Paddle wheel help

Discussion in 'Boat Design' started by G4s1198, Dec 6, 2021.

  1. fredrosse
    Joined: Jan 2005
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    fredrosse USACE Steam

    A few suggestions:
    12 floats is OK, and I would use a slightly smaller wheel diameter, such that the inside diameter of the floats are not submerged. 12 floats you currently have is OK
    Your engine gearing is too slow, design for about 70-75 RPM of your wheel, based on about 44 inches outside diameter. If your boat weight is less than one ton (2240 lbs), then you can get about 5 knots with plenty of power to spare using your IC engine. Floats should be cupped for ideal drag through the water (this is desired), and typical lunch trays, cut in half, are close to ideal here. I have found typical centrifugal clutches slip and overheat when using a typical HF IC engine, and a belt clutch with an Idler engagement is recommended here, Plenty of snow blowers use this setup, go to Home Depot and have a look.

    During the era of USA sidewheelers (1840 - 1920), virtually all of them used a single cylinder steam engine, and the engines had to be stopped and started with the engine NOT at top dead center and NOT at bottom dead center. Virtually all of them had both wheels on a single shaft, perhaps one in a thousand used independently driven paddle wheels. Yes, with independent wheel control you could turn on a dime, but they just were not built that way. As to disc wheels with the floats mounted between, I guess that would work OK, but again, they were just not built that way, so during the nearly 100 years of evolution for the sidewheel propulsion, disc type wheels evidently provided no significant advantage.

    The Margaret S uses 14 floats, 8 inches deep x 12 inches wide on a 44 inch outside diameter wheel, 28 inch inside diameter.
    For better propulsion efficiency, the floats should have a somewhat cupped shape, to increase their "Coefficient of drag" when forcing through the water. I used 12 x 16 fiberglass lunch trays, cut in half to make 8 x 12 floats, with the un-cupped edge at the outer radius. With this configuration, at about 70 RPM and 2 horsepower will get about 5 knots. This is pushing the real limit of "Hull Speed" for a displacement boat, and increasing beyond this limit is not practical.

    The paddle box covers are needed or you will be soaked real good, the first time I ran the Margaret S with none, I had about 500 pounds of water thrown into the boat while traveling about 100 yards.
     
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  2. Andrew Kirk
    Joined: Jul 2021
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    Location: Chorley UK

    Andrew Kirk Pedal boater.

    This would be heavy, I'm sure, but looks as if it would work well....
     
  3. G4s1198
    Joined: Feb 2020
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    G4s1198 Junior Member

    Good insights fredrosse! Question though, I always heard that the larger the paddlewheel the more efficient, what would be the benefit of a smaller diameter wheel? Faster rotation? I did end up swapping out the centrifugal clutch with a torque converter which seems to work much better.
     
  4. BlueBell
    Joined: May 2017
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    BlueBell . . . . .

    Less weight and windage.
    Lower cost and, perhaps, less work.
     
  5. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Baloney.
    Find a picture of the Mississippi river paddlewheel boats.
    Those wheels are 1 1/2 stories high. And 4 times as wide.

    If you want to go slow these are fine.
    If you want to go faster then follow proved examples.

    IMHO.

    Fredrosse, floats should be cupped which way?
    What drag are you trying to reduce?
    When the float is in the water don't you want the max force produced?
    Which drag are you talking about?
     
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  6. rangebowdrie
    Joined: Nov 2009
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    rangebowdrie Senior Member

    Larger diameter is always more efficient, as it has more arc-travel thru the water.
    The floats spend more time providing thrust, rather than forcing the water down or lifting it up.
     
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  7. DogCavalry
    Joined: Sep 2019
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    As BB says. Minor advantages, not worth the loss of efficiency.
     
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  8. fredrosse
    Joined: Jan 2005
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    Location: Philadelphia PA

    fredrosse USACE Steam

    "floats should be cupped which way?"
    ANS: As the float passes into the water, the cupped shape increases drag, and the wheel propulsion is more efficient with increased drag.


    What drag are you trying to reduce?
    ANS: Not trying to reduce drag, higher drag coefficient is desired. More drag = More Force = Pushes Boat forward.

    When the float is in the water don't you want the max force produced?
    ANS: Yes want maximum force on float, with minimum slip. This is accomplished with high drag coefficient.

    Which drag are you talking about?
    ANS: As the float travels in the water it is traveling rearward faster than the boat hull is moving forward. Thus there is relative velocity of float moving through the water, forcing the water rearward, with resulting force on float in the forward direction.

    The attached picture shows the lunch tray orientation, cupped trays have higher drag coefficient = more thrust
    This picture shows wheel with only 7 floats, later doubled up on these (14 floats on each wheel) for better propulsion.
     

    Attached Files:

  9. G4s1198
    Joined: Feb 2020
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    G4s1198 Junior Member

    So the consensus is smaller diameter wheel and give up the efficiency of a larger wheel for speed?
     
  10. G4s1198
    Joined: Feb 2020
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    G4s1198 Junior Member

    Also I’m trying to wrap my head around this idea: so does more drag which equals more thrust equal more speed? Or does the wheel have to rotate faster to gain more speed? Thanks again for all your answers I’m learning a lot
     
  11. Will Gilmore
    Joined: Aug 2017
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    Will Gilmore Senior Member

    Military Alligator prototype.jpg LVT1.jpg

    The cupped blades on the track made for more focused power to drive the LVT-1 and the Alligator faster than a flat blade.

    -Will
     
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  12. DogCavalry
    Joined: Sep 2019
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    No. You won't get speed with a small high speed wheel, unless you have power to spare. Extravagant amounts of extra power. If you want you to go as fast as possible with little power, bigger wheels.
     
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  13. upchurchmr
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    upchurchmr Senior Member

    +1 for DogCalvary's answer.
     
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  14. fredrosse
    Joined: Jan 2005
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    Location: Philadelphia PA

    fredrosse USACE Steam

    "You won't get speed with a small high speed wheel, unless you have power to spare. Extravagant amounts of extra power."

    This is true, however the hull we are discussing will be limited by displacement speeds, about 5 knots, and that will require only about 2 horsepower to reach hull speed. From that perspective, the 6 horsepower HF IC engine does have "Extravagant amounts of extra power".

    "If you want you to go as fast as possible with little power, bigger wheels."

    This is also true, as bigger wheels will enter and leave the water more closely approximating the horizontal motion, which is the more ideal vector for propulsion. However big diameter wheels lead to more windage problems, larger paddle boxes, and significantly more wheel/paddlebox construction difficulty. Based on these considerations, IMHO the boat being discussed here should settle on wheels with about 44 inch outside diameter, maybe a little less. In boats everything involves compromises, and settling on the "best" compromise(s) is always up for discussion.
     

  15. fredrosse
    Joined: Jan 2005
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    Location: Philadelphia PA

    fredrosse USACE Steam

    "Also I’m trying to wrap my head around this idea: so does more drag which equals more thrust equal more speed? Or does the wheel have to rotate faster to gain more speed?"

    Perhaps a way to get a perspective on this is to look at rowing a typical "rowboat", or even a canoe. The single human powered paddle, or twin oars function very similar to the sidewheeler we are discussing here.

    Imagine a paddle shaped like a baseball bat, low drag, and not a very efficient way to paddle a canoe. So when the paddle is pulled through the water, you want the paddle to have more drag, hence the shapes typical to paddles and oars we typically see, much more drag than a baseball bat, simply because of its shape. To pull the properly shaped paddle through the water takes far more force from the person rowing, and that added force is directly transferred into pushing the boat ahead. So, with more drag you get more force and thus more speed.

    And yes, to go faster you need to paddle faster. So the answer is yes, to go faster you need to maximize the drag of the paddle(s), as well as move the paddle(s) faster. Remember the drag force is inexorably tied to the relative speed of the paddle pushing through the still water. To generate force on the paddle, the paddle needs a relative velocity through the still water. (This is what is called "slip" for typical boat propellers, and a propeller will not generate any propulsive force unless there is slip). As the boat speed increases, the relative speed of the paddle(s) with respect to the still water will decrease, unless the paddle speed relative to the boat hull is increased.
     
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