Mothquito with "Increased Foiling System"

Discussion in 'Multihulls' started by Doug Lord, Feb 19, 2018.

  1. Doug Lord
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    Doug Lord Flight Ready

  2. UpOnStands
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    UpOnStands Senior Member

    I thought that the conventional wisdom was that curving the foil outboard was a bad idea as side slip would destroy lift on the leeward foil.
    Looks like no videos yet, will be interesting to watch
     
    Last edited: Feb 19, 2018
  3. Doug Lord
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    Doug Lord Flight Ready

    These foils appear to work well:

    Open 60 foil scuttlebutt 8-12-15.jpg

    Open 60 Jean Pierre Dick.jpg
     
  4. Tiny Turnip
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    Tiny Turnip Senior Member

    More information here:

    And now for something completely different: Introducing the Mothquito https://www.sail-world.com/news/202253/And-now-for-something-completely-different

    [​IMG]

    More information through the link.
     
  5. UpOnStands
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    UpOnStands Senior Member

    umm, from your post of May 19, 2107
    "C" board as drawn facing outboard is a bad idea(very draggy) : you would have high pressure on the top side(due to leeway) and low pressure on the bottom-just exactly the opposite of what you want. The only way an outward facing board works well is if it doesn't develop lateral resistance and does develop vertical lift.

    BTW the photo Outboard foil on Q23. red =flight waterline:
    seems to be incorrect as the foil is far too close to the surface to provide any lift. Some confusion here?
     
  6. Doug Lord
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    Doug Lord Flight Ready

    I have no idea what you're talking about on the Q23--give me a link and I'll check it out. Q 23 foils don't develop the lateral resistance for the boat as do most other foils-just lift. They work like shallow surface piercing foils and also develop lift from planing when very close to the surface.
    Greg Ketterman used a version of an "L" foil on his Hobie trifoiler with the bottom pointed inboard. He rigged a boat with the same foil pointed outboard and found it was slower. When I asked him about it he used almost the exact same words you do in paragraph one above. He pointed out that T-foils with the daggerboard vertical also have a problem with high and low pressure on the same side.
    The Open 60 foils work more like uptip foils with the outboard vertical portion more or less equivalent to the daggerboard portion on an uptip foil at least as I understand it.

    Experimental Trifoiler with foils pointing outboard:
    Hobie Trifoiler outward pointing foils.jpeg

    Hobie trifoiler foil-normally pointing inboard:
    Hobie trifoiler foil.jpg

    Illustration by Greg Ketterman of why he thinks the Hobie trifoiler is faster than a boat with T-foils(assuming vertical daggerboards) . Note that he shows high and low pressure on the same side of the t-foils which he says is draggy:

    Ketterman-trifoiler illustration of lift.jpg
     
    Last edited: Feb 21, 2018
  7. UpOnStands
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    UpOnStands Senior Member

  8. Doug Lord
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    Doug Lord Flight Ready

    Is this the illustration you were referring to? Its accurate for the original "Q" foils but not for the latest foils which have a more pronounced curve and are deeper in the middle third of the foil. Lateral resistance is provided by the keel, not the hydrofoil.

    Quant 23 foil illustration.jpg

    Newest "Q" foil:
    Quant 23 new foil 4-27-16.jpg

    Q23 with original mainfoil very shallow:
    Quant 23 Benoit Marie 2.jpg
     
  9. UpOnStands
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    UpOnStands Senior Member


    This is the photo I am referring to. From Q23 the foil appears to plane rather than provide hydrodynamic lift.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    It does both at different times.....

    Q-23 with spin flying.jpg
    Quant 23 production 3 crew.JPG

    Quant 17
    Quant 17.jpg
     
  11. Doug Lord
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    Doug Lord Flight Ready

    ----------------------------------------
    You realize I was talking about Gropers(or your) "C" foil and not the "Q" foil? The "Q" foil doesn't develop lateral resistance so the problems Greg was talking about don't happen with Welbourn foils.
    I don't consider an Open60 foil "outward pointing" since the tip points up and apparently works pretty well developing both vertical lift and lateral resistance. The foil on the Mothquito may work like the Open 60 foil at least on the lee side.
     
  12. UpOnStands
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    UpOnStands Senior Member

    Would like to talk to Greg.
    As the boat heels to lee, the inward pointing L foil develops additional lift from the leg. The outward pointing L foil loses lift due to the leg interfering hydrodynamically with the foil underneath.
    The big problem is that L foils (and Q foils) are not suitable for cruisers. Groupers idea is for a cruiser so the foil must be removable from the top w/o losing a lot of internal space. Full on foiling was not his design objective.
     
    Last edited: Feb 20, 2018
  13. OzFred
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    OzFred Senior Member

    You have a very peculiar and unique definition of "outward pointing".

    The Mothquito foils operate very similarly to the surface piercing V foils on Doug Halsey's Broomstick trimaran (the site even calls them V foils). I'd be extremely surprised if there was sufficient leeway for there to be high and low pressure on the same side (i.e. top or bottom) of either foil. Even if there is, so what? It's how the boat sails compared to it's design goals that matters, not some technical oddity.
     
    Last edited: Feb 21, 2018
  14. Doug Lord
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    Doug Lord Flight Ready


  15. CT249
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    CT249 Senior Member

    How much wind with the Mothquito take to develop enough speed to foil, given what appears to be a very draggy shape? And how will those low-freeboard bows work in chop when at high displacement speeds? The closest comparable boat did not perform at all well in its first light-air regatta, where they were often finishing behind a boat rated slower than a Laser 4.7.

    The slide-out rudder system looks like something that will be extremely hard to engineer in an environment of salt, sand and high loads. After decades, expensive windsurfer masts still get stuck together at the sleeve.
     
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