Electric hydrofoil prop

Discussion in 'Props' started by cmaas, Sep 8, 2020.

  1. cmaas
    Joined: Sep 2007
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    Location: USA

    cmaas Junior Member

    Or, in the case of this hydrofoil, we consume about 7hp at 11 knots.
     
  2. alan craig
    Joined: Jul 2012
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    alan craig Senior Member

    I watched the video of what happens when you remove power and, like others, noticed that the outboard tilts due to drag. I re read the initial post about the problem and wondered: could the outboard leg be tilting forwards at higher thrust levels due to combined elasticity of all the transom and outboard parts? And the longer moment between point of thrust and transom clamp? This would tilt the propeller and foil in a way which gives more lift, which might explain why you have to trim the foil negative. Very interesting project; I have a little DIY electric outboard but not in the same power range as yours.
     
    bajansailor likes this.
  3. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Yes, my example aimed at "the worst case" to demonstrate max velocity levels. That said, it would be interesting to know the actual propeller dia and pitch plus shaft rpms, to see if there is scope for propulsion improvements aside from the lift problem. When you say "consume", does it include all electrical losses, and do you know the efficiency of the control unit?
     
  4. cmaas
    Joined: Sep 2007
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    cmaas Junior Member

    Yes. I think you are exactly right. We got some new video today that seems to show what you've described. I'll get it loaded shortly.
     

  5. cmaas
    Joined: Sep 2007
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    cmaas Junior Member

    In this video I am accelerating to over 11 knots which has been the maximum speed the boat would go before losing lift and dropping. I was entirely wrong that lift from the prop was causing the stern to rise and the bow to drop. Instead as I accelerate the main foil loads up and, because its pivot point is forward of its balance point, it causes the too flexible wands to bend and the foil loses aoa and lift. Stiffer wands should be the fix.

    The other issue, as some of you have pointed out, is that flex in the outboard bracket is causing both the sudden stern drop on deceleration and also allowing the prop and foil to tilt as power is applied so that what was negative aoa in the shop changes to something close to 0 aoa under load.

    I was hesitant to post my questions here as so often forum discussions turn into useless shitshows. The thoughtful insights you guys have provided have really put me on the path to correcting my problems. Thank you!

    Now to get some numbers to baekmo in hopes that he can shed some light on propeller selection.
     
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