compressed air propulsion

Discussion in 'DIY Marinizing' started by bnhk88, Aug 8, 2009.

  1. bnhk88
    Joined: Aug 2009
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    bnhk88 New Member

    would it be possible to propel a canoe with compressed air?

    the only thing i have thought of so far is to have a 12volt compressor fill air tanks and use an impact gun to power a drive shaft with a propeller.

    its just a shot in the dark. i dont know how much air pressure would be needed? would a 12 volt compressor have enough power? could you use a power inverter and use a 110 compressor? would a car battery provide enough power for a couple hours on the river?

    just looking for some superior knowledge. im not set on this idea just throwing it around. any suggestions or alternatives would be appreciated.

    thanks

    bnhk88
     
  2. wardd
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    wardd Senior Member

    sure if you only need 5 mins of power

    anything more and the tanks would probably sink the canoe
     
  3. Guest625101138

    Guest625101138 Previous Member

    Yes. If well engineered it is comparable with using batteries with electric drive.

    There are a few air powered cars in development such as this one:
    http://www.popularmechanics.com/automotive/new_cars/4217016.html

    If you look around for car information it will give you an idea of what is happening. In a boat the air motor would be used to rotate a prop instead of wheels.

    I designed a one-shot air powered rocket for a movie stunt. The motor was a 20ft length of pipe filled with water and pressurised from a small 3000psi air bottle through a valve and flow restrictor. Only good for a single shot but very fast acceleration.

    Overall the air system is much less efficient than an electrical system but that it is not really an issue with a canoe. The main requirement is energy density, namely energy stored for weight, and an air system is not too bad in this regard. Initially you would probably be able to refuel at the local service centre for free. At least until they woke up to you coming in every second day with an air cylinder to charge up.

    Most systems would use higher pressure than normal shop pressure as it keeps the size of the cylinder down. But weight is more of an issue with a canoe. You would need to look at low weight pressure bottles. A high torque miniature motor connected directly to a prop and a control valve is all that is needed. Probably want to exhaust away from the prop.
     
  4. pistnbroke
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    pistnbroke I try

    So That Would Be A Ww2 Torpedo Then
     
  5. CDK
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    CDK retired engineer

    If you are thinking about a battery, forget the compressor and the impact gun but use an electric motor and a prop instead.
    You could however use compressed air as energy storage, but then you need much higher pressure, like a diver's bottle, otherwise you carry only a few minutes worth.
    Pneumatic tools are very inefficient, they would waste most of the energy in your bottle. You could experiment with a venturi type pump, like the one divers use to uncover objects in the seabed. It is also inefficient but has no moving parts and could provide an almost noiseless propulsion for a canoe.
     
  6. MattZ
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    MattZ Junior Member

    Might want to use an air drill instead of an impact wrench. Quieter, and probably more efficient. That, or a die grinder with like 300:1 gear reduction.
     
  7. hoytedow
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    hoytedow Wood Butcher

    You could always try the old vinegar and baking soda routine.
     
  8. Jimbo1490
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    Jimbo1490 Senior Member

    Air tool motors have really terrible efficiency. All they are is sliding vane eccentric rotors, after all. They make a lot of power in a small package but that is about their best attribute.

    My Dynabrade sanders are all rated .5 hp but it takes about 2HP worth of air compressor to drive one of them- and I LIKE air tools!

    WWII torpedos (and modern ones, too!) use very efficient axial piston motors to efficiently harness the compressed air. The storage trick would be to store the air in the liquid phase. I have not looked at what pressure you would need at iso std, but I would guess it's 2500 psi or more. But if you stored that way and used efficient piston motors, you could get reasonable duration.

    In the end it's just a neat engineering puzzle as it has no hope of competing economically with an ICE.

    Jimbo
     
  9. MattZ
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    MattZ Junior Member

    You'd have to cryogenically cool the air to liquefy it. No amount of pressure can liquefy air at room temperature.
     
  10. portacruise
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    portacruise Senior Member

    The answer to your question is YES, you can propel a canoe with compressed air. But there are simpler, more efficient and less costly ways to do it. The car battery could provide a couple of hours or more depending on speed when used directly with a trolling motor, but a deep cycle battery would last much longer.

    Porta

     
  11. Bob E
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    Bob E some day

  12. srimes
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    srimes Senior Member

    The highest energy storage density that would be practical would be a CO2 tank as that is stored in liquid form. That could work great but would be expensive to refill. Liquid N2 would be great too but where would you get it?

    If you want to recharge it yourself then regular compressed air is the easiest, either 125psi shop pressure or 2000 psi diver's tank.

    The plus side of shop pressure tanks is they provide good flotation too.
     
  13. srimes
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    srimes Senior Member

    oh and you would want a much more efficient motor than an air tool motor. It'd be basically the same as a steam engine, just operating at much cooler temps. I'd try building one with an air cylinder, small diameter long stroke, with a large expansion ratio. It would look and sound (and feel!) cool anyway.
     
  14. hoytedow
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    hoytedow Wood Butcher

    Steam would be cheaper, because it can run on garbage, scrap lumber or un-recycleable types of plastic and paper waste, saving landfills. It takes energy to compress the gas in the first place, much of which is thermal, and wind turbine energy kills more birds than the Exxon Valdez and solar takes up too much land area for the amount of energy derived, so why not use steam in the first place? The water that comes out as steam is cleaner than it went in, and you could even partially clean "gray" water in the process.
     

  15. hoytedow
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    hoytedow Wood Butcher

    As the h2o supply dwindles, flotation increases as well.
     
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