Wing-drive

That is exactly one of it's strong points! On reaching courses that make for the smoothest passages, a Wing-Drive makes very good sense. Particularly for a short handed crew.

Because the effort is reduced, a couple could handle a larger boat. For the same amount of crew effort the larger/longer boat might well make faster passages than a more highly stressed smaller boat.

The larger boat could also be an efficient motor-sailer, and the Wing-Drive would reduce fuel consumption when there is not enough wind to use the wing as the sole source of power.

 

Here's another thing to think about.

The drive force from the sails acts at an angle to the apparent wind. What happens to the drive force when the boat is turned?

If the AoA is 15deg to the apparent wind, the force from the sails acts at some angle greater than 105 degrees to the apparent wind.

When the boat is sailed so the drive force in the direction of travel, 100% of the force is driving the boat. On other headings the only a portion of the sail force is driving the boat, the other portion is heeling the boat.

When the boat is turned 45deg away from the optimum angle of 100% drive, the drive vector is 70% of the total force and the heel vector is 70% of the total force.

If the optimum angle is 105 deg, a heading of 150 apparent or 60 apparent would give a 70% drive vector.

165 or 45 apparent gives a drive vector of 50%

180 or 30 apparent gives a drive vector of about 26%

When the apparent wind is ahead of the beam, the boat's speed adds to the apparent wind speed and compensates for some of the geometric loss with an increase in force due to velocity.

When the apparent wind is behind the beam, the boat's speed reduces the apparent wind speed and the drive force suffers both the geometric reduction and a velocity reduction.

Traditional rigs handle this by adding area when sailing off the wind.

Racing wing sail boats are fast enough to always sail with the apparent wind ahead of the beam.

This would seem to put the fixed area wing sail at a disadvantage if the course sailed ever put the apparent wind very far aft of the beam.

Is this considered when designing a system?

For example, a design point of S/L = .9 at AWA = 165 and 15 knots true wind, the rig would have to be twice as large as a rig designed for AWA = 105.

 

Thanks for starting to understand the reason why I invented the Wing-Drive. To not repeat all what I have been saying. Have a look to #1, #13, #17, #19, #22, #25, #28.

 

Rhough is young but learning. Langtsam aber sicher!

 

My only problem with the idea is the concept of a hard wing. Personally, I would be happy to lose a bit of speed and use a soft wing that I can pull down if I end up in a situation.

Fact is, winds can change their direction very fast. They do not blow from one direction steadily. A pair of solid wings coupled in the same foot would inevitably rotate with the wind. That could be a wild rotation. Forces spreading through the structure of a hull could be large enough even with fairly moderate winds to snap it and make a hole on the top of the cabin. One wave and you are gone.

 

Gentlemen, Lets not get too academic with wingsail vs softsail theory.
Wingsails ,unless incredibly built or sailed would always have more lift because of their thickness , making the wind travel further on the lee side reducing pressure etc etc. With a tail attached or similar they will track apparent wind shifts with remarkable ability. The proof is in sailing them as I have for over 12 years. They are different and behave differently so you relearn sailing techniques as in bearing off angle of attack when climbing high up wind, and leaving other sailors staring in disbelief.
Have another look at my site www.wingsails.net
There is still a romantic feeling with soft sails though and part of the sailors joy is to trim sails but that can be said of a wing too.
As for wind changes and gusts ,after being on a small tri in a gale I'll stick to my wingsail thanks.

 

Respectfully suggest you do some research. The formula for lift is:

Lift = coef x area x density x velocity^2

There is no part of the equation that has anything to to do with thickness/chord ratio. There are literally thousands of pages of airfoil research and data available on line.

What is true is that a thick (12% or so) section may be able to generate a higher CL that a thin section. When a 12% section is compared to a 24% section there in no gain.

I limited my argument to soft sails vs symmetrical wings. Certainly a cambered foil of moderate thickness can have a higher CL max than an uncambered foil.

It is hard to find a single element foil that generates much above 1.6CL, while main/jib combinations routinely generate CL over 2.

There are clear advantages to moderately thick foils and advantages to hard skinned (rather than fabric) foils. No one has brought those up for debate.

 

I haven't read all of this thread in detail, but it seems that RHough is getting some unfair stick. A thick foil does not produce more lift than a thin one. Within reason, a more curved surface does - but that is not the same thing. This link, a paper from Cambridge University (so, a very, very good source), shows that a thin foil produces more lift than a thick one.
http://ej.iop.org/links/q35/tX4w9wXDo8GWBW,dYnR36Q/pe3_6_001 .pdf

 

Kim, have you raced against other small multis much? If you're still on Copeton you'd have no racing would you?

What sort of boats has the wingsail raced against?

 

Not much racing at Copeton and when there are cats around they sail off in a different direction mostly. Have had some runs with others a while ago but have made improvements since. We did take the tri to Yamba in january and ran beside a twilite race of some larger boats up to a Farr f39 and we seemed to be doing well , especially since they were in a channel on a reach and we were climbing to them over sandflats with 2 ft of water in places and with the small wing.
How come you know Copeton? where do you live ,might be able to have a sail 1 day
To RHough .As for doing more research I do mine on the water. Experience is a great teacher, as for the formulas you would have to agree that a wing having thickness has a higher c/l than a sail, yes

 

No, thickness does not create lift.
No, a single symmetrical foil cannot produce as much lift as a main and jib.
No, a single symmetrical foil of smaller area cannot produce as much drive as a main and jib.
No, a single symmetrical foil powered boat will not be as fast as main and jib of equal area.

 

I'm in Sydney but I've always been interested in the country sailing scene....not that there is much of it left with the drought!

When you say "there's not much racing", you imply there is some at Copeton; I thought it had all stopped and even NESC at Malpas was looking bad?

Good to hear there's some sailing there, even more reason to pass through Copeton on my way back from my next trip to Bourke etc!

 

Do you mean that 520 ft^2 Sail has more lift than 520 ft^2 Wing?
Don’t you think you are missing something called angle of incident or AOA?

 

Did you actually read the paper I posted the link to? This shows, quite clearly, that an asymmetric foil (a sail) produces more lift than a symmetrical one (a wing), due to the effect of the windward side of the foil. There are a number of reasons why traditional sails are not as efficient (Lift/Drag ratio, not the same as lift) as glider wings, notably aspect ratio being limited by stability, the interference of the mast, the stretchyness of cloth and less detailed design, but the section shape of a sail does create more lift. Also. all other things being equal the asymmetric foil will operate at a lower angle of attack. A low aspect ratio sail/wing will produce more lift than a high AR one, but at the expense of more drag.

 

Please note - I like the concept of the wingsail/ wingdrive, I just want to clear up any technical quibbles.