The design of soft wing sails for cruising

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

  1. groper
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    groper Senior Member

    Well like most things, i dont believe its as simple as this...

    A higher L/D foil will make the same power with less sail area. So, if there is less sail area carried, some (or all?) of this reduction must offset against the heeling moment when comparing the high aspect sail vs a lower aspect sail of increased area despite the lower CE.


    We all agree that the higher aspect sail (or higher L/D sail) will do much better upwind, but another point worth noting concerning running downwind, is a sail which can be sheeted out past abeam ship so that its leading edge is aft of its roach, and has the appropriate trim to generate lift, is more powerful than a sail which is simply using its area to generate drag like a traditional square rigger or parachute. So with this sheeting ability, the higher aspect sail should also do better downwind aswell - unless running DDW where the appropriate trim cant be achieved.

    So many things to consider, and one of the important ones is the boat itself and what kind of speeds can be achieved with the sail power available. One idealistic solution will be different to another of when vessel speeds are very different. So the whole rig i dont think can be viewed in isolation. Simply considering "a wing sail for cruising" is too broad of subject to hash out in much detail unless we are discussing rigging a specific type of boat and how much emphasis is placed on performance vs practicality.

    The end plate on the bottom of the sail is a great way of increasing efficiency. You dont see it happen very often as its not viewed as practical by most cruising sailors. The boat would need to be designed originally with allowances for this in mind and not create a nuisance for day to day usage.

    Most cruising sailors dont even use rotating masts due to the added complexity - which is relatively small in comparison to some of the subject matter discussed here already. Just adding a rotating wing mast will add a considerable performance improvement to any standard existing rig, yet its amazingly unpopular... i guess most figure that the boat requires too much maintenance as it is!
     
  2. Will Fraser
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    Will Fraser Senior Member

    Is there any additional complications or pitfalls involved in this forward-of-beam sheeting?
    When you gybe, would you use two sets of sheets (one on either side of the mast) so that the sail can swing over ahead of the mast?

    From a stability perspective, a gust could cause a heeling force to windward, depending on the point of sail and sheeting angle, for example. I learned this the hard way on a cat-rigged dinghy.
    I know one of the free-standing ketch rig proponents (Sponberg) cites it as being very stable for running ddw with the sails set wing-and-wing
     
  3. groper
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    groper Senior Member

    There's problems with everything... Design is all about trade offs...

    I fail to see the point of designing a soft wing sail for cruising, if it's going to be a low aspect ratio . Why? Because the l/d ratio will be poor no matter what shape the sail is, or whether it's soft or rigid or made of carbon or bamboo!

    "Low aspect ratio" and "wing" should be mutually exclusive terms. A good analogy would be " designing foam core ballasted keels" ... Why you would want to do it, when the gains to be had are excluded in the first design constraint!?
     
  4. Will Fraser
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    Will Fraser Senior Member

    See the very first paragraph of this thread. It does perform better, possibly in part due to its greater tolerance for varying AoA in a heaving sea. Perhaps David could elaborate on the "better handling" he cites, just to get rid of some of the subjectivity of his comment?
     
  5. David Tyler
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    David Tyler J. R. A. Committee Member

    A sail on an unstayed mast can be sheeted out past abeam, yes, but then the steering gets very peculiar, with unexpected lee helm at times, and a vane gear can't steer accurately.

    Absolutely.

    Yes, a reality check is needed here. There would need to be a +/-45 degree quadrant of flat, clear deck, perpendicular to the mast, with no ventilators, hatches, cleats, dinghies, running lines ... ain't gonna happen, in the real world.

    A boat with a wing mast will never stop sailing. I've watched a cat with a wing mast at anchor in Papeete tacking to and fro, snubbing on the anchor each time quite hard. Not for me, or for any cruiser with sense. Whatever the performance benefit.
     
  6. David Tyler
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    David Tyler J. R. A. Committee Member

    " ... but the performance is better than a pure junk rig. ... I'd rather like to go back to this rig, as it was actually even easier to handle than pure junk rig, on top of the performance advantage."

    Junk rig doesn't flog, reefs quickly and easily, furls instantly, runs downwind faster than bermudan rig, can be made from low grade materials, is fail-safe (let go every line in sight, and the sail neatly self stows) etc, etc. See the thread on the advantages of junk rig for more. A wing sail derived from junk rig has these advantages, plus some more:
    1) the yard hauling parrel that must be adjusted after raising or lowering the sail is no longer there. This is quite a heavily loaded line on a big junk rig, and adds to the workload when reefing in heavy weather. In my previous wing rig, the luff hauling parrel, that peaks up the junk rig yard and gets rid of the creases, was also dispensed with, but I now intend to put it back in, so that's no long a plus point.
    2) the top of a junk sail is usually more or less triangular, with its area further aft than the rest of the sail. This means that when deeply reefed the CE drifts further aft, when we would like it to come forward. The wing sail, as I've drawn it, does the opposite; the CE comes forward when deeply reefed.
     
  7. groper
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    groper Senior Member

    trying to get to sleep last night, laying in bed, had an epiphany...

    I imagined an easily driven catamaran (im a multi bloke) with 4 rigid wingsails mounted on a very clean deck. A schooner rig on each hull with cabin in the middle... Each wing sail quite low and small in comparison to a single masted rig - more like 4 windsurfer size rigs but higher aspect ratio and 2 elements. The wings are fixed to rotating plates in the deck, the deckplates are rotated via DC motors. No sheeting lines or ropes at all anywhere on deck, infinately variable 360degree sheeting...

    Due to the small size of the wings, each can easily derigged and the spars layed flat on deck, placed down the sides on each catwalk abreast of the central cabin... an alternate solution would be folding spars, hinged above the deck, and folded into the same position. Yet another solution would be telescoping masts, so that they remain upright, but at half their full height to reduce windage in a storm etc...

    I should do a rendering of it as the picture was very clear in my mind :)
     
  8. Will Fraser
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    Will Fraser Senior Member

    Another nutter on board!:p At least I am not the only one then!

    That is exactly how I envisioned getting the most use of a wingsail, but instead of dc motors, using a closed loop sheet around a drum below deck at the base of the mast. Or even a free-rotating rig that self-trims by means of trim tabs.
    A dc motor would however open the option for all kinds of automatic sheeting if linked up to the windex via some control electronics...but this is getting w-a-a-a-y off topic here. Better get a new thread going.

    If I understand Tom Speer correctly, splitting up the rig into multiple parts with divided areas will only give an induced drag benefit if all the sails are separated perpendicularly across the direction of the wind. In other words, when close hauled on a port tack your port bow sail and stbd stern sail will be streamwise aligned to the wind and will have a combined induced drag of a sail with their areas combined but with the same luff length, i.e. half the aspect ratio of one of the small sails.
    The same will happen on a beam reach where the front pair and stern pair of sails each act as a single unit with reduced AR. Not that it matters that much on a reach I imagine?
    It will certainly create some interesting sheeting possibilities for running ddw though!
     
  9. FAST FRED
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    FAST FRED Senior Member

    I am still stumped as to why a cruiser , that is not bound by measuring rules from the race measure folks is willing to add complexity and expense..

    Simply sizing the entire rig larger for light weather and using modern reefing techniques should obtain the highest boat speed underway .

    The car guys say you cant beet cubic inches, take a look at the sail area of 100 years ago (re reliable engines) and go BIG area.
     
  10. groper
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    groper Senior Member

    It pushes the design spiral upward - more sail area = more structure, more cost, more time to build, more weight - which mean more power needed to acheive same speed.

    A small but extremely efficient sail will make just as much power as a large inefficient one... but it will be easier to handle, cost less, weigh less etc etc - the is the correct direction in which to go IMHO.
     
  11. FAST FRED
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    FAST FRED Senior Member

    NO spiral required at all.

    With the 1st reef in the boat would have the same stability , the same build , almost same cost.



    The 3 ,4 or 5 ft added to the mast height for very light weather speed , would not weigh enough to be a handicap in normal (8K-10K of wind +) conditions.

    Even though most folks use the iron topsail under 5K of breeze it is quite sailable , with enough sail.

    Downwind the extra area would be a blast , and impose no undue loads.
     
  12. groper
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    groper Senior Member

    a taller mast = stronger and stiffer mast. Its an exponential relationship btw, so only a few feet higher gets heavier and more costly real quick.

    A few feet higher increases the shroud and forestay angles (if a stayed rig) and the mast compression loads go up not just from increased area, but poorer shroud angles aswell. If unstayed, the mast section gets way heavier, again exponetially as the cantilever beam bending equations show.

    Then the boat needs to be designed and built to handle the exponentially higher maximum loads - different story if talking about retro fitting an existing boat as you have to work with what you already have, but a new design from scratch would be considerably lighter if the maximum height of the rig can be reduced.

    Rob Dennys proa concepts clearly show what is possible if the negative spiral is adopted, going for less weight, less structure, less sail area etc etc. You wouldnt beleive a 15m cruising multihull could weigh 2.2 tonnes with an unstayed rotating rig and sail at better than the windspeed with a build time of 3500hours -unless you had seen it... http://www.harryproa.com/index.php/design/21-visionarry-series/7-visionarry-sport

    They are also building folding unstayed masts at present, and trending toward a twin unstayed schooner rig for varioius reasons, although a full size schooner hasnt been built yet, only smaller beach cat size test bed...
     
  13. David Tyler
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    David Tyler J. R. A. Committee Member

    Have a look at :

    http://www.yacht.de/service/heft_info/innovativ-der-fluegel-fuer-alle/a86617.html

    It appears that Group Beneteau is about to develop a wing sail for cruisers.
    This is exactly what I thought could happen, and ought to happen: that a major player should look at the Omer wing, and the lower tech attempts of myself and others, and put some serious money into development and tooling. No, it won't be a junk rig derivative, so they'll be missing some of the advantages that we see. It's a pity the photos don't show the head of the sail, I'd like to see that.

    But I foresee that in 50 years from now, this kind of rig, or something like it, will be the norm, and the pointy top bermudan rig will be seen as quaint, and retro, the same way as gaff rig is seen now. It will only be used to keep alive the old-fashioned ways of our grandfathers, like using a sextant instead of GPS.

    I see that the prototype Beneteau rig suffers from the same thing as mine - the convex windward side just aft of the luff gets corrugated, as it collapses inwards a little, there being nothing to hold it out. I don't think this is serious, though as the air speed is very low here.
     
  14. David Tyler
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    David Tyler J. R. A. Committee Member

    I think you're missing the point, Fred. I just read Casino Royale (1953) again. Bond is driving a 4 1/2 litre Bentley (25 HP is quoted, but surely it was more?). In that era of motor development, as you couldn't yet manage efficiency, you had to go big instead. When they get to the chase, he puts his foot down, and manages 120 mph. I'd take a bet that there are many well-engineered modern saloons of 2 litres, with efficient fuel-injected, 4 valve per cylinder engines, that could breeze past him.

    Our rule of thumb with junk rig is to put on as much as the boat will carry, because it's so easy to reef. When converting a production boat, we generally look at the main + big genoa area, which is enough, and then if possible squeeze on a bit more.

    OK, so now we've got as much area as we can fit. What then? Why, go for more power per unit area, of course!

    To go back to my design brief, as listed earlier - I'm aiming to match the performance of a well set up modern bermudan rigged cruising vessel, but with higher efficiency, as measured by miles per unit of cost, miles per unit of crew effort and hassle, miles per unit of complexity and level of technology. In automotive terms, I'm aiming for the equivalent to a diesel engine for a RV, that has enough torque for the difficult surfaces, enough power to get up the hills, yet is undemanding to drive, very easy to live with when cruising across the wide open plains and starts easily when I turn the key.

    Complexity? This is what I've always found is such a difficult concept to get across to the more conservative sailors - that the modern bermudan rig is more complex, has more components waiting to fail, than any junk sail, or any derivative of it. They look at something they're not used to, and can only see that it's complex, when in fact it's only different.
     

  15. Skyak
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    Skyak Senior Member

    I have been reading and following the builders of 'Paradox' micro cruisers. They are stout little 14 foot skiff micro-cruisers that lack all performance features -no keel, body weight kept internal -no ballast shifting, super low aspect ratio sail ~1 max reefing to ~0.2. And yet they make impressive trips! They put more miles in their wake than most boats twice their size.

    The reason I mention it here and now is that IMHO, the thing that makes the boat work is the continuously reefable flat sail rig with low center of effort. Thrust is what we want from a sail rig and righting moment is generally what we pay for it. Lift/drag is a fine measure of a wing but it is a not a direct measurement of rig value.
     
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