Interesting story on Sailing Anarchy today about the serations on Humpback fins. Seemes these bumps improve lift efficiency ~20% and there's a company exploring application to all sorts of blades...wind turbines, fans & sailboat masts/blades included.

Humpback Tech

I read that but didn't think they increased overall efficiency but they were proposed to be more efficient at high angles of attack and to enable a foil a higher angle of attack before stalling.

Airplanes have been using something similar for years, they call them vortex generators, they help keep the flow attached at high angles of attack, for more lift and a lower stall speed, but they do not make you go faster.

DC and the boys tried some ribbed stick on plastic sheets on the bottom of their AC boats some years back, I don't know if they ever decided it was much faster or not.

From the WhalePower company's website:

"The 16 degree stall angle found in the first wind tunnel experiment has been enhanced to produce airfoils that don't stall until they reach an astounding 31 degrees - far above anything previously known.
Unlike virtually every other airfoil which can stall violently and even damage the machines they‘re employed on, tubercle airfoils always stall gradually. That changes the rules for turbines -- forever. "

So, they might be helpful on sails and rudders more than daggerboards...
Those 'tubercles' might lessen the consequences of over-sheeting (probably except heeling moment).
Interesting invention!

less-so on rudders. You need high efficiency at relatively low angles of attack for rudders. Increased stall resistance isn't that beneficial if you're trading off straight line efficiency.

You might be able to use a smaller, higher aspect rudder blade if stall point is improved compared to rraditional designs.

Finally! the secret weapon I have been waiting for! That elusive adjantage that has thus far eluded me. now as soon as i learn to keep a consistant course and stop teabagging each time i make a 'minor' adjustment i will be UNSTOPPABLE.

Another victory for science following the lead of nature! Wouter I think you told me I was intellectually challenged for pushing this idea as I remember. Can't imagine you would have told the wright brothers that about the bird wing.
So tell me why your math and aerodynamic/hydrodynamic genius, experience and arrogance has not come up with this most basic understanding of "leading edge" (excuse the pun) sailing understanding....cause I know you know it all...just been keeping this under the bed?

: )

luv it when that happens.

One of the simplest and most interesting vortex generation tricks I saw was used on a sailplane. It was an adhesive strip similar to the fabric part of velcro with rounded serrations on one edge. The strip was placed serrated edge forwards just before main camber point near the leading edge of the wings.

Another one (from the book "More Sail Trim" edited by Anne Madden)was the placement of rows of offset holes (approx 1/4") placed at approx 1/3 (I think) chord in the sail. The air leakage created stabilising vortices on the leeward side delaying separation of the flow and hence turbulent drag. The sails apparently demonstrated greater tolerance to poor sail trim and enabled the boat to point higher.

Cheshirecatman

Same example for pipe organs, they put grooves on the pipes where the air escapes and sound eminates...if they don't, the airflow is not laminar (smooth flowing and straight) and the sound 'wobbles'. It seems to be true for any fluid, including water.

Please provide me with a link to the actual post containing that quote. I don't remember saying anything to that extent and it is not in line with my general thinking to disgard such a biosphere derived technology.

I do remember calling you intellectually challenged on many other occasions where you indeed made very awkward conclusions that often went almost directly against common sense. Sadly this situation is not one of those in my opinion.





You can just as well claim that Einstein was a dumb [censored] as he didn't invent or predict the rise of the personal computer !

A single person can only do so much in one life time and aerodynamics is NOT my engineering speciality. That is despite the fact that I know more about aero and hydro dynamics then 95% of the forum people out there.

You guys also "invent" to much Wouterisms, I have never said anything negative or discouraging about these humpback whale fins or technologies derived from it. You may think or wish that I have but I didn't.

I'm sure you are just on your knees begging for a occurance where something I said is proven wrong in no unmistakenable terms just so you leverage that to invalidate all that I've wrote and said over many years. This wish is much more associated with your personal frustration than any significant likelyhood of me being wrong in real life.

If this makes you sleep better at night to I guess it is harmless enough, but I will repeat what I said to you several weeks ago. Ignoring what I say and write or simply discarting it because I said it will only make a larger fool of yourself. You may well hate me for whatever reasons you may have but that still doesn't mean that what I write and say are any less scientifically true.

Good night !

Wouter

Air injection has been under extensive research on airplane wings; in search of various benefits.

Trip turbulators like your adhesive strip have found application as far as the suits that speed skaters use on the 400 meter icy oval.

Neither of these idea's is very young. I personally learned about them back in the earlier 90's.

Personally, I do not see the benefits of a higher stall angle on a racing sailboat. A good sailor, that you have to be to win a race anyway, is already capable of keeping the mainsail out of being stalled.

Based on what I read so far with respect to sails, none of them experience fully laminair boundery layers along the full length of the sails anyway. It is my initial expectation that going for a full turbulant boundery layer along the cord of sail will not lead to significantly large benefits. It may make poorly skilled sailors better by having them stall the sail less but may not do much at all for skilled sailors.

Mind you the guys are testing the humpback whale fin for windturbines where indeed the proces of stalling a portion of the wing can be very serious. If is often associate with large and rapidly changing force changes at the root of the blades and the drive train in the hub of the windturbine. The turbines are getting so large that these effects can seriously damage the windturbine or its blades. So here a very large stall angle is not an efficiently improving principle per se but rather an improvement in dependability - low maintaince requirement.

Still, very interesting research. I'm awaiting their first official paper. Wouldn't be the first time where scientists promise to turn lead into cold and where their officially peer reviewed paper falls "slightly short" of that.

Wouter

I can do that. Just put the lead in the freezer and it "turns into cold". <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />

Everybody makes mistakes. They don't necessarily invalidate other statements, especially unrelated ones.

According to Wikipedia transmutation is possible, only too expensive. Check the article in wikipedia from which the following quote and reference were extracted:

Wouter
Surely off the wind the technology is relevant. Trying to keep flow attached to the main on a broad reach is the whole trick, and the drag penalty of turbulators is acceptable because of the vector direction of it?
In practical terms, wouldn't some course stitching about a foot or two from the leading edge of a spin. maybe help as a trip?

Alternative, you could direct your halyards (main and spinnaker) up the side of your mast. Wires have been used to "trip the boundary layer" on scale model ship towing tank tests.

Using turbulence over the low pressure side of a foil to create greater lift at high angles of attack (or increase angle of attack before stalling) is already implemented on atleast one plane, the F16.

Well you hit that one like a Mako shark Wouter. Thanks. : )

Concorde can't land or take off without such vortices.

It is used on many figther planes now.

Wouter

Actually, Concorde can't land or take off ever again without big $$$ <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />