Wing Sails on Proas!
Single element wingsails are not much better than soft sails, as you say (though “not much” remains in the range of 20-30% higher Cl and 50-70% lower Cd, numbers any soft sailor would kill for!)
This would be a good point if were actually true. If I may quote Tom Speer form a thread on the Boatdesign forum regarding thick airfoils:
Quote:
Originally Posted by markmal:
...Does all this mean that just making a “thin” soft sail baggier will give thrust comparable with a “thick” wing sail of similar leeward curvature?
If so, why advanced Oracle cats use wing sails?
Reply for Tom Speer:
First of all, congratulations for actually running some numbers to answer your questions about aerodynamics!
You are right that at a given operating point, a thin section will out perform a thick section. The reason is simple. When you add thickness to a camber line, you raise the velocity on both sides. Higher velocities mean more skin friction. A higher peak velocity means it is harder to slow the flow down without separation. So, from an aerodynamic point of view, thin is good.
Thick sections have an advantage when you need to operate over a wide range of operating conditions. The thin section will develop a pronounced leading edge pressure peak on either the leeward or windward side when operating outside of its design operating condition. Whether this is a problem or not depends on the operating range you need and your ability to reconfigure the thin section to match the operating condition.
End quote.
What this is saying is that as long as you can keep a soft sail drawing correctly, it will out perform a thick wing. Most half competent sailors can do that. When a soft sail is overpowered (operating away from its design point), you reduce the area by reefing it and that brings it back to it’s design point.
Perhaps because of the hype that has surrounded wingsails over the years, most people believe that wings per se, are better than soft sails in all respects. It is this misconception that I am trying to dispel.
In my opinion (and others, including yourself), single element wings ought not be used on small boats, especially when adding a flap is not a big deal either cost wise or controls wise. You, Tom Speer, myself and also Peter Worsley have *all* agreed on this subject, and yet you seem to persist in denigrating wings as so-so performers while solely basing your arguments on the poorest performing of wings.
Firstly, this statement contradicts your previous statement. If single element wingsails really were superior to soft sails, why wouldn’t you use one on a small boat?
We have established that if you add high lift devices to a solid wing, you can get high lift coefficients, higher than those that have currently been measured on a soft sail system. I wouldn’t say that it is not possible to achieve the same with a soft sail system, but it is more easily achievable with a solid wing. Generally the high lift devices are only fully deployed downwind, simply due to the high drag associated with high lift (this is the same regardless of whether the rig is a soft or a hard sail). With a soft sail system, if you want more thrust downwind, it is easier and more cost effective to put up a spinnaker than it is to try and get more lift out of the working sail area.
Mal.
—Quoted from Mal:
Over the years I have read about many attempts at wingsails. Most of them fail. But if you analyse them, the reason they fail is usually in the execution of the idea, not in the idea itself. Most are too heavy, too small, too high above the deck and pay little or no attention to issues like planform shape, thickness distribution or twist.Mal is painting with a pretty broad brush here. Sure, not everyone is an aeronautical engineer, but when I search YouTube’s site for “wingsail” I get 3400 videos of wingsailed boats succeeding; searching “wingsail fail” yields 400 only. This doesn’t sound to me like “most of them fail.” I wonder how many erstwhile soft-sailboat designs succeed?
More specifically, most of them fail to impress. You can put any largish flat surface up over a boat and you’ll probably be able to get it sail in a forward direction to some degree. If forward motion is your measure of success, then so be it. However, despite the 3400 videos and countless other documented experiments over at least 40 years, I go down to my local sailing club and I see no wingsails being used. If you add up all of the boats using wingsails in club racing (where you expect to see them being used if they perform as advertised) around the world, the number would still be approximately zero. To me, that’s a fail.
However, that doesn’t mean I think that wingsails are completely pointless. Most of the issues for holding wingsails back revolve around materials and manufacture, To date, wingsails that are actually superior to soft sails are mostly confined to very expensive high performance craft. but over time, if people keep pushing the envelope with materials and building techniques, they might become more mainstream.
With regard to proas, wingsails may offer benefits that go beyond just improved performance, e.g. easier shunting or new methods of steering as mentioned previously.
Mal.
John Wright just forwarded an excellent article on the saildrone.
http://www.wired.com/autopia/2014/02/saildrone/#slide-id-155781
Lots to digest
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This a great thread.
The whole self-trimming wing sail idea is really cool. Especially on a proa - It makes tacking way easier.
As mentioned earlier in this thread, I think the wing is most valuable on boats that will have apparent wind on the beam or forward. For slower boats sailing at deeper angles, I wonder how much heeling force will be applied to the boat, and how much rolling it will want to do in a seaway? That is probably monohull thinking, but unfortunately I don’t have many miles on multihulls (yet). Maybe Santa will bring me an Outrigger Junior for Christmas this year and I can rectify that problem.
Anyway, I thought this would be of interest. My dad went on a recon mission and grabbed a shot of the big wing mentioned in the story, which is mounted on a 50-ft (or so) trimaran and here it is (below). I got to take an in-person look at the saildrone a while ago also, but alas that was before I understood how cool the wing was (thanks to this thread) otherwise I would have looked a little closer. I spent most of the time looking at the hull.
As for the new wing, I think it is interesting that the tail is mounted at the top of the wing instead of the middle. An advantage is that it provides a small amount of righting moment up high, where it will do more good. It will also disrupt the vortex off the top of the wing, but I haven’t decided yet if that is good or bad for induced drag. If there is any flexibility in the wing to twist along the length, it will cause the wing to twist in the wrong direction (closed at the top, and open at the bottom), though I don’t imagine it will twist much.
Looks like there is a single control element on the tail much like saildrone, and the main wing is a single element. From the article it looks like they want a very simple wing to put on ferries where they can throttle on or off. I think this is probably the best way to do that.
Cheers,
-Kimbal.
(PS - Unfortunately I cant eat wheat anymore, so I’m going to have to do something about my name here. No more burritos for me.)
Great catch, Kimbal! Thanks to your dad for the recon work. That IS curious about the top mounted air rudder. One reason might be to take advantage of increased wind speed aloft, thus a smaller rudder could be used. I can’t tell if there is a fwd counter-weight or not from the pic.
BTW, I eat veggie burritos all the time. (oh wait, I saw “meat” when you wrote “wheat”.) never mind.
Hey Kimbal, great catch. Don’t change your handle too soon - there are many gluten free/wheat free products available now, even burritos! mmmgfburrito?
Cheers,
dairy free Curtis
The name and even the graphics on that wing tail, Greenbird, make me think of this…
http://www.youtube.com/watch?v=TRFRQXPtXTs
Obviously not the same wing though…
The name Photon Composites on the shaft of the tail end leads to a dead website….
Hi,
The reason why I joined Proafile are threads like this one.
Sailing world has conservative convictions that lead over the ages to frozen concepts, that are hard to overcome. Evolution has been more on the materials science side and less on broader aspects like concept and philosophy.
That said, my interest on future ecology and sustainable ways of living has over the years made me dream about sails sliding across the oceans at steady pace, relying just on the breeze that passes by…
Wind generators have recently gave birth to an interesting,low-cost idea that I have the strong belief can work…but no funds to prove it.
Small vertical shaft units, used to give power to isolate houses and remote areas have a market of their own.
The “Square Rigger”, sold by Tradewind Renewable Energy, has a short mast, cloth sails that orientate itselves when their path is moving upwind in order to reduce drag and a high torque output, enough to move a propeller underwater, with the help of a torque transmission.
Who knows?
An idea I mull over from time to time is that of a wind-powered “water tractor” - essentially this is just a vertical axis wind turbine that’s matched up to a Voith Schneider propeller. In between the two would be a stumpy barrel of a boat hull, providing buoyancy. Such a device, in the right environment, could work quite well as a tow boat, hauling barges or the like from point A to point B.
An idea I mull over from time to time is that of a wind-powered “water tractor” - essentially this is just a vertical axis wind turbine that’s matched up to a Voith Schneider propeller. In between the two would be a stumpy barrel of a boat hull, providing buoyancy. Such a device, in the right environment, could work quite well as a tow boat, hauling barges or the like from point A to point B.
I love the concept! What about stability, though? You have the same heeling moments any sailboat has—and the same limits to performance. How do you propose to deal with too much wind? Do you envision this as a manned vehicle, or a drone? Is there any advantage to retrofit it into an existing boat as a permanent installation, rather than a second tow boat?
Dave
You could couple the Voith Schneider Propeller (see Wikipedia link below)
http://en.wikipedia.org/wiki/Voith_Schneider_Propeller
to almost the same thing, but in the air. See below the “Tradewind Renewable Energy” product: The Square Rigger:
http://www.youtube.com/watch?v=9nR3goj7oXg
The big difference is one is converting rotational power in thrust (the VSP) while the other one is doing… the opposite.
It solves the problem of too much wind with reefable sails… but I am not sure of the efficiency of the thing.
I am sure that at the expense of more gearing and pushrods, one could replace each of those sails by a two piece wing (main element and flap behind it), where the mechanical controls deal only with the angle of the rear small section relative to the front main element. The main element would pivot freely.
All of this is nice and dandy, but I see on big problem though…
Someone, please correct me if I am wrong, but if I remember well, the forces generated by wings (and therefore the power generated by a rotating wingmill made of wings) is directly proportional to the density of the fluid it is immersed in….
You see where I am going with this; knowing that density of air is about 1.2 kg/m3… and that fresh water is 1000 kg/m3; if you do your calculations for the sizing of the propeller in the water for your boat… you need basically something ONE THOUSAND time bigger (so 32.6 times taller and 32.6 times wider) on deck to have enough hompf to drive the underwater propeller… at a comparable speed compared to the related fluids…
Right?
If I am correct with the “comparable speed” comment, that might be the savior…
The lift and drag forces on a wing profile is proportional to:
- the density of the fluid, as stated above
- the surface area of the wing
- and the velocity of the fluid SQUARED.
So if you play with the size of not only each wing, but the diameter of the aerial parts, maybe it can work… or maybe not.
This video below gives some real examples that are not very promising…
http://www.youtube.com/watch?v=NC7GGEO3AGk (do yourself a favor, turn off the sound so you do not get the cheesy “muzak”)
At 1.25 in the video, those 4 big turbines on top of the building will produce *** on average, 24/7*** 22.8 kW… or 30.5 HP (listed as 200,000 kWh per year)
At 2:30 in the video; that turbine on the roof of the big catamaran is 10 HP.
That’s it!
When you know the size of the diesel engines on a tub boat… I don’t see how a wind turbine is going to generate enough power to drive it…
The only other parameter I can think of, to play with is time…
Run the turbine 100% of the time, store the energy in batteries, and run the propeller only 1% of the time….
In the hullabaloo of alternative energy, people tend to forget that sailing is *already* the single most efficient method of net transfer of the momentum in the wind to momentum in the boat. This guy says it best:
“Sailing involves no thermodynamic cycle and generates little heat. Sailboats react mechanically to the forces of the wind without any train of energy-losing conversions in the path of action.
“As a consequence, the theoretical efficiency of transferring the momentum of a moving column of air to the momentum of a boat can be as high as the best windmills, even before windmills perform useful work: close to 60%. [Right at the Betz limit, already. —DAC]
“Sailing has the highest potential of any means for exploiting the cheap, renewable, clean power of the wind.”
—Bernard Smith
Sailoons and Fliptackers; The Limits to High-Speed Sailing
Dave, of course, you are right; the less transformation and intermeditate steps for the transfer of power from the wind to the thrust power of the vessel, the less losses.
But you still have to be realistic on the scale of power needed. What I am saying is that the amount of horse power packed on a fairly small volume tug boat which is basically the biggest diesel engine you can shoe in the smallest possible hull is way higher than what you can reproduce/capture from the wind on a similar size vessel.
Well hello, I decided to quit just lurking about and say something. I’m really excited about wingsails, ever since I had a Solcat18 that I sailed on Lake Castaic CA I just knew there had to be a better way. Then you guys showed me Worsley’s work and the light came on. As soon as I can grasp posting a photo I’ll do it. The gist of my thought is 50/50 main and secondary elements with a largish cam driving a follower pivoting 85 to 90% back on the main element driving the secondary element directly (as one piece) with the tail fin driven off that. Thanks to Tom Speer and John Eisenlohr for inspiration beyond Worsley’s work.
Best regards, Roy
If we see further, it is from standing on the shoulders of giants.
Simple and direct, a lot to like. Hope to hear more as things develop.
Welcome,
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