Anti Vortex Panels

Discussion in 'Multihulls' started by Meanz Beanz, May 28, 2008.

  1. Meanz Beanz
    Joined: Jun 2007
    Posts: 2,280
    Likes: 33, Points: 0, Legacy Rep: 585
    Location: Lower East ?

    Meanz Beanz Boom Doom Gloom Boom

  2. champ0815
    Joined: Apr 2008
    Posts: 117
    Likes: 6, Points: 18, Legacy Rep: 56
    Location: Munich, Germany

    champ0815 Senior Member

    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?
     
  3. Meanz Beanz
    Joined: Jun 2007
    Posts: 2,280
    Likes: 33, Points: 0, Legacy Rep: 585
    Location: Lower East ?

    Meanz Beanz Boom Doom Gloom Boom

    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 ?
     
  4. RHough
    Joined: Nov 2005
    Posts: 1,792
    Likes: 61, Points: 0, Legacy Rep: 793
    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    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.
     
  5. Meanz Beanz
    Joined: Jun 2007
    Posts: 2,280
    Likes: 33, Points: 0, Legacy Rep: 585
    Location: Lower East ?

    Meanz Beanz Boom Doom Gloom Boom

  6. Meanz Beanz
    Joined: Jun 2007
    Posts: 2,280
    Likes: 33, Points: 0, Legacy Rep: 585
    Location: Lower East ?

    Meanz Beanz Boom Doom Gloom Boom

    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.
     
  7. marshmat
    Joined: Apr 2005
    Posts: 4,127
    Likes: 149, Points: 63, Legacy Rep: 2043
    Location: Ontario

    marshmat Senior Member

    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.
     
  8. RHough
    Joined: Nov 2005
    Posts: 1,792
    Likes: 61, Points: 0, Legacy Rep: 793
    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    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. :D

    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 ... :(
     
    1 person likes this.
  9. Meanz Beanz
    Joined: Jun 2007
    Posts: 2,280
    Likes: 33, Points: 0, Legacy Rep: 585
    Location: Lower East ?

    Meanz Beanz Boom Doom Gloom Boom

    I think dimples only work for spheres :D
     
  10. Meanz Beanz
    Joined: Jun 2007
    Posts: 2,280
    Likes: 33, Points: 0, Legacy Rep: 585
    Location: Lower East ?

    Meanz Beanz Boom Doom Gloom Boom

    Thanks Matt. Its one I will keep tabs on out of curiosity more than anything else.
     
  11. bobg3723
    Joined: Aug 2005
    Posts: 278
    Likes: 7, Points: 18, Legacy Rep: 95
    Location: Crystal, MN - USA

    bobg3723 Senior Member

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

    Bob
     
  12. Richard Woods
    Joined: Jun 2006
    Posts: 2,209
    Likes: 175, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    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
     
  13. RHough
    Joined: Nov 2005
    Posts: 1,792
    Likes: 61, Points: 0, Legacy Rep: 793
    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    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.
     
    1 person likes this.
  14. Meanz Beanz
    Joined: Jun 2007
    Posts: 2,280
    Likes: 33, Points: 0, Legacy Rep: 585
    Location: Lower East ?

    Meanz Beanz Boom Doom Gloom Boom

    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
     

  15. Meanz Beanz
    Joined: Jun 2007
    Posts: 2,280
    Likes: 33, Points: 0, Legacy Rep: 585
    Location: Lower East ?

    Meanz Beanz Boom Doom Gloom Boom

    Good points!
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.