electric hydrofoil

Discussion in 'Propulsion' started by Carter Beall, Jun 27, 2016.

  1. Carter Beall
    Joined: Jun 2016
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    Location: Charleston, SC

    Carter Beall Junior Member

    Hello, I found a windsurfer on a trash pile that floats, and I am wondering if I can get enough thrust by putting an electric trolling motor on the back to get out of the water on homemade wooden hydrofoils. It will move at a good 5 or so mph with just a paddle, and considering that a human is 1/14 horsepower average, I would think that I could go pretty fast with some sort of motor. Does this have any potential to work? The trolling motor that I am looking at says that it produces 30 lbs of force.
     
  2. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    The problem with the trolling motor ratings is that they are rated st zero or near zero spoef. At 5mph they will no longer provide rated thrust but a fraction of it. Equally the props are optimized for low speeds.

    Generally all electric setups suffer modtly from energy storage. 60lb of batteries might be a bug deal on a small board.
     
  3. Carter Beall
    Joined: Jun 2016
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    Carter Beall Junior Member

    thank you for that. This is just for fun, so my goal is really only to get out of the water on a hydrofoil without spending a lot of money. It sounds like the trolling motor may not work then. Is there any other sort of motor that I could try? The problem is having a long enough shaft to reach the water while up on hydrofoils.
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The problem with electric propulsion on a lightweight application (like this) is energy storage. Assuming you can mount a big enough motor, you'll need a really long extension cord or a bank of batteries. The cord saves a lot of weight, but is a wee bit inconvenient, while the batteries just weigh a lot.
     
  5. Carter Beall
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    Carter Beall Junior Member

    yeah, the extension cord would be pretty inconvenient, unless hooked to a generator that was on a motorboat that could stay by the board or something. I do have a small outboard engine that I could mount on it, but it is quite heavy. Do you think it could work?
     
  6. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Hi CB,
    yes - it can be done with an electric motor and an adequate propeller.
    Problems exist so that they can be solved. ;)
    A 30 lb trolling motor is a bit scarce, though it could let you attain a fair (albeit slow in absolute terms) foiling speed. But I would rather opt for a 50 lb one, if possible. That one could make you have some fun.
     
  7. Carter Beall
    Joined: Jun 2016
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    Location: Charleston, SC

    Carter Beall Junior Member

    Thanks, I may go with the 50 lb though that is almost 160 dollars if it will work. Otherwise do you think that a chainsaw rigged up to drive a propeller would work better? I have cheaper access to old chainsaws.
     
  8. Carter Beall
    Joined: Jun 2016
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    Carter Beall Junior Member

    Could I fit the trolling motor with a new homemade propeller? or just a new propeller from somewhere else?
     
  9. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    You won't save anything by chosing to modify a chainsaw. A trolling motor comes as a relatively cheap complete package - motor, gearing, shaft, wiring, propeller (which will have to be changed, as Kerosene rightly pointed out).
    With a chainsaw, you would have to build from scratch all the components of the drivetrain. And building from scratch is rarely a cost-effective option, in terms of both time and money. Just building the foil and fixing it to the board will be a sufficiently demanding and time-consuming job - I wouldn't add more complexity to the project than what is strictly necessary.

    In other words, if it was my project I'd try to use as many off-the-shelf components as possible, in order to have that thing in the water ASAP.

    About the other question - yes, it is perfectly possible to make a new prop, though it is a job which requires considerable manual skills and precision.
    Another option, a simpler one, is to re-pitch or cup a commercial aluminium prop, like: http://www.youngprops.com/minnkota.htm.
     
  10. Carter Beall
    Joined: Jun 2016
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    Carter Beall Junior Member

    ok great, hopefully I will be able to try this in the next few months
     

  11. Ian Brown
    Joined: Aug 2017
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    Location: Canada

    Ian Brown New Member

    Yes, that would work. www.diy-electric-hydrofoil.com
     
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