how come no multihull toy RC sail boats?

Discussion in 'Multihulls' started by Squidly-Diddly, Mar 22, 2020.

  1. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Reason I'm interested in multihull RC sail boat has to do with the way all the mono-hull RC boats have exaggerated long skinny keels ending in bulb.

    I'd like to be able to launch, sail and recover a sailing RC boat in shallow ponds and without needing to get muddy and wet past my knees.

    While cat and tri boats wont sail upwind as well as a mono, it occurs to me that an RC could be designed to do so reasonably well, since no need for big bridge deck.

    Yeah, I get it that the mainstream of RC sailboats is about a racing class where groups meetup at certain ideal locations. But I'm thinking an ultra shallow RC boat would allow use in all sorts of new areas.
     
  2. BlueBell
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    BlueBell Ahhhhh...

    Well, there you go.
    Stayed or unstayed?
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Some wiseacre will have the answer, but I'm tipping it has to do with stability and scaling, and that at small scale a sail cat will tip over too easily.
     
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  4. Tiny Turnip
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    Tiny Turnip Senior Member

    I think you're on the money, Mr E. And it would then be a long wait at the side of the lake.
     
  5. Doug Halsey
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    Doug Halsey Senior Member

    Check out the Mini40 class. I think recent ones are mostly foilers, but there are also plenty of conventional cats & tris. P5210861.JPG
     
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  6. alan craig
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    alan craig Senior Member

    There's a ready to run r/c cat called the Joysway Binary, only 16" long. You could also saw off half the fin of a typical mono and fit a slightly heavier ballast.
     
  7. Richard Woods
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    Richard Woods Woods Designs

  8. alan craig
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    alan craig Senior Member

    ....and there is the Thunder Tiger Volans tri, 39" long.
     
  9. Squidly-Diddly
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    Squidly-Diddly Senior Member

    that Joysway looks about right. Its got pretty deep daggerboards, but I'm sure those could be shortened with some loss of performance but no real risk.
     
  10. Squidly-Diddly
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    Squidly-Diddly Senior Member

  11. DogCavalry
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    DogCavalry Senior Member

    Tipping moment scales as the third power of relative size. Righting moment scales as the fourth power. So very small sailboats have minuscule stability compared to the exact same form scaled up.
    Wetted surface vs sail area is a fixed relationship. Viscous drag close to the ground limits wind speed for tiny vessels, and good thing or they'd blow away. With the unfavorable scaling relationship, however, it is difficult to get enough lift, at
    L=cl*d*v² to overcome wetted surface area drag.
     
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  12. Doug Halsey
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    Doug Halsey Senior Member

    Your instincts are basically right. Models operate at much smaller Reynolds numbers than we're used to dealing with, and that can cause problems, especially for the very small & slow ones.

    Once the foilers take off and speed up though, it becomes less of a problem for them.
     
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  13. Tiny Turnip
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    Tiny Turnip Senior Member

    Here's the Ripmax Joysway Binary. I was rather liking one myself. But the end of the video shows the problem
     
  14. DogCavalry
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    DogCavalry Senior Member

    Pitchpole!
     

  15. DogCavalry
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    DogCavalry Senior Member

    At that scale, all the moments of inertia are completely out of proportion with mass, wetted surface drag, and airfoil forces.
     
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