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990 Posts

Wait for Jon (Sleepercp) to chime in. He'll handle it.

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7,464 Posts

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2,234 Posts

Hull speed is determined by nozzle velocity and area (thrust) with the drag from the hull taken off the top...

Too much math for me...eh

GT hand

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4,549 Posts

Not fast or quick enough!!!!!!!!! you will always look for more.what is the rpm to mph lets say 6000 rpm with an A cut impeller and the same with an B cut and B/C cut

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10,102 Posts

As stated lots of variables. At the same RPM the A will move more water but the B or B/C my well be quicker and the A may out mph them but it might take 1/4 mile to find out. BP298 will have a good idea I'd bet.what is the rpm to mph lets say 6000 rpm with an A cut impeller and the same with an B cut and B/C cut

S CP

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2,225 Posts

Cy

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6,591 Posts

nay nay... if you know what kind of boat it is, how much it weighs, how much hp it's making at what rpm, everything there is to know about the pump (what it is, what's in it, who did it?), a person can make a reasonable guesstimate that will be in the ballpark.BP298 will have a good idea I'd bet.

S CP

no way someone can say x rpm = x mph, solely based on impeller size without some idea of the rest of the package...

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10,102 Posts

Sorry about that; I didn't finish my thought last night, Cold medicine and beer sphssnay nay... if you know what kind of boat it is, how much it weighs, how much hp it's making at what rpm, everything there is to know about the pump (what it is, what's in it, who did it?), a person can make a reasonable guesstimate that will be in the ballpark.

no way someone can say x rpm = x mph, solely based on impeller size without some idea of the rest of the package...

Someone would need a baseline to work from then someone with lots of experience (like you) could make an educated guess. bulb

S CP

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1,417 Posts

Cold medicine and beer sphss

S CP

Right On!!! devil

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7,464 Posts

Chuck Once more all will be dependent on the boat ,the weight of the boat the motor ,where the motor makes power (power band) and what you want from the boat From what you've told me I'm not sure yoour not pretty close to "optimum" right now, good to chat last nite , enjoyed the nostalgia hand Tomok so what is the def. and the performance gains and lose from one impeller to the next an A to B to B/C

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6,591 Posts

ok, here's a very generalized answer.ok so what is the def. and the performance gains and lose from one impeller to the next an A to B to B/C

if you have a pump at standard tolerance, you remove an A impeller, and replace it with another impeller with exactly the same measurements, except the vanes are cut to a B size, you should gain somewhere between 250-300 rpm.

as a very hypothetical example, say, with an A, your engine stops climbing at 5000rpm. but, your "peak" hp is 6000 rpm, and the curve indicates 6000 rpm is 70hp greater than it is at 5000 rpm. if the curve is linear, it "looks" like there is an increase of about 7 hp/100 rpm. so if you change out to a B, same model, make, everything the same except it's a B, you should gain 250-300rpm, which allows the pump to absorb approximately 21 more hp - converted to thrust. slightly greater thrust, slightly greater speed, quicker acceleration, and perhaps, slightly more than a 300rpm gain. the same concept applies to b/c, c, or d... it's all about the hp curve, and how much additional thrust can be developed at a higher rpm.

again, this is a very generalized answer to your question. there are many many curveballs, as in what if you did this, what if you did that, that can alter the standard answer.

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1,354 Posts

bp are you ready 4 the final'sok, here's a very generalized answer.

if you have a pump at standard tolerance, you remove an A impeller, and replace it with another impeller with exactly the same measurements, except the vanes are cut to a B size, you should gain somewhere between 250-300 rpm.BUT, that is totally dependent on your engine's hp curve at the A rpm, and the B rpm... because, it's all about absorbed hp - how much hp is converted to thrust, regardless of impeller size.

as a very hypothetical example, say, with an A, your engine stops climbing at 5000rpm. but, your "peak" hp is 6000 rpm, and the curve indicates 6000 rpm is 70hp greater than it is at 5000 rpm. if the curve is linear, it "looks" like there is an increase of about 7 hp/100 rpm. so if you change out to a B, same model, make, everything the same except it's a B, you should gain 250-300rpm, which allows the pump to absorb approximately 21 more hp - converted to thrust. slightly greater thrust, slightly greater speed, quicker acceleration, and perhaps, slightly more than a 300rpm gain. the same concept applies to b/c, c, or d... it's all about the hp curve, and how much additional thrust can be developed at a higher rpm.

again, this is a very generalized answer to your question. there are many many curveballs, as in what if you did this, what if you did that, that can alter the standard answer.

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6,591 Posts

nah. gotta wash the truck, wash the awning, fill the gas cans...bp are you ready 4 the final's

so much to do, and only 2 weeks to giter done.... don't wanna get in a rush.

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