Spira w a twist.

Discussion in 'Boatbuilding' started by Easy Rider, Nov 29, 2015.

  1. PAR
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    PAR Yacht Designer/Builder

    Flam is typically a convex section, while flare is concave, though both do splay outward from the hull's centerline.

    Again, the Atkins design was specifically intended for carvel or batten seam, with sheet goods a possibility, after some cursing. Yep, you could bend 3/4" oak planks around that hull form, but see my comment in the previous sentence. Molding (ashcroft or whatever) can be done on about any set of shapes.

    [​IMG]

    There's some twist, but this wouldn't be all that bad, just a little inventive adjective creation in the forward sections. This type of hull would do better with a building process, that can introduce some edge set in the planks, without much harm, such as carvel, batten seam, lapstrake, etc. Sheet goods (metal, plywood, etc.) can be done, but . . .
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    It should be a very simple matter to design a flat-bottom skiff that does not require any torturing of the sheathing, I can't see why it needs to be stuck with the idea of straight framing, the frames should meet whatever shape the skin is developed to follow, not the other way round.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Precisely, though there is some latitude, often intentional to get a specific set of shapes, the easiest builds are truly developed, not just close. Software has made this a relatively simple thing to check, which wasn't always the case.
     
  4. Easy Rider
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    Easy Rider Senior Member

    http://bateau.com/studyplans/FL26_study.php?prod=FL26

    This boat caught my eye and is very similar to Marcia. The most interesting thing about it is the slotted topsides to achieve flare .. or a substitute for same. Dealing w the slots w wood and adhesive may be more trouble than just planking Marcia. They don't say how the flare/slots are finished but I have a hunch it's FG tape arranged in some way.

    Of course if I used these plans the stern would need to be modified for OB power. Anybody familiar w this boat or the plans?
     
  5. PAR
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    PAR Yacht Designer/Builder

    Yeah, slitting the forward sections is a quick and easy way to introduce some compound into the planking. I have a few designs that do this too. It increases the goo factor a bit, but on a taped seam build, not such a big deal. If going this route on a hull form, I'd like to see a lot more shape. Marcia's forward sections would look a lot better with this treatment.
     
  6. Easy Rider
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    Easy Rider Senior Member

    Thanks PAR I was hoping you'd respond.
    But it leads to another question.
    Is the planking intended to remain vertical and form sorta spray rails? I wondered why the stem wasn't saw tooth shaped. How might that work?
    I was influenced by the graphics on the Bateau study plans. If a good way to fill the "step" was found it would make an interesting topside on many boats .. especially dories and other boats w a lot of flare. They of course don't need it as much as more slab sided boats and the "step side" planking may look odd.
    I assume now from your post that the planking is intended to follow the forms or frames. The result being a smooth topside.
     
  7. PAR
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    PAR Yacht Designer/Builder

    The slits simply permit the plywood to lay down on the molds, it remains in alignment with the other pieces, with a pie wedge shape missing. This wedge shaped gap is filled with goo and fabric, ultimately making the area a homogenous unit, as if it was molded. Simply put, no bumps, teeth, laps or rails, just smooth sided with more curvature than possible with unslit sheet goods.

    On a design I did several years ago, I was hopeful the planking would "torture" into position. When the builder started on the first hull, he complained the temporary screws were pulling out of the stem and wouldn't "suck down" the planking in this area (I think he was trying to use drywall screws to pull the planking in). Oops, he was pretty bummed about it, but I recommended he take a circular saw and slit the planking in two places, equal distant from the second chine to the sheer, then screw each section to the stem. He still moaned a bit, but the planking did eventually lie down. He filled the gaps, smoothed it off and all was well under paint. I've never built this particular design, but I'm pretty sure I could have "convinced" the planking to lay on the stem, without the slits, but he wasn't an experienced builder and needed a solution he could live with. He wasn't convinced it would be very strong with the slits and back fill, but I assured him it would actually be a little stronger, because of the fabrics, filler and goo, making plastic and 'glass stringers in the bow. It's an old trick that metal and plywood fabricators have used, to get things to conform.
     

  8. Easy Rider
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    Easy Rider Senior Member

    Thanks PAR,
    It's great when you learn something .. and when it's about boats .........
     
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