Anti Vortex Plates instead of boards?

Discussion in 'Hydrodynamics and Aerodynamics' started by DennisRB, Oct 7, 2011.

  1. DennisRB
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    DennisRB Senior Member

    I was looking at Bernd Kohlers Site. I like the simplicity of his designs and his unwillingness to sacrifice performance and seaworthiness for extra cabin space.

    He argues that his antivortex plates used on the bottom of a hard chine/asymetric hull works better than low aspect keels and as good as boards. He says that his cats fitted with these will point as high as any good mono.

    See pdf file on vortex plates

    http://www.ikarus342000.com/Antivortexp.pdf

    [​IMG]

    I quite like this design. Recently I made a thread on a beachable yacht and I liked the compucraft monos, but I think this will be a lot more fun to sail. It would be hard to know if the accommodations would be satisfactory without actually seeing the boat though.

    [​IMG]

    Edit, try this link. If it does not work I have no idea as all the links work when I click on them. Google earch "ikarus designs" to find the site then look up the catamarans, particularly PELICAN and KD860.

    http://www.ikarus342000.com/
     
  2. gonzo
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    gonzo Senior Member

    The links are broken but the photo shows a shallow keel. "Anti-vortex" is a marketing name.
     
  3. DennisRB
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    DennisRB Senior Member

    The links work when I use them? Does anyone else have the prob? You may be mistaking the photo as a hull on its side. What you see in the pic of the "keel", is a hull in the upright position as sailed. What looks like a small keel is in fact horizontal not vertical. See here http://www.ikarus342000.com/Onkran1.jpg

    I agree "anti vortex" does sound like a marketing name. Lets call them endplates, or winglets.
     
  4. Doug Lord
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    Doug Lord Flight Ready

    Dennis, the pdf was ok but the next two don't work right. The one in your last post works ok. There is a thread in Open Discussion about a guy Yrvind(?) who is sailing a very, very small "cruising" boat. He used a variation on these foils. You might check that discussion-it was fairly recent so you shouldn't have to start at the begining.
     
  5. CatBuilder

    CatBuilder Previous Member

    Well, many of the airplanes have them on the wing tips... so maybe.

    I wonder if that guy who used to work at Boeing (sorry, forgot your screen name) will pipe in here and comment.

    I bet he has some valuable input.
     
  6. Petros
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    Petros Senior Member

    These devices are a form of end plate, the idea is to make the whole hull act like a low aspect ratio keel by "end plating" the hull. It seems to work, it is a great idea. It solves a lot of building problems as well accommodations. But it just seems like it would be so inefficient. It would be nice to actually see some comparison with shallow keels, has anyone done tank or CFD tests of these devices?. It seems to me there should be a way of optimizing the shape as well.

    They still would be vulnerable to damage, but not nearly as much as a fin keel. For a cruiser that needs shallow draft is is a great innovation, simple, no moving parts, yeilds a flat bottom hull.
     
  7. DennisRB
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    DennisRB Senior Member

    Try this link. If it does not work I have no idea as all the links work when I click on them. Google earch "ikarus designs" to find the site then look up the catamarans, particularly PELICAN and KD860.

    http://www.ikarus342000.com/

    I like the speed of construction, ease of use and shallow beachable draft.

    I fly and build RC gliders so I know about winglets, endplates and fences. I found that endplates reduce stalling and increase lift at slow speeds, but reduce top speed and create drag at higher speeds. My models are slope soarers where there is a lot of lift energy available, so I am not sure if the comparison is relevant. I found my planes were better without them but less forgiving if flown badly.

    The designer claims an average sailing speed of 9.8K over the 11 years he has owned and lived aboard his Pelican 11.5m cat. Weight is 2.2T plywood hard chine.

    If you think of a hull as a low aspect foil itself. The endplate shown seems too small to do much compared to the same devices on plane wings?
     
  8. Petros
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    Petros Senior Member

    Yes they would be small compared to a winglet, but the hull is already in the water and the idea is to capture a part of the flow to give some "lateral resistance" or sideways lift to counter the wind force.

    Yes it will increase drag, so does a fin keel. The reason you have a keel, or need these "anti-vortex" devices, is so when the wind is blowing the boat sideways you reduce the amount of leeway (or sideways slip). The larger you make these the less it will slip, but the more drag you will have. This is also true of a fin keel, the larger the better to limit sideways slip. Since cruising boats typically have low aspect ratio keels, they have a lot of slip already. But it is not always practical to have a very deep profiled wing keel for everyday cruising, specially if you do not want your anchorages to be limited (and when looking for safe harbor you do not always have a choice). And on smaller pocket cruisers it makes it difficult to trailer, hence the retractable keel, that adds some complexity but also takes up valuable interior space.

    Same concept as a sailplane, but the lift holds up the aircraft. On an aircraft wing the winglets allows a lower aspect ratio wing act like a higher aspect ratio wing. If you have no span limit than it is always far better just to increase the aspect ratio. The very large aircraft like military or 747 have a limited number of airfields where they can safely land, so instead of making the span larger they put on winglets. That is the only place they have an advantage, all the rest used on small buiz-jets are just marketing.

    On a shallow draft sailboat you either get crappy windward performance, or you have a retractable keel, or compromise with something like these devices. For a trailer sailor it is a great invention. A deep keel would be better for performance, but then it would not be good for shallow anchorages, beaching or trailering.

    This in effect is an easy way to eliminate a keel, even if less than ideal in terms of sailing performance. Everything is a compromise, this one has very large benefits for beachable hulls. You will never forget to retract it before heading to the beach.

    And it seems to me that there would be even more benefit if the hull bottom shape and end-plate geometry could be optimized to generate as much lateral force as possible with as little induced and wetted area drag as possible. There are gains to be made I am sure. It will never outperform a deep high aspect ratio fin keel, but it could likely be optimized to perform better than a short stumpy low aspect ratio keel.
     
  9. gonzo
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    gonzo Senior Member

    The link gets me to a website and then it logs out and gives an error message.
     
  10. DennisRB
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    DennisRB Senior Member

    Sorry about the links. They all work when I click them so I do not know what I can do other than to suggest you google earch "ikarus designs" to find the site then look up the catamarans, particularly PELICAN and KD860, if you are still interested.
     
  11. Richard Woods
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    Richard Woods Woods Designs

    I always worry about claims for "breakthroughs" in design. Especially when they are not proven on the race course - the only true test of performance. Any boat is fast on its own.

    9.8 knots as an average cruising speed seems very high. After all Phil Welds 50ft Moxie trimaran only averaged 7.8 when he won the 1980 OSTAR. And that was racing, not cruising, in the N Atlantic where winds are higher than in the Med (where I believe Kohler sails - although I may be wrong about that)

    It seems hard to believe that a small fin can do as well as even a LAR keel

    Over 20 years ago I fitted an end plate to one of my 24ft Strider Club catamarans. In fact the boat I sailed to the USSR in 1989. I sailed in convoy with two identical sister ships for 3000 miles. It's very rare that you get identical boats sailing together even for short distances, never mind thousands of miles. And usually "identical" boats are loaded differently, have different sail makers etc. These boats were all the same and furthermore, the skill level of the sailors was pretty much equal.

    I didn't find and noticeable improvement in performance. However I did find the endplates were prone to damage and it was totally impossible to clean fouling off the bottom of the plates.

    747s flew for years without winglets. They appeared on the 400 version and were the obvious visible difference between the new planes and the old ones.

    I asked a British aircraft designer (also very respected, and chief designer for some famous planes) about the winglets. He told me, as I suspected, that they were a marketing tool.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  12. tom28571
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    tom28571 Senior Member

    This kind of "keel" has been used for years by Matt Layden on several of his designs beginning with Paradox. He has raced in the 300 mile Everglades Challenge and won once, I think. They do not look like they would work as well as they apparently do. I have watched Matt short tacking one of his boats and was surprised at the small amount of leeway. Matt's versions are simply extensions of the flat bottom a few inches on each side. He calls them "chine runners".

    Website: http://www.microcruising.com/pictures.htm

    Details showing the runners http://www.microcruising.com/Sketch1.ht
     
  13. DennisRB
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    DennisRB Senior Member

    Thanks Richard. Thats pretty much what I was thinking. That speed seems way too high. When you mean, endplates on the Strider, do you mean on the boards or hulls? As I understand it the Strider has round hulls with daggerboards? Bernd says that the endplates on the hulls only work with a specific hard chine hull shape.

    Regarding 747 winglets. That is what I heard too in terms of what can be expected by just fitting a generic winglet. However if engineered specifically like these, gains will be had (apparently). However the relative size of these is huge compared to ones on Bernds cats. I wonder if most aircraft designers agree they are a marketing tool?

    [​IMG]
     
  14. DennisRB
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    DennisRB Senior Member

    Thanks tom. There is a thread here on chine runners.

    http://www.boatdesign.net/forums/open-discussion/chine-runners-21394.html

    I think they work more like a normal skeg keel as they dig in when the boat heels (monohull). AFAICT The chine runner that is doing the most work is the one on the leeward side. This is a little different to what Berdn is suggesting. The tiplet that is doing the work is on the windward side of the hull and does not require heel. However you could say that chine runner has a similar effect to a tiplet when the boat is not heeling much, but a mono will heel a lot when sailed to windward. I think we are looking at different but possibly somewhat related effects here.
     

  15. Richard Woods
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    Richard Woods Woods Designs

    The Strider Club had LAR keels and it was on one of those that I fitted the end plates

    That was another interesting test, BTW. The same basic Strider hull and rig, one with a LAR keels the other, original version, with daggerboards. Again very few people really test the differences in isolation. Usually they change other things as well which make any comparisons meaningless.

    For sure the daggerboarded boat is ALWAYS the better sailing boat. There can be no debate about that.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
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