Anti Vortex Panels

[Meanz Beanz]

KDesigns Anti Vortex Panels.

http://www.ikarus342000.com/Avorart.htm

What do you think?

[champ0815]

Wouldn't it be more efficient to position the panels on the outside of the hulls to prevent the flow to the low pressure side, rather than "just" guiding the flow?

[Meanz Beanz]

I really don't know, I am kinda suprised that they work at all and I was hoping to get some informed opinion. If they work as well as LARS they could be a good option in some cases, but ?

[RHough]

Originally Posted by Meanz Beanz

I really don't know, I am kinda suprised that they work at all and I was hoping to get some informed opinion. If they work as well as LARS they could be a good option in some cases, but ?

Located inboard makes them work (if they do). The high pressure is outboard on the leeward hull, and the vortex this gimmick is trying to reduce/prevent is on the windward side. It looks to me like they are treating the leeward hull as very stubby wing and the Anti Vortex frap/thingy/whatever as a winglet. I think they might improve a very bad hull, but they aren't going to make a boat sail as high as if it had daggerboards.

You pay an increased surface area drag and an intersection drag penalty all the time, nit just when the hull is trying to lift to weather. There was a debate some time ago that had people claiming that just the lateral resistance being higher than the forward resistance is what allowed ships to make good to weather, that they went forward easily (compared to sideways) and that was enough to get them to sail into the wind.

I don't know of a body of research on extremely low A:R foils (as a hull would be) I know that 'conventional' foil theory works like a damn in the 4-8 A:R range and gets goofy below that. The 1/4 chord Mean Aero Centre is one of the things that moves at low A:R (closer to 50% or 1/2 chord) at A:R = 1.5 or so (keels).

I don't think the information provided is enough to say for sure, but it has enough of the "it works on airplanes, therefore it must also work ..." smell to it that I tend not to believe it.

[Meanz Beanz]

Thanks for that Retro Dude!

The designer is the only one that I can find who has trialed it and commented on the web so its not what you call unbiased.

The KD860 has them and is being put into production in Turkey...

http://ikarus342000.com/P86page.htm

http://www.kesmarin.com/index.htm

Might be one to keep an eye on ? You never know

[Meanz Beanz]

The hulls have the proven trapezoid cross section as the PELICAN. For wind ward performance the boat has anti-vortex panels. These work a lot better as low aspect ratio keels and are not as prone to damage as boards. Besides, whay spoil one of the best advantages of a multi hull, low draft, to enter coves etc a keel boat never can enter?

I think that the shape of the hull is important, somewhere he makes a comment about not being sure if they would work well with a rounded bilge section.

[marshmat]

The fundamental principle appears to be similar to that responsible for the vertical winglets on modern airliners, and for the winged keel bulbs of some racing yachts. It is a fundamentally sound and potentially very effective concept, albeit one that is not easy to implement well. A good engineering solution? Possibly. Good CFD flow fields will be necessary to really get the most out of the concept; guesswork alone wouldn't be enough.

[RHough]

Originally Posted by marshmat

The fundamental principle appears to be similar to that responsible for the vertical winglets on modern airliners, and for the winged keel bulbs of some racing yachts. It is a fundamentally sound and potentially very effective concept, albeit one that is not easy to implement well. A good engineering solution? Possibly. Good CFD flow fields will be necessary to really get the most out of the concept; guesswork alone wouldn't be enough.

I agree, going to take some high priced testing or simulation to prove that they work ...

I also think that if you mounted them vertically instead of horizontally, you would have two itty-bitty dagger boards that would do more to limit leeway and have less drag than mounting them in the anti-vortex position.

As far as the horizontal mounting keeping the draft shallow ... don't they look a little bit like anchor flukes? What kind of stress will they see of you beach the cat then try to back off?

I'll bet if you put golf ball dimples on them they would work even better ...

Sorry ... I'll stop ...

[Meanz Beanz]

I think dimples only work for spheres

[Meanz Beanz]

Originally Posted by marshmat

The fundamental principle appears to be similar to that responsible for the vertical winglets on modern airliners, and for the winged keel bulbs of some racing yachts. It is a fundamentally sound and potentially very effective concept, albeit one that is not easy to implement well. A good engineering solution? Possibly. Good CFD flow fields will be necessary to really get the most out of the concept; guesswork alone wouldn't be enough.

Thanks Matt. Its one I will keep tabs on out of curiosity more than anything else.

[bobg3723]

Originally Posted by RHough

I'll bet if you put golf ball dimples on them they would work even better ...

Sharks skins been theorized to do for undwater bodies what the Bournoulii Effect does for golf balls in flight.

Bob

[Richard Woods]

I tried them 20 years ago on a Strider Club. Sailing against sister ships there didn't seem to be any real advantage. However I was always nervous about drying out and I couldn't scrub the bottom of the wing without jacking the boat up.

So I never used them again. If you want a good windward sailing boat use daggerboards.

I once asked a highly qualified aircraft designer about the winglets seen on, for example, the 747 - 400. He said they were more of a marketing gimmick more than anything else.

Hope that helps

Richard Woods of Woods Designs

www.sailingcatamarans.com

[RHough]

Originally Posted by bobg3723

Sharks skins been theorized to do for undwater bodies what the Bournoulii Effect does for golf balls in flight.

Bob

Oh goodie, that means my stock in Flying Hog Airlines is worth something?

Yes, boundary layer control (dimples, sharks skin, 3M riblets) can have a positive effect under very specific conditions. In the case of a golf ball, attached turbulent flow has less drag than separated flow at the speed a golf ball flies in air. The sharks skin idea lead to rubber bottom paint that was v e r y s l o w on racing sailboats. The 3M riblets worked to reduce the thickness of the turbulent boundary layer on a 12 Meter sailboat around 1.34 S/L ratio. None of the ideas seem to work for all the applications that the ideas have been patented for or outside the operating conditions for which they were designed.

Most of this stuff is junk science. The Anti-Vortex Plates, might work ... if they are sized exactly right and placed in exactly the right place and the boat sails at the right speed and has the right leeway angle. Wing tip plates and winglets work on airliners because they are designed to work at cruise speed. This speed is known and the winglet can be designed to counter the vortex that occurs in that flight condition. They do not operate close to a free surface and are not subject to the changes in pitch and the heave motion that these plates are working in. Sailing is far from a near steady-state condition. The change in the angle of the local flow as the hull rises and falls in each wave is going to change size and shape of the vortex that the plate is trying to control, in fact as the boat pitches and heaves in a seaway they may create a vortex that didn't exist before they were added. Not enough data to say, but I'm a doubter.

[Meanz Beanz]

The sister ships you where sailing against, what did they have LAR keels or dagger boards? When you say no real advantage that implies that they where as fast, is that right?

Thanks for the reply, at least you have sailed with them!

Cheers
MBz

[Meanz Beanz]

Originally Posted by RHough

Most of this stuff is junk science. The Anti-Vortex Plates, might work ... if they are sized exactly right and placed in exactly the right place and the boat sails at the right speed and has the right leeway angle. Wing tip plates and winglets work on airliners because they are designed to work at cruise speed. This speed is known and the winglet can be designed to counter the vortex that occurs in that flight condition. They do not operate close to a free surface and are not subject to the changes in pitch and the heave motion that these plates are working in. Sailing is far from a near steady-state condition. The change in the angle of the local flow as the hull rises and falls in each wave is going to change size and shape of the vortex that the plate is trying to control, in fact as the boat pitches and heaves in a seaway they may create a vortex that didn't exist before they were added. Not enough data to say, but I'm a doubter.

Good points!