reefing a rigid wing sail

Discussion in 'Boat Design' started by endeavor, Dec 18, 2013.

  1. Baltic Bandit

    Baltic Bandit Previous Member

    Do it all the time with camber induced windsurfer sails.
     
  2. endeavor
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    endeavor Junior Member

    The fact that it could be moored with the sail up, means that it does not need reefing points. Am I correct when I state that this applies for 2 part wingsails as well (assuming the 2 elements are lined up straight)?

    Also, trimming a 2 part wingsail will be more difficult, but it also allows for better performance, and as I would be targeting the younger generation with the wingsail, performance is all that really matters to them.
     
  3. Baltic Bandit

    Baltic Bandit Previous Member

    Well most wings are going to be "two part" as camber control is important. But for performance you want a third element - a "slot control" and you also want twist control - and if you have differential amounts of twist control in different sections, theoretically it should be possible to set the rig up so that you have offsetting lift forces that just cause the wing to feather but in practice that's not really been done
     
  4. endeavor
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    endeavor Junior Member

    why is it not done in practice? does it not work, or has it just not been done yet?
    I know the AC 45's would keep their wings up, but only for a specific wind range.

    How would an unstayed mast work with the wing? all of the wings sit on a ball mount so that they can freely spin in any direction...
    Do you have any ideas? or has it been done before?
     
  5. PAR
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    PAR Yacht Designer/Builder

    A windsurfer doesn't moor and is easily knocked over. You can't moor a ridged wing on anything, unless you can protect it (read put in a barn) from shifting gusts. A wing mast with a soft sail has trouble enough with the sail doused and the wing free to rotate in heavy wind strengths.

    There are a number of engineering approaches to holding a free standing stick upright, usually involving a lower step that of course permits rotation and an upper bearing at the partners. So, essentially the wing is "captured" at it's base with enough purchase to hold it up right in the anticipated wind strengths expected.

    At a dock, like the A/C boats, you can dog the rig down, but there's a limit to this tactic as well. Small aircraft have a similar problem in big winds.
     
  6. Baltic Bandit

    Baltic Bandit Previous Member

    When you raise a windsurfer sail in the middle of the water, you essentially allow it to auto-feather. and there will be shifting gusts, particularly if it s blowing over 15. most wing masts are stayed and thus have a limit to their rotation. Same with small aircraft.

    Tower cranes have that problem as well. and they way they address it is by having power and auto-feathering built into their controllers.

    So if you built a rigid wing say with 3 panels for twist control, which at the dock/mooring you could configure as having +-+ deflection essentially creating the equiv of a TE brake, you would turn the wing into a wind vane.

    that would leave you with the challenge of having enough lateral stability for a rapid - say 30 degree gust shift harder with a multi-hull than with a monohull

    there is the issue of course at a dock of having enough lateral space for that swing to not hit other boats.

    Now that said, this is hypothetical. I would like to try and build it someday.
     
  7. endeavor
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    endeavor Junior Member

    So would reefing the sail even be necessary?
    would it have a significant increase in performance if the wing was able to decrease in size as well as lower the center of effort in extreme winds (reef)?
    Or would it be just fine to sail the full surface area of the rigid wings up while sailing?
    I know reefing a soft sail is necessary, but that is because of the limited rotation, as well as not being able to make both sides symmetrical (+-+).
    I would like to build a wing like this as well, but if I make an unstayed rig, I will have to find a boat other than my Hobie 16 :( It will have to be a trimaran (or monohull).

    What about a telescoping wingsail with even just 2 or 3 parts? They could be "shells" mounted around a solid mast (mast=unstayed and non-rotating). When at a mooring or in extremely heavy winds, lowering the COE and decreasing the SA would make a big difference, allowing it to feather with even less righting moment and less power.
     
  8. PAR
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    PAR Yacht Designer/Builder

    This is my point Endeavor, this Bandit fellow is talking about maybe trying his hypothetical, while I'm telling you in the real world, a moored wing will capsize, no if, ands or buts. The physics aren't inexplicable.

    No rigid foil will ever be able to self feather fast enough in some conditions, so it needs to be reefed or doused. Considering the efficiency of this design trend, dousing (how ever accomplished) is the only reliable method to keep the boat upright, while unattended on a mooring.

    Reefing is just one method and it doesn't matter if the sail is a soft cambered plane or a fully shaped foil. With current materials and techniques, stays will be mandatory for a multi segmented rigid. In time materials and engineering may address this, though currently it's just not practical.

    Where I live, we can get hurricane force winds in summer thunder storm, which can come up in minutes sometimes. Leaving even a partly reefed rigid to fend for itself on a mooring under these conditions is just guaranteeing you can't get insurance at the very least. Simply put, sometimes you just have the "strip the stick", regardless of how it might be arranged.
     
  9. Baltic Bandit

    Baltic Bandit Previous Member

    well it will only captsize if the unfeathered gust force is high enough that it exceeds the rm of the rest of the boat. On a multi-hull this is quite feasible. On a keelboat, much less so. Its true that a keel boat on bare poles (traditional ones) can be blown into a knockdown -but the circumstances are extraordinary for inshore conditions

    So as long as you stay outside those extremes, I don't see why you need to douse the rig. Nor are stays mandatory for a multi-segmented rigid wing. Stays allow you to build a lighter wing but there are plenty of airplanes that have wings of that size without stays. all carrying load factors PSM in excess of what the sailing mast does - the real issue is cost-performance. You can have a much more expensive wing on a $200 million 787, than you can on a AC catamaran who's total budget including design is $200 million
     
  10. endeavor
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    endeavor Junior Member

    I agree with Baltic bandit... to a certain point. PAR does have a point with it being just too much sail. 1st of all, it will be on a trimaran - I am not a monohull kinda guy (except the VOR 70's and open 60's) and if we are targeting a younger generation with faster boats, then multihull is the way to go. Dousing only the 2nd element of the wing is one idea, as just the first section of the mast shouldn't be a problem - look at the Jet Services catamaran - their wing mast was huge.
    Also, like I say with the "antenna" wing mast, it will reduce the wing size by 1/2 or more. That should definitely be able to handle heavy winds w/o a problem.
    I'll draw out some sketches when I get a chance to show you what I have in mind.
     
  11. Baltic Bandit

    Baltic Bandit Previous Member

    Well another interesting idea I've not seen explored is whether you can leave the ribs and the main beam hoisted but douse the covering. yes you still have more weight and drag aloft than you would with a normal reef - but you no longer have the lifting surface effect. and while its true that you would not get as tight a fit as with a heat shrink wrapped surface, with some clever engineering I suspect you could get close without a huge amount of excess weight aloft. Think zipper and elastic cloth. as in you would actually have a "sail" that would hoist on two bolt rope tracks on either side of the surface, with the cloth wrapping around the LE or TE of the element.

    when hoisted, you would clip on a thin halyard that would pull the zip to the top, taking up the slack in the cloth (aided by an elastic panel section.

    To reef, you pull down the zipper, lower the sock part of the way (or the whole way) reset the halyard(s) and pull the zipper back up.

    the mechanism of the elements continues to work as is.
     
  12. endeavor
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    endeavor Junior Member

    That is a genius idea!
    I never really thought about just raising the cloth part of the sail.
    Another idea I had was if you had the solid fore-part of the wing as a "D" shape. There would be 2 furlers at the edges that would furl out over the ribs, and pulled taught by a pully system at the rear end of the wing. I don't know if I explained it well, but it should theoretically work well. The only thing is that it would not be able to be reefed...

    What about having the ribs on hinges so that they could fold downwards into the "D" shaped fore-part of the wing? It would be like the spine of an animal with the stem pieces that are raised, and pull the skin tight. There would only need to be one halyard attached to the rib pieces running to the top of the mast. What do you think?
     
  13. Skyak
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    Skyak Senior Member

    BB my understanding of wings is that at low reynolds numbers the thick section does not produce significantly better performance than an optimized cambered flat -so at low apparent wind speeds and small chords on the typical monohull the development dollar is better spent elsewhere -aspect ratio, planform, light weight, shape control. On larger boats you have more incentive for the thickness but wing sail management difficulties grow faster than benefits. Low drag wing sails can not help a high drag hull.

    The big opportunities for wing sails are in large low drag vessels. RE is higher from the longer chord and the low drag allows the boat to run up into high apparent wind speeds -multiplying the benefit. Conversely the flat conventional sails run out of angle of attack going upwind on a low drag hull.

    It's a shame wings have not been able to win on moths. I am not ready to conclude they are just too small but results are not promising. I don't anticipate a foiling 2 man mono class any time soon and I suspect cats will split into foiling and non with the majority in the non class. This all tells me that wings as we know them will not go high volume anytime soon.
     
  14. endeavor
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    endeavor Junior Member

    Do you think ANY type of wings will ever grow? Soft wings? Or just no wings at all? I think there might be wings in the future, all we need is some development incentive - which we don't have. Also, for a new boat to include a wing, it will be only experimental (similar to foiling boats), because they are so new. while soft sails have been around for so many years, it can be very accurately predicted, and there aren't really any engineering feats to overcome when designing a soft sail rig.

    I included 2 pictures of the ideas I discussed earlier for reefing the sail. The first one is purely tensioning the cloth part of the sail. The second is putting the ribs on hinges. Tell me what you guys think.
     

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  15. Skyak
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    Skyak Senior Member

    There will be more wings in the future. I expect they will be the preferred airfoil on hydrofoiling sail craft that operate at a Reynolds number of 100,000 and over. For general guidance you can simplify that to boat speed times cord length. A foiling four man boat would be stupid to not use a wing if they are dedicated to maximum performance -I think that is supported by theory and practice. I guess you might consider C cats an indication that wing sails are required to win 2 man open foiling class but they have a very restrictive sail area limit so that is foggy. If a wing could win a single hand one man open class it would expand the boundaries and indicate that wings are a competitive advantage in all larger open classes with similar low drag. It would also be groundbreaking in terms of wings for non-professional non-sponsored sailors.

    I think that there is merit to large masts shaped to foil leading edge profiles with smooth transitions to the fabric (like you are doing). I have been on this board over a year and several times I have been beaten down by posters with more experience over the value of such rigs compared to today's high performance skinny mast rigs. It doesn't mean they are right but it is an indication that they won't 'join-em' till you 'beat-em'.

    So market wise there are the cost no object pros -small number, very demanding, know more than you -no sale. And then there are the competitive amateurs -cost sensitive, show me, followers of fashion. Tough sell and even when they are beat many will change the rules and continue to sail old flat sails. Outside of these there is a small number of sail enthusiasts that would enjoy being part of the development -angel investors of this new technology -if you find one treat them well and hold on tight. Then there are people that just have money and want something cool -this is where I would look for a small fraction of a market much larger than current sailing.
     
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