Squeezing more RM out of keel with controllable flap?

Discussion in 'Boat Design' started by pironiero, Jul 30, 2021.

  1. pironiero
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    pironiero Senior Member

    I was thinking around of idea of squeezing more RM out of keel, have anyone tried something like this?
    Basically its a controllable flap on the end of the bulb, for its basic functionality we need only add a pitch axis with can be made with a couple of flexible cords, one thick metal one that will keep the flap horizontal and one smaller one that will put a tension on a flap to adjust its angle.
    Here is a picture and a video attached.
    It's a draft so don't be too harsh on my modeling skills please.

    [​IMG]
     

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  2. tlouth7
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    tlouth7 Senior Member

    Your flap appears to create lift in the direction of the keel strut, is that correct? If so, it doesn't add any righting moment.

    You need to create a force with a component normal to the keel strut, but note that such a force will also contribute to leeway.

    If you have a canting keel then why not just cant it further?
     
  3. pironiero
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    pironiero Senior Member

    Here is a video without downloading
     
  4. pironiero
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    pironiero Senior Member

    No, I just wanted to show that it can roll as well
    and i meant squeezing more out of canting keel, more than its angle can allow
     
  5. tlouth7
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    tlouth7 Senior Member

    Ah so the flap is always ~parallel to the water surface? And the resulting force always ~vertical? That makes sense!

    I guess the question is whether the added drag from thickening the keel strut to fit the (complex) linkage, plus the drag from the flap, is less than the drag associated with other ways to increase righting moment (widen boat, add mass to keel bulb etc).
     
  6. pironiero
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    pironiero Senior Member

    yes, that is the idea
     
  7. pironiero
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    pironiero Senior Member

    It's not complex, it's just two cords running through the keel, no electronics needed, and several bushings, maybe couple of gears
     
  8. quick_dry
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    quick_dry New Member

    Would this be for an offshore racer? I imagine the equivalent could be done on Ultim tris like Gitana or Sodebo to increase RM since they already have flaps on foils in a similar position as a canted keel. But I imagine the pitfalls could be likened to the days of sealed of underbody aero on F1/hillclimb cars - good until they're not. If the flap holding you _down_ ventilated then it would suddenly lose all effectiveness - you'd be on a fully powered up boat, losing the RM from the flap. The other situation I was thinking of was in seas where you're crashing through and the boat speed is going from high to suddenly low but the windspeed stays the same, you're losing righting moment as it slows, and the RM you need isn't there until you're moving quickly again.

    That said, I thought there was a 'twisting' system on some very new offshore racers to alter the keel's AOA relative to the boat so that as it cants higher, it turns the leading edge of the keel downward - but this wasn't to improve the righting moment from the bulb, it was to counteract a fully canted keel becoming a lifting surface as the boat's bow lifts or from the asymmetrical lift with the foils on a modern IMOCA.
     
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  9. pironiero
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    pironiero Senior Member

    that's the thing with high aspect sport boat keels, isn't it?
     
  10. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Why no airplane wing style flaps on keels? Stronger wind the greater the need for RM but the boat also goes faster so more RM on given amount of flap activation on keel.
    Just like airplane wing flap a keel flap would be toward end of keel for leverage.
    The idea would be to use flap instead of weight so sailing downwind or in light winds is faster.
    Seems like it would be cheap and simple. Just a rod from flap up through keel for manual adjustment (but I guess could be automatic self RM leveling pretty easy too).

    Sure its some drag but the idea is you only get drag when you've also got good power from strong wind.
     
  11. Dolfiman
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    Dolfiman Senior Member

    I investigated this idea on this thread, naming it a "dynamic ballast" i.e. an articulated foil at the tip of the keel wing and able to provide negative force like a weight, but the conclusions are usually negative and , when positive in some cases, did not worth the complexity of the system :
    Dynamic ballast https://www.boatdesign.net/threads/dynamic-ballast.59729/
     
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  12. wet feet
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    wet feet Senior Member

    As an exercise in speculating I suppose the topic occupies some thoughts for a while.Beyond that,and without a particular end use in sight,its hard to see what the concept would achieve that wouldn't be as easily achieved by adding the weight of the control mechanism to the ballast bulb.There is cost to consider and which particular boat might be used to trial the concept.You could also increase the righting moment by encouraging the boat's cat to sleep on the windward side.With a canting keel foiler,which also has water ballast,efforts are more likely to be focused on improving the L/D ratio of the foils as this is an easier aspect of performance to yield benefits.The process of thinking of an avenue to explore for extra performance is often fascinating but the true test is putting those concepts on the race course where the truth comes out.
     
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  13. pironiero
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    pironiero Senior Member

    The thing is- that thing is HUMONGOUS and its basically a new version of a T keel bulb with too much complexity, in my case-its just a flap, if it's not working- just unscrew it and go, you basically don't loose anything its cheap and simple.
    And if for some reason it works-we can adjust the shape to squeeze every last drop of performance, i think it will provide some amount of RM, the most complex thing is to figuring out how to make the flap stay horizontal to surface of the water without any complex electronics.

    I dont mean that your work is worthless, what im trying to say is you went in too deep right from the beninging
     
  14. Skyak
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    Skyak Senior Member

    There is nothing so expensive as that which doesn't work.
    You should not be so dismissive when someone offers a workable solution and quantifies the result.
     
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  15. pironiero
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    pironiero Senior Member

    I am not dismissive, these are just my thoughts, I will study your information, I just havent had time to do it yet.
     
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