Wingmast - how much kick is needed?

Discussion in 'Sailboats' started by sigurd, May 20, 2016.

  1. sigurd
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    sigurd Pompuous Pangolin

    Designng a high AR wingmast rig, freestanding/wishboom with kick as the only twist control. Can choose a normal block system or a lever kick. The lever kick gives less downhaul range but has less friction.

    How much up/down movement is needed for the clew?
    Specifically thinking of high AR wingmast rigs, like A-class cats and Gary Baigent's rigs.
     
  2. Gary Baigent
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    Gary Baigent Senior Member

    Not much. You should have a flat sail, imo, completely flat because of multihull speed and your wing mast rotation - which will provide most of your sail fullness and twist - therefore the clew is not going to move up or down very much. That is if your mast is of decent chord measurement, meaning not just a rotating small chord spar. That is just my opinion; others may disagree - and probably will.
    Excuse my ignorance but the term "kick" do you mean mast spanner positioning for mast rotation? If so I prefer double purchase block and tackle ... because you will be varying mast rotation depending on wind strength and course sailed.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    As best I can tell the use of the word "kicker" is British for "boom vang". "Kick" must be Norwegian shorthand for the same thing?
    It would be interesting to know where these words originated?
     
  4. Stumble
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    Stumble Senior Member

    I am not sure how you would only have a downhaul to control twist, where did the mainsheet go?

    On my A-Cat I have a 16:1 downhaul with about 8" of travel. But I wish I had more purchase, trying to max it out is almost impossible. The clew is controlled by the sheet and has about 2' of travel top to bottom on a 12:1 cascade, which is plenty of sheet purchase.
     
  5. sigurd
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    sigurd Pompuous Pangolin

    Sorry for the misuse of terms. I was referring to boom vang when I wrote 'kick'.

    Stumble, do you in fact mean boom vang when you say 'downhaul'?
    I'm used to downhaul being synonym to cunningham.
    To answer the question, there isn't a suitable place for the mainsheet traveller track. So I can't then use the sheet for pulling down the clew. Hence a wishbone to make it easier to vang.

    In Norwegian, a 'vang' is or used to be referring to a piece of land such as a meadow, hillside or similar.

    Anyway, I can't accomodate 2' up/down with a lever, must use blocks. Thanks for the input.

    EDIT: Gary, mast is about 1/4 of the total chord.
     
  6. Gary Baigent
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    Gary Baigent Senior Member

    Sigurd, then that is a decent sized mast; they can be brutish things in a blow ... this coming from someone who has been bitten in the past from being too greedy.
    if you've got a wishbone, I would have thought you don't need a vang/kick.
    Post an image of your boat. Cheers.
     
  7. Stumble
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    Stumble Senior Member

    Sigurd,

    On the A-Cat there is no vang the mainsheet does all the work.

    Downhaul and Cunningham are the same.

    If you have space issues you may want to take a look at something called a G-Nav. It's like a vang but on top of the boom instead of underneath it, and pushed down on the boom. A number of race boats use them, and they work very well, while clearing up the space under the boom for other things.
     
  8. sigurd
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    sigurd Pompuous Pangolin

    Ah I understand then, Greg. Gnav (vang backwards) looks like a nice solution, it does need a stiff and strong boom though. The wishbone is mostly just in compression so might be lighter.

    Gary, really? That it works without vang on a windsurfer is different to a big wingmast rig I would think? Even if you can use the foot of the sail for leech tension, wouldn't it just be giving up a most valuable control over twist? Can you please elaborate?

    Yea, I hear what you are saying about huge unreefable wings. It is going to be free standing though, and I might put a vane on the boom for short term anchoring, pull it down for longer term. Also it'll telescope to well within boat length.

    The boat, it's just 4 quarters of a catamaran at this point, going back together in a different fashion with 4 bows (not a quadmaran). Mast is stepped on a narrow hull, that is why there is no space for the traveller track.
    But I've started drawing the rig in 3d. Still very raw and in lack of details, sorry.

    EDIT: About the 'spanner', it'll be replaced by 'mast rotation limiter lines' from the front of the boom to the wide point of the mast.
     

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  9. Gary Baigent
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    Gary Baigent Senior Member

    Sigurd, me old mate, the purpose of wing mast spanner/kick/whatever is to control the OVER rotation of the mast - to get the correct airflow from mast to sail on the LEEWARD side. Your art work shows a "double" luff sail with the mast rotated in line with the mainsail clew. Doesn't work like that. That is, if you want to extract the most power from your rig. You're also going to have to widen the wishbone forward span sections - otherwis your wishbone leeward side is going to foul the sail - and airflow. Post more drawings ... and then all the "experts" here will work it out for you. Cheers.
     
  10. sigurd
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    sigurd Pompuous Pangolin

    Thanks Gary, no it really is supposed to be showing a wingmast with a boltrope track (except I haven't drawn the track).

    Let me rotate it to sailing condition and snap another pic...

    EDIT: So you can see how it is supposed to be balanced to increase mast rotation (camber) due to wind pressure and by the placement of the sheet a bit behind the cloth center of pressure. The limiter lines I mention, they stop it from over-rotating. How are your masts balanced, which way do they want to rotate if you let go the spanner?

    EDIT: So you still think the boom is too narrow, the bagginess too small on the sail as drawn? I think you're right, should be a bit wider in the front.
     

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  11. sigurd
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    sigurd Pompuous Pangolin

    The planform. ~11m luff, ~2m total chord. Sail chord just over 1.5m.
     

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  12. gggGuest
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    gggGuest ...

    IME the inward loads from the kicker can be phenomenal, and make mast rotation very difficult. A conventional solution is to have the gooseneck not on the rotating mast, but on a short fixed section at the bottom. Similarly its good to avoid a push kicker because again you are putting horizontal loads into the mast which affect rotation. Of course other solutions are possible but complexity multiplies beyond reason.

    Lever systems can have a lot of value in this sort of situation because you can do some juggling of pivot points and other arrangements to avoid the problem of the kicker purchase with a very low boom having a very poor operating angle. Think about levers primarily for getting good operating angles and then using a purchase to get power. The Finn dinghy setup may give some clues.

    Looking at your planform sketch I would consider having a conventional boom roughly where your wishbone is, with a stump up to that height so that everything to do with the kicker loads is within that system, and then have a semi separate fairing round the bottom of the mast and stump, vaguely like a 49er.

    Maybe the attached gives an idea?

    But there's another thing that worries me. Radical wing mast setups are notoriously difficult to get right, and 11m of height is enough to require some serious engineering. Might it be worth prototyping the concept in half scale on a smaller boat just so that you can knock the bugs out before spending really serious money?
     

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  13. sigurd
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    sigurd Pompuous Pangolin

    Thanks, ggg, interesting. But but. If the gooseneck is fixed to the boat and not on the mast, won't that make the rotation /more/ forced by sail pull?
    The way I think, is that the sail trim should ideally be completely unaffected by mast rotation relative to the sail. If that is the case, then the rotation does not have a bias towards either camber or noncamber. The way to do that is to put both pivots - gooseneck and vang 'root' - inline with the sailtrack. The only thing preventing free rotation in that case is the friction which comes with the huge loads.

    I could maybe do that but the gooseneck would then be interrupting the sailtrack. ?.
    So what I did was put boom pivot and vang pivot in front of, but as close as possible to, the track (in the top-down sketch i was too lazy to pivot the boom and sail independently so the boom is a bit skewed).
    I think the way I drew it is exacly like phillips had (pic), although I'm not certain of where they terminated the vang.

    I'm going to ponder your suggestion more, maybe I didn't understand it properly.

    If I made a smaller proto rig then I'd need another boat for it too, thought has crossed my mind. 'Nadoproa, which is going to carry the (21 sqm or so) rig that we are discussing, is 7-8 meters (pic).

    Look at Gary's red boat, Groucho Marx, gooseneck almost inline with sailtrack.
     

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  14. catsketcher
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    catsketcher Senior Member

    Geometry looks wrong

    I have wishbone rig that I love (regular readers will know this already). Your sailplan is very high aspect and the wishbone won't do much as drawn.

    Any curved wishbone or gnav will bend under compression, jusr like a vang stretches. The leech loads on this rig will be immense and as such the loads in the wishbone would have to be even greater to hold the clew in position. In reality the wishbone will bend and allow the clew to lift way up.

    Sailboards got it right with wishbones pretty much straight away. Use a similarly proportioned rig and put the wishbone is the same place as a board and things work. My cat has its wishbone mounted about 1/4 of the way up the main luff. Any further down and it won't work.

    So I would drop the wishbone or get the rigs into some sort of normal aspect ratio - this rig will be hard to use with its incredible aspect ratio.

    cheers

    Phil
     

  15. Gary Baigent
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    Gary Baigent Senior Member

    Sigurd, Years ago I tried a half wishbone setup on Misguided Angel; there were two wing masts around 11 metres tall set halfway out on the single main beam and because there was no track to attach the main sheet to (just open space and air) I thought the quite steeply angled half wishbones would work okay. They didn't. They were acceptable in lighter winds and beam or broad reaching in the same conditions but hopeless when beating. Because the heavily carbon reinforced booms would flex and bend, so the clews rose and moved forward and the sail falloff looked really ugly. I tried various changes to reduce this but still failed miserably. One was to have a half wishbone with a sort of conventional second boom at mast base and attached solidly to wishbone "clew" making a triangle. Nope.
    You may be okay with conventional wishbones but they have to be attached well up the mast to get the correct angle to the clew ... and then you're getting high loads up the mast (different to having a boom attached to the solid mast base spanner) - also here you are with a superior and aerodynamic wing mast - and then you have this draggy contraption upsetting wind flow to sail right where you don't want it. Team Philips had same problem. Also they had to have been very heavy construction (I'm guessing near solid carbon) to take loads.
    One solution I thought about but didn't try (and I think it would work) was to split the main into two sails just above the single STRAIGHT boom attached on the heavily reinforced position where the sail track would have originally run. This is complicated and you're going to have to figure out a way to attach the two sails to mast. Otherwise it has to be a double luff main to the peak with same boom setup inside sail. Weight and complexity - but it will work.
    Scimitar had double luff with angled single boom as did a couple of Italian C Classes. But they had conventional main sheet systems to reduce sheeting problems - whereas you don't. Cheers.
    ps: added an old image of Misguided Angel's double rig.
     

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