you all think?"
I think you're headed in the right direction. The exit flow from the back side of the impeller blades does travel a shorter distance to the bowl vanes for the larger impeller. BTW, not "veins" as in blood to the head. Please guys lets get the difference between veins and vanes? Look it up if you don't trust me. How many times do I gotta post this for us jetters? We got no veins in our jets!!!
Oh never mind.
Anyways, according to the article, impellers were mocked up and wear ring clearances set equal. Good start. That implies wear ring clearance loss nearly the same between impellers. Cool. But the different impeller cuts may also generate turbulant or flow losses depending on blade-to-vane spacing. As drysumpjet posted?
Those losses hard to know or predict but can be measured with testing.
I'm glad Cyclone tested, thoroughly enjoyed the article and not detracting in any way from that.
BUT.
I don't understand the AT AA impeller cut dimensions reported in his article or why his AA only turned 150 rpms less than his A. There's something wrong with that data. His A and B results matched...the AA didn't. To understand more, first question the test data...make sense? Pump charts for AT show the AA more aggresive than the Berk AA. Yet the Berk AA will turn 400 rpm less then the Berk A. So why did Cyclone's AT AA only turn 150 rpm less than the AT A? Something doesn't add up so I posted.
That's one issue.
-----------
Not to confuse, but consider another perspective. I have back-to-back impeller sizing tests from another source, very well respected btw, that shows top speed with an Aggressor A/B cut. And his engine power similar in power to Cyclone.
His top speed not achieved with an Aggressor AA and not even AT 9.5. In fact, by switching from the AA and A cut, a gain of 9 mph...a bit more than Cyclone reported switching from A to AA. And my souce indicated switching from the AT 9.5 to the Aggressor A cut good for about 12 mph gain
AT 9.5 top speed: 89.3
Aggressor A top speed: 101.8
BTW, the AT 9.5 is a bit more "aggressive" than the Aggressor AA or A cut. So bigger is better?
I'd be happy to post detailed results, but the data was shared in private, so I'll check with the author first.
jer

[OkieDave]

I trusted source told me once when I was buying a new Dominator pump (1988) to cut 90 thousanths off the front of the bowl to move the bowl forward. I did that then as well as cutting a 4-5 degree angle on the back of the bowl to eliminate the need for a wedge. I ran that pump in several boats and in fact it is in my Gull-wing boat now. It always ran good and I never used a stuffer. I just finished doing a new pump for my cheyenne and I did the same mods to it. Not sure if it helps because I have no way of doing a real comparison.

[kojac]

"Maybe it's not sneaking past the wear ring... perhaps the location of the impellor's output in the bowl is the critical factor. To expand on this observation, with the larger impellors, the water has a shorter distance to travel as it is "pushed" by the back side of the impellor's vein to where it enters the stationary vein of the bowl.
I'm probably way off base, what do you all think?"
I think you're headed in the right direction. The exit flow from the back side of the impeller blades does travel a shorter distance to the bowl vanes for the larger impeller. BTW, not "veins" as in blood to the head. Please guys lets get the difference between veins and vanes? Look it up if you don't trust me. How many times do I gotta post this for us jetters? We got no veins in our jets!!!
Oh never mind.
Anyways, according to the article, impellers were mocked up and wear ring clearances set equal. Good start. That implies wear ring clearance loss nearly the same between impellers. Cool. But the different impeller cuts may also generate turbulant or flow losses depending on blade-to-vane spacing. As drysumpjet posted?
Those losses hard to know or predict but can be measured with testing.
I'm glad Cyclone tested, thoroughly enjoyed the article and not detracting in any way from that.
BUT.
I don't understand the AT AA impeller cut dimensions reported in his article or why his AA only turned 150 rpms less than his A. There's something wrong with that data. His A and B results matched...the AA didn't. To understand more, first question the test data...make sense? Pump charts for AT show the AA more aggresive than the Berk AA. Yet the Berk AA will turn 400 rpm less then the Berk A. So why did Cyclone's AT AA only turn 150 rpm less than the AT A? Something doesn't add up so I posted.
That's one issue.
-----------
Not to confuse, but consider another perspective. I have back-to-back impeller sizing tests from another source, very well respected btw, that shows top speed with an Aggressor A/B cut. And his engine power similar in power to Cyclone.
His top speed not achieved with an Aggressor AA and not even AT 9.5. In fact, by switching from the AA and A cut, a gain of 9 mph...a bit more than Cyclone reported switching from A to AA. And my souce indicated switching from the AT 9.5 to the Aggressor A cut good for about 12 mph gain
AT 9.5 top speed: 89.3
Aggressor A top speed: 101.8
BTW, the AT 9.5 is a bit more "aggressive" than the Aggressor AA or A cut. So bigger is better?
I'd be happy to post detailed results, but the data was shared in private, so I'll check with the author first.
jer
Jer,
Interesting, the AT 9.5 achieved a top speed of 89.3 and the Aggressor obtained a top speed of 101.8
The smaller cut impellar probably allowed the motor to RPM higher to achieve more of it's usable horsepower.
Did you have the RPM data to confirm this?
Were either of the impellars detailed or were they just cut to stock.?

[cyclone]

Here's my thoughts on the whole question of why one impeller may achieve a higher top speed than another, which I didn't print because its tough for me to prove; I think that where top speed is concerned, you have to pick your impeller based upon which one you think will get your boat into its "happy zone",which is to say, peak powerband. For my motor, that is around 6,500 rpm. Anything past 6,500 and the horsepower begins to fall off. If you have to cut down the impeller to get your motor into its peak powerband where its' really going to come alive, you might not go faster if you are decreasing the efficiency of the impeller faster than you are increasing the efficiency of the motor. In my case, a larger impeller (AA) worked out better and put my motor exactly where it wanted to be rpm-wise. The smaller impellers,although they did allow the motor to rev past its peak rpm range, did not make the boat go faster.
As for the question of the data, the test was run multiple times to make sure the what I was reading was correct. Could there be something funky about that particular AA impeller that made it work differently than your data says it should? of course.
The point to of the story though was to say here is what these three different impeller sizes did to this particular boat's performance. It's to get you thinking which I'm glad it seems to be doing. Hopefully, there was at least one nugget of info in the article that will shed some light on your own boat's performance.

[bp]

I don't understand the AT AA impeller cut dimensions reported in his article or why his AA only turned 150 rpms less than his A. There's something wrong with that data. His A and B results matched...the AA didn't. To understand more, first question the test data...make sense? Pump charts for AT show the AA more aggresive than the Berk AA. Yet the Berk AA will turn 400 rpm less then the Berk A. So why did Cyclone's AT AA only turn 150 rpm less than the AT A? Something doesn't add up so I posted.
jer
based on things i've seen playing with other impellers, i think he's pretty close in rpm, aa to a; could be 200, but close. 250 a to b, not so sure since he's going over the top.

[LVjetboy]

"Interesting, the AT 9.5 achieved a top speed of 89.3 and the Aggressor obtained a top speed of 101.8
The smaller cut impellar probably allowed the motor to RPM higher to achieve more of it's usable horsepower.
Did you have the RPM data to confirm this?"
Yes, speed, rpm and dyno results...for AT 9.5 and Aggressor AA through C cut. Duane, would it be ok if I posted them?
"based on things i've seen playing with other impellers, i think he's pretty close in rpm, aa to a; could be 200, but close. 250 a to b, not so sure since he's going over the top."
Bp, Mikes rpm change from A to B was +350, seems reasonable based on impeller curves. Sure he's over the top with the B, but less actual power delivered than calculated would only underpredict the rpm delta. His delta from AA to A nowhere near what I'd expect. Uhm, gotta run no time to explain will post again tonight.
jer