Dinghy 13 ft with bi-convex sections option

Discussion in 'Sailboats' started by Dolfiman, Apr 22, 2019.

  1. Dolfiman
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    Dolfiman Senior Member

    I understand that it is usual for some designs to help start planning (RS Aero), but some other modern design like the Melges 14 have not such chine although good all-around performing dinghy. So I will stay simple without that kind of chine.
     
  2. gggGuest
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    gggGuest ...

    Its more complicated than that. The sharp transition and the steep topside gives less wave drag and a number of other beneficial consequences. But those may well not be important or even useful for your design aims.
     
  3. Dolfiman
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    Dolfiman Senior Member

    Thanks for this another instructive link ! (for me), the one above and also this one a bit lower in the same web page, telling the story of the successive breakthroughs in Moth design :
    And now for something completely different - The International Moth story https://www.yachtsandyachting.com/news/215173/And-now-for-something-completely-different
    (to note some minor mistakes in the text about french sailors : Marie Faroux >>> it is Marie-Claude Fauroux, and idem his well known brother is Jacques Fauroux. He is now semi retired but his naval architect cabinet is still active, led by his son Nicolas : Constructeur bateaux à moteur à Mougins, voiliers, catamarans et régates à Cannes, SARL Groupe Fauroux http://fauroux-construction-bois-06.com/naval/constructeur-bateaux-a-moteur-mougins-voiliers-catamarans-regates-cannes.html#compétences)
     
    Doug Halsey likes this.
  4. Dolfiman
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    Dolfiman Senior Member

    Back to my initial objectives (as detailed in quote #1), I have eventually converge to 2 versions : Bi-convex soft and Convex-concav-hard chine, sharing (quasi) the same dimensions, inc. beam waterline Bwl (I am fixed on a Bwl ~ 1,00 m, in relation with the design payload 95 kg), hydrostatics, stability and righting moment features. On the performance side, I wonder what could be the best one, hoping at least that both could give fun to sail without demanding skills re. stability and physical/acrobatic posture re. RM. Probably that I have a preference for the Bi-convex soft one, it is more subjective than rational I confess.
    Versions like the Bump one are really another approach, where Bwl is deliberatly important (Bwl/Bhull > 0,8) to focus on the stability, and requiring a sailing at 10° to 15° to reduce the wetted surface.
     
  5. Dolfiman
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    Dolfiman Senior Member

    Well, I did it eventually … :) , i.e. introducing such lower hard chine as transition between the convex and the concav part of each sections. I converge to a Bwl of 1,12 m, a bit more than the 2 previous versions but the wetted surface at 10°-12° heel angles is the same. That leads to greater stability, both initially (+ 75% for the GM at 0° heel angle when the payload 95 kg is at the center) and for the dynamic reserve during manoeuvers (I compare the aera below the GZ curve for the 0°-25°, still for the payload at the center). As regard performance, … ?
     

    Attached Files:

    Doug Lord likes this.
  6. gggGuest
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    gggGuest ...

    That's looking quite nice...
     
  7. revintage
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    revintage Senior Member

  8. Dolfiman
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    Dolfiman Senior Member

    Thanks Doug and gggGuest for your likes.
    I had also a look on the new (2018) First 14 Beneteau, a « convex-hard-concav » (to take my non-poetical typology) dinghy hull, 4,27 m (14ft) x 1,70 m, designed by Sam Manuard who comes from the Mini650 world :
    - the Bwl seems quite generous (not minimalist at least) to offer a pleasant stability, for one or two persons,
    - the originality is to offer one, two or three sails which can be operated like by an ocean singlehandler during his day sailing depending of the wind force or direction : main, main + jib, main + assymetrical spi, main + jib + assymetrical spi.
    - and to keep a good balance, two daggerboard wells are proposed, the second behind the first on the central line : with the mainsail only, you use the aft well, with the main + jib the fore one, or even with the two daggerboards back to back if necessary in some cases.
    Web site : First 14 | Beneteau https://www.beneteau.com/fr/first/first-14
    A light trolley design is also proposed :

    In planning mode :
     
    Doug Lord likes this.
  9. CT 249
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    CT 249 Senior Member

    The 14 looks to have some nice touches, but a couple of points concern me. One is the trolley concept;. trying to get the screws (or whatever they are) in place in a chop and sandy water could be a major problem, but of course the bolt-on wheels could work on hard ground and flat water.

    I still don't understand the idea of having the BMAX at the transom, which is what the 14 seems to have like other Open-inspired boats. It's similar to the concept that was seen to be flawed years ago in development class dinghies. There are advantages but the development classes tended to move to having comparatively narrower sterns to allow the stern to sink low under crew weight and pop the bow out to prevent nosediving, as with the Merlins and NS14 below.

    images.jpg P2210443s.jpg

    2009-03-31_085925_flight24.jpg
     
    OzFred likes this.

  10. OzFred
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    OzFred Senior Member

    Though in the planning video it does seem to keep the bow up nicely, and the gunwale is cut away near the transom so the crew isn't expected to sit on the back corner. I'd like to see it going downwind in +20kn and decent chop to see if it works though.

    A lot of trim issues could be solved, or at least attenuated, with a horizontal foil on the rudder, a la I14. I really don't understand the reluctance of classes, particularly new ones, to adopt it. Not one seems to think it's a good idea, even though it's well proven in I14s and, to a lesser extent, Moths ("lesser" because they transitioned to full foiling before they optimised their rudder foils, IMHO of course).
     
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