From classic bow to scow bow

Discussion in 'Sailboats' started by Dolfiman, Feb 17, 2018.

  1. Doug Lord
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    Doug Lord Flight Ready

    And to some extent, the Quant 23:
    Quant 23 bow 2.jpg

    Quant 23 bow.jpg
     
  2. Gunnar Sommerlund
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    Gunnar Sommerlund Marine Engineer

    May i ask what sofwware have been used for these
    [​IMG]
     
  3. Dolfiman
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    Dolfiman Senior Member

    Dear Gunnar, Thanks for your interest, I use the spreadsheet application Gene-Hull for early stage design that I am developing step by step. I have opened a thread months ago on the Software forum on that development, where are now versions 2,2 .
    Gene-Hull : hull generation for sailing yacht early stage design https://www.boatdesign.net/threads/gene-hull-hull-generation-for-sailing-yacht-early-stage-design.58962/

    Here attached is the last version 2,3 just finished for U shape hull, named "Gene-Hull UE 2.3", that I used for this scow bow exploration + the User Guide.
    The application is given with the case "Imoca 60 Scow 1,1" in the input data, and the User guide.
    Free of use and open source, developed on Open Office 4.0.1 (worked also on Libre Office).
     

    Attached Files:

  4. Dolfiman
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    Dolfiman Senior Member

    I did a complementary exploration for the Imoca 60 case (here attached), about the balance relation between Scow bow and Lwl for a given Loa, that some of you have evoked.

    By developing a longer front overhang close to the water surface, one can introduce a bit of Scow roundness in the front waterline while remaining classic for the sheer line. It is of course at the sacrifice of the Lwl at rest (for a given Loa as ruled in the Imoca class), but upwind for Froude around 0,35 , with the pitch-down trim inherent to these beamy boat, you can recover a lot of this lost Lwl, and reaching/downwind you can expect the beneficial effect of a scow bow. I investigated this option for the hull in the Imoca rules (Scow = 0,037) and 3 Lwl : 17,50m, 16,60 m and 15,70 m for Loa 18,28 m. And for the comparison, I did the same exploration with a moderate dose of Scow (0,33), but then a hull out of the Imoca rules, and with the same 3 Lwl.

    Such half-overhang half-scow bow, beyond the search of an optimal for speed, could also be beneficial to avoid most of the green water generated by a full vertical bow piercing the waves at 20+ knots, unpleasant if not draggy.

    All that not new in fact, somewhat in line with the extravagant front overhang of the Sonderklasses one century ago, like the beautiful Tilly XV here below, photos and video :
    Sonderklasse https://peggybawn.wordpress.com/2013/02/24/sonderklasse/
     

    Attached Files:

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  5. Dolfiman
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    Dolfiman Senior Member

    Excerpt of the interview in english of NA Marc Lombard about his Class 40 new design, the Lift 40 named "Carac" (the sponsor) :
    Marc Lombard: On the design side, the optimisation is made mainly on hull shape which has far more volume forward, allowing a greater power at commonly used heel angles. Large investigation on CFD program was made on this boat to increase usable power without penalty on drag side, to preserve at most performances on full downwind conditions. To achieve this we worked a lot on the shape of hull both under and over flotation line, including deck lateral shape, the goal to achieve minimum measured power but maximum sailing power. Forward stem and keel line slope is also a major key in the design, it is developed to move forward the centre of immersed pressure as soon as the bow comes down. It is a critical compromise which without CFD we would have been unable to adjust the necessary amount of slope: Too much would lead to increased drag all round, too little would lead to bow down and through-wave-behaviour large problems. This is also one reason we tried not to go to full scow stem like on certain mini designs: We believe that there is a possible compromise with a less ugly shape than scow stem that I don’t like in heavy weather as a possible structural weakness. Beside this, large optimisation was made on appendages. With an even thinner keel for example, larger lifting rudders. This is to allow a larger amount of rake of the mast and perfect steering balance. This was necessary with extreme volume of the hull forward, and keeping bow up all the time.”
    The full interview :
    Marc Lombard on the brand new LIFT 40 Racing Yacht | http://no-frills-sailing.com/marc-lombard-on-the-brand-new-lift-40-racing-yacht/
     

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  6. Dolfiman
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    Dolfiman Senior Member

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  7. Dolfiman
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    Dolfiman Senior Member

    Another design with scow bow is under construction for the Mini 650 series class, the Vector 6,5 , builder Yacht Service (a polish yard) and NA Etienne Bertrand (specialised on Mini design, Proto 802 and Série Ofcet 6,50). You can notice that the bow shape is a bit different from D.Raison designs :
    Vector 6,5. : Vector 6.5, le scow a la cote en Mini https://www.bateaux.com/article/27501/vector-6-5-scow-a-cote-mini
    Yacht service : YS Production Sail Boats http://www.yachtservice.com.pl/jachty-zaglowe-en.html
    Etienne Bertrand interview, on scow design :
    Etienne Bertrand, l'architecte naval spécialiste du Mini https://www.bateaux.com/article/27502/etienne-bertrand-l-architecte-naval-specialiste-mini
     
  8. Southern Cross
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    Southern Cross Senior Member

    A new interesting take on the bow. An exageration of the Hugo Boss IMOCA 60. Maybe it should have it's own thread.

    The Carkreek Fast 40 Ran.
     
  9. Dolfiman
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    Dolfiman Senior Member

    Really a futuristic look, like a stealth ship with a reduced radar signature ;) . The hard chine line seems captured from a CFD computed waterline at heel 25°-30° and above the weight reduction logic is pushed to an extrem.
    But I think the bow cannot be categorized in the bow scow typology, so yes may be it deserves a specific thread.
    It is the opportunity to highlight on another advantage of a bow scow when that kind of boat is sailed hard downwind in rough sea : the risk of pitch poling capsize is a lot less. This video illustrating this risk :
     
  10. CT249
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    CT249 Senior Member

    When there were lots of scow Moths they were notorious for nosediving. Similarly, cats and skiffs have gone away from adding volume at the bow to prevent nosediving (which is pretty much the scow route) and have reduced volume (as in Ran) to stop the bow "tripping". So it's arguable that a scow would normally be worse for nosediving, or at least worse in a bad nosedive.
     
  11. Dolfiman
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    Dolfiman Senior Member

    I put this comment with in mind "big" scow bow as designed for Mini650, with more round fore volumes and freeboard than scow Moths.
     
  12. Dolfiman
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    Dolfiman Senior Member

    Excerpt from an interview of Simon Koster, third at last Mini transat with a scow bow proto :
    Q: "The first three prototypes have rounded bows. Is it the end of sharp noses?"
    SKoster : It's nice that we finally get to do that! It's been so long since it should have been done. It is certain that we will have less to pimp on foils if we allow the round bows. After that, the round bows must fit on the big boats, that's another question. But a rounded bow is more powerful, it's impressive because it goes really fast. After, sometimes it's hard because it hits hard, it makes noise but there is no doubt that it works. There are no more questions to ask. The only question is whether we can do this on a larger scale with the structure that holds. I see that nobody has wanted to try but since everyone is talking about foils now and nobody talks about round ends, I feel that it will never happen."
    Q: "Why are there no rounded bows in Imoca and Class40?"
    S.Koster : "Because they are all blocked by the gauge. Because they are afraid that boats will become obsolete. Then, the foils have arrived and they give the possibility of modifying old boats to reboost them. And this idea pleases everyone because, on paper, it costs less. But it remains a wrong trade-off : an old boat with foils will never be more efficient than a new boat with foils. In Imoca, if you put a hull with scow roundness underneath, I do not know what it will give at the mast."

    Reference link :
    Mini-Transat. Simon Koster : "Plein de moments magiques..." http://www.letelegramme.fr/voile/mini-transat-simon-koster-plein-de-moments-magiques-15-11-2017-11742147.php
     
  13. Dolfiman
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    Dolfiman Senior Member

    Two other photos , the bow and the general view : Fast40 bow.jpg Fast 40 general view.jpg
     
  14. BlueBell
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    BlueBell Ahhhhh...

    Love the video!
    More sail!!!
    Kidding...
     

  15. Dolfiman
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    Dolfiman Senior Member

    More views of the hull of this new Carkeek Fast 40 Ran through the video of its launch. Not a classic bow neither scow one, I would say arrow front lines even more accentuated because of the inverted bow :
     
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