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Old 23-05-2017, 01:17   #76
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Re: Remember the Walker Wingsail ?

In comparing conventional single surface sails, soft wings and rigid wings it is wise to consider the Reynolds number effect.

If you do not like rigid wings then do not use them, simple.

Wing sailor.
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Old 23-05-2017, 03:18   #77
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Re: Remember the Walker Wingsail ?

It's not that I don't like wingsails - it's that there are many inaccurate claims about them, such as the claim that prompted my first post in this thread. Another example is linked to a soft wing pictured here - articles claim that soft sails must be triangular because boats need backstays (wrong) and that a triangular sail is the worst possible shape - wrong again, a triangular sail can easily be trimmed to produce elliptical loading and you don't actually want elliptical loading all the time if you are constrained by righting moment.

If the proponents of wingsails were more considered in their marketing then I would just not sail one. But when they make exaggerated claims that denigrate other rigs, surely we have the right to discuss it?
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Old 23-05-2017, 04:56   #78
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Re: Remember the Walker Wingsail ?

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When Walker Wingsail systems sued Yachting World magazine,
I hadn't heard of this before and it could be a big part of the failure.

Regardless of who was technically right, you don't bite the hand that feeds you and in the day, magazines were where you picked up new buyers. A lot of the magazines are affiliated and even the ones that aren't won't paint as rosy of a picture.

Not saying it's right or wrong just that it could explain a lot.

As far as the technology, the rigid sails do have a major drawback. They are often compared to airplane wings but airplane wings are asymmetrical. An asymmetrical wing-sail would be awesome on one tack and horrible on the other. A cloth sail on the other hand while technically not as efficient, will reshape itself on each tack. With new fully battened sails in the hands of skilled sailors, I suspect the cloth sails get the edge.
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Old 23-05-2017, 05:36   #79
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Re: Remember the Walker Wingsail ?

Actually, as a former sailing mag editor, I'd say that the Walker defamation case could have helped wingsails, by making it obvious that if any mag dared speak of them in an unfavourable way then they could find themselves out of business. That may have lead to things like the frankly silly and poorly-informed article I referred to which claimed that yachts needed backstays and inferred that triangular sails were the worst possible shape - complete rot according to the guys that design wingsails that actually work.

The real issue with the Walker Wingsail case wasn't that the boat didn't perform as well as claimed - even the Walker's own expert witness pretty much admitted that. Where Yachting World fell down was that they insinuated that Walker had been over-stating his claims for financial gain, I think. They got a huge judgment against them and were going to appeal but it was settled out of court.

I remember reading the test and the judgment. If I recall correctly, YW put on their own testing gear (as several mags did at the time) and found that the WW just did not go well. It could just have been a case where the truth hurts.

One of the things that I always find amusing and frustrating about wingsail fans is that so many of them spend so much time making claims and never backing them up. The Omer guy told us he would be doing boat-on-boat testing against a sistership about a decade ago. He still hasn't. There's another wingsail company that is making great performance claims but for some reason they don't seem to have ever put their "superior" sails up against a boat from the same class in competition - even when they sailed on the same river as an active open-design class that would probably have welcomed them.

Wingsail people, like many fans of "alternative" rigs, will often claim that their rigs are banned by the "conservatives" but of course there are many events where they are allowed. Wingsails have been allowed in A Class cats, 18 Square cats, speed sailing, windsurfing, some shorthanded racing classes, skiffs, Moths, etc. For some reason many of their fans tend to ignore the fact that they have failed in these classes, or managed to avoid actually turning up to the start line. "Put up or shut up" is a pretty simple maxim......

Of course, wingsails work really well in some other classes where different factors apply. It's just a pity that so many wingsail fans keep on making derogatory comments about conventional boats and classes.
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Old 23-05-2017, 06:59   #80
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Re: Remember the Walker Wingsail ?

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Actually, as a former sailing mag editor, I'd say that the Walker defamation case could have helped wingsails, by making it obvious that if any mag dared speak of them in an unfavourable way then they could find themselves out of business. That may have lead to things like the frankly silly and poorly-informed article I referred to which claimed that yachts needed backstays and inferred that triangular sails were the worst possible shape - complete rot according to the guys that design wingsails that actually work.
Not buying that sueing could have helped. At best it would shut down any article (well thought out or not), which is a death blow for a new technology trying to catch on. It's really hard to get something new going when people refuse to talk about it.

I do agree fans of a technology overstating the capabilities does undermine a lot of new technologies. I see the same thing with electric drive trains. Lots of claims but when you ask for real life comparisons, they never show up.
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Old 23-05-2017, 10:20   #81
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Re: Remember the Walker Wingsail ?

By all means discuss the comparison of sails and wings, but do so in an objective manner, you are wandering around the subject.
Meanwhile have a good look at a rigged conventional sail and then go and look at the wing of a glider. tell me what you see and compare.
As for exaggerated claims, they come from all directions. A sailmaker was trying to explain to me the "laminar flow" of a sail, as I was looking at an example of alluminium mast, sail, rigging and all the bits. Otherwise known as an aerodynamic drag fest.

I sail and sometimes I fly gliders, I am aware of the comparison.

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Old 23-05-2017, 11:09   #82
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Re: Remember the Walker Wingsail ?

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As for exaggerated claims, they come from all directions. A sailmaker was trying to explain to me the "laminar flow" of a sail, ...

Wing sailor
The difference is when someone talking about established technology feeds you a line of BS, everyone knows it's BS, so they are quickly marginalized by everyone, even those who believe the established technology is better. Plus it's typically pretty easy to find data to support or undermine any assertions.

When talking about new technology, there are often a lot exotic theories but when you ask for hard real world data from similar boats in similar conditions...crickets chirping....

I think a big part of why wing sails haven't taken off is the average cruising boat isn't typically limited by the power the sails can generate. Being able to back the boat up by a flip of a switch is a neat trick but not of much practical use.
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Old 23-05-2017, 20:21   #83
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Re: Remember the Walker Wingsail ?

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By all means discuss the comparison of sails and wings, but do so in an objective manner, you are wandering around the subject.
Meanwhile have a good look at a rigged conventional sail and then go and look at the wing of a glider. tell me what you see and compare.
As for exaggerated claims, they come from all directions. A sailmaker was trying to explain to me the "laminar flow" of a sail, as I was looking at an example of alluminium mast, sail, rigging and all the bits. Otherwise known as an aerodynamic drag fest.

I sail and sometimes I fly gliders, I am aware of the comparison.

Wing sailor
What I think about glider wings compared to sails isn't really relevant - what is relevant is the opinion of world-renowned experts like MIT aerodynamics professor Mark Drela. He's said "Thin airfoils are capable of the highest CL and CL/CD values.....such a thin airfoil is pretty much out of the question on an airplane, even before structural consideration are brought in. But a soft sail allows the possibility of changing the camber of a thin airfoil, which can greatly extend the low-drag range if done appropriately. So a thin airfoil which always has the appropriate camber shape dialed in at any given operating point will in general be superior to a thick airfoil. "

Prof Drela is a designer of the wings of the world-record holding human-powered aircraft and the world record-holding human-powered hydrofoil and he was involved in the design of America's Cup winning wingsails. He also points out that "What type of wing or sail is best for any type of vehicle depends a great deal on what dominates the drag of the vehicle...On a sailplane, the D_wingsail (wing profile + induced drags) is nearly everything. D_parasite (fuselage + tail) is tiny by comparison. So L/D ~ L / D_wingsail
which is maximized with a slender cantilever wing like you see on any sailplane.

But on a sailboat, D_parasite (hull hydro + aero drags) is huge by comparison. So to maximize L/D you want a large lift L to "dilute" this large D_parasite, even if D_wingsail is also made large as a result. Large lift naturally favors multi-element sails, for all the reasons listed by AMO Smith. This is especially the case if the sail area is constrained by rules or whatever."


So one of the world's leading experts in the field points out that what works for a glider will not normally work for a sailboat, although some foilers are getting close to the right regime.

There are of course also many other factors. Gliders are not interface vehicles, with all that means in terms of wind sheer across the span. They do not spend a lot of time with an apparent airspeed of 5 knots or less, nor does their angle of attack change dramatically for long periods as with a boat.

All of these remarks have to be seen in context of the very big claims made for wingsails. Derek Kelsall writes that Walker claimed that the wing sail "would change sailing for ever and for the better'. Walker claimed 150 of the 47 footers would be sold each year.The total production of yachts over 45ft, in UK at the time was less than half this number."

Finally, I'm still puzzled about one thing that I've never had an answer about - if wingsails work so much better on offshore-style boats, then why hasn't one of them turned up to one of the many races that would welcome them and beaten the conventional boats? They've been around for decades now - why not go out and demonstrate the claims on the water instead of on the internet?
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