Flowrider Design

Discussion in 'Boat Design' started by HowToLou, Sep 1, 2015.

  1. HowToLou
    Joined: Sep 2015
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    Location: Indianapolis

    HowToLou New Member

    I will apologize, up front. I know a flowrider is not a boat, but I need help moving lots of water, fast, and this forum seems like it has the brains for that.

    I want to build a flowrider, surfing machine, like those on the largest cruise ships. The factory flowriders have a 140HP electric pump that moves 30,000 gallons per pminute and generates a 3 inch thick by 10 foot wide sheet of water, moving up a hill at 25 to 35mph. The rider stands on flowboard, and rides much like a wake skate, but with no rope.

    I can build the large reservior that will be the water recycling tank, and the sloped riding surface, but I need help designing the water pumping system. I would like to keep the pumping system under $1,000.

    I thought of using a Waverunner engine and pump, but at that HP, the cost would be too high.

    This is where I don't know what I am doing:

    I want to make my wave 15 ft wide, so I was thinking I could power it with a 200-300 HP car engine. Big pumps cost a LOT of money, because they are not very common. I was thinking I could maybe drive a 12 inch boat prop to force water into a 13 inch pipe. From there, I would have to build a manifold system to split this flow into 60 two-inch pipes that would feed the flow jets that make the sheet wave.

    Am I even close to a reasonable design? What prop size and pitch would I connect to a car engine? How inefficient will my cheap pop and tube pump be? Any other ideas, suggestions?

    Thanks,
    Lou
     
  2. fredrosse
    Joined: Jan 2005
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    Location: Philadelphia PA

    fredrosse USACE Steam

    Flowrider

    There are a few inconsistencies in your post:

    "The factory flowriders have a 140HP electric pump that moves 30,000 gallons per pminute (GPM) and generates a 3 inch thick by 10 foot wide sheet of water, moving up a hill at 25 to 35mph."

    Actually, pumping that quantity of water at your stated conditions would take well over 200 horsepower at 25MPH, and over 450 horsepower at 35MPH.

    You need to get some more accurate information if you want to copy the design, and just make it 150% of the size you describe. Also note that copying someones design may infringe on their rights, which may result in legal complications.

    As far as using a boat propeller for the pumping element, this is a relatively low head pumping condition, (30 to 40 feet of head) and a boat propeller could function well.

    "I was thinking I could maybe drive a 12 inch boat prop to force water into a 13 inch pipe."

    That is possible, but at 45,000 GPM you would need a 24 to 30 inch pipe manifold to keep parasitic losses reasonable, and better to have a larger propeller, probably 18 to 22 inch diameter. Of course, horsepower required would be proportionally greater.
     
  3. HowToLou
    Joined: Sep 2015
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    Location: Indianapolis

    HowToLou New Member

    More questions

    Great! I was hoping I would find someone here that knew a lot about props and pumping. Thank you for your reply.

    OK, I only know for sure that the motor is 140 hp and the sheet is 10 feet wide. It "feels" like it is 3 inches thick, but maybe it's only 1 inch. I'll see if I can measure the jets, the next time I am there.

    I don't know where to begin, mathematically. How do you get from water volume and velocity to HP?

    How do you come up with 30-40 foot of head. Is that the total vertical distance the water has to travel? I will pumping water up maybe one foot or so, and then spraying it about another 4ft up the hill. It has to be strong and fast, to keep me suspended on my flowboard.

    I did not state the flow rate correctly. Its 30,000 gallons per minute for a 20ft wide wave. Mine will be 15ft wide, so more like 23,500 gallons per minute.

    Is parasitic loss cavitation, or something else? Are you saying it is better to have a slower turning large prop than a faster turning small one?

    Here is my attempt at some calculations. Am I even close? Say I have an 15 inch diameter prop with an 11 pitch. I am a total newbie, but I think this means it moves 11 inches of water per revolution. , So a 15 inch diameter by 11 inch long cylinder of water is about 8.4 gallons. If the engine is running at say 3000 RPMs, it would be pushing 25,000 gallons per minute. Also, at 11 inches per rev, the water would be moving at 30mph.
    Is that right? What am I missing? I am sure I am not thinking of something.

    Thanks, Lou
     
  4. HowToLou
    Joined: Sep 2015
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    Location: Indianapolis

    HowToLou New Member

    Ok, I just found the formula for HP. In my example above, I would need 235 HP.

    Oh, and I never did respond to your question of legality. I am building this for my own private use only.

    Thanks,
    Lou
     
  5. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    Hi Lou,

    converted in metric units and rounded:
    30,000 gal/min = 114,000 dm³/min = 1.9 m³/s
    35 mph = 56.3 km/h = 16 m/s
    20' = 6.1 m

    The thickness of the flowing "water sheet" is (1.9 m³/s) / (15.6 m/s) / (6.1 m) = 0.02 m (about 3/4').

    The pump has to accelerate the water stream to a velocity of 16 m/s and to lift (1st step) it 0,3 m.

    The minimum power (without any losses) = (1,900 kg/s) / 2 * (16 m/s)² + (1,900 kg/s) * 9,81 m/s² * 0,3 m = 240,000 Watt (= 320 HP)

    Reduced to the planned 15' it is 240 HP, which meets the power you stated above.

    But: this minimum power is not the real amount of power you will need, because the calculation includes no losses due to friction, drag, energy conversion and so on.

    The power of a motor is normally given by its energy consumption, the power transmitted to the driven shaft is much less. In addition the propeller will not transmit the shaft power to the water without significant loss.
     

  6. HowToLou
    Joined: Sep 2015
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    Location: Indianapolis

    HowToLou New Member

    Thanks for the calculations. It sounds like I'm in the right ballpark. A factory flow rider produces a 10 foot wide wave with a 140 hp electric motor. A 300 horsepower gasoline engine should be able to manage a 15 foot wide wave. Here is a video of a guy that built his own wave with twin 90 hp outboards. http://youtu.be/3CEMjhPNFdA
    Lou
     
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