The edge of the N 20 ?

Discussion in 'Multihulls' started by Erwan, Dec 3, 2010.

  1. Erwan
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    Erwan Senior Member

    Hi everybody,

    On some other forums, the new Nacra 20 carbon is the subject of dedicated
    threads.

    It is not my purpose as I dont sail this boat. Instead, I would like to bring a boat design perspective.

    Considering all the informations available on the forums, it seems that the Nacra outperforms the Marstrom M20.

    It is common knowledge that the weight is an hudge driver of performance for a cat, especially downwind with the kite.

    If the Nacra Carbon 20 is 170kg and if the Marstrom F20 upgraded with jib is 115kg, then the question is :

    How is it possible such a weight difference can be offseted by other qualities, making the heavier boat faster than the lighter one ?

    Regards to all

    Erwan
     
  2. Doug Lord
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    Doug Lord Flight Ready

    N20

    The Nacra 20 thread is here: http://www.boatdesign.net/forums/multihulls/nacra-20-lifting-foils-29749.html

    It might be that the lifting foils on the Nacra are making the difference though I'm not familiar with the Marstrom-yet.

    UPDATE: checked out the M20-they don't show lifting foils on the website though I'm fairly sure I read about an M20 modified with them. At any rate, that could be the Nacra's performance edge.
     
  3. Erwan
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    Erwan Senior Member

    Thanks Doug,

    I saw the thread, and as mentionned, the M20 as a retrofit option with curved foils, so it is not the discriminant.
    Furthermore, it seems that despite Morelli&Melvin design, its has been developped by Nacra Nederland, and they have used the M20 (all versions)as a benchmark to get a better boat.

    They (not Nacra) used the same approach to design the new A-Cat DNA, using the NIKITA for benchmark.

    That is why the question remains

    regards

    Erwan
     
  4. Doug Lord
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    Doug Lord Flight Ready

    ===================
    Erwan, what is the sail area of the Marstrom with the jib? Been to their site and don't see it....
    Found this on SA:

    Xander Pols won the Round Texel in 07 and 08 and here is what he says about the N20carbon:

    "Hi all! I can say that the new Nacra 20-Carbon is mutch faster than the M-20. I sailed the M-20 for the last 8 years and won the round Texel race two times with it. But this year i lost all the races against the Nacra-20. It was frustrating to see. So i sold mine M-20 and ordered a Nacra 20. I advice everyone who wants to be he fasted on the water, to do the same!!!
     
  5. Erwan
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    Erwan Senior Member

    Hi Dough,

    The M 20 has around 21 sqm for the main and at least 5 for the jib

    I am cautious with the msg where the guy explains you he has swap his M20 for a Nacra F20.

    The weight difference is significant enough to raise some question.

    Or may be the M20 was a "dog" an ultra-light dog ?
     
  6. Doug Lord
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    Doug Lord Flight Ready

    ==============
    This is a good topic for design considerations especially if we can come up with an answer. I don't understand how the Nacra 20 can be so much better
    unless it was the foils. I'll keep looking into it-if you find something post it here....
     
  7. Erwan
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    Erwan Senior Member

    Thanks for your kind consideration Doug, I am happy you agree with me about a potential design issue which could explain how such a gap can be closed by smart hull shape or global consistency.

    About the curved foils, as Marstrom builds the best asymetric centerboard for A-Cat, I suspect it cannot be the only reason for closing the theorical performance gap.

    Anyway, when a foil provides lift, it generates also induced drag, function of lift squared. Unfortunatly I don't see any free lunch on this side.

    Combination of appropriate hull's volume distribution and lifting foil can provide positive effect on pitching and better rig efficiency.

    But to quantify, if everything equal, for small cats, if you can consider roughly 1% extra weight equal 0.5% extra drag, a 55kg penalty is around 17% of total sailing weight including crew.

    It not a F20 it is a wizard, a magic cat, a challenging question if information available so far are reliable.

    I am afraid we will have to wait for the next Texel round to have more elements, unless a one to one is organized somewhere.

    But in any case, I consider the F20 carbon is a great achievement, it brings new blood in the formula 20 world, which was more a virtual classe than an actual one.

    Regards

    Erwan
     
  8. Pouakai
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    Pouakai Junior Member

    Erwan - I see from other threads that the M20 'as built' weights might be significantly higher than quoted on their webpage. Therefore the weight difference may not be significant at all.

    Also, regarding the F20 class - there isn't one! And if there was the Nacra F20 wouldn't fit the proposed rule. It's a shame but in a way a really good thing as there is now a de-facto unrestricted 20 ft cat class based on winning the Texel.
     
  9. Erwan
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    Erwan Senior Member

    Thanks Pouakai,

    Interesting insider information, sure it is a part of the explanation, but from 110kg for the cat-boat, or 115kg /120kg with jib, even if it is 15% too optimitic, which is a hudge difference, we will still get a 30kg weight give-up, nearly 10% of total displacement, to me it is still enough to make a difference, but the difference is in tthe other direction.

    We have to wait and see before to open the wallet, but the reasonnable weight (170) should be a guarantee for reliability.

    Regards

    Erwan
     
  10. Pouakai
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    Pouakai Junior Member

    Not insider information - just gleaned from other sites.

    Took me a while to find the thread the weights were on: http://www.catsailor.com/forums/ubbthreads.php?ubb=showflat&Number=224729&page=1

    It could be the weight difference is less than 20 lbs. Add in mods like wider beams, more sail, curved boards etc and the weight difference might be negligible. I'm assuming the F20 can be driven a lot harder downwind which is where the advantage might be. That certainly seems to be the case in the Formula classes.

    I haven't even seen the nacra 20 in the flesh yet - maybe at next years texel if my boat is this side of the channel and the weather is ok.

    I would love to be back sailing 20's of any kind, but not having to find a crew on my F16 is a lot easier.
     

  11. Erwan
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    Erwan Senior Member

    Thanks Pouakai,

    Very insightfull information, some remarks remind me something: I had opportunity in 2007 or 2008 to talk with F18 HT crews in a common race with standart F18 in open sea.
    And in choppy water and windy conditions, they reported the 130kg F 18 HT seem to rebound on the chop like a ping-pong ball, and therefore not easy to achieve full power.

    Of course, another element could be the crew's quality, or/and hull design to explain this theorical lack of relative performance.

    Thanks for the link, it testifies that very often, the same questions or ideas can spark independently at the same time in different place.

    So with regards to the info available so far, the F 20 seems to be a good deal as long as you have the crew.

    But the point is it as physically demanding as a Tornado, but it is probably another thread, unless a special friendly-user feature/design , could make this boat not so demanding.
    If this kind of assumption makes sense, may be we have here another part of the explanation of the F20 edge.

    I would bet the maximum hull beam (no cat beam) is a bit narrower on the F 20;
    the transom as well.

    Thanks and Regards

    Erwan
     
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