The design of soft wing sails for cruising

Discussion in 'Boat Design' started by David Tyler, Jan 19, 2014.

  1. David Tyler
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    David Tyler J. R. A. Committee Member

    Agreed. Yet there is a problem with this, in a soft wing. If the luff is broad and gently curved, it is rather difficult to keep it in shape. It tries to collapse inwards. There is an answer to this: on my last wing-sails, I retrofitted little "riblets" between the main battens, to keep the forward 5% in shape. I was hoping not to have to do that again.
     
  2. P Flados
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    P Flados Senior Member

    I understand. I was wondering if construction considerations had led to the shape.

    Life is full of choices and sometimes we just have to pick one that bothers us the least.
     
  3. redreuben
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    redreuben redreuben

  4. P Flados
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    P Flados Senior Member

    I did make a cut at trying to generate a dat file similar to your proposed shape.

    Turns out the performance is nearly the same as what I ended up with.
     

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  5. capt vimes
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    capt vimes Senior Member

    sorry, but i do not see that working...
    the sail and its battens should be downhauled as low as possible and thus given you a very short length of line to stretch... and i have not even mentioned that those lines will be stretched already since you need to bring some tension in the halyard to give the sail/wing a proper shape.
    depending now on the placement of the block relative to the mast, only very limited points of sail will be the result...

    think that one through again, because i have been right at that stage already and found only subpar solutions to make it really an easy-to-use cruising rig for a short handed crew...
    and in non of those configurations of mine i could eliminate the issue of having winches and blocks on the mast/boom...
    freestanding, rotating mast - halyards can only be manhandled at the mast
    freestanding, fixed mast and rotating boom/battens - reeflines and downhaulers at the boom/battens because they need to rotate as well.
     
  6. David Tyler
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    David Tyler J. R. A. Committee Member

    I'll have to remind you that i speak from the experience of 40,000 miles or so under this rig, the length and breadth of both the Atlantic and the Pacific, from 2005 to 2010. Bermudan sailors are used to pulling hard on the corners of a triangle to get it into shape, and have to adjust their thinking when considering the junk rig and its derivatives, where the sail simply hangs from the halyard, needing little to hold its lower edge down. If you get too enthusiastic at tensioning the downhaul, sailing to windward, and then bear away onto a run, it's the work of a moment to ease the downhaul an inch or two.
     
  7. David Tyler
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    David Tyler J. R. A. Committee Member

    I can't really see this as a major advance. It seems to be nothing more than a double-thickness bermudan mainsail, with only moderate thickness, and a very weird cross section. N60 foil section is claimed, but having finally found that in an ancient NACA document, it's completely dissimilar. The graph of Cp shows a nasty spike at the LE, at a very moderate alpha, because of the strange shape.
    Can anyone else see any advantages to this approach?
     
  8. David Tyler
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    David Tyler J. R. A. Committee Member

    Thank you. As I said above, I think I'm now in favour of e422 until something better comes along. Cl and Cd seem to be about the same as for the two sections you evaluated, but max Cl/Cd seems to go up from about 90 (at alpha = 10), to 109 (at alpha = 8), at Re = 500,000. Actually Re= 1,000,000 is about the lowest I'm interested in, that being 7 knots of wind with a chord of 4.44 metres.
     
  9. JosephT
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    JosephT Senior Member

    David, do you have any YouTube/video references trimming this soft wing sail rig? It would be interesting to examine the rig in action and see how you trim this boat out, how many crew are required, etc.

    Also, how quickly can the mainsail be dropped (in minutes/seconds) with a typical crew?

    I did find this video, but it doesn't provide any hands-on action shots.

     
  10. David Tyler
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    David Tyler J. R. A. Committee Member

    You've spurred me on to upload some footage taken in the middle of the Tasman Sea, just after a heavy squall had passed through. Naturally, the water doesn't look as rough as it did at the time! There's no sail-handling involved though.

    http://youtu.be/2nO3BTM7NAc

    Poor quality, I regret to say, because I'm on a very slow marina WiFi).

    How many crew are required? Just one. That's the whole point: this is a rig for short-handed cruising.

    How quickly can the mainsail be dropped (in minutes/seconds) with a typical crew? About 2 - 3 seconds, if I just let go the halyard (then the sheet has to be gathered in, which takes longer).
     
  11. JosephT
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    JosephT Senior Member

    Thanks David, it's always nice to see the frothy swells of an exciting ocean. Your video & feedback answer a lot of questions. The fact that you've sailed in the psychotic Tasman sea under this rig says a lot right there, not to mention the bonus of single handed sailing capability. That is a big plus. In due time I suspect it will catch on with other sailors who would rather spend more time sailing that trimming all day/night.

    Do you have any rigging diagrams that describe this rig in greater detail? I'm curious how the wing foils retract/collapse when you reef in the main. If you don't have any handy no worries. Just post when you can...even a sketch will do.

    Cheers,

    Joseph
     
  12. David Tyler
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    David Tyler J. R. A. Committee Member

    Photos taken when the alloy battens were made in NZ

    Here are just a few photos:
     

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  13. redreuben
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    redreuben redreuben

    Wing systems.

    Simplicity.
     
  14. David Tyler
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    David Tyler J. R. A. Committee Member

    Yes, simplicity is good. That's why I use an unstayed mast. If it's designed right, and built right, it's very difficult to make it fall down. That's why I stick with junk rig and its derivatives. Nothing simpler to build and use.

    In contrast, a stayed mast is very complex. Try counting up all the different components. And insecure. All it takes is one little pin to fall out, to cause the whole rig to come crashing down.

    But how about the sail itself? What is there inside the sail that produces the shape? What about the complexity of the cars on the track on the mast? How can the sail be reefed? There are many things that make it complex, and maybe some that make it suitable for racing, but none that make it suitable for cruising, and that's the focus of my interest.
     

  15. JosephT
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    JosephT Senior Member

    I do admire the simplicity of the design. The sail frames remind me of the canvas/dope aircraft skins on older wooden planes, only you are just going with canvas without the dope & paint.

    Speaking of squalls, how have the sails & frames held up in storms? What amount of sail maintenance is required as compared to the standard set of sails (eg sloop main, jib)?
     
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