Using hydrofoil for race kayak stability

Discussion in 'Hydrodynamics and Aerodynamics' started by rallyhybrid, Sep 14, 2018 at 4:16 PM.

  1. rallyhybrid
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    rallyhybrid Junior Member

    So here's the plan. As a very late comer to flat water marathon racing (60ish) I am looking at ways to increase boat speed (reduce drag) without risk of falling in.
    My first attempt at this was to buy a racing K1 and build outriggers with streamlined foam floats either side which was quite effective. My latest thought is to replace the floats with a foil on the outriggers around the C0f G point primarily to provide stability through lift but also perhaps to use a size of foil that will partially lift the hull out of the water so reducing surface drag.
    So advice sought.
    Do I go for the sleekest hull and minimal foils just to keep it upright or seek to use something with more lift to gain a bit of elevation.
    I don't want to go to the Flyak extreme where I am so far out of the water I can't use a conventional paddle stroke. My target speed is 6-7 mph over 10 miles on flat water.
    Thanks in advance!
     
  2. BlueBell
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    BlueBell Ahhhhh...

    I would suggest plan or option A.
     
  3. rallyhybrid
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    rallyhybrid Junior Member

    Yes, that was my thought too. Any suggestions what foil to use and where I could source it??
     
  4. BlueBell
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    BlueBell Ahhhhh...

    They tend to be expensive but are available.
    Are you at all interested in making one?
     
  5. rallyhybrid
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    rallyhybrid Junior Member

    Was hoping to buy something or adapt a foil from another application??
     
  6. Doug Lord
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    Doug Lord Flight Ready

    You might consider researching RC helicopter carbon fiber blades. The major problem with them may be thickness-ideally the foil you use should probably be a round an 8% Thickness/Chord ratio-just a guess. Many RC heli blades are 12%+. But do the research and you may come up with something workable. You might want to determine a viable area by experimenting. If you're willing to do the work you could build some experimental foils using epoxy glass sheet or carbon fiber sheet. Once you determine a workable area the RC heli blades may be an advantage. Using epoxy glass and a grinder to shape experimental blades is nasty work so make sure to use a respirator and a dust suit.....
    Another possibility is using high aspect ratio surfboard fins -at least experimentally if you can find them-new or used cheap enough.
     
  7. rallyhybrid
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    rallyhybrid Junior Member

    Thanks guys these are good ideas. My first idea was to look at a boomerang profile but the ones I bought were crude profiles with a curved top and flat base. RC heli blades are a good idea...I'll look at this. I've also bought some alloy wing section from Crazy foil, but this is probably overkill for a low lift stabiliser. Could still cut these up and make some small wings but this doesn't feel like the best way. Can adapt stuff in my workshop, but time/work restraints won't allow me to make something from scratch. A good resource to buy wings and foils sections would be helpful...I can't find much other than retailers that sell expensive board kits. Please keep suggestions coming. Cheers
     
  8. BlueBell
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    BlueBell Ahhhhh...

    Fair enough.
    I got a set of expired Robinson 22 helicopter blades for free.
    One day they're worth $60K, the next they are worthless as they expire at 2200 hours of use.
    A section of the main rotor blade would do the trick.
    There are places to buy pre-made wings but they are very expensive as I recall.

    A nice feature of your application is the wing can be fixed angle of attack.
    Adjustable of course but fixed while underway and making-way.
    This makes installation so much less complicated.
     
  9. rallyhybrid
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    rallyhybrid Junior Member

    Looking at the myriad of RC heli blades on ebay. This looks like a really good way forward. Lots of low cost carbon offerings.
    Just need to get the size right to get the best stability/drag compromise.
    As you say, Bluebell, a big advantage is that the installation should be simple, I'm thinking just an inverted T with some fine trim adjustment.
    Will advise on progress.
    Thanks
     
  10. Doug Lord
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    Doug Lord Flight Ready

    I think you might be better off with a version of DSS foils-one foil sticking out of each side of the boat rather than a single t-foil. The distance between the two would act to increase stability... I would start with the least area and thinnest blade first. You could make a trunk that allows the blades to be easily changed.

    DSS--Farr.jpg

    DSS for multihulls.jpg
     
  11. BlueBell
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    BlueBell Ahhhhh...

    Just remember a 1/4" plywood wing would work.
    Not as well as a NACA wing but I wouldn't get carried away with an expensive wing.

    Wouldn't it be fun to put a small electric motor in the strut-wing "T" union with an R/C prop.
    No battery, just a solar flex panel for a little daytime assist.
    Perhaps not your thing, just throwing it out there.

    A point I'd like to make is the strut will offer a roll damping factor at speed.
     
  12. rallyhybrid
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    rallyhybrid Junior Member

    Hi Doug,

    my plan is to have outriggers (say like the oar rigs on a racing scull) and one 'T' foil either side.
    This will allow the kayak hull to work to its design shape without any additional turbulance from the foil.
    As you poit out Bluebell I will get damping at speed so should get away with something simple and low drag.
    I like the motor drive idea but might get disqualified from my race!!!
    Thanks for the help chaps!
     

  13. Doug Lord
    Joined: May 2009
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    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    rh, I don't think you'd have any additional turbulence from the foil at the hull but you will have additional drag from the vertical strut supporting each t-foil due to piercing the waters surface.
    The hull acts like an endplate on the inboard end of each hull mounted foil increasing the foil's efficiency. Also, with the t-foil you'll have the drag from two tips each side whereas with the hull version drag from only one tip each side.
    However, the center of lift of the t-foil may be able to be further outboard which will help with roll stability.
    Good luck!
     
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