Solid wing mizzen

Discussion in 'Boat Design' started by Clarkey, Sep 15, 2010.

  1. Clarkey
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    Clarkey Junior Member

    I have read many threads on various fora extolling the virtues of a mizzen on small daysailers and beachcruisers. Most seem to acknowledge that the drive that they contribute is minimal but that they function very well as an air rudder and to keep the boat head to wind whilst anchoring and reefing. Would it be worth considering a rigid wing for these duties? It could freely pivot like a weathervane when not required causing minimal drag and no flogging then simply be locked in position when it is required to help hold the boat at the desired attitude to the wind.

    A simple structure in foam/veneer like a model aircraft wing would be a decent place to start I think.
     
  2. NoEyeDeer
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    NoEyeDeer Senior Member

    Interesting line of thought but the problems are that you can't reef it, and wings are extremely efficient at generating lift at low angles of attack. This means that slight changes in wind direction would be likely to sail the arse end of your boat all over the place IMO.
     
  3. Petros
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    Petros Senior Member

    An efficient foil design would not have to be very large to be effective, so if you make is small enough to fold down out of the way (so it lays across the transom for example), it would be worth experimenting with.

    Say something in the 3 ft long and perhaps 10 in wide range, more or less.
     
  4. Windmaster
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    Windmaster Senior Member

    It's a good idea. The "no reef" problem is not really a problem if you have a tailvane to keep it perfectly aligned into the wind when it can weathervane. If you want it to provide thrust you just adjust the tailvane. I've built wingsail boats working on this principle. I'm thinking of not only having a solid wing "mizzen" but also another one at the front of the boat. Please see my website at http://www.sailwings net or http://www.sailwings.net/windthrusters.html
     
  5. philSweet
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    philSweet Senior Member

    Not sure what qualifies as small here. I can't see any potential advantages at all in really small boats- say 500 to 1500 pounds, But if a 28 foot sharpie is what you're thinking, then maybe. The mizzen itself is small enough to be stepped by hand and is used as a gin pole to help get the mainmast up. It could probably be set a bit further aft, combined with a cassette rudder just forward of it. This gives you the ability to ghost over flats and beach the boat. In Florida Bay (outside the Park, of course), you can drift for miles over a 2 foot bottom netting crabs and lobsters or jigging for trout. The sharpie rig lets you control the drift rate, heading, and course to make best use of the light and sea conditions for seeing the bottom. In small, narrow, light craft such as sharpies, the higher lift to drag ratio could help offset the loss of available righting moment as boats get scaled smaller.

    The issues I see in making it practical are-
    Inconvenience of not being able to get rid of it like a sail, or storing it if you did.

    Noise. If you increase the coefficient of lift, you increase noise. Alot.

    You're considering replacing a system that has been developed over a century and has evolved to have the best mechanical response/damping for the particular hull. This needs to be modelled and emulated. Direct mechanical linkages cannot provide this sort of time delay damping, it has to be built-in downsteam of the mechanical control, or done electronically.

    If you plan to use the fin controlled wing, deciding what you want the fin to do exactly is going to take some serious thinking. Start by arranging for it to emulate the rig it replaces in terms of steering moment and gust response. You want to avoid any cyclical reponses that are similar to the natural response of the skipper at the helm.
     
    Last edited: Sep 16, 2010
  6. Stephen Ditmore
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    Stephen Ditmore Senior Member

    My final project design at the Landing School was a ketch with a stayed fractional, bendy mainmast and a freestanding wing mizzen mast. This is a rotating wing mast as seen on some multihulls - it supports a soft sail.

    If you're going to power up the mizzen you might want the lateral area to be well aft and the mainmast to be well forward. A bowsprit might help.

    My thought was to lock the wing mizzen on center when at anchor, the theory being that if it's far enough aft the boat will weathercock rather than sail forward. For this to work, though, it's possible the CLR needs to be well forward (contrary to what I said before). Perhaps the answer is an aft centerboard that is lowered under sail and raised at anchor.

    With respect to swinging at anchor, doesn't raising a (flatish) mizzen generally STEADY a boat that tends to sail on its mooring?

    Windmaster's design reminds me of the Walker Wing: http://www.solarnavigator.net/wing_sails.htm
     
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  7. Stephen Ditmore
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    Stephen Ditmore Senior Member

    What if the mizzen sheet (or mizzen traveller) were rigged into the steering to compensate for the increased load on a skeg-hung rudder in a gust. Then turning the helm to compensate for sudden weather helm would simultaneously turn the rudder and ease the mizzen.

    With a freestanding mizzen and a stayed main, the mizzen mast would bend off in a gust (regardless of whether you do what I suggest in the last paragraph).

    You don't think a system that dumps air from the mizzen in a gust would give the helmsperson the experience of a lighter helm & greater directional stability?
     
  8. Clarkey
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    Clarkey Junior Member

    To be honest I was proposing a very simple system that freely weathercocks when not required but can be clamped to fix the boat in a given orientation relative to the wind. I am not really trying to extract any drive/lift from it.

    The application I actually had in mind was for a cruising rowboat. Some of the ocean rowing boats seem to be adopting ever more complex rudder/autopilot/adjustable daggerboard arrangements to keep the boat on course relative to the wind and I just wondered if these foils could all be eliminated and replaced by an air rudder. Of course it would be illegal for ocean rowing races but I just want to cruise.

    Is a tail/stabiliser required or would a symmetrical aerofoil weathercock reliably around a spar located at the leading edge? Could flutter be an issue in high winds?
     
  9. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I think the flutter will not be a problem if you use a decent rigid airfoil. Figure the center of the force is a quarter to a third of chord length from the leading edge. The lever is from that to the turning axis. As long as 85% or more of the area is behind the axis it should weathercock unless the resistance to its doing so is signif.
     
  10. philSweet
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    philSweet Senior Member

    Stephen,

    I agree with all you said. My point with the control mechanism was to "first, do no harm". If you want to make life easier for the helmsman, please don't confuse the poor guy with perturbations that happen at the same frequency as the boat's response to helm inputs. Sharpie masts were traditionally very bendy and of
    green saplings. They were also usually set up to snap before capsizing the boat. They were replaced frequently. What was the displacement of your project boat?

    Not sure I agree with the anchoring procedure though. The boat may want to lie to a shifting current and not the wind. A fixed foil would add a lot of energy to the boat under some circumstances. not what you want at anchor.
     
    Last edited: Sep 16, 2010
  11. Windmaster
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    Windmaster Senior Member

    You need to be careful about flutter. Have you ever thought there may be a reason that aircraft have tails (stabilisers) with a considerable moment arm? Aircraft control surfaces sometimes suffer flutter and have be mass balanced.
     

  12. philSweet
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    philSweet Senior Member

    Clarkey,

    You are trying to extract drive / lift from it- in the beamwise direction instead of in the direction of travel. I think flutter is a given for any surface producing lift in air. No reason for it to be a show stopper though, a foil probably has a lower energy flutter than a round mast. You just have to deal with the flutter with a bit of ingenuity.
     
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