Welcome to the home of soft wingsails, sails of the future!

Just a quick note on the so called rigid, solid or hard wingsails, currently being pushed through the America's Cup. They are not worth any consideration. They have no future at all, and it is only a matter of time and reason when they will be abandoned forever. Soft wingsails based on ribs and battens are hopeless as well. There is a drawback common to all these wingsails, which is that they require two or more degrees of freedom - the second one for making the foil asymmetrical.

Things are heating up around the next America's Cup. The officials have lifted the ban on advanced sails, but let us look in which direction they are leading the sport - because in most people's minds the Cup is still about sportsmanship, craftsmanship, defending and challenging, and not about policies, bureaucracy and glamour.

To begin, let us review some of the AC34 Rules that are relevant to wingsails:

(ee) wing means a rigid or semi-rigid structure (encompassing a traditional yacht's mast and mainsail structures), similar to an aircraft wing fixed approximately vertically to provide propulsion from the wind;

5.2 The AC72 Yacht shall have one wing and the only permitted soft sails are jibs, code zeros and gennakers as defined herein.

10.3 Further to Protocol Article 29.6, the Wing Spar shall be capable of being disassembled into two separate sections. The lower Wing Spar section shall be at least 18.000 m, and no more than 19.900 m in length.

This is an interesting rule! More than two sections are strictly forbidden, probably for some yet unknown scientific reasons. Why anybody on earth would care about the number of wing spar sections? Who knows ... maybe Google ... or Oracle's design team?

10.6 The total area enclosed within the perimeterline of the wing in wing measurement position shall not be greater than 260.00 m2 nor less than 255.00 m2.

Another interesting rule! This neat formula might be in place, under assumption that all wingsails are equally efficient – which is not the case, particularly with regard to the 'official' AC flapping wingsail.

The portion of the photo on the right (from the AC Facebook profile) shows the imperfect section of the AC45 wingsail  - the sharp 'elbow' inevitably producing turbulence in the laminar air flow just behind the main part of the wing.

Theoretically, the perfect wing section should look somewhat like this:

Below is the section of a wing made for challenging the sailing speed record. Obviously, it is absolutely rigid, and designed for port tack only. It is useless for any other purpose, but illustrates how a high performance wingsail section should look like:

Pictured below is a soft wingsail prototype, with the ability to vary the most important section parameters easily (leading edge shape and radius, thickness and its position), and - with only one degree of freedom (angle of attack):

A wingsail that can assume such a smooth shape on either tack (must be soft, of course) is superior to solid wings of the AC45 type (and penetrating the AC72 arena). Such a wing would be more efficient, and would yield the same thrust with a smaller wing area (say 220 m2) - but a smaller area is something not allowed by this Rule!

10.12 The weight of the wing in wing measurement condition shall be not less than 1325 kg, and the center of gravity shall be not less than 17.000 m above the wing base plane.

Any comments??? Setting the maximum weight could definitely make some sense, in stimulating designers in search of lightest possible rigs (isn't that a dream?), improving stability, preventing accidents and making handling easier. But proposing the minimum weight with such astonishing scientific precision? What is the formula? There is only one: excluding lighter wings (than the 'official' one) from competition. Well, a lighter wing can easily be made heavier, by inserting, say, a length of lead pipe into the spar, but carefully - not below 17.000 m! Feasible, but insane!!!

Martin McElwee of ETNZ comments; "Everyone is aiming for a minimum weight rig. You have this weight to spend - you can spend it on the tube or on the rigging or a combination. You could put really heavy rigging on and less carbon in the tube or light rigging and more carbon in the tube. It's a trade off between these options." And it shows the importance of the rig's weight...

During the historic match between BMW Oracle and Alinghi, we were able to watch something spectacular: Oracle removed the headsail and continued to accelerate with the wing alone, a feat that has never been accomplished before.
Dirk de Ridder, Oracle's wingsail trimmer, said, "Over probably 9-10 knot breeze it's more efficient without the headsail, and the wing is working at maximum efficiency at that windspeed, and there was no surprise we were better upwind against Alinghi with the wing only....Once we get to over 10 knots we're at our absolute best and probably more wind we'd even be better. So good to see in the lighter wind up the first beat we were actually going quite well -- we were very very pleased."
In one of their first AC45 trials, the Artemis Racing team dropped the headsail and sailed under the wing alone for much of the long upwind sessions. "We found that it was actually faster upwind without the headsail," Paul Cayard noted, "and we were probably able to point a bit higher as well."
Traditionalists are probably scratching their heads now - what ever happened to the famous "slot effect"?
Could this new feature change the traditional rig architecture and the AC34 Rules creators' minds?
Obviously, both the headsail and headstay could be removed. Could we expect another phenomenon in downwind sailing? Could the wing alone show equal or better results than with spinnakers and similar drag producing devices? One thing is certain: trials of this kind have never been performed, at least not in a thorough scientific manner, backed up by proper theoretical analysis. On a modest scale, this 'Bernoulli running' has been tried - on our long proposed microsailboat, with thrilling results...

Employing a wingsail as a sole propulsion device would require removing stays and shrouds, thus allowing the wing absolutely free 360° rotation. Its leading spar in this case must be freestanding, held normally in two points. To get familiar with freestanding rigs, check Eric Sponberg's excellent article on the topic:

http://www.sponbergyachtdesign.com/StateoftheArt.htm

The wires have always stood in the way of booms, and now wings, but were necessary in times of wooden masts. Those times are long behind us. With emerging new materials and technologies, freestanding masts have become nothing unusual to see, and 'throwing away these shackles' would certainly contribute to the sport's development.

Allowing a wingsail to feather in case of emergency will automatically depower it, and prevent accidents, capsizes and damage. But with a stayed rig, the wing cannot go beyond the nearest shroud. During one of Oracle Racing's early training sessions on the Hauraki Gulf, the leeward bow dug in the water and the trampoline was nearly engulfed. The same Dirk de Ridder said afterwards, "We've done similar things with other 40-footers and had bad results. We're very happy we could get out of it. Nothing was damaged. The wing hit the sideshrouds very hard, but there was no damage."

Mark Ott, co-founder and executive vice president of Seattle-based Harbor Wing Technologies, the first company to employ a wing that rotates 360 degrees and uses a multihull as a platform, commented, "BMW ORACLE'S boat represents the pinnacle of race boat design; however, the nature of this design limits the wing sail's range of motion due to the shroud and forestay wires used to support it. This design limitation causes these wing sails to be impractical for use by the average sailor. By not allowing the wing full 360-degree rotational capability in everyday sailing conditions, it is bound to it be held on a shroud wire by the wind and damaged, or worse, possibly causing the boat to capsize."

Before the AC45 World Series started, several capsizes of the AC45 cats were seen - let's say the crews were getting familiar with the new beasts. But what happened during the actual ACWS races (remember Plymouth?) has become alarming - the Capsize Club has proudly been established, and everybody was welcome! Any of the things mentioned above might have contributed to these mishaps: imperfect wing section, a too large sail area,  excessive weight of rigid wingsails, a too high center of gravity, hitting a shroud...but the caravan keeps going on...

Such a radical  change in the rig architecture would certainly require acceptance by the America's Cup officials and rewriting of the Rules - which is not likely to happen.
From the interview with Pete Melvin (cupinfo.com):
"Some might wonder about a conflict of interest when a Class Rule author becomes a designer of that very same class, but for Melvin the design task is no easier because of it.  He faces the same questions everyone else does.  It's difficult to know for sure which paths to pursue with the new boat". 
As can be seen, the question of the conflict of interest has been elegantly dodged. Should we expect from the designers of the 'official' wingsail to abandon the vested, perfected version of something inherently imperfect, and choose options that make more sense?
Yes, in a perfect world.
There was a new feature introduced (and quickly abandoned)  at americascup.com, the official America's Cup website. It was called Mailbag, and was intended for taking on reader questions.

One of the early comments that arrived in the Mailbag was:
"It's great to be able to witness the evolution of sailing as we speak. I do not think however that the future is about monos or multis anymore... At this point it's all about the wing sail technology. I won't be surprised if the monos adopt the wings too. I think even the commercial marine industry should take a look in to this development. All the best to AC34!"

The answer was:
"You may be right on the wing technology being something that spreads further than competitions like the America's Cup. But there are significant obstacles, one of them being the handling of the wing when the boat isn't sailing. During the last Cup, the BMW ORACLE Racing team devoted a large amount of time and resource into figuring this out - and there were no easy answers. The wing on the AC45 is smaller, and so more manageable, but as you can see in some of the wing handling videos, it still requires more than a few skilled people to move it around. I think someone will have to come up with a new way of handling the wing when the boat isn't sailing before it become practical for more widespread use. But there are a lot of smart, innovative people who work on America's Cup teams. This is the first time many of them will be working with wings. I'd be very surprised if we don't see some innovations in the next three years."

From one side, it may seem like a perfect example of thinking 'inside the box' - limited, closed-minded, stupid. Personally, I don't believe that this Mailbag person, apparently a member of the America's Cup staff, is not aware of other wingsail designs and options that already solved some of these 'significant obstacles' and do not need years to be invented. The problem is that these smarter wingsails have not been conceived by the 'smart, innovative people who work on America's Cup teams'. So, in today's world of business, such a position is understandable - to some extent. On the other side are the clients who, just like any other clients, are supposedly free to shop around and look for better deals.
So far, they have already been forced to purchase million dollar one-design AC45 cats, and race them until the big event in 2013. What is the chance that the teams, who once mastered these AC45 machines, will proceed with the same type of wings - this time larger, AC72 wings? Huge, there should be no doubt about it.
Challengers, good luck :)!!!

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