The new SUN FAST 3300 with a double concave line

Discussion in 'Sailboats' started by Dolfiman, Jan 9, 2019.

  1. Dolfiman
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    Dolfiman Senior Member

    I highlight on this new design because of its innovative hull, with a double concave line, a first to my knowledge for such modern beamy monohull, and the signatures behind : a design due to the association of Daniel Andrieu (the naval architect behind the Sun Fast line, an expert in optimizing for the IRC rating rule) and Guillaume Verdier, with a strong investigation with computational fluid dynamics tools by Véronique Soulé (on the picture), the expert working with G. Verdier. A design line that reminds the one of the Ultim Gitana 17 amas, although working in very different conditions.
    A boat to follow, launch of the first prototype by next spring :
    Nouveau voilier SUN FAST 3300 | Jeanneau https://www.jeanneau.fr/articles/1417-nouveau-voilier-sun-fast-3300
    Jeanneau confirms the launch of the new Sun Fast 3300 set for the European spring of 2019 https://www.sail-world.com/news/212941/New-Jeanneau-Sun-Fast-3300
     
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  2. Doug Lord
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    Doug Lord Flight Ready

    Last edited: Jan 9, 2019
  3. Mikko Brummer
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    Mikko Brummer Senior Member

    Dolfiman, a GeneHull model for SF 3300?
     
  4. Dolfiman
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    Dolfiman Senior Member

    Ok, I take up the challenge ;)

    My tentative interpretation of the rationale of such double concave line :

    *** For that type of hull very beamy towards the rear, a disadvantage which can become a big flaw is the tendency to nose down with heel angle due to these rear volumes, and in particular when downwind with breeze.
    *** This flaw has been partly countered in recent years by the tendency to increase the fore volumes with rounded bow, up to to do a bit of scow bow, e.g. the Lift 40 designed by Marc Lombard ("Veedol" , who won the last Class 40 Route du Rhum).
    *** Another way to compensate the nose down flaw results from the use of foils of which lift force can pitch up the boat and prevent from nose down (Imoca foilers, Figaro 3)
    *** Here, it is this double concavity that provides a solution: the rear concavity will tend to amplify the depression effect, ie a hydrodynamic force downwards, while the front concavity will have the opposite effect, increase the hydrodynamic pressure and therefore create a force upward. All in all, a pitch-up moment that will tend to increase with speed, ie when you need it.
    ** Such hull, with an accentuated rocker curvature in the middle, is usually beneficial also for the reduction of the wetted surface but associated with a low Cp. This would be a big defect at around Froude 0.4 if the boat was a classic medium-heavy one, but for these large, light and over-canvased boat that are able to overcome the Froude 0,4 hump and go up to Froude 0.7 to 0.8, where the hydrodynamic pressure forces become preponderant, it is no longer a problem. That's also why the rear concavity ends with a flat horizontal at the transom, favorable for the surf mode But may be she could have a performance relative drop between the light winds and the planning mode.
     
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  5. Mikko Brummer
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    Mikko Brummer Senior Member

    Talking with Juan K some time ago, about the Open 60 IMOCA and Volvo, he said that these boats always sail heeled at about 25 degrees, and the full bows add to the waterline when heeled.
     
  6. Dolfiman
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    Dolfiman Senior Member

    I propose you attached this numerical Concav33 generated with Gene-Hull. For that, I introduce a new function in order to generate a dose of concavity in the front part of the keel line, pilots by an adimensional parameter called Fore Concav (in cell B24 of the file also attached). For the rear part concavity, it was already possible with Gene-Hull, by just lower enough the transom rear end (parameter Z tab ar in cell B27). You can try another Concav33 hull with the file attached by just changing Fore Concav and/or Z tab ar , and adjusting the displacement by changing the hull draft Tc (cell B14).
    Yes, these beamy hulls are designed to have a peak efficiency at about 25° heel angle, leading to a great amount of righting moment RM, a reduced wetted surface Sw and a reduced beam waterline Bwl : the resulting floatation surface, although very oblique / boat axis (about 7° to 8°), does not give a penalising extra drag, it is usually a winning formula. In the Concav33 case, when at heel 25° and over, the floatation shape tends to the one of an equivalent hull without concavity, + the aimed dynamic pressure (surpression in the front part, depression in the rear part) should occur alongside the windward line of the floatation shape I presume : of course CFD tools and a lot of iterations on the hull shape are necessary to balance all that perfectly.


    Sun fast 3300 p Pict3 Sun Fast 3300.jpeg Pict4 Sun Fast 3300.jpeg Pict5 Sun fast 3300.jpeg ictures thanks to Forum Sailing Anarchy :
     

    Attached Files:

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  7. pogo
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    pogo ingenious dilletante

  8. Mikko Brummer
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    Mikko Brummer Senior Member

    Great job, Dolfiman! Thank you very much for your effort. I will certainly take a closer look later, maybe run a CFD comparison if I find the time. Your keel has a bulb, so you did not model "the structure and shape of the keel, carefully studied on this new racing yacht, also enable a reduction in drag and an optimized center of gravity" ;-)

    One thing that comes to mind, if the mid-ship section is V-shaped, while the ends are U-shaped, the hull will float deeper on its ends when heeled and the nasty effect of Cp getting ridiculous is less when the boat is closer and over its hull speed. The old Scandinavian skerry-cruiser way.
     
  9. DCockey
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    DCockey Senior Member

    Concave buttocks on hulls of planing power boats is typically called "hook" and is nothing new.
     
  10. Dolfiman
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    Dolfiman Senior Member

    If I refer to the description of a "hook" given by Jehardiman in this thread /quote#2, it is both a concavity and the transom end lower that the hull immediately before :
    Hull is "Hooked" at the transom ??? https://www.boatdesign.net/threads/hull-is-hooked-at-the-transom.15793/
    For SF 3300, one can see the rear concavity finishing by a flat horizontal plane at the very end, and in my opinion the effect expected by the designers is mostly a succion from a dynamic depression. Here is the interview of D. Andrieu (In French), quite vague on the double concave expected advantage (from 5:32), deliberately I think, but the video itself gives interesting views of the hull lines.
    Exclusif - Daniel Andrieux nous explique les 4 grandes innovations du nouveau Jeanneau Sun Fast 3300 - ActuNautique.com http://www.actunautique.com/2018/12/exclusif-daniel-andrieux-nous-explique-les-4-grandes-innovations-du-nouveau-jeanneau-sun-fast-3300.html
     
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  11. sharpii2
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    sharpii2 Senior Member

    Looks to me like this is mostly an attempt to lower the boat's CG without going for a shorter DWL or increasing the displacement. It may also be an attempt at rule beating. But since the IRC rule is not published (at least not to my knowledge)I have no way of knowing. Going with this potbelly hump in the middle does not decrease whetted area; it increases it. A fair curve is always going to be shorter (per area under it) than a lumpy one. This hump lowers the top of the keel and its supporting structure as well as (in all liklyhood) some water tanks.

    Sailing at slow speeds with little wind, this hump probably causes little extra drag. At higher speeds the boat is heeled over, so much less of it is being dragged through the water.
     
  12. Dolfiman
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    Dolfiman Senior Member

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  13. DCockey
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    DCockey Senior Member

  14. OzFred
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    OzFred Senior Member

    Well spotted:

    "This has kept the water line fairly short, versus the overall hull length. When combined with the high hull volume, this has hit a sweet spot under many rating rules, and is beneficial to performance overall."​
     

  15. Dolfiman
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    Dolfiman Senior Member

    Here is a video of the Sun Fast World Cup 2109 which includes some sequences showing the Sun Fast 3300 prototype in demonstration within this event (the boat with black and orange stripes), upwind and downwind under assymetric spi : it seems that she is significantly nose up when compared to others, in particular downwind under spi, the first meter of keel line is quasi above the water >>> the (searched) effect of the concave line ?
     
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