Wing Sails on Proas!
I wasn’t totally kidding about the explosive charge to jettison the rig! A bent push/pull rod or blown bearing could be a disaster.
Or maybe the explosives are just a security blanket….which is a funny thing to say….
Maybe explosives is going a bit far, but a method of quickly dumping the rig should be a consideration.
It would be nice to know more about the Walker Wingsail. In the promotion videos they seem to claim that one of their prototypes survived a hurricane, but I haven’t come across any detailed accounts of what actually occurred. It would also be interesting to know if the Walker Wingsail venture failed due to technical and/or performance issues or simply due to cost.
On of the things I worry about with automated or semi-automated wingsails is that it can take the fun out of sailing. If the system can fully tend to itself (as per the computerised Walker Wingsail), you may as well have a motor boat! Maybe the Walker Wingsail simply missed the point.
It would be nice to know more about the Walker Wingsail. In the promotion videos they seem to claim that one of their prototypes survived a hurricane, but I haven’t come across any detailed accounts of what actually occurred. It would also be interesting to know if the Walker Wingsail venture failed due to technical and/or performance issues or simply due to cost.
Having had significant experience in failed startups, autopsies on ventures generally aren’t simple or easy to reduce to one cause. In my opinion, technical and performance problems are far down the list in probable causes. There are uncountable functioning, great product concepts that blew up on the launch pad. Money, time, leadership, inaccurate market vision and an unbalanced mix of skills are far more likely culprits. The boating market is a particularly tough target with a buying public that frequently avoids (or actively tries to kill) anything new or different. Herreshoff had a little trouble introducing performance multihulls to the racing world.
On of the things I worry about with automated or semi-automated wingsails is that it can take the fun out of sailing. If the system can fully tend to itself (as per the computerised Walker Wingsail), you may as well have a motor boat! Maybe the Walker Wingsail simply missed the point.
I agree with your assessment. Sailing is an anachronism. Proa sailing is much more so. Part of the appeal of any specialized, offbeat activity is that it takes hard to acquire skills and expertise. Anything that reduces the elite to the mundane is usually self defeating.
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Bill
While this thread is titled ‘Wing Sails on Proas’, the focus would appear to be on the tailplane control system. The use of a tailplane to control the rig is really a separate issue to wingsails per se. A tailplane could, for instance, be applied to soft sail rig such as a ballestron rig. If you did this, you get the advantages of using a tailplane (self aligning, virtually fingertip control, quick response, easy shunting) combined with a reefable sail system.
Mal.
I agree with your assessment. Sailing is an anachronism. Proa sailing is much more so. Part of the appeal of any specialized, offbeat activity is that it takes hard to acquire skills and expertise. Anything that reduces the elite to the mundane is usually self defeating.
For those of us who are getting on a bit and are not as nimble as we once were, a self-trimming wing sail may well keep us on the water for a few years longer than would otherwise be the case. And if we still haven’t lost the need for speed then a STWS on a proa sure beats a noisy, smelly powerboat…
Peter
While this thread is titled ‘Wing Sails on Proas’, the focus would appear to be on the tailplane control system. The use of a tailplane to control the rig is really a separate issue to wingsails per se. A tailplane could, for instance, be applied to soft sail rig such as a ballestron rig. If you did this, you get the advantages of using a tailplane (self aligning, virtually fingertip control, quick response, easy shunting) combined with a reefable sail system.
Mal.
For those of us who are getting on a bit and are not as nimble as we once were, a self-trimming wing sail may well keep us on the water for a few years longer than would otherwise be the case. And if we still haven’t lost the need for speed then a STWS on a proa sure beats a noisy, smelly powerboat…
Peter
I’m on the wrong side of fifty. I hate to admit I can’t move as fast as I used to. I certainly understand the need to choose a platform appropriate to my capabilities.
There is no doubt about the performance benefits of wing sails after the last two America’s Cups and the last few C-Class Catamaran Championships (Little America’s Cup). There are a lot of real-world drawbacks as well. Cost. Storage. Raising and lowering. Fragility. Fail-safe operation. Transport.
I know some of the people involved in the C-Class wing sail efforts. Fred Eaton has invested over a million dollars in his wing sail boat development. Steve Clark pioneered the current generation of wings and controls (Patient Lady, Cogito forward). These guys openly shared their developments which led to the BMW tri and current America’s Cup wings. They will be the first to tell anyone about the benefits and liabilities of hard wings in the real world.
Self trimming wing sails address SOME of the problems with this technology but not all of them. BMW Oracle employed Magnus Clarke as a nightwatch wing monitor for the BMW tri America’s Cup boat - his job? Making sure the wing was feathered when the boat wasn’t sailing. Magnus is a world champion designer and sailor in the C-Class.
I think Mal Smith is right to steer the conversation towards self trimming wing mast / soft sails and Ballestron rigs. Proas are all about efficiency - including economic efficiency and operational efficiency.
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Bill S.
The big appeal of wingsails is the commonly held belief that they are more efficient than soft sails. This belief comes from the use of solid wings for aircraft. However, the operating parameters for aircraft wings and sails are quite different.
Aircraft wings need to produce high lift for take off and landing but for most of the flight time they operate at low lift coefficients and the important parameter is low drag. Aircraft wings operate in relatively steady air streams. Aircraft wings generally only have to prove lift in one direction (up), so you can build a wing with an asymmetrical section.
Sails must produce high lift with the lowest possible heeling moment. Low drag only effects upwind pointing angle and is not particularly important except on very high performance sailing boats which generate a lot of apparent wind. Sails operate in unsteady airflow with a steep velocity gradient, they generally have to be operated with much more twist than would be required for an aircraft wing. Boats must be tacked, so sails have to able to alternatively produce lift on either side of the sail
Wings with thin cambered sections (such as soft sails) are capable of producing high lift with good lift to drag ratios, but they are very draggy when you try to operate them at low angles of attack. Fortunately, on a yacht it is possible to reef the sail when less lift is required. This allows the sail to continue to operate at a high lift coefficients (CL) and has the added benefit that it lowers the centre of effort (COE), thus reducing the heeling moment for the same amount of lift (or higher lift for the same heeling moment). This is a big benefit on a sailing vessel. When you tack a boat with a soft sail, the sail camber automatically takes up the correct shape for whichever tack you are on
Solid, thick section wings with a single symmetrical element will generally develop less lift than a thin cambered section wing or sail. It is difficult to twist a single solid element. The can’t be reefed, but they will have low drag when feathered. The COE remains in the same position when feathered so heeling moment is not reduced if the total lift remains the same. They are generally heavier than an equivalent soft sail rig. Overall, single element wings are fairly useless as sails.
Multiple element slotted wings can produce very high lift coefficients (better than soft sails), with the added benefit that they can be feathered, allowing them to operate at low CL with low drag, but the COE remains at the same location so heeling moment is not reduced if the total lift remains the same. It is possible to twist a multi element wing, this was Steve Clark’s big contribution to the C-Class cat wing technology. Prior to that, twist was achieved by splitting the flap into multiple elements. Multi element wings are still heavier than an equivalent soft sail, hence why we only see them used with success on stable, non heeling platforms (multihulls), otherwise any efficiency benefit of the wing is lost due to loss of stability due to weight aloft. The low drag of a feathered wing does benefit very high speed craft such as foiling catamarans when sailing upwind.
Overall, multi element wings can be beneficial if you have the right platform, lots of time and money, and you don’t care about practical issues like like storage, mooring or road transport.
I think Mal Smith is right to steer the conversation towards self trimming wing mast / soft sails and Ballestron rigs. Proas are all about efficiency - including economic efficiency and operational efficiency.
I like the very simple and apparently efficient Wharram soft wing sail/gaff-sail hybrid. It does look a lot like the currently popular fat-head sails, but with less drag from the mast due to the sail wrapping around the mast.
It was very simple to build as a scale model, and it seemed very effective when i tried it.
Cheers,
Johannes
I like those too, and I have often wondered how well they hoist and drop. I never saw the two halyard system for tensioning the sleeve before. Very interesting.
I had heard that sleeve luff sails don’t like to come down.
Here’s more wing sail goodness, via Beneteau R&D. Sign up this guy for short stop, he’s a natural.
In case any of you haven’t seen this one…...
http://www.onesails.com/wingsails.php
My only comments on soft wing sails are:
Hi tech sail fabrics don’t last too long when you crumple them up repeatedly, ie every time you lower the sail.
Another price you pay for reefable soft wing sails is increased mast size and weight (and windage in the case of sleeve sails) due to the increased panel (unstayed) length of mast. Unstayed masts are even bigger and heavier.
Another price you pay for reefable soft wing sails is increased mast size and weight (and windage in the case of sleeve sails) due to the increased panel (unstayed) length of mast.
The mast will usually be shorter and the sails have a lower CE than a comparable triangular bermudan rig/sail. You get the same effective aspect-ratio with a squarish Wharram soft wing-sail as a much taller (20 - 30%) triangular bermudan sail. This will more then compensate for the slightly thicker mast-section and higher drag.
Cheers,
Johannes
Compared to modern square top sail construction the Wharram solution has additional weight and windage aloft with the mini gaff, the supporting mast tip and the extra exposed halliards. I guess that it would have inferior gust response as well.
Cheers,
Rob
Please forgive me for the crosspost; seems I came into this topic sideways (via link on the Multihulls list to the Dymaxion thread), and jumped on that without finding this thread (confused? me too!) This is lightly edited for subject; the complete post includes some thoughts on hull construction of the Dymaxion as well as wings:
[quote Author=Dave Culp] I have a strong feeling that wings on boats are going to be a hot R&D space over the next few years. Perhaps here—and now—is as good a place to start as any. 😉
First, in defense of single-piece, non flapped wings and eliminating reefing, please note that http://www.saildrone.com now has more than 6000 open ocean miles on it, and that completely unmanned. Never reefs, never needs to, hasn’t broken yet.
Second, Worsley’s trail boom control. This is not new, but his utter simplicity in making it work is. His system is 100% mechanical—no computer, no electricity, no hydraulics. Everything built of cheap DIY/hardware store parts. The setting mechanism is set and forget, the boat self-steers a compass course with wing self-adjusting forever (as long as the batteries for the rudders don’t go flat!) The tail is the “throttle” and, if set on low speed, will bravely and simply drive the boat—through hurricanes. I recommend reading his website carefully and watching his video—the one showing how the mechanism works—a dozen times. http://www.youtube.com/watch?v=jGo4bRHI22o
Wings. I am of the opinion that hard wings, up to 100-150 sq ft, can be built uber-simply and uber-cheaply of hotwire-cut foam, a bit of strategically inserted wood strips (google “ribbon spars”) and finished off with heavy duty heat-shrink plastic (the kind used to winterize boats)—true “monocoque” construction where the skin takes the forces. The R/C airplane crowd is leading the parade on this technology—google “foamies”.
I’m currently building 5’ and 6’ sections working to optimize and simplify the materials and procedures, then will go to 10’ span and see where it leads. The weight is on the order of 1.5X the lightest carbon-fiber-and-nomex splendor that the AC guys use, and that’s at 20’ span. Cost is negligible; materials are on the order of $5 sq ft of finished wing—half that at experimental/dinghy sizes, 1/4 that for 5’ experimental model wings. These are astonishingly durable if the right foam is used in the right places (can you say “pool noodle”?) simple to repair (packing tape) and cheap enough that if you completely prang one, you’ll salvage the hardware bits and get the spare wing parts out of the back of your car. The technique works with or without flaps on the wings (easier to transport if it comes apart) and once you get finished with the essentially flat learning curve, you can hotwire all the parts for a pretty sizeable wing in an afternoon.
I may even be able to make a case for building hulls of the foam/heat-shrink though I’m not sure just yet. The engineering pencils out but the reinforcements, mast step, foil and ama mounts etc. labor and costs may push the final cost higher than “disposable” warrants. Does anybody here have experience in papier mache tubing for things like crossbeams and stub masts? If you substitute water-based varnish for flour paste, the stuff is completely waterproof. Wonder what would happen if you soaked SonoTubes (for casting concrete piers) in shellac for a week or two?
[quote=Editor]The tailplane controlled wing really only comes into it’s own when it is free-standing, with no stays to limit the rotation. On broad reaching or running courses it is possible to sail with the tailplane aiming backwards and still provide safe and efficient forward driving thrust for the boat, with no danger of a gybe.
Completely agree.
Dave Culp
Some observations on what others are saying on this thread. Sorry I need to play catch-up!
First a bit of overview:
IMO, tailplane control of wingsails are a synergistic and useful combination for several reasons. It is hard to trim a wing accurately. Telltales don’t stream the same way they do on soft sails, are hard to see on the “back” side, but the toughest thing is that a wing’s thrust varies greatly, over a very small range of angles of attack. Wings took forever to catch on in windsurfing—and still are very uncommon—because the rider simply can’t react swiftly enough to keep from being catapulted over the bow as the power comes on. Their solution is to use bendy rigs whose flexibility is tuned to precisely match the sailor’s ability to resist changes in thrust over time.
A soft sail doesn’t even attempt to follow the micro-variations in wind direction. Watch any windvane; real wind direction varies on an average frequency of a couple seconds (even faster in light winds), and with a magnitude from 2-20 degrees or even more. See attached file, or: http://www.dcss.org/Wind_Variation.png This is data I gathered personally during a research project.
There is no hope of reacting to these variations with a boomed soft sail, so the fact that soft sails aren’t very sensitive to small changes isn’t a disadvantage. However, the tradeoff is that they are relatively inefficient all the time. Being able to capture useful energy from these variations is a very great advantage of wings. Even a wingsail can only do it if there is a tailplane—or big motor and hydraulic system/control system.
Tailplanes on soft sails are a fine idea—I don’t know why they are rare with. However, for purposes of this thread, the synergistic combination of hard wing and tailplane renders the thread very much on-topic, even for proas. 😉
Somebody mentioned that, from practical considerations, wingsails offer little or no advantage over soft sails for proas. I disagree. Wing sails can deliver far greater lift coefficients than soft sails (2-3 for a simple 2-element wing without twist control, versus 1-1.5 for a typical mainsail or jib).
Second, the greatest requirement for righting moment for any sailcraft is when hard on the wind, therefore at the rig’s highest L/D. At this condition there isn’t as great a difference in the wing’s versus soft sail’s lift coefficient, but as the wing’s drag is much less (half, even a third), net overturning moment is much reduced. For a given amount of thrust delivered into the boat, the wing sail has significantly less overturning moment—the boat heels less. Put another way, for a given overturning moment, the wing can deliver significantly more thrust before the boat capsizes than the soft sail.
These two features—higher lift coefficient and reduced heeling moment per unit thrust are additive—for the same “horsepower” you can have a shorter rig, delivering more power per unit area, with much-reduced overturning moment. What the designer does with this has many options—you can build a lighter, less rigid boat if you wish. Or a free-standing rig with significantly less reinforcing. Or a narrower boat. Or you can pile on all the wing you can carry and sail very fast. Or you can build a smaller rig (20%?) and spend less money on your boat. I’m not making this stuff up. Every study performed in the last 70 years has decided in favor of wings over cloth and every class of sailing yacht which is allowed to carry them do horizon jobs on their soft-sailed competitors.
Dave Culp
I think the drawings as you have them are correct - with the tail angled the right way to give lift on the main wing in the right direction. If you don’t want to cross over the control rods (cables?) for the tail then you could put the pivot for the square stirrup towards the leading edge of the wing. This would also help the counter-balancing a (very wee) bit.
As far as I can see, the only, trivial, drawback to the design is that you can’t get underway if the wind is dead ahead or astern since moving the cam doesn’t move the stirrup. For all the times that is going to happen you can carry a paddle… :o)
Peter
Nope, I think Skip’s backwards, at least according to Peter’s YouTube vid here: http://www.youtube.com/watch?v=jGo4bRHI22o
In other news, Peter shared this drawing with me (see attached). It’s possible to have both a main wing AND a flap/second element, BOTH controlled by a single tail vane. With this, on offwind courses you can camber up the wing and get much higher lift coefficient, or “fine” it out and minimize power. It’s not optimized, but it’s gonna be a bunch better than no second element, and hey, it’s all automatic, so what’s not to like?
Dave Culp