Help with Electric Hydrofoil Airboat

Discussion in 'Boat Design' started by Carlazzomark, Mar 12, 2019.

  1. Carlazzomark
    Joined: Oct 2006
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    Location: Michigan

    Carlazzomark Junior Member

    I have a 12' (3.66m) trimaran which I would like to turn into an electric hydrofoil airboat.

    Questions:

    1. Does anyone know of an 24-48 volt outdoor motor capable of turning a 48 inch or so pusher prop powerful enough to get the boat (1000 pounds total weight, boat and people) up on a hydrofoil?

    2. Any ideas for a retractable hydrofoil for a trimaran?

    Everything above the deck in the photo can be removed in the reconfiguration.

    Thanks
     

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  2. kerosene
    Joined: Jul 2006
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    Location: finland

    kerosene Senior Member

    No.
    I give a no to the general concept of:
    -12 ft tri (quite short for getting near foiling speeds)
    -retractable foils (retractable in itself is not impossible but add weight and complexity)
    -electric powertrain for such srtup is really challenging as more power means more batteries means more power needed...

    Electric foilers so far are:
    -hitech builds, heavily engineered, carbon compositrs etc.
    -optimized for one purpose an generally _very_ limited range

    What is your ballpark budget and ideas for power (hp or kw)?

    Sorry to be negative.
     
  3. Dejay
    Joined: Mar 2018
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    Dejay Junior Member

    EDIT: I'll just recommend the book "Hydrofoils by Ray Vellinga". It features formulas and also designs for foils.
     
    Last edited: Mar 12, 2019
  4. Carlazzomark
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    Location: Michigan

    Carlazzomark Junior Member

    Kerosene, I have no problem with your comments; they were negative in a knowledgeable way! If you have time, I would like some more information, such as:
    - please explain why 12' is too short for foils. I see foiled windsurfers all the time here at Lake Como. Is it a weight to length issue?
    - there retractable foils I am thinking of are not high tech. I thinking about a hinged or daggerboard type design which could simply be opened/dropped into position once out of shallow water, then locked.
    - as for power needed, this is one reason I posted. I have no idea how much power a standard swamp/airboat needs, but I would guess that I would need less. I am not looking for super speed, just a nice pace on foil.

    Thanks
     
  5. Carlazzomark
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    Carlazzomark Junior Member

    Deejay,

    Thanks, I will check it out. I am a dream and not a technical guy, but I know folks close by who are.
     
  6. Carlazzomark
    Joined: Oct 2006
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    Carlazzomark Junior Member

    Deejay,

    I just watched his video and bought the book, to be delivered tomorrow. Thanks for the tip.
     
  7. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    The book is a great first step.
    You will learn weight is the enemy.
    Too bad it has to be retractable, it adds complexity.
    It is completely doable.
     
  8. Dejay
    Joined: Mar 2018
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    Dejay Junior Member

    The formula aren't complicated from what I've seen. Simple arithmetic and interest will do.

    Depending on how you want to use the boat, building a new one as a very simple lightweight platform might be easier. And cheaper because if you use less weight you need less surface area foil and less power.

    Lift = Velocity² * SurfaceAreaFromAbove * CoefficientOfLift

    Drag = Velocity² * SurfaceFromFront * CoefficientOfDrag

    Power = Velocity³ * SurfaceFromFront * CoefficientOfDrag

    So as far as I understand it (and I only skimmed the book so far, and there are some intricacies to the foil, laminar flow, the coefficient of lift and angle of attack) you can make the surface larger to lift lots of weight and only need linearly more power. Making it fast is another matter.

    As long as your total wetted surface of the foils is lower than the wetted surface of your boat (incl. the added displacement from the weight of the foils) you should be more energy efficient / faster. Roughly ballpark. I think.

    I'd be interested about your ideas for tractable mechanisms!

    PS:
     
  9. Heimfried
    Joined: Apr 2015
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    Heimfried Senior Member

    Be careful with the coefficient of drag. While in physics and generally it is used with surface from front as you said, most tables and graphs in avionics and nautics use the surface area from above simply for practical reasons, which leads to a much smaller coefficient. Vellinga states this on page 50 and 52 of his book ("caveat"), but missed to follow his own hint. So the given example on page 50 and 51 (comparison between a plate and a NACA 0033 profile is wrong, because the c(D) = 0.04 of the NACA profile corresponds to the vertically projected surface.

    Edit (03-16-19): May be, I understood the things about the NACA 0033 profile wrongly. I've got some original publications about theory and measurements of NACA wing profiles. When I read Vellingas example I tried to find data for the NACA 0033 profile at the web but wasn't successful. Therefore I compared with NACA 0025 which is a wing profile.
     
    Last edited: Mar 16, 2019 at 6:08 PM
  10. Dejay
    Joined: Mar 2018
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    Dejay Junior Member

    Thanks I was wondering about that!

    So the droplet we see in the side view would be a droplet from the top as well and the c(D) = 0.04 would have to be multiplied with the surface area of the droplet, not the circle?

    Does he include more tables for airfoils in the book? I haven't found them.
     
  11. Heimfried
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    Heimfried Senior Member

    I don't know, if the NACA ever was measuring droplets (head on view = circle). I only know of wings and the side view of the droplet is the cross section then.
    No more tables of Data in the Vellinga book.
    Look at the Bibliography at the book: "Abbott Doenhoff Theory of Wing Sections. ... Airfoil Data". You will find it as pdf somewhere in the Web. And there are a lot of other sources in the web, some of them also mentioned in this Bibliography.
     
  12. Carlazzomark
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    Carlazzomark Junior Member

    BlueBell,
    It does no absolutely need to be retractable. Both lakes I will use it on are universally deep to the shore almost everywhere. And I was not thinking of super sophisticated system.

    Thanks,

    Mark
     
  13. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Hi Mark,

    Why do it if it's not necessary?
    The added complexity means added challenge, design, compromise, weight, cost, work, and maintenance.

    Did your book arrive?

    Can you get rid of the centre pontoon?

    You have the budget for Lifepo4 batteries, right?

    "Everything above the deck in the photo can be removed in the reconfiguration."
    Does that include the pilot?
     
  14. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Lol, no response, I guess the book arrived.
     

  15. alan craig
    Joined: Jul 2012
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    alan craig Senior Member

    Bluebell got there before me; remove the centre pontoon to reduce weight, wetted area and for lower centre of gravity (with remaining pontoons immersed a bit more).
     
    BlueBell likes this.
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