Discussion in 'Propulsion' started by drortiz1, Sep 20, 2012.

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### SamSamSenior Member

I didn't read too much of this thread. It doesn't matter what it all weighs, 1 RPM a minute should take about 1/3 hp.

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### drortiz1Junior Member

Thank you all for the help!!

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### drortiz1Junior Member

DCockey:
I was using a completely different approach. I was calculating the Force of the water against one paddle using the ∫▒〖(water desity)(cross-sectional area of paddle)(length of paddle)〗, and I use the depth of the pool (lake) as limits of integration. this whole deal came up to be :
∫_1^3▒〖62.4(1-y)11dy=62.4(11y-11/2 y^2 〗)=62.4(11(3)-11/2 (9) )-(11(1)-11/2 (1) )= 1372.8lbs#=times 2 paddle 2750lbs#=times wheel radius=2750*7.5=20625lbs#*ft=5250/5252=3.93HP
my answer is different by a lot am I complicating this more than it has to be ? your calculation was much easier but I have one question is Cd some kind of constant factor?
thanks

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### DCockeySenior Member

Cd is "drag coefficient" and is a standard, non-dimensional coefficient used to characterize the drag of bluff bodies. Cd is defined as:

Cd = Drag / (0.5 * Fluid Density * Velocity^2 * Reference Area)

For "bluff bodies" the projected frontal area is usually used as the reference area.(1) For a bluff body Cd is (almost) independent of velocity as long as the flow is turbulent over most of the body (and not fast enough that compressibility effects are significant).

Cd based on frontal area is slightly less than 1.2 for a square, sharp edged plate, and close to 2 for a very high aspect ratio, sharp edged plate, both normal to the oncoming flow.

Your approach appears to equate the drag force to the weight of a volume of water, and the drag force is independent of speed. The drag force for an object moving through a fluid is usually close to proportional to the speed squared.

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(1) Note that the value of Cd for an object depends on the choice of reference area. Other commonly used choices are the "wetted surface area", the planview area and the immersed volume^2/3. It is important to note the choice of reference area when comparing Cd values for different objects. For example the Cd values given for aircraft are frequently based on planview area which is much greater for an aircraft than frontal area and consequently the numerical value of Cd based on planview area will be much lower than if Cd is based on frontal area for an aircraft.

5. ### FrostyPrevious Member

The basics of this is ridiculous . If this is a visual amuzment then why involve such mathematical formula do do nothing but splash water.

Have a pump running water over the revolving wheel and why does it need to weigh 12000 lbs thats 6 tons --for what.

Who will look and see that the paddles dont touch the water if water is running over the wheel.

If the boat is tied to a dock then massive power will be needed to rotate paddles in the water. If the boat is driven by a submerged propeller then the movement of the boat will turn the wheel for free. infact you could even take power from the wheel.

The basics here need re designing.

6. ### Submarine TomPrevious Member

Drotiz1,

You gotta admit, this does look rather silly from a boaters point of view.

Is this simply a matter of "more money than brains"?

I guess being a casino, anything goes.

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### drortiz1Junior Member

Frosty:
Yes, you have a very valid point. I myself share the same idea it is not very cost productive to build such a mechanisms with no reason other than to tell people "look our paddle wheel turns, and is a real paddle wheel" However, I also believe that is good to learn new things when the opportunity present itself. Who knows maybe in the future I may have to deal with a design of a paddle wheel that will actually do its job other than amuse people, and by then I will have a little more knowledge on how to approach and solve the problem thanks to all the mathematical formulas that I learned today.
Tom:
You are right, this wheel is going to cost close to \$70,000.00 it is ridiculous but it is what the customer wants.

8. ### Submarine TomPrevious Member

LOL, well, it must be nice 'eh!

Have fun.

9. ### FrostyPrevious Member

Only because he doe'snt understand , is he like the Newspaper Editor in Spiderman.

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### PetrosSenior Member

the object is to attract customers, and a fancy and authentic operational paddle wheel helps get people in the door to put their money on the table, than it does it job.

That is the only function of the wheel in this instance. and "authentic" look and feel will cost as much as building the real thing, even more. The crab that tom hanks stabs with a stick in Cast Away cost over one million dollars to make for example, they did not want to kill a real crab! That could have bought a lot of crab!

The owner/architect of the casino asked to build an authentic water wheel, you give him a price, and he says "okay", who are we to argue. Give him what he wants. I have done that several times, way over inflating the price because I knew it was going to be difficult, the client says "okay", and than I regret it later, should have told him I was too busy.

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### keroseneSenior Member

Petros I agree with you in general. But the 1 million dollar crab has to be an urban legend. I am familiar with special FX industry and things are financially very competitive there. Sure it was probably extremely pricey compared to using real one but you don't spend a million on a crab.

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### PetrosSenior Member

maybe it did not cost \$1 million (thought that is the story I heard, and I used to live in southern CA and have been around movie making before, everything they do is very costly), they clearly spent a lot of money making a mechanical crab for that one short take in the movie. I could have made them a spear with a clamp on the end to hold a real crab for about \$50, with no harm coming to the crab. The point being is that they were willing to spend a lot of money to get the look of the "real" thing.

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### hoytedowCarbon Based Life Form

Get 'em drunk enough they won't notice if the wheels fell off.

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### hoytedowCarbon Based Life Form

No tequila though. That causes pregnancy.

15. ### FrostyPrevious Member

Unsuccessfully too I might add, It did not look too convincing on my HD 76 inch LCD 3 D surround sound.

Did you know Tom has nasal hairs?

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