Mr Fussy, hey Bugs that's perfect name as your sail making skills are awesome.
The 34.04 knots on a borrowed Bugs sail in 1989 Tangomoana for a then 75kg proves your ability.
The Bugs Sails 4.5 & 4m you made for Glenory were sweet, fast and easy to sail, just didn't get the NW wind for speed sailing.
Then the Hot Sails Maui era was great to be involved at the same factory.
Hope all good cheers Greg

sailquik said..
I was talking to Mal Wright about his fin design analysis software (Finmaker) yesterday. I wonder of it could handle the shape of a sail?

He says probably not.

sailquik said..

I wonder if it is partly because, recently, research into this stuff is done in computer models and mathematics so there is nothing interesting to show that would make much sense to the general public, especially if it is done for a private investor?

That's pretty much the case. When I was involved in the America's Cup in 2007 teams were using CFD, but were also doing extensive towing tank and wind tunnel testing. By the 2013 America's Cup, the top teams were doing everything with CFD, primarily RANS (Reynolds Averaged Navier-Stokes) codes such as Fluent or Fine Marine, as well as potential flow methods such as Splash.

If you want to try out some serious CFD yourself you can download OpenFOAM (www.openfoam.com/download/), an open source CFD code, but be warned, it's a bear.

sailquik said..

Pacey said..
If you want to try out some serious CFD yourself you can download OpenFOAM (www.openfoam.com/download/), an open source CFD code, but be warned, it's a bear.

Thanks Andrew. You are right. It is daunting just trying to work out how to install and run it, and I haven't even got to the program itself! I think I'll pass.....

If you don't know enough to write your own CFD code you probably won't get the right answer from a canned program anyway. For example, canned statistical programs are misapplied and misinterpreted more often than not, particularly in the soft sciences like biology. About the only ones that get statistics right are insurance companies and high stakes gamblers - because their survival depends on it. It has been said that 90% of the statistics quoted by politicians in interviews are made up on the spot.

barney831 said..
It has been said that 90% of the statistics quoted by politicians in interviews are made up on the spot.

Did you just make that up ?

-12 percent less wing area than the comparable elliptical spanload wing

link:
technology-afrc.ndc.nasa.gov/featurestory/prandtl-wing-design

Pacey said..

sailquik said..

I wonder if it is partly because, recently, research into this stuff is done in computer models and mathematics so there is nothing interesting to show that would make much sense to the general public, especially if it is done for a private investor?

That's pretty much the case. When I was involved in the America's Cup in 2007 teams were using CFD, but were also doing extensive towing tank and wind tunnel testing. By the 2013 America's Cup, the top teams were doing everything with CFD, primarily RANS (Reynolds Averaged Navier-Stokes) codes such as Fluent or Fine Marine, as well as potential flow methods such as Splash.

If you want to try out some serious CFD yourself you can download OpenFOAM (www.openfoam.com/download/), an open source CFD code, but be warned, it's a bear.

RANS!
Reynolds had been dead and gone for so long before acronyms came into usage you would have had to have spelled it out for him as well.

en.wikipedia.org/wiki/Reynolds-averaged_Navier-Stokes_equations

Apparently Feynman spent years mulling over the turbulence issue and gave up.

`Turbulence is the most important unsolved problem of classical physics.'

- Richard Feynman -


But I suppose as computers get bigger and faster they can push the averaging cutoff down and down.

How well do the modern CFD programs predict the specifics of what we see in the old video. Do they nail the transition to turbulence, the exact outline of the turbulent boundary layer? The friction in the boundary layer etc.?

yoyo said..
from Sailquik's link

"The new wing has 22 percent more span and 11 percent less area, resulting in an immediate 12 percent drag reduction."

If you reduce the area 11% you get an 11% drag reduction. If you increase span 22% you increase lift in relation to area. So you get back to the original lift with the extra 11% area. The only magic here is the USPTO allows you to patent non-new and non-novel ideas which all other countries would not.

I thought it was implied that lift remained the same without having to go back to the original wing area? The premise is that the Bell curve slantwise flow change reduces induced drag for the tip vortex.

sailquik said..
The US government claims a Patent on this wing design!!

And even their own patent design produces unequivocal evidence of 'prior art' quoting it was actually 'invented ' by Prandtl and Horten Bros up to 80 years ago!

When I went to work at the Boeing Scientific Research Lab in the '60s, one of the old timers said to me;
'Barney, it doesn't matter how smart you think you are;
it doesn't matter how smart you really are;
when it comes to aviation there is nothing that hasn't been tried.'

I remember that like it was yesterday.

Floppy head=no tip vortex

Downwash gives downward velocity component in the free-stream ahead of the wing, at the wing and far downstream.
Here you can see how downwash (caused by tip vortex)behind wing,change local realtive airflow infront wing.This " new" airflow is now effective airflow which wing "feels" it.Wing AoA is reduced and lift vector is tilted back causing more drag.This is induced drag.
This is reason why we must decrease vortex on sail tip,one way to do this is have floppy head,because floppy head is indication that leeward and windward sail pressure is almost equal , so we minimize tip vortex.
It is very counter intuitive how downwash behind wing can change airflow infront wing,but this is way it goes in real 3D wing/sail.

I actually had a chance to do some small amount of experimenting last Friday.
I had been playing with a prototype 5.2m speed sail and rigging it on different combinations of masts , comparing it with the production sail that was actually evolved from it and is extremely close in shape.
I had discovered that I could rig it with extreme twist, but still keep the draft depth the same in the bottom half of the sail using different masts. There was quite a lot of difference between the two sails, one rigged normally on the standard mast, and the other rigged to the extreme. So this was an experiment I could do that might tell me something.

My intention was to rig both sails and try them side by side. Unfortunately, eagerness to get on the water (watching the perfect squalls come though while rigging) sabotaged my experiment and by the time I had rigged my 4.7m (normally) and the 5.2m at the extreme, I lost patience and hit the water with the 5.2m. The irony is that I still missed the best early wind.

But, I did get a few good squalls witch I thought should have yeilded more speed. The rig just did not feel 'fast' and my speeds concurred. Not only that, but it did not feel particularly stable either. I was fighting the rig on the square run in and when I hit the course, it didn't feel good, powerful or fast. I perservered for a few runs to make sure it was not just me or the conditions, but eventually got frustrated with it.

Now I had a problem, as I had not rigged the standard sail for comparison, and I knew that I didn't want to waste time doing that now in case I missed the next good squall. So I grabbed the 4.7m, which was looking really nice , hoping the wind would continue to strengthen so I would have enough for the smaller sail.

As luck would have it, that is exactly what happened!

The next good squall was my best run of the day by quite a margin, and this sail felt great. A few more runs in lesser squalls confirmed it beyond doubt. The 'extreme twist' rigged sail just didnt work as well as the standard one, even though the latter was half a meter smaller.

I am sure I will have to repeat the experiment using both the 5.2's, but I am pretty confident that the extremely twisted set sail did not work as well. I noted that the more extreme twist I got, the more 'static' the twist became, and I think that was a important factor as well.

But I think this was a great finding. Sometimes the only way to be sure about an experiment or idea is to take it to the extreme. Yes, that was too far. All the theory in the world is great, but in the end one still has to test the ideas in the real world.

Ticked that off, now to try some other slightly different things.

Funny, I did the same. Went with a 18 at the start (46 kt fin) and just couldn't get it and crashed a few times. Swapped to a 21.5 board came up and got my fastest times. I don't know that Friday was a good test day. Fun and brutal but couldn't measure much from it. I did think about weight but the lulls killed that idea

barney831 said..
Optimum sail twist is a function of board speed to wind speed ratio (aka Foehn Number; Kenney 2001). When hyperwind sailing at high Foehn Numbers, the optimum twist is zero.

Windsurfers are not very efficient and generally sail at less than Foehn Number 1.5. The optimum sail twist with height for a windsurfer can be calculated if both the board speed and wind gradient (increase in wind speed with height) are measured. Alternatively, a typical spanwise sail twist distribution can be calculated for a typical board speed and typical wind gradient in order to get a feeling for the order of magnitude of optimum twist (i.e. how much twist is too much).

Here is some hyperwind sailing data collected while out for an afternoon sail; not a speed trial.

Conditions:
- light winds typically 8 to 10 knots; 10 knots was used as input to the numerical model computing the maximum speed polars (blue lines on the polar plot)

Results: plotted with GPSResults

- 3.4 sq m sail; ZERO twist; ZERO camber
- GT-31 gps speed data are the red circles on the polar plot
- max speed measured was 37 knots

Ref: Kenney, B.C., 2001. Hyperwind Sailing, Catalyst, J. Am. Yacht Res. Soc., 6, 24-26.

Hi Barney,

Took me a while to ponder over this.

Am assuming that your statement about twist in the first line is in reference to Elliptical span load lift distribution and Gradient.

If this is the case, using a bell shaped lift distribution with perhaps a slightly taller, higher aspect sail, and some twist will change that.

I pointed out in another post some reasons why I don't think wind gradient is a significant factor in speed windsurfing in many of the very flat terrain places we sail. Perhaps this would be true of many ice lake venues also?

That begs the quesion of if, in the high (water) drag environment windsurfing tends to inhabit, (closer to 1:1.25 true wind to speed ratios at top speed) the low centre of effort in the sail, and the drag reduction from something like the Prandl model make more difference?

^^ Thats very interesting reading! So solar wind, if i remember correctly Arthur C Clarke wrote about that when i was a kid. Stuck in my mind since then. The piece i read was related to space n zero gravity. But it does exist here on our planet? Wow!!

The fact that a windsurfer once held the world speed record is a testement to how slow almost all other sailing boats still are.

The big foiling cats a trimarans will top out at around 50 knots, hitting the cavitation wall, unless they can figure out how to make supercavitating foils work

Sailrocket is substantially more different from 'sail boats' and 'foiling boats' than even a windsurfer is. They have blown the records out of the water. It has reinvented what we think of as 'sailing'. Their record will be untouched for decades, if not longer.

I just want to get as close to 50kts as I can. Hell, I would be over the moon to even get another PB at my age!