Wing-drive

Thanks for your information.
According to my calculation this is the speed-power figures for your Catamaran.

LWL= 11 meters. Weight = 7.5 ton.
S/L Ratio Boat Speed knots Power BHP
0.94 5.4 3.8
1.09 6.3 7.6
1.28 7.2 15.0
1.32 7.6 22.7
1.40 8.1 30.7

To obtain these speeds this power has to be produced by the wings.
The power a wing can produce per sq/met of wing at Coef,1.0 is approx.

Wind Speed knots HP /sq/met.
5 0.05
10 0.22
15 0.5
20 0.89
25 1.39
If you have 2 X 220 sq/ft symmetrical wings in the Wing-Drive it will give you 4-5 knots in light wind and power to reach hull speed in 20 knots wind.

If you wings have higher Coef. It is easy to calculate how many sq/met you need.

Wing-Drive has two wings to be able to have the sufficient wing aria without the capsizing risk of a high rig.

Kjell Dahlberg

 

440ft^2 vs 860ft^2

440 x 1.0 x .0012 x v^2 vs

860 x 2.0 x .0012 x v^2

440 x 1.0 x .0012 = .528, so force = .528 x v^2

860 x 2.0 x .0012 = 2.064, so force = 2.064 x v^2

Since v^2 is the same, at any wind speed the soft sails produce almost 4 times the force of the wing sail.

At any speed below hull speed the soft sails will be faster, since they have 4 times the power.

If the Wing Drive needs 20 knots to reach hull speed it works out to 20^2 x 0.528 or 211.2. The soft sails have enough power to reach hull speed in only 10.1 knots.

What am I missing? How is the Wing-Drive more efficient?

I think that the concept of using a lightly loaded trim tab control to adjust and maintain the AOA of the foils is elegant. Every year older I am the less I like grinding sheets on every tack. A low effort, self tacking rig would be wonderful.

That said, the claims I've read about wing sails being more efficient and having lower drag when weathercocking are wishful thinking at best and intentionally misleading at worst.

Lift is always 90deg to the free stream direction. Wing or soft sail no matter. Since lift is area x coef x density x velocity^2, a symmetric section of max CL = 1.0 would have to have twice the area of a cambered section of max CL 2.0. Soft sails reach CL 2.0 for main and jib every day.

Off the wind the advantage to soft sails is even greater. Off-wind sails operate at CL as high as 2.6 and in many cases the sail area is more than doubled. Now the 440ft^2 at CL=1 is competing against 1720ft^2 at CL=2.5. The soft sails have almost a 10 to 1 advantage in power.

IIRC the average wind speed on the planet is about 10 knots, thus a properly sized sail plan must be able to drive the boat at close to hull speed in 5 knots apparent downwind and 12-15 knots apparent upwind. I just don't see how a fixed area rig with no camber adjustment can hope to compete against a rig that has variable area and camber.

 

How often can you keep the sails trimmed to the optimum AoA while the boat is chancing course?
How big sail can you use in + 20 knots of apparent wind speed?
May I ask you how big engine do you have in your catamaran?

 

I don't wish to argue. I have no problem trimming sails.

Upwind I can carry a full main and a 150% LP Genoa in 20 Apparent (about 15 true)

Downwind I can carry full main and spinnaker in 20 Apparent (about 27 knots true if DDW).

Sailboats don't have engines.

 

Many thanks for all your information. I understand that you are a real cloth sailor and you don’t need a Wing-Drive.

 

Nice exchange, RHough. It's always nice to see how things really work.

 

When something sounds to good to be true it usually is not true.

The claim that for equal power the wing has smaller area is not true.

Since for equal power at 1/2 the CL you need 2x the area.

The 1/2 area wing was tested in a wind tunnel and has 90% of the drag of the full sized bare rig.

For a real comparison, you need a wing rig with twice the area and not half. If half the area has 90% of the drag, then twice the area will have 4 x 90% or 360% of the drag of a equal power soft rig.

Ease of use is obvious, lower risk of capsize is also obvious (only 1/4 the power). The verifiable features are cast into doubt by the obviously false claims.

What concerns me is the claim that the fully rigged craft can be berthed or moored with the wing in place. As long as the 1/4 power 1/2 area scale is used I have no reason to doubt the 90% drag claim. However, a full sized wing rig (double the area and 360% of the drag when moored) would become a hazard in any anchorage or marina.

I'm not convinced that the rigged wing could react quickly enough to keep the drive force at zero or near zero in the violent eddies that exist in marinas during storms. Given the voracity of the other claims I'm inclined to doubt this one too.

 

You say that you don’t like to argue. I think it is good to argue about important things.
I think you only compare power number but how about the safety onboard. What will happen with your boat if you had the need of making a suddenly +45 degree course change when you riding the main sail and the spinnaker in 27 knots wind? With the Wing-Drive you can make any course changes without the need of alter the set wing angle. I think this is a point to keep in mind.

 

Sceptical as I am about most of the claims here, as in my earlier post, I have to say that if Mr Hough really believes a soft sail is more efficient than a solid rig then he desperately needs to get out more.

 

I think the Wing Drive has many good features. The automatic reaction to changes in wind sped and angles is one of them. I like the idea, I think it has merit and has practical applications.

I took issue with some of the hyped-up statements that have been posted. The design is good, let it stand on the merits it has. Don't cloud the good points with obvious hype.

 

I aggree. Hype is a bad thing. Look, for example, at what americans still bull about today: man on the moon...
If that is not mass histeria, nothing is.
Hype is bad.
And get metres in you as well. I just measured my foot and it came out that your boat was 14 metres long...

You wish.

 

LOL ... since I never said that (nor do I think it) I'll offer to meet you at the library. We can work on reading comprehension and basic aerodynamics.

What I stated and supported with numbers is: A wing sail that works at CL of 1 cannot produce as much force as a soft sail working at a CL of 2 if both have the same area.

Multi-element cambered wings are completely different from the two symmetrical foils used in the Wing Drive.

For equal area, a wing sail can certainly be designed to have as much or more lift with less drag than a soft sail. I never said otherwise.

You are absolutely correct, I need to get out more. It's 4C, pissing down rain, my boat is on the hard getting a major refit and I've been swamped at work ...

 

Delusional a bit as well, aren't we? As you can see from the above quote, you actually DID say it.


Al the while forgetting that Kjell is emphasising SAFETY!!!!!!!!!!!!!, not the speed. He does recognise that to match standard rig's power you need TWO wings, because symmetrical wings do not create much of a lift.

What's with all this obsession with speed down North side of the globe? Where are you balooneys are rushing to? Showing off your meagre knowledge by talking nonsense around? The difference between a rug on a mast and a superefficient cloth sail is a couple of knots. Like that matters if your boat is 7.5 tonns!

 

Thanks for this opinion.
I think that the use of Wing-Drive can open up the possibility for people that like to make long trip with their boat without the need to have strong skilled sailors onboard.

 

Did say what?, at least quote what you are trying to dispute. I said that a half sized wing cannot produce as much force as a full sized soft rig. I never said that a soft rig of equal size is more efficient than a hard sail.

I never ignored the safety aspect. In fact I complimented some features of the design. Kjell is the one that said the two wings had less total area than the "rug on a mast" He also did not dispute the fact that the smaller area at lower lift could not produce as much power as a standard rig. Who is delusional?

What difference does a couple of knots make? Using Kjell's example of a boat that has a speed of 7.2 knots at S/L = 1.28, 2 knots is 27%. Most people care about a 25%+ loss in speed.

What part of Force = coef x area x density x speed^2 don't you understand? If that is nonsense ... tell NASA.

Why not demonstrate with facts that I've misunderstood something? Why personal attacks?