All this pump effeciency talk/comparison

Infomaniac said:

I'm asking a question and apparently poorly.

If a boat turns XYZ impeller less RPM with more HP that another boat...... how do we know the pump is more effecient and moving more water rather than just restrictive?

Restrictive seems to me would do the same thing. Cause less RPM with more HP

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Sorry, I can answer that question better, typically when a pump is restrictive it will cavitate the impeller and thus letting it spin higher rpm with less water flow. If the water is unable to properly load the impeller it will cause that cavitation. As water flows around the veins inside the pump it can either do one of two things create air bubbles and caviation or flow smoothly around the veins and allow water to enter and exit the impeller/ volute assembly with a certain pressure and head.

With turbos and forced induction these are nothing more than air pumps. Have very similar properties as to how they flow. Now with a turbo or blower the boost number that we see is taken down stream of the pump and is a measure of restriction. That is why when you change something like exhaust to less restrictive the boost pressure goes down and making the efficiency increase.

How this applies to a water pump is looking down stream of the impeller you have to look at the exit volute(or in this case the bowl and nozzle assembly) The nozzle diameter is the last (restriction if you want to call it) that the water sees. By changing that nozzle will change flow inside the pump as well, now not all restriction is a bad thing. This is where thrust is created thus moving the boat forward. If you make the nozzle too big will be just as bad as making it too small. You have to have a balanced flow into and out of the pump to be efficient otherwise cavitation is a direct result, and it won't matter how much power you put to the impeller.

As a side note that is why most of the really fast boats are running data acquisition, we are trying to balance the pressures in the pump to make it the most efficient. The data before and after the impeller is very important and it taken at several points along the way.

I was somewhat heading there on my last post and you closed that thread on me when I hit " enter". punch

The short answer is trail and error. You need clocks at the races or data acq. to have an idea. A radar gun or GPS will not answer the question. I have a new AT HH "A" sitting that I'm going to run against my current MPD Legend "B"( 6,200 off the bottle 99.8 mph best and 6,800 109 on the bottle) it will be run as is out of the box to see what it does,it's expected to turn 5,800-5,900 off the bottle, it will then be detailed to turn an expected 6,500-6,600 off the bottle.

I've been told by a few here to expect the HH to ET better but loose a few mph. That is something that is not measurable without clocks. My Radar/Laptop testing system will be able to do it but without it you would need the track.

The impeller charts that have been posted by me and others have worked well for me in the past. They do not work for a MPD detailed impeller. You can use Jack's impeller for this exercise. The impeller charts say that a "B" impeller will absorb 825 hp at 6,800 rpm. The MPD "B" absorbs 825hp at 6,200 which reads like an " A+" on the chart. The fact that the MPD impeller "bites" more does that equate to being more efficient? That's a good question. If I ran an "A+" at 6,200 and the boat ran 99 and the smaller cut MPD "B" turned 6,200 at 99 I'd say the smaller impeller is more efficient.

Other than a Pump dyno (test bed) the only particle way to test is ET and MPH over a set distance and 660' it probably good enough for that.

I was hoping to see some posted info over this past year on the in-boat impeller dyno (strain gauge attached to the input shaft in the boat).

Edit: I've worked on this in the past with our boat by taking the mph and dividing it by the rpm it took to achieve it. IE 99(mph)/62 (6200 rpm) = 1.59 mph per 100 rpm. If a different impeller propelled the boat at 104 mph at 6,400 that would be 104/64=1.62 mph per 100 rpm. Which is more efficient ? This is mph and has nothing to do with ET.

At one point the AT 9.25 AA ran 93mph at 5,200= 93/52(100) = 1.78 mph per 100 rpm. If the current Legend was that efficient it would be 1.78 mph x 62(100)rpm= 110.3 mph
As it is the Legend is 99/62(100) = 1.59 mph per 100 rpm.

When I run the new AT HH I will compare the mph/RPM using this system. It's the best way I've been able to figure how to do it. But I'm up for suggestions ?

That's a hell of a goal. I could be done playing with the boat.

Just my .02

Sleeper CP

Infomaniac said:

So I posted my engine HP as 800 and I was turning an "A" impeller 6,500 RPM

It was pointed out that there is no way and my pump is ineffecient.

As it turns out yes the pump was not loading properly.

So...... With all the recent comparisons of this boat pump turns this impeller this RPM with this HP but this boat only turns the same impeller this much less RPM with more hp so the pump is more effecient.

How do we know the more effecient pump is actually moving more water? The boat goes much faster and quicker than the boat with the same impeller but more RPM?

Seems to me that a restrictive pump would load the engine down giving a false impression of more effecient. Less RPM like a cavitating pump gives more RPM

How do we actually know more water is being moved because the pump is more effecient? Based on just HP and RPM

Click to expand...

Info,
I have asked myself the same question many times over the last 20 years of testing boats with different impellars and engine combo's.
When I first got my 1999 19 ft. stealth set up by Tom Papp I installed a 572 blown chevy that made 930hp on the dyno. I ran an aggressor pump with a stock a/b aggressor impellar that turned 6900 rpm's. Tom set the pump and droop snoot with no wedges and a place divertor. The boat went 99mph on the radar gun. After installing a stuffer plate, different loader, dropping the shoe, changing the shoe to a backcut shoe from Jack Mcclure, changing to a short droop and various other changes one at a time the boat eventually ran 117mph and with no changes to the motor the rpm's dropped to 6400. I had Jack blueprint the pump and he modified the impellar. The rpm's dropped to 5950 by the computer and still went 117 mph.
Each change I made had a direct effect on the lowering of the rpm's and each change gave an increase in speed.
Hope this does not muddy up the question too much.
Kojac

Infomaniac said:

So I posted my engine HP as 800 and I was turning an "A" impeller 6,500 RPM

It was pointed out that there is no way and my pump is ineffecient.

As it turns out yes the pump was not loading properly.

So...... With all the recent comparisons of this boat pump turns this impeller this RPM with this HP but this boat only turns the same impeller this much less RPM with more hp so the pump is more effecient.

How do we know the more effecient pump is actually moving more water? The boat goes much faster and quicker than the boat with the same impeller but more RPM?

Seems to me that a restrictive pump would load the engine down giving a false impression of more effecient. Less RPM like a cavitating pump gives more RPM

How do we actually know more water is being moved because the pump is more effecient? Based on just HP and RPM

Click to expand...

It's not, nor will it ever be that simple.......There are way too many things coming into play that just X RPM and Y impeller..

You have to see the pump as a small component of a larger machine. Let's say the pump was 100% efficient (Impossible BTW) and was installed in a 1000 HP 6000 RPM scenerio (that's an assload of torque). just the angle the pump is installed in the hull can make an incredible difference in the outcome as far as efficiency (not fuel mileage, but use of pump pressure to obtain outlet speed and volume/thrust).

The same setup, spinning say 7000 RPM with a pump efficiency of 80% (pretty real) may have a better result because of the way the pump is instaled in the hull, we are talking enourmous amounts of water and literally bending it for a nano second and making a 300-600 pound change of pressure and expect the results to be spot on each time. From what I have seen, no two pumps are the same.

Interesting question in the "how do we know more water is moving" part, if more water is being moved, the pressure differential will increase, period.

GT hand

I'm not a pump guru, i built mine and it is nice and tight, but my pump understanding is still very limited. Saying that, one thing i have heard, which seems to bring up differing ideas from pump guy to pump guy is intake pressure. I've heard some say they want the least amount of intake pressure possible without cavitation, and i've heard some say they want to see the maximum amount of intake pressure that still allow for safe shutdown. (I think I'm remembering this correctly) But it seems to me this is a debate where people are all over the board, yet in my head it also seems that this would be a large resistance factor...or load the impeller has to overcome that would effect rpm and efficiency.

Am i thinking about this correctly? There are many that know way more about this than me, but thought id bring it up, because it was the first thing i thought of while reading this effeciency/rpm/hp question.

AP

kojac said:

Info,
I have asked myself the same question many times over the last 20 years of testing boats with different impellars and engine combo's.
When I first got my 1999 19 ft. stealth set up by Tom Papp I installed a 572 blown chevy that made 930hp on the dyno. I ran an aggressor pump with a stock a/b aggressor impellar that turned 6900 rpm's. Tom set the pump and droop snoot with no wedges and a place divertor. The boat went 99mph on the radar gun. After installing a stuffer plate, different loader, dropping the shoe, changing the shoe to a backcut shoe from Jack Mcclure, changing to a short droop and various other changes one at a time the boat eventually ran 117mph and with no changes to the motor the rpm's dropped to 6400. I had Jack blueprint the pump and he modified the impellar. The rpm's dropped to 5950 by the computer and still went 117 mph.
Each change I made had a direct effect on the lowering of the rpm's and each change gave an increase in speed.
Hope this does not muddy up the question too much.
Kojac

Click to expand...

Apply my formula to that.

99/69(100 rpm)= 1.43 mph per 100 rpm

117/64 (100 rpm) = 1.82 mph per 100 rpm

117/59.5 (100 rpm) = 1.96 mph per 100 rpm

That's a perfect example of increased efficency devil

S CP

Bif Inch Ford Lover

Sah-weeet! Somebody is asking the right questions!!!
I will be getting into a long rant when I put out Vol 2 of the Handbook. For now I will try to keep it short.

The mythical, magical "Impeller HP curves" are only useful for one scenario that I can think of: Making an approximate match of motor hp/rpm to an approximate impeller size. Now this IS a useful scenario which is why a lot of people like them.

But the charts are USELESS for comparing one make/model of impeller to another. And they are USELESS for expressing what the pump/impeller's power conversion efficiency is. (Converting shaft HP into hydraulic HP.)

An industrial cake batter mixer can have the exact same absorbed power curve as an "AA" cut impeller, but it won't generate one mouse turd of thrust. The more efficient a pump/impeller system is at converting shaft power to hydraulic power, the more potential it has at creating thrust. The power conversion efficiency of a pump/impeller system is = output (hydraulic) power / input (shaft) power.

Shaft power is a well understood formula that takes rpm and observed torque and converts into units of HP or kW or any other recognized power unit of measure. On a dyno it is easy to measure. In a boat you need to have a "dynamic torque ring" (or similar sensor) installed if you want to measure shaft power into the pump. It is doable but expensive.

Hydraulic power is also a well understood formula that takes flow rate and pressure and converts into units of HP or kW. On a boat, pressure is easy to measure and (accurate) flow rate is really hard. There are several types of flow rate meters/sensors but they all have tradeoffs and most of them can't work well in the environment of a jet boat (and with the 1,000's of gpm we are talking about).

The most practical way of trying to get accurate flow rate data is to use a pitot tube in the flow downstream of the impeller - most likely after the split bowl face. The sensor has to be rigged to read "dynamic pressure". And even then, you still have to make assumptions about what the water density and velocity profile is at the location you are sensing.

But IF you do all of this and talk yourself into believing that you are getting accurate shaft torque and flow rate data, then you can infer what the efficiency of the pump/impeller system is and can compare one make/design of hardware with another. If you had this data, then you could create a VERY useful graph that would look kind of like this:

In my example, Impeller #1 is better because it moves more flow with less input HP. If impeller vendors had these kinds of charts, we jet boaters could make much better decisions. Now to defend the vendors, with the size of customer market we have, they can't really justify the economics of doing these tests.

Sleeper CP said:

The short answer is trialand error. You need clocks at the races or data acq. to have an idea.

Click to expand...

not always trial and error. if you have clocks and data, test results can be -somewhat- predictable. without that info, then you're getting into trial and error. there are many things i've tested where i knew the boat would go faster/quicker, or slower, before i ever tested it - i may not have known exactly how much quicker or slower, but i knew there would be a change. and, just to toss another wrench into it, a known result from a change at one track can be very different at another track that has different characteristics.

Sleeper CP said:

A radar gun or GPS will not answer the question. I have a new AT HH "A" sitting that I'm going to run against my current MPD Legend "B"( 6,200 off the bottle 99.8 mph best and 6,800 109 on the bottle) it will be run as is out of the box to see what it does,it's expected to turn 5,800-5,900 off the bottle, it will then be detailed to turn an expected 6,500-6,600 off the bottle.

I've been told by a few here to expect the HH to ET better but loose a few mph. That is something that is not measurable without clocks. My Radar/Laptop testing system will be able to do it but without it you would need the track.

The impeller charts that have been posted by me and others have worked well for me in the past. They do not work for a MPD detailed impeller. You can use Jack's impeller for this exercise. The impeller charts say that a "B" impeller will absorb 825 hp at 6,800 rpm. The MPD "B" absorbs 825hp at 6,200 which reads like an " A+" on the chart. The fact that the MPD impeller "bites" more does that equate to being more efficient? That's a good question. If I ran an "A+" at 6,200 and the boat ran 99 and the smaller cut MPD "B" turned 6,200 at 99 I'd say the smaller impeller is more efficient.

Click to expand...

true. but one more thing - different brand impellers that are blueprinted by mpd behave differently. for example, years ago when we changed from an mpd blueprinted berk B to an mpd blueprinted legend B, we lost around 200 rpm while going .20+ quicker.

Sleeper CP said:

Other than a Pump dyno (test bed) the only particle way to test is ET and MPH over a set distance and 660' it probably good enough for that.

Sleeper CP

Click to expand...

disagree. 660' is not enough to get a valid comparison.

Widowmaker said:

If you make the nozzle too big will be just as bad as making it too small. You have to have a balanced flow into and out of the pump to be efficient otherwise cavitation is a direct result, and it won't matter how much power you put to the impeller.

Click to expand...

the effect of going large diameter or small diameter is very different. i've tested from 3.23 to 2.90. both will result in slower speed/et, but how that occurs is very different. and i've never cavitated anything due to nozzle diamter changes.

Widowmaker said:

As a side note that is why most of the really fast boats are running data acquisition, we are trying to balance the pressures in the pump to make it the most efficient. The data before and after the impeller is very important and it taken at several points along the way.

Click to expand...

true, but a boat doesn't have to be really fast to benefit from data acquisition. data doesn't make the boat run faster or quicker. but it's an invaluable tool, along with what the boat looked like, what it felt like, and what the timeslip said.

i'm not one of the guys that is trying to run as absolutely fast as the boat can go everytime i go on the water. been there, done that, not what i'm interested in. at any race location, from oregon to arkansas, i have very little time to plant the boat on a number, and then know what changes will make it very slightly quicker or slower. then i can race.
at a recent race, i'm sitting next to a boat in my class, driver leaves and i can hear a problem. after i run, sitting next to the driver, i say "hey, it did this...", and the driver (knowing there's something not right, but not exactly when/where) asks me to explain what i saw to the crewchief, so i do. couple qualifying rounds later, i'm sitting next to it again, and it does something different (still not right). i go tell the crewchief what i saw that time. by the 2nd round of elims (which is a little late), they finally have it responding correctly so they redlight...
while data wouldn't have fixed their problem or pointed directly at the cause, the crewchief would have been able to see exactly what happened when, and the effect, which is invaluable when you've got to thrash on something to get it working right.

info, given your stated hp, your engine is spinning considerably too much rpm for an A impeller. i would have to run my C to get the engine close to that rpm, and it's making quite a bit more than 800 at 6500. why your pump is performing like this is just speculation.
where/when is your next race? will you be going to marble falls?