Torque or Horsepower?

[GlastronGuy]

Who said?:
"Cubic inches make torque, and torque is what makes the jetboat run."

[Cas]

got bored scratching yourself I see............

[MudPumper]

Didn't I read that in the new ***boat somewhere???

[GlastronGuy]

Originally posted by Cas
got bored scratching yourself I see............
:)

[LVjetboy]

Somebody who didn't know what they were talking about.
jer

[MudPumper]

Originally posted by LVjetboy
Somebody who didn't know what they were talking about.
jer
I'm not claiming to know shit about it but I think Greg Shoemaker does!!!!!!

[Cas]

actually, Pops1 touched on the reason why Greg and many others are correct in one of his most recent posts in the "Is your bowl hydraulically correct" thread. The real answer is.....both :)
here's what he wrote:
If you are starting to stuff your bowl too early pressure builds, cutting down the output of the impeller. Remember this some very high percentage of your motion comes from frontal pull by the impeller. I have never been able to find the Math Man that can tie this down for me. I think the % is upper 90s- On a prop its cup pitch and size determines the forward motion per rev. less slippage of 10-20%
On a Jet you have no slippage as the water is incapsulated Yet we have volumn, pitch & thrust. I am overplaying the story to get your mind to a thinking point of forward pull vs all pressure thrust. Under this scenario Torque and HP play the strong power to the future of Jets- It just keeps getting better!

[MudPumper]

The whole pull thing has always intrigued me. If you have ever looked at the nozzel on a jet from inside the boat while it is moving with a diverter up you will see that the pump is completely out of the water and shooting the water into the air. So there can be very little thrust. It must all be pull.

[JEThro]

Thrust is important if your getting some "tang". Pull is what you do when your not.

[cruser]

Here we go again. Thrust is the result of accelerating mass in a specific direction. It has nothing to do with the environment around the mass. There does not have to be something to push against. It is all about the "for every action there is an equal and opposite reaction" law. This was described a long time ago and is still true today. If this were not true, rocket ships in space would not accelerate because they have nothing to push against.
As an experiment, go out to your patio or any other hard surface and stand on roller-skates or something else that rolls easily. Using your garden hose with an adjustable nozzle on it, squirt water straight out from your body. If the hose pressure is high enough and you are squirting using the most concentrated stream setting, you will start to move backward. Try squirting the side of the house or any other solid object. You won't accelerate any faster because the water is "pushing" on that surface. If you adjust the nozzle until you have a less concentrated stream, you won't move as fast, if at all. This is because the water is pushing in many different directions at the same time, each direction canceling out the opposites ones resulting in little or no thrust. Also the water is accelerated less when not as tightly concentrated when using the other settings. Essentially the same volume of water is coming out on both settings, pushing against the same air, the only things substantially different is the speed and unified direction the water exits the nozzle, thus producing thrust.
The main reason for moving the pump out of the water is to reduce drag.
cruzer

[HammerDown]

Originally posted by MudPumper
The whole pull thing has always intrigued me. If you have ever looked at the nozzel on a jet from inside the boat while it is moving with a diverter up you will see that the pump is completely out of the water and shooting the water into the air. So there can be very little thrust. It must all be pull.
Hmmm, so then the Jet Engines hanging off a airplanes wing is pulling it through the air and not pushing it...doubtful. A jet pumps thrust doesn't need to be hitting the water to cause thrust or foward movement...however it would have more force from the resistance of the water...but it doesn't need it for foward movent.
Experiment....any garden hose with a trigger handle. Turn the water on at the hose...pull the trigger. The pressure or (thrust) from the water leaving the hose forces your hand in the oposite direction of the water exiting. Try the same experiment with the trigger under water, like in a pool. More force due to the stream of water hitting something.
Another one...take a fire fighter holding a high pressure hose. It wants to force him backward. Now take that same situation and direct it towards a wall. More thrust/force...but (almost) the same effect as if he was shooting it in the air. Less but still enough to cause a Jet Boat to move foward. The stream of water will always be faster leaving the pump then the foward speed of the Boat.
This is what makes them appear to be going soooo slow on the water when viewed from the beach etc.
Hey Jer...jump in any time.:)

[American Turbine Man]

cruser
I thought that when you pulled the trigger on a garden hose the movement was a result of someone at the water plant pulling on the hose. JUST KIDDING
So far your explanation has been the best.

[HammerDown]

Originally posted by American Turbine Man
cruser
I thought that when you pulled the trigger on a garden hose the movement was a result of someone at the water plant pulling on the hose. JUST KIDDING
So far your explanation has been the best.
And mine was dog meat?...Just Kidding...lol

[LVjetboy]

"I'm not claiming to know shit about it but I think Greg Shoemaker does!!!!!!
Keep thinking MudPumper...and question everything you hear or read. Even if it's in Hot Boat Magazine.
I don't mean to be too hard on Greg. He has years of experience to add to our hobby and many satisfied customers. I just miss the former Jet Tech writer. He was more "technically" oriented in my opinion...read some of the old Jet Tech columns to get a perspective.
And just because someone has years experience in the jet boat industry doesn't mean they automatically know everything about physics or why a pump works. Greg knows more about pumps and jet boat setup than me. Does that guarantee he understands more about torque vs power and performance? Or the physics behind how a pump produces thrust? Not necessarily.
Let's look at the limited, and I think somewhat guarded comments he made in the latest Jet Tech column about power vs. torque:
1) "A much wider variety of impeller sizes will enable you to hold the rpm down to the desired peak torque and horsepower range of the engine."
In the context of Cliff's twin turbo 468, GS suggests rpm in the 5200 to 5600 range. Seems reasonable. However, "holding the rpm down to peak torque" means something different to performance than matching the rpm to peak power. Or some vague "horsepower range" whatever that means. To me, the above quote implies matching an impeller to peak torque gives best performance. But without any real explaination or detail in Gregs Jet Tech column, the comment on "horsepower range" dilutes that torque thought and seems to cater to both camps.
2) "Cubic inches make torque, and torque is what makes a jetboat run"
My opinion is maximum power to the impeller means maximum thrust and determines how fast you jet will both accelerate and run. In other words, Power to the Impeller is what makes a Jet Boat run! And when it comes to performance, most jetters think about acceleration and top speed, not gas mileage or engine reliability. So the field's wide open to small cubes and turbos or more power with less weight...depending on impeller cut efficiency of course. Big cubic inches BTW makes both power and torque...can't change one without the other. The bigger the cubes the more power you can deliver to the impeller with a peak at a lower rpm depending on build. But the combination of peak power (and impeller cut efficiency) in the end determines your performance...not peak torque.
Focus on building an engine-impeller combo that delivers maximum power (not torque) to your impeller within a reasonable cut size and rpm (efficiency) and you'll get maximum performance. In fact, if you focus on your engines power curve, and your pumps efficiency curve (based on impeller cut and rpm) you'll know the best performance combo.
3) "When it comes to a small block, it has been my experience that we have to run a smaller impeller to put the motor into a better torque and hp range."
GS hints at impeller matching here, but doesn't seem to take a position on peak torque or power...just another vague reference to a range. Overall, I found his latest Jet Tech comments not all that enlightening.
jer

[sleekcraft76]

hold a fire hose, water does not need to impact an odject to produce thrust.

[Jet Hydro]

Originally posted by sleekcraft76
hold a fire hose, water does not need to impact an odject to produce thrust. Point it at a brick wall @ about 6" to 12"and see if it knocks you on your ass.

[Jetmugg]

This has been explained before, in a massive amount of detail, down to the atom-to-atom interactions at the imeller face.
The plain truth of jet boat propulsion (or fire hose propulsion) is that the exit stream does not have to "hit" anything to provide thrust. Your jet boat will not speed up if you go under a low bridge with your diverter up. A fire fighter is not subjected to any greater force if the stream of water hits a building or flies over a cliff.
Until you accept these fundamental facts, you simply don't understand how any kind of "jet" propulsion works.
Steve.

[Cas]

all this kind of goes back to a question, or was it a statement...can't remember, about how much suction does a pump create?
Does the sucking action of the pump have any effect on top end speed?
How about when hitting the throttle from a dead stop? If you find the nuetral position of the reverse gate and hit the throttle, what does you hull do? If it's like mine, it'll twist a bit and move downward.
In putting the reverse gate down, is the pump still pushing water out or is it now pulling it in? both?
While in the reverse position again, is it TQ that's moving the mass or is it HP? How about if you needed to back up a river?
wow! so many unanswered questions and there's more where those came from

[LVjetboy]

Actually, if I had more experience I wouldn't mind doing the Jet Tech column. I like to write and don't mind answering questions...in great detail :)
But my experience is limited to certain topics. I know very little about different hull mfgs or history. Not much experience with setup issues. Never did the liquid 1/4. A backyard mechanic's knowledge of engine building...etc
Now if I had the experience of someone like Jack or Duane? Plus my background in engineering? I could write a great Jet Tech column.
Like I said, I don't mean to beat up on Greg. GlasstronGuy offered the quote and I just followed up on it.
jer

[Blown 472]

Originally posted by LVjetboy
Actually, if I had more experience I wouldn't mind doing the Jet Tech column. I like to write and don't mind answering questions...in great detail :)
But my experience is limited to certain topics. I know very little about different hull mfgs or history. Not much experience with setup issues. Never did the liquid 1/4. A backyard mechanic's knowledge of engine building...etc
Now if I had the experience of someone like Jack or Duane? Plus my background in engineering? I could write a great Jet Tech column.
Like I said, I don't mean to beat up on Greg. GlasstronGuy offered the quote and I just followed up on it.
jer
Some how I dont think 15 page reply would be in order.:D :D

[MudPumper]

Should have known all those worms were gonna fly out of that can!!!:D

[Bow Tie Omega]

Originally posted by sleekcraft76
hold a fire hose, water does not need to impact an odject to produce thrust.
But you forget, that thing called the hose is what helps make it shoot the way it does. And yes, the water impacts air, just like in a turbine, air impacts air. That is why the higher you get altitude wise, the less thrust you have, that is why a turbine would not work in space

[MudPumper]

Careful Riodog, you might touch a nerve. LMAO.:D

[Duane HTP]

The stream of water may impact a little air, but that's sure as hell NOT what is pushing the boat. It's still Newton's Third Law. Get a Physics book, and study it. Then you'll get the picture.

[565edge]

Duane check your pm's.Thanks.

[Duane HTP]

565 edge check yours. you have the answer.

[GlastronGuy]

Originally posted by Duane HTP
565 edge check yours. you have the answer.
Are you guys passing notes in class, again?
;)

[jweeks123]

Originally posted by LVjetboy
Hp Rules!
jer
but,,,,,but what about all the torque it takes to suck the boat along?
jw

[Cas]

Originally posted by Duane HTP
The stream of water may impact a little air, but that's sure as hell NOT what is pushing the boat. It's still Newton's Third Law. Get a Physics book, and study it. Then you'll get the picture.
Duane,
Isn't there really more going on than just the 3rd Law? Sure, we have 4 types of forces, gravity, applied, friction and air resistance working against the movement of the boat . Doesn't inertia and unbalanced force also come into play? There seems to be a lot going on here.
All of those forces need something to overcome them and that's where the torque comes into play, yes?
I'm sure you can probably tell by the question that I'm a novice at this stuff.

[LVjetboy]

Steve, I think the quote you posted is misleading. That is if someone assumes it's fact. Let's look at it a bit further...
"If you are starting to stuff your bowl too early pressure builds, cutting down the output of the impeller."
I don't think over-pressurizing the intake will "cut down" on impeller output or bowl pressure or nozzle exit velocity...all things meaning thrust. But it could increase intake drag.
"Remember this some very high percentage of your motion comes from frontal pull by the impeller."
Not sure what he meant by frontal pull, but some reading this may assume it means the pump is sucking itself along...which of course is not true.
"On a Jet you have no slippage as the water is incapsulated Yet we have volumn, pitch & thrust. I am overplaying the story to get your mind to a thinking point of forward pull vs all pressure thrust."
This again seems to imply a sucking thrust vs a pressure thrust? I don't mean to misinterpret this sentence, but at best his comment is confusing. As for slippage, I believe we can experience the same or a very similar condition a prop guys see. The fact that our water flows through a pump housing doesn't mean "slippage" is impossible.
jer

[LVjetboy]

Rio, already heard the pay scale...maybe why they can't get good help?
Mud, jet's don't suck themselves across the lake. Unless you're talking to a prop guy? Then it's, "Jets suck period!"
Neither do they push themselves across by shooting the jet at water or air or a bridge or a wall. As cruser and AMT man and Jetmugg and Duane already pointed out. The sucking and shooting at something to move forward is myth. Repeated by those who don't understand how a jet moves or try to apply "common sense" to figure it out. If you want to learn more about this topic, read or listen to those who understand the basic physics...not always as simple as "common sense."
And not always from a source you'd like to consider as "the jet boat expert."
jer

[LVjetboy]

"But you forget, that thing called the hose is what helps make it shoot the way it does. And yes, the water impacts air, just like in a turbine, air impacts air. That is why the higher you get altitude wise, the less thrust you have, that is why a turbine would not work in space"
Actually, a jet aircraft turbine engine would work in space if you fed air to the intake. Why? That's your homework assignment Omega.
jer

[LVjetboy]

So what moves a jet? Jet pump thrust offset by drag. Drag as in water and air. Mostly water drag by way of hull design and setup. Jet pump thrust a by-product of the change in water momentum a pump design can deliver with x amount of power applied to the impeller. As cruser already posted...
"Thrust is the result of accelerating mass in a specific direction. It has nothing to do with the environment around the mass. There does not have to be something to push against. It is all about the "for every action there is an equal and opposite reaction" law. This was described a long time ago and is still true today. If this were not true, rocket ships in space would not accelerate because they have nothing to push against."
So what does that change in water momentum mean? Strangely enough, it can be calculated w/physics...(1)
http://members.cox.net/lvjetboy/BerkTable.jpg
Shown graphically as...
http://members.cox.net/lvjetboy/BerkThrust.jpg
Or compared to measured exit velocity data...
http://members.cox.net/lvjetboy/NozzleExit.jpg
Or if you prefer, a reference from another source (not me)...
"Simply, the Berkeley jet drive in your boat is matched to the engine and will deliver about 1400-1800 pounds of thrust while pumping 3000 to 4000 gallons of water every minute at a pressure of 60 to 180 pounds per square inch (PSI)."
Not a bad estimate.
(1) Thrust calculated with the following equation:
Thrust = p/Gc*A2*(Um2/0.6818)^2*(1-A2/A1*cos(theta))
Guess what? The more thrust the more acceleration and speed. Thrust is a product of power to the impeller modified by impeller efficiency. Speed the end result of thrust counteracted by drag. So when all is considered, your jet boat's performance depends on power to the impeller (thrust), efficiency and drag.
If you don't like physics, or don't understand equations...I'm sorry. Ask questions. Or blow it off as uncool geeky stuff. Your choice.
jer

[LVjetboy]

Ok, let's talk a bit about "common sense" and good ole boy trial and error lake tuning.
Do you think trial and error landed a rover on Mars? How many trial and error's would it take at $300 million a pop? What does common sense mean when it comes to calculating the perfect trajectory, acceleration, fuel, gravitational effects, etc. to hit orbit and decend to the surface of another planet 100 million miles away? Kinda like skeet shooting just lead it and fire away??
You think you could do it with a high school education or even a bachelors in science for that matter? These accomplishments take a detailed knowledge of physics in many fields. Far above any efforts put into our ancient pump designs. I've tried to understand advanced rocket science stuff and couldn't even begin. Way more than any of us can figure with a six pack or vodka and coke. That I can guarantee.
Think about that...
There are engineers and scientists out there that know and comprehend so much more than you or me it would make your head spin. So maybe they don't drive jet boats? Or that NASA doesn't fund our hobby. Does that mean our pumps are optimum? Or that high school "common sense" or trial and erro should rule our pump technology?
Not even.
jer

[LVjetboy]

Oh I'm sorry, my last posts a bit controversial and shark-like. My bad. Oops, and a few charts and graphs not to everyone's liking. How rude of me. :D Let's just all just get along, agree with one another, and show that v-driver love...
jer

[miketsouth]

Originally posted by LVjetboy
So what moves a jet? Jet pump thrust offset by drag. Drag as in water and air. Mostly water drag by way of hull design and setup.
Jer, you present the information in an easy to understand, objective, graphic and concise way.
I think the guys are pulling your leg and nobody actually believes that a jet pump pulls the boat thru the water or that the water has to hit something to produce thrust. They just want to see them wonderfull graphs:D
I know i do. It helps get the big picture.
I dont think you gonna convince anyone about the horsepower thing. Maybe GS used torque (he must have a good understanding of these things) because of the audience targeted.
And it is not just a matter of semantics it is a matter of dogma. Torque seems to be a misguided religion.
On the other hand, i believe the statement quoted above misses one property of the jet drive system as it exists today. Yes, of course, the bricks (you may have left this out on purpose since you felt that even the most basic properties of matter and energy needed amplification)
I look at my boat and how much of it is in the water at 60mph and wonder how just a few feet of it could produce THAT much drag that a 150HP bass boat (that i just walked from the git and couldnt pull me up on a ski) just went by me.
I look at them lice and their HP/weight ratio that cant get by me, and how much drag they got. Couldnt be much.
I look at some of the jets i have seen that get lots of more MPH than me with the same HP because of good intake design and massaging and the math that compares the speed/mass of the water in the intake to the speed/mass of the water in the outlet and know that there are bricks to overcome.
and i have some ideas on how to do it.
i am somewhat dogmatic about jets too. My feeling is that if you are looking for speed out of a jet with the current pumps' inlet design you are playing with your dick. They are great for acceleration from the git and very simple to work on and maintain. They are fun and easy to drive and i like a rooster tail, especially when it refracts the morning or evening sun into a brilliant rainbow. And i am a pussy and it scares me to go real fast.
mikeT

[cruser]

LVJetBoy,
I don't have a degree but I have been polluted by exposure to some college math. Also, of the 1500 people in the corporate group I work in, probably 700 of them are phds so I am used to thinking in a more analytical way. My understanding of this topic is based on experience, observation and common sense(don't assume common sense is all that common).
I like the graphs and equations but, I think a bit more explanation of the terms in the math would help me and maybe a few others. I think that this is a standard equation and that some of the terms are standard values and others come from the graphs you attached but, without a physics backround they are just symbols.
Thrust = p/Gc*A2*(Um2/0.6818)^2*(1-A2/A1*cos(theta))
cruser

[bottom feeder]

Originally posted by LVjetboy
Steve, I think the quote you posted is misleading. That is if someone assumes it's fact. Let's look at it a bit further...
"If you are starting to stuff your bowl too early pressure builds, cutting down the output of the impeller."
I don't think over-pressurizing the intake will "cut down" on impeller output or bowl pressure or nozzle exit velocity...all things meaning thrust. But it could increase intake drag.
"Remember this some very high percentage of your motion comes from frontal pull by the impeller."
Not sure what he meant by frontal pull, but some reading this may assume it means the pump is sucking itself along...which of course is not true.
"On a Jet you have no slippage as the water is incapsulated Yet we have volumn, pitch & thrust. I am overplaying the story to get your mind to a thinking point of forward pull vs all pressure thrust."
This again seems to imply a sucking thrust vs a pressure thrust? I don't mean to misinterpret this sentence, but at best his comment is confusing. As for slippage, I believe we can experience the same or a very similar condition a prop guys see. The fact that our water flows through a pump housing doesn't mean "slippage" is impossible.
jer
Lvjet:
With respect do I answer you!
I look forward to seeing/ hearing your views on things jet boat related. You seem to shine best when you feel challenged as most engineers do. So sharpen your pencil.
"If you are starting to stuff your bowl too early pressure builds, cutting down the output of the impeller."
Well looks like Pops1 was talking about bowl pressure not intake pressure?
I don't think over-pressurizing the intake will "cut down" on impeller output or bowl pressure or nozzle exit velocity...all things meaning thrust. But it could increase intake drag.
Yes sir belive you are right on target with this one. Mostly
The high bowl pressure will not degrade the impeller bowl or nozzle velocity to much degree. The higher intake pressure does increase the density of this water. This may result in more horse power applied to the shaft. As far as the added drag is concerned I do not think it is as much of a consideration from a engineering standpoint as the effect it has on the trust producing capibility of our jet unit. more later.
"Remember this some very high percentage of your motion comes from frontal pull by the impeller."
Not sure what he meant by frontal pull, but some reading this may assume it means the pump is sucking itself along...which of course is not true.
Hit the nail on the head with this one! more later
"On a Jet you have no slippage as the water is incapsulated Yet we have volumn, pitch & thrust. I am overplaying the story to get your mind to a thinking point of forward pull vs all pressure thrust."
This again seems to imply a sucking thrust vs a pressure thrust? I don't mean to misinterpret this sentence, but at best his comment is confusing. As for slippage, I believe we can experience the same or a very similar condition a prop guys see. The fact that our water flows through a pump housing doesn't mean "slippage" is impossible.
Hit that sob agin! more later
Bottom Feeder.

[bottom feeder]

"Remember this some very high percentage of your motion comes from frontal pull by the impeller."
This in no way applies that the pump/boat or you are being pulled! What is being pulled? Water!
What happens when your impeller cavitates? The water in the impeller is pushed out by the back of the spinning blade. Right? There is a low pressure zone in front of the impeller right? This is caused by air in flow right? It is from within the water (low pressure) or getting a gulp of the thin stuff upon your boat trying to go into some low earth orbit. Maby you have overcome the huge gravitatonal forces that induce these horible friction forces that make our jets some much slower than the spinny thing boats.
Ok my "common sense" not a degree tells me that the same hull same weight has the same coeficent of friction.
My "common sense" allso tells me the prop boat has something projecting into the water surface.
My "common sense" will now say this protrusion into the water is going to induce more drag.
Now my "common sense" has failed me how is it the prop boat is faster.
Well now it's getting sticky Maby "off topic"
Back to "common sense" facts. The increase in suction housing pressure will not induce a large degree of drag on the hull. The intake pressure is increased by forward speed, amount of bite (loaders etc) and the impellers ability to flow the water through it! Thats all.
Examples: Hood scoop on a prostocker. Air speed and opening size for the most part. but you say what about all that drag induced by the scoop protuding off the hood by 18 inches? Well the only way to increase drag is to increase frontal area! If the scoop is not taller than the windsheild you have not increased the frontal area or the drag! There is some degee of drag induced with the scoop till air speed rams enough air into it to fill compleatly with the amount air of pressure it was designed for. Then the additonal air passes over the high pressure region and no drag is produced.
Here is another one My 1984 red neck cadilac (pick up for the not so redneck) It has clutch fan why? well at 50 MPH the air being pushed through the rad has more velocity that the fan has at the rpm to go this speed. The suction housing (fan shroud) is overloading my impellers (fan) ability to flow the required air mass at this given velocity.
Back to the topic!
To answer your question with good ol "common sense" the decrease in performance from high bowl pressures are not drag induced. It is from you own principal thrust !! Yes your boat and every one elses is propelled buy THRUST. The loss is in the details! If we have higher intake presure with the same nozzle pressure the diferential between them is lower. This results in lower thrust.
This is what frontal pull is about. Most people who have talked with jet builders have herd of it. It has more to do with making thrust than any area of the jet. Air or water. If you improve the forward pull you improve the ability to load more water. More water loaded into the impeller = more thrust producing capibility. Not allways more thrust, lack of HP to impeller (as some like the horse power figures over torque) will be required to move this added supply of water.
As I said before the bowl and nozzle are veiwed as control devices.
If you run a jet tubine without the Bowl/nozzle guess what. Ka boom. Same with our pumps. Now dont get me wrong. With the wrong bowl and nozzle thrust can and will be greatly decresed. This must be matched to the "frontal pull"
Simplifyed verson for us common folk
Im about as common as they come.:o
Water at intake face of impeller.
Rotating four blade impeller
Blade #1 cuts a thin layer of water and accelerates it to the back.
Blade #2 cuts a thin layer of water and accelerates it to the back.
Blade #3 cuts a thin layer of water and accelerates it to the back.
Blade #4 cuts a thin layer of water and accelerates it to the back.
One revolution and we are cavitating!!
Now with "Frontal Pull"
Water at intake face of impeller.
Rotating four blade impeller
Blade #1 cuts a thin layer of water and accelerates it to the back.
Low pressure on traliing edge pulls water in.
Blade #2 cuts a thin layer of water and accelerates it to the back.
Low pressure on traliing edge pulls water in.
Blade #3 cuts a thin layer of water and accelerates it to the back.
Low pressure on traliing edge pulls water in.
Blade #4 cuts a thin layer of water and accelerates it to the back.
Low pressure on traliing edge pulls water in.
rev #2
Blade #1 cuts a thin layer of water and accelerates it to the back.
Low pressure on traliing edge pulls water in.
Blade #2 cuts a thin layer of water and accelerates it to the back.
Low pressure on traliing edge pulls water in.
Blade #3 cuts a thin layer of water and accelerates it to the back.
Low pressure on traliing edge pulls water in.
Blade #4 cuts a thin layer of water and accelerates it to the back.
Low pressure on traliing edge pulls water in.
Hey maww come quick I thinks its werkn.
No disrespect ment to anyone.
If your going Shark Fishn let me know I gots a 13 foot fishn boat with a low tower for spotten thems suckers. Even gots me a fishn pole with some good strong string.
Keep Up with the posts were only at the front end of this sucker oops JET.
Bottom Feeder
High School flunky
Maby not so?

[HammerDown]

Thrust = p/Gc*A2*(Um2/0.6818)^2*(1-A2/A1*cos(theta))
[/B]
I concur....:rolleyes:

[bottom feeder]

Deleted. Not worth the time it took me to type it. I will not lower myself.
There is a place for design and a place for engineering. The designer simply generates concepts and ideas. Most engineers have the ability to test said designs, and prove or disprove said design. Comparing development of the jet drive to a trip to Mars is reaching a bit. Anyone who would challenge the education of someone they have never had a discusion with has a few problems. No discusion just attacks on my mental capacity.
As always
Much Respect
Bottom Feeder

[Chris J]

Damit:
My fat fingers bounced me around the internet again. Any of you rocket scientist know a short cut to the jet boat forum.... crap now my beer's empty too..:D

[mickeyfinn]

Originally posted by Duane HTP
The stream of water may impact a little air, but that's sure as hell NOT what is pushing the boat. It's still Newton's Third Law. Get a Physics book, and study it. Then you'll get the picture.
Duane is absolutely correct. It is not the water pushing against the air nor is it the water pushing against the water in the lake. The third law explains this pretty easily. What is actually propelling a jet boat is the force of the water LEAVING the pump which is pushing the boat forward. It also takes looking at the unbalanced forces and forces of inertia. A body of mass at rest will stay at rest unless some force moves it. Inertia is simply an objects resistance to change in motion. In the case of a jet boat the lake water is essentially at rest. The pump impeller imparts a force upon the water ejecting it from the nozzle. Every action must have an equal and opposite reaction so therefore as the pump is pushing the water out of the pump the water's resistance to change in motion PUSHES the boat forward. A body at rest or a body in motion will stay that way unless other forces act to change it. In other words if you could flip a switch and eliminate friction once the boat was at speed you could then turn off the engine and maintain that speed forever. Call it bricks if you like but what appears to be keeping a jet from continuing to accelerate has to be also attributed at least in part to the third law. Bowl pressure is basically a measurement of how much the forward motion of the boat is trying to push that water forward. In response to that the water is also trying to push the boat backwards. I don't have a jet but it would seem to me that the most efficient point would be to have a pressure on the suction side of the pump of almost zero. This should reduce some of the drag created by building the bowl pressure. Not sure what the best way to do this without just transferring the losses to another point but I think it is a step in the right direction. Perhaps an variable oriface on the intake could increase performance?

[LVjetboy]

Geez BottomFeeder, your posts longer than mine :)
As for education level and degrees, they mean nothing to a persons worth or mental capacity for that matter. However, to better understand the physics behind how a pump works? Education comes in handy, whether formal or otherwise. And when it comes to designing pumps, engineering is key.
In the aircraft engine industry, engineers both design and supervise testing of new designs. Technicans make the parts and often run tests and collected data. From my experience in that industry, there was no designer who just sat around thinking up new ideas that engineers could test. The designer was the engineer. The part maker and testor was a technican. In fact, to develop a new concept, extensive engineering background and experience was essential. Knowledge of compressible flow, heat transfer, stress mechanics, engine performance all went into a new design...done by engineers.
Comparing Mars to pumps was a stretch, but only in the level of complexity and the brainpower applied to the hardware designs. Mars is still a good example of how engineering and knowledge of physics can do amazing things that pure trial and error would never achieve. And if that same level of engineering and knowledge was applied to our pump designs? We'd be cookin'
In that respect, Mars is a good example of why these things are important...so I went with it.
You had a lot of other thoughts on the forward pull thing I'd like to comment on...but gotta run...more later.
jer

[LVjetboy]

Cruser, here's how I got to that equation...
First draw a control volume around the entire pump to eliminate the need to know internal pressures, flow viscous drag forces, etc. Things hard to know....
http://members.cox.net/lvjetboy/PumpSection.gif
Where only thing crossing boundaries are inflow and outflow, shaft power input and housing bolt forces on the hull.
For fluids entering and exiting the control volume pictured above, Newton’s second law says the rate of change in fluid momentum is equal to the resultant force and takes place in the direction of that force…another way of saying F = ma in a fluid environment. This is what gives us thrust.
Fluid momentum at the intake (1) is the mass flow rate dm/dt times the mean fluid velocity Um1. So the resultant force is:
F = dm/dt(Um2 – Um1)
The mass flow rate is related to flow area and velocity, and conservation of mass says it stays the same between inlet (1) and nozzle exit (2) so,
dm/dt = pA1Um1 = pA2Um2
where p = fluid density, for incompressible water no change.
A1 = intake area
A2 = nozzle area
Substituting resultant force becomes,
F = pA2Um2(Um2 – Um1)
Since intake velocity has both vertical and axial components, the force on our pump control volume has two components. For thrust we look at the axial component…related by an angle let's call it theta, between Um and the axial direction. So thrust, Faxial, becomes:
Faxial = pA2Um2[Um2cos(theta2) – Um1cos(theta1)]
Conservation of mass relates Um1 to Um2 as shown above. So the quantity (A2/A1)Um2 can be substituted for Um1 and Um2 factored out. Also if we assume the exit nozzle angle theta2 is zero, thrust simplifies to,
Faxial = pA2(Um2)**2[1- (A2/A1)cos(theta1)]
When the fudge factor* Gc is cranked in and a unit conversion the equation becomes,
Thrust = p/Gc*A2*(Um2/0.6818)^2*(1-A2/A1*cos(theta))
Where,
Water density: p = 62 lbm/cuft
Nozzle exit area: A2 = 0.058 sqft (3.25 inch nozzle)
Intake area: A1 = 0.240 sqft (measured)
Intake angle: theta1 = 20 deg (wag)
Fudge Factor: Gc = 32.174
Side note: What is Gc? A long long time ago, English units got messed up by a clueless dork, so now we live with that mistake by sticking a Gc units fudge factor into F = ma. Gotta match your units. Also, Um is mean velocity. A pitot in the center of the nozzle may measure a speed somewhat higher than mean velocity.
That's good enough for now, but if anyone has more questions I'd be happy to give more detail.
jer

[miketsouth]

you talkin to me?:D :D

[OkieDave]

I allways think of it as an auger, screwing its way through the water. Maybe thats more the jet ski type pumps. But the pressure inside the bowl is pushing against all sides of the bowl except the opening at the nozzle where the water exits. so the pressure on the back side of the impellor is not balanced because of the escaping water out the nozzle. so it pushes the boat forward. is that right?

[Cas]

Originally posted by LVjetboy
Gotta match your units.
jer
that's exactly what I told my wife........

[bottom feeder]

Lvjetboy!
Thank you the info. I do not mean to insult you or your background. As before I have the utmost respect for you and all others. I just like to mix stuff up sometimes it makes people back up and look at things all over in a new light. This is something I notice you are vary good at. Yor replies are direct and to the point. Agin Thank You.
Bottom Feeder.

[OMEGA_BUBBLE_JET]

I think we can all agree that most jet boats are slower with the diverter all the way up. Now with that said is that because more of the discharge is spraying into the air or because the water is making a sharp upward turn at the discharge increasing drag???
Omega

[rivercrazy]

Your burying the transom and causing additional drag;)

[toad polumsky]

Trim your nozzle all the way up and then look inside the bore where the steering nozzle and the up down nozzle transition. The area that the jet stream has to pass through has been pinched off. I think this also has something to do with speed loss when the diverter is all the way up.

[cruser]

Maybe but I think it is more because you are pushing the Stern down.
Bottom Feeder, very good posts. Did indeed make me think.
cruzer

[Duane HTP]

Jer, Where did you come up with the bowl pressures on your chart? They seem awfully low compared to what I'm used to working with. Wouldn't that throw your final calculations off? Just wondering! or was that just for example purposes?
Yes, Cas, all of those forces are involved, but The third Law is the dominating one involved here by far.

[American Turbine Man]

I agree with Duane. I have conducted dynamic bowl pressure test. My test indicated 175 psi with a 3.125 dia.nozzle discharge and over 200 psi with a 2.625 while spinning a "B" impeller 5300. Its been a long time but, I think my 350 chevy would make 125 psi.
ATM

[Rexone]

If thrust had to "hit" something to work, the thrusters on the space shuttle and satelites would have no effect because of nothing to hit (as in no air). Fact is they do work and is exactly how these vehicles manuever in space. Just another example.

[Chris J]

I think we can all agree that most jet boats are slower with the diverter all the way up
You don't suppose its because you're applying force (thrust) at an angle to motion. If you do any wrenching you'll learn in a hurry the affects of angular force.
If anything I would think pushing against water would create some back pressure. This would reduce nozzle velocity which in turn would actually slow you down. But hell what would I know. I just a technician.

[LVjetboy]

"I think we can all agree that most jet boats are slower with the diverter all the way up. Now with that said is that because more of the discharge is spraying into the air or because the water is making a sharp upward turn at the discharge increasing drag??"
Omega, there's a couple factors. First of all, I believe the biggest hit comes from what ChrisJ just posted...applying force at an angle to your forward motion reduces the axial component. To maximize thrust (not necessarily speed), you want your nozzle pointed level to the lake surface. I can work some numbers to show why I think this is the biggest hit if you like.
Second, the added down force of an "up" nozzle may increase transom drag as rivercrazy and cruser suggest. But some of that can be counteracted by more aerodynamic lift reducing overall hull drag. The combination of those two behaviors and which one dominates depends on hull design. Clearly, if your boat hull gets no aero lift from the up nose rotation, then more down force on the transom a bad thing. And a small nose up change on a tunnel may reduce hull drag more than a small nose up change on a deep v. Overall I don't think this effect as important as the force component Chris mentioned, but it's still there.
Finally, there's the added flow path restriction toad posted. This also reduces thrust although to a lessor extent I believe. Anytime you bend flow there are losses. So the less bending the better.
The combination of these three means extreme up nozzle usually a bad thing for speed. How much "up" is extreme depends and hull design (potential for aero lift), speed (influences aero lift), weight (factors in hull drag) and setup. Every jet will have that optimum up position depending on design. Whether or not your trim control can overshoot that optimum angle is another question...
jer

[LVjetboy]

Duane, bowl pressures (in black) are taken from a static flow test conducted by the American Turbine Pump Company of a factory direct Berkeley pump with an off-the-shelf AA impeller. They were published in HBM's February 1990 issue. Bowl pressure in blue is an extrapolation based on a curve fit of measured datum.
Those pressures may be lower than what you're used to because of a stock Berkeley running in a static pit with lower intake pressure. No ram effect, no flowing, no tight clearances. Other than that, I do not know. Maybe ask AMT man? I can only use what little information is out there.
The bowl pressure was not used in my calculation of thrust only flow rate and nozzle size, so if their pressure gage was inaccurate that would not affect my thrust calculation. Reportably, they used a Haliburton flow meter meeting calibration standards. I based nozzle size on what I believe is a standard Berkeley nozzle.
jer

[Rexone]

Originally posted by LVjetboy
"I think we can all agree that most jet boats are slower with the diverter all the way up. Now with that said is that because more of the discharge is spraying into the air or because the water is making a sharp upward turn at the discharge increasing drag??"
Omega, there's a couple factors. First of all, I believe the biggest hit comes from what ChrisJ just posted...applying force at an angle to your forward motion reduces the axial component. To maximize thrust (not necessarily speed), you want your nozzle pointed level to the lake surface. I can work some numbers to show why I think this is the biggest hit if you like.
Second, the added down force of an "up" nozzle may increase transom drag as rivercrazy and cruser suggest. But some of that can be counteracted by more aerodynamic lift reducing overall hull drag. The combination of those two behaviors and which one dominates depends on hull design. Clearly, if your boat hull gets no aero lift from the up nose rotation, then more down force on the transom a bad thing. And a small nose up change on a tunnel may reduce hull drag more than a small nose up change on a deep v. Overall I don't think this effect as important as the force component Chris mentioned, but it's still there.
jer
I agree with Jer and the others 100% on this. Imagine the space shuttle crusing along in a straight line with no turning thrust or external forces being applied. It keeps going straight, or at least in it's set orbit, unchanging is my point. Now apply a thruster at a 5º angle. What happens? The space shuttle changes path in the opposite direction of the thrust.
Apply this to a boat. Crusing along in a straight line (thrust angle at zero or optimum for boat). Change the thrust angle and you change the direction the boat wants to go (in this case nose up, transom down). Same principle in steering the boat... nozzle changes angle, boat turns (with equal force as the up thrust I might add). Since the boat is glued to the water with gravity unlike the space shuttle it does not take off and fly upward (at least most don't, I don't recommend you try this with blown fuel jet). The thrust angle change has made the forward straight line thrust less effective in driving the boat forward (less speed forward) and driving the transom down has increased drag, which in turn also decreases speed. I doubt you'll find many if any cases where the drag factor of the transom in the water is overcome by increases in aerodynamics of raising the front of the boat. Water is much harder to push forward than air. Plus most boats with the nose excessively high will be less aerodynamic (pushing more air too).
all the above would apply to a boat of average good bottom design that doesn't have a built in hook or some other performance problem inherent to hull design that might actually react favorably to high thrust angle. In other words if you have a real dog to start in terms of hull design problems, you might actually end up with a little faster dog with excessive up thrust. But it's still gonna be a dog compared to a good straight properly designed bottom. That's the only case I can imagine a speed increase or even staying the same with high roost.

[LVjetboy]

American Turbine Man. What is your background? Just curious. Are you related to the company? If so can you explain better the test I'm refering to?
I used a 3.25 nozzle for thrust calculation. A smaller Berkeley nozzle may affect the bowl pressure you measured. From my understanding, a 3.25 nozzle was used for the test data reported in the HBM article? Also there's static vs. dynamic and that influence on bowl pressure. Were both your tests at the same hull speed with the same B impeller "My test indicated 175 psi with a 3.125 nozzle discharge and over 200 psi with a 2.625 while spinning a "B" impeller 5300." If so, what would you estimate the pressure for a 3.25 nozzle?
More importantly, if you're related to the company, are there any plans to do further testing and comparisons? As devoted jet boaters, we have very little information to go on here.
jer

[LVjetboy]

Geez Mike, go back to your happy place. If we keep agreeing...people are gonna talk.
:D
jer

[LVjetboy]

Okiedave,
Unfortunately, our jet boats are the same as a jet ski when it comes to physics.
But a simplistic view of bowl pressure pushing on all sides of the pump except the opening of the nozzle doesn't give the right answer. You also need to consider mass inflow and outflow. So no, the simplistic is wrong. For example, with a bowl pressure of 113 psi and a standard (3.25) nozzle with 8.3 square inches would be 940 lbs of thrust. Far short of the calculated 1960 lbf. And far short of reported thrust...even for a jet ski.
If there was an easy way I'd do it. But a control volume and understanding physics is the only way to estimate thrust. There's the total force and the pressure force when combined gives resultant force or thrust. If you choose your control volume wisely, you can eliminate the forces you don't know. That's why I surrounded the pump with a control volume. The pump housing is at atmospheric pressure. The intake may be more, but that force vertical and doesn't affect axial force or thrust. The nozzle exit area is at atmospheric pressure because water unlike air is incompressible. So the pressure force not a factor with that cv. Only the total force or change in momentum.
jer

[LVjetboy]

BottomFeeder, I wanted to respond to a few of your comments but ran out of time.
You posted, ”My “common sense” tells me the prop boat has something projecting into the water and this protrusion in going to induce more drag. Now my “common sense” has failed me how is it the prop boat is faster.”
While common sense helps, it doesn’t always lead to the right conclusion. Think about swinging a rock in a circle over your head. Since the string is pulling inward on the rock, common sense says there must be a force pulling out on the rock as it goes in a circle. Physics says nope, there is no such force. Common sense leads to the wrong conclusion.
With a prop, like you say, that extra stuff hanging causes drag, common sense. A pump intake has very little if any sticking down so no drag, right? But pump intakes can and do have drag. A drag that increases as intake pressure goes up. For example, the more shoe, the faster your jet slows on throttle lift…intake drag. You may not feel the difference with the throttle in and your top speed may be the same to a point. The lifting effect of an overcharged intake may help reduce hull drag…off-setting the added intake drag…but it’s still there. Even once “filled” the intake still produces drag. The very fact that intake pressure goes up means scooping more water and decelerating that water. The force on the intake caused by converting water velocity to static pressure is a drag force.
A side note: In your pro stock hood scoop example, you mention no change in frontal area so conclude no change in drag. But total drag is a sum of several types: Form, aerodynamic, parasitic etc. A hood scoop has components of each. While the scoop may not increase frontal area or form drag, there is an effect from the scoops parasitic and aerodynamic drag. And once the scoop is “filled” it still produces drag. Air drag is a weaker function of speed than water drag, so at pro stock speeds, adding a hood scoop and the associated drag not significant enough to worry about. But that doesn’t mean it’s not there.
Props have drag too as you mention. The v-drive has a shaft, support and rudder, the i/o a lower unit. Obviously both have props. Each part dragging through the water will have a loss associated with speed, surface area and shape. Is that drag more than intake drag? My guess is yes, but that’s just a guess. And intake drag may be a bit more than common sense dictates. So why are props faster? Assuming same power, hulls, weight and ride set, the speed difference between the prop and the jet in my opinion comes from drive efficiency. Power input does not equal the same power to the water.
Once water enters the pump and travels through the impeller, it’s accelerated through the bowl vanes and out the nozzle. Any interior surface in contact with the moving water has drag losses…to the tune of a cubic function of speed if I remember. The more surface area in contact the more drag. That’s why raising a lower unit can have a dramatic effect on prop boat speed…less surface in contact with water. In the case of the pump, there’s nothing sticking down but all that fast moving water is routed up and through the interior of the pump, with a total surface at least as large as the lower unit. Don’t forget bowl vanes add a lot of surface area in contact with fast moving water. With nozzle exit speeds of 100+ mph (see table above), you can imagine drag losses in the pump can be huge. Even the impeller shroud adds surface area and viscous losses at the wear ring interface, slowing down the impeller…something a prop doesn’t have. These losses mean less shaft power is converted to thrust…a pump less efficient than the prop.
There are of course other differences. Like the need to keep the intake loaded limiting your jets ability to “air out” like a prop can. But I’m guessing for a set-back pump, that’s less a factor. And even at speeds well below “air out” speeds, I think a prop’s more efficient than a jet…other things equal.
jer

[Duane HTP]

applying force at an angle to your forward motion reduces the axial component. To maximize thrust (not necessarily speed), you want your nozzle pointed level to the lake surface.
Second, the added down force of an "up" nozzle may increase transom drag as rivercrazy and cruser suggest.
Jer, don't mean to steal your interesting thread, but do you realized you just did an advertisement for our Snoot and explained why they work?

[Ken F]

[QUOTE]Originally posted by LVjetboy
While common sense helps, it doesn?t always lead to the right conclusion. Think about swinging a rock in a circle over your head. Since the string is pulling inward on the rock, common sense says there must be a force pulling out on the rock as it goes in a circle. Physics says nope, there is no such force. Common sense leads to the wrong conclusion.
Jer,
In your above quote, what happened to centrifigual force? Why does that not apply in your example? is that not what keeps the string taught?
Ken F

[Duane HTP]

Ken, I believe it is centerfugal force that keeps the string tight. The rock is not trying to pull out, it is trying to keep going straight. The string is trying to make it turn in a circular motion. Some one correct me if I'm wrong.

[OMEGA_BUBBLE_JET]

Originally posted by Duane HTP
Jer, don't mean to steal your interesting thread, but do you realized you just did an advertisement for out Snoot and explained why they work?
:D :D :D :D maybe you guys in Kansas know what you're doing after all;)
Omega

[LVjetboy]

Duane...yes on the snoot.
Ken, there's no such thing as centrifugal force...only centripetal force. Are you sure you want me to get into that?
:D
jer

[Ken F]

Jer, yep I would very much like you to get into that. You've got me really curious now! Not to hijack the thread, possibly a brief explination?
Nevermind.....found it in one of the wifes physics books. DAMNIT. I learned something today!
Ken

[Bense468]

This has been a great thread.

[UBFJ #454]

"centrifugal force. The component of apparent force on a body in nonlinear motion, as observed from that body, that is directed away from the center of curvature or axis of rotation."
"centripetal" ..... "Directed or moving toward a center or axis."
Both ... P. 119, The American Heritage DICTIONARY Of The English Language, June, 1978.
No Such Thing As "Centrifugal Force" ???

[LVjetboy]

"The component of apparent force..."
Don't believe everything your read. Even if you read it on the net, or if it's published in a dictionary. Think about it...
In what reference frame are Newton's Laws applicable? You know, the ol' F=ma? Or an objects stays the same until an external force applied? Remember, a change in velocity...ie acceleration in Newton's Law, (a)...not always a change in magnitude, also can be a change in velocity direction with the same magnitude.
Here's an interesting quote...
"This is sometimes summarized by saying that under Newton, F = ma, but under Aristotle F = mv, where v is the velocity. Thus, according to Aristotle there is only a velocity if there is a force, but according to Newton an object with a certain velocity maintains that velocity unless a force acts on it to cause an acceleration (that is, a change in the velocity). As we have noted earlier in conjunction with the discussion of Galileo, Aristotle's view seems to be more in accord with "COMMON SENSE", but that is because of a failure to appreciate the role played by frictional forces. Once account is taken of all forces acting in a given situation it is the dynamics of Galileo and Newton, not of Aristotle, that are found to be in accord with the observations."
Although Newton, Aristotle and Galileo (all great minds) proposed theories in their spare time between episodes of "Who Wants to be a Millionare," which pro was right? Are we as a culture not thinking as deeply these days? Wait...that's a bit off topic.
But who's theories got that rover on Mars?
It's all a matter of physics...
Physics is the truth about what is happening. Not my opinion or a jet boat pro's opinion. I can be wrong, they can be wrong. Common sense can fail, but the truth's based on physics by definition. Not by common sense explaination. Whether it be a rover on Mars or our jets across the lake. Whether it be a pro or racer explaining or just another jetter.
The truth is out there. Embrace it. Learn all you can. Push the limits.
jer

[American Turbine Man]

OK, it’s my time on the soap box.
Stern drive boats are faster than jet boats all things being equal. Stern drives have a tremendous leverage on the hull to reduce wetted surface. At top speed stern drives are more efficient than jets. At cruise speed jets can be more efficient than stern drives. Let me explain.
In 1991 American Turbine entered into a project with Four Winns Boat company. Four Winns sent us an 18 ft Horizon 180 stern drive with a 302 Ford. We removed the drive and installed our American Turbine jet, so the only variable was the propulsion system. The results were the stern drive was 3-4 mph faster, the jet a little quicker, but the most amazing thing was the stern drive used 20% more fuel at 30 mph. It was so amazing that Four Winns sent down two of their engineers to test the boat, confirming our data.
Keep in mind they could have propped-up the stern drive and gotten better fuel economy at cruise, but acceleration and ski towing would have suffered greatly.
So I am saying, when you say props are more efficient you must specify the conditions.
My 20ft welded aluminum boat with our SD312 and 350 Chevy uses 7.2 gph at 30 mph, that computes to 4.2 mpg. Read some of the stern drive boat test look at the fuel consumption at 30 mph. My boat accelerates 0-30mph less than 7 seconds. Its top speed is 47.5 mph at 3900 rpm’s pushing about 18 square feet of windshield. Boat weight is 3875 lbs with two aboard. It will run in 9 inches of water so, bring on your stern drives I get to choose the course.
”My “common sense” tells me the prop boat has something projecting into the water and this protrusion in going to induce more drag.
Response
If you are talking about stern drives yes, you do have the drag of the lower unit. But the wetted surface of the jet hull has much more drag. A comparison of a tournament ski boat to a jet boat might be closer. Those tournament boats are real fuel hogs.
Air entrapment boat with jets run closer to stern drives because of natural lift. In this example the jet has extra drag due to the fact that the jet intake must be submerged.
Duane, bowl pressures (in black) are taken from a static flow test conducted by the American Turbine Pump Company of a factory direct Berkeley pump with an off-the-shelf AA impeller. They were published in HBM's February 1990 issue. Bowl pressure in blue is an extrapolation based on a curve fit of measured datum.
Those pressures may be lower than what you're used to because of a stock Berkeley running in a static pit with lower intake pressure. No ram effect, no flowing, no tight clearances. Other than that, I do not know. Maybe ask AMT man? I can only use what little information is out there.
The bowl pressure was not used in my calculation of thrust only flow rate and nozzle size, so if their pressure gage was inaccurate that would not affect my thrust calculation. Reportably, they used a Haliburton flow meter meeting calibration standards. I based nozzle size on what I believe is a standard Berkeley nozzle.
Response
jer
Jer, I think I have those test I will look. You are right those were static test and ATP test equipment is very accurate. They test at 1750 rpm and extrapolate to higher RPM,s. The pressure readings posted earlier were actual boat test under operating conditions. I probably have those test also. By the way the Berkeley nozzle diameter is 3.25” and the Dominator is 3.187”. American Turbine can be 3.00-3.312”dia. by way of inserts.
More importantly, if you're related to the company, are there any plans to do further testing and comparisons? As devoted jet boaters, we have very little information to go on here.
Response
At American Turbine we are always testing, but we are concerned with more than
just speed. We have some young hot rod guys coming up, I guarantee they will develop some “speed parts”.
For example, with a bowl pressure of 113 psi and a standard (3.25) nozzle with 8.3 square inches would be 940 lbs of thrust. Far short of the calculated 1960 lbf. And far short of reported thrust...even for a jet ski.
Response
When we do thrust test we tie the boat to the dock and pull against a dynometer. A 350 and SD309 will pull about 1100 lbs our SD312 will pull 1375lbs.
I not even getting in on “the string thing”.
I am done for a while.
ATM

[Ken F]

Originally posted by BEAR_454PE
"centrifugal force. The component of apparent force on a body in nonlinear motion, as observed from that body, that is directed away from the center of curvature or axis of rotation."
"centripetal" ..... "Directed or moving toward a center or axis."
Both ... P. 119, The American Heritage DICTIONARY Of The English Language, June, 1978.
No Such Thing As "Centrifugal Force" ???
Bear, those were my thoughts exactly.
However, after reading the wifes Physics book, the string is the centripetal force, or the force keeping the rock going in a circle, rather than going straight. (pulling it toward the center of the circle) In other words, if you let go of the string, or it broke, the rock would to straight all of a sudden.
Think of a hot-wheels car going through the "loop". the speed of the car keeps it planted to the track. If there is enough speed, it will continue up the loop, upside down across the top of the loop, then down the other side. The car is wanting to go straight, but the track makes it go in a loop.
In this example, the track is the Centripital force I believe, though applied to the opposite side from the rock example.
another example is the ride at the amusement park.....the spinning cage where the floor drops out. The cage that you are stuck against is the centripital force keeping you going in a circle. I had always thought it was centrifigual force too!!!
I'd really like to hear someone expound on this a bit further. It's really interesting to me. Makes you think about things a lot deeper than I ever had before!
Ken F

[pops1]

Originally posted by American Turbine Man
OK, it’s my time on the soap box.
I not even getting in on “the string thing”.
I am done for a while.
ATM Ron GOOD POINTS AND WELCOME.

[pops1]

Originally posted by LVjetboy
Duane, bowl pressures (in black) are taken from a static flow test conducted by the American Turbine Pump Company of a factory direct Berkeley pump with an off-the-shelf AA impeller. They were published in HBM's February 1990 issue. Bowl pressure in blue is an extrapolation based on a curve fit of measured datum.
Those pressures may be lower than what you're used to because of a stock Berkeley running in a static pit with lower intake pressure. No ram effect, no flowing, no tight clearances. Other than that, I do not know. Maybe ask AMT man? I can only use what little information is out there.
The bowl pressure was not used in my calculation of thrust only flow rate and nozzle size, so if their pressure gage was inaccurate that would not affect my thrust calculation. Reportably, they used a Haliburton flow meter meeting calibration standards. I based nozzle size on what I believe is a standard Berkeley nozzle.
jer Bowl Design plays far more role here then given credit. pressure is the product of thrust & volumn. Design sets the intent in the bowl. We have a much stronger wrap in our fire bowls than we do in our current design levels of jet pumps. Back when Berkeley was developing its pump another team from auroria pump was playing with pump and bowl designs. There bowl was made from a series of tubes in a wrapped turbine fashion. The bowl discharged 2- 2 1/2'above the water.
Both teams would sometimes run into each other at the stadium on test days. Auroria pump made a suction that was so low to the water it dragged the bowl. Ross Wilder and others I know ran this suction and did well with it. The intent was to reduce the height of water lift to the Impeller.
Back to the Bowl thing -each bowl has its own pressure curve by design and total flow volumn. What we have never understood is why would you discharge at the end of the bowl, a high degree of angle to the transistion of the nozzle housing. most all of the older bowls crash water into the side walls of the housing before being re-directed to the flow line. Our thought Under this same straight water plan is to follow it up with a straightner in our longer droop.
To you h20 newton guy's! what size micron is water!
The same pull test was done by the same people of 4 winn's
on our JR drive a 7" impeller drive. Test was sanctioned by Gibb's Motor's for there test unit on the its new car. That pump pulled 985 pounds static pull. It even outpulled a Axial Flow Hamilton pump mounted into a second unit with a little larger motor. Since that time we have designed and produced a second larger flowing Bowl for our Jr Drive. We hope to one day get that combo tested.
Is Pull! the same as Thrust!. Hmmmmm

[bottom feeder]

Many thanks to all.
So how many people thought about the drag induced by the water flowing through the pump, compared to the lower unit on the other design? Thats why It was posted, The replies were right on. The answers are thare, If you ask the questions. Much thanks AT man, LVjetboy, Pops, And all others. Man you all got more than a one liner from REXONE. Nice job!
Bottom Feeder

[LVjetboy]

ATM, thanks for posting. Your low speed efficiency results are interesting...not totally surprising. I've seen other cruise speed comparisons between jet and prop. But I usually think in terms of full throttle and top speed where the internal water drag losses of a pump are huge. If you find any other info on pump tests I'd love to know more. Why don't we have pump efficiency or performance curves based on impeller cut and rpm? Isn't that a standard in the pump industry?
Also, when you do a static dock thrust test and measure 1100 lbf, do you think that thrust varies from static to top speed in a jet boat? If so by how much? My guess is a little, but not by much. Also, what was the power output of that 350 used for testing?
Pops, I have a straightener or flow divider in my Berk droop. Been thinking about removing it now that I have more flow. Do you think that's a good idea? This's one of those questions a CFD program may answer. Fairly steady boundary conditions and fixed or non-rotating geometry. Not related to hull design or anything other than total thrust. Or I could just hog it out and hope for the best? Trial and error. But pump and droop design engineers should know this. Will cutting the drag of a divider more than offset a flow straighteners benefit in turbulence reduction? If so, at what flow rate?
"The same pull test was done by the same people of 4 winn's our JR drive a 7" impeller drive. Test was sanctioned by Gibb's Motor's for there test unit on the its new car. That pump pulled 985 pounds static pull. Is Pull! the same as Thrust!. Hmmmmm"
For a static pull, I'd say pull is equal to thrust. So the JR drive pump pulled 985 lbf. What power (not torque) was applied the that pump? Our pump mfg's rarely quote thrust. But jet ski mfgs? Check it out...
2003 Kawasaki Ultra 150
http://members.cox.net/lvjetboy/JetSki.jpg
HORSEPOWER: 145hp @ 7000rpm
THRUST: 904 lbs
DRY WEIGHT 613 lbs
They seem a bit more in tune with the numbers.
So let's say your typical jet boat BB has 300+ hp at the lake, double the hp and more than triple the weight of a jet ski. Do you think a 320 hp BB thrust could be 1800 lbs? Well, let's see...double 145 hp, you get 290 hp and double 904 you get 1808 lbs. Not scientific but I'm thinking a typical jet boat with a mild BB can put out 1800 lbs of thrust. ATM's post was 1100 to 1375 lbs with a small block 350 of unknown power.
jer

[Old Guy]

Just a brief thought regarding common sense. The finest engineering education in the world is not worth much without the "common sense" to know which laws apply to the situation at hand.
"In the land of the blind, the one eyed man is king"

[LVjetboy]

No doubt Old Guy. And guess what? There may be engineers with both understanding of physics and common sense. How can this be??
jer

[American Turbine Man]

Also, when you do a static dock thrust test and measure 1100 lbf, do you think that thrust varies from static to top speed in a jet boat? If so by how much? My guess is a little, but not by much. Also, what was the power output of that 350 used for testing?
Response
I am sure the thrust increases if the boat is under way. I have thought about dragging a sea anchor to test the results but it would be difficult to duplicate conditions from test to test.
I have a straightener or flow divider in my Berk droop. Been thinking about removing it now that I have more flow.
Response
Taking out the vane will cause a swirl in the water flow when you let off the throttle, it transmits a jerk to the steering wheel. If you look at the bowl end of a droop snoot with the nozzle installed you see how much nozzle is blocked off. American Turbine and Dominator snoots have a vertical vane.
But jet ski mfgs? Check it out...
2003 Kawasaki Ultra 150
HORSEPOWER: 145hp @ 7000rpm
THRUST: 904 lbs
DRY WEIGHT 613 lbs
They seem a bit more in tune with the numbers.
Response
PWC use axia flow jets they produce more thrust for the horse power but at a lower velocity
So let's say your typical jet boat BB has 300+ hp at the lake, double the hp and more than triple the weight of a jet ski. Do you think a 320 hp BB thrust could be 1800 lbs? Well, let's see...double 145 hp, you get 290 hp and double 904 you get 1808 lbs. Not scientific but I'm thinking a typical jet boat with a mild BB can put out 1800 lbs of thrust. ATM's post was 1100 to 1375 lbs with a small block 350 of unknown power.
Response
My 350 is advertised at 307hp, probably making an actual 250hp.
The thrust is not linear with horse power so, doubling the power will not double the thrust. We have tested our SD312 with a 502 EFI (415) hp will pull about 1500 lbs.

[Cs19]

Thanks ATman. Thats some good info there.
That kawasaki PWC above actually does use a mixed flow pump, its one of the few PWCs that has that style pump.I used to own that same PWC and it was fast for a jet ski.