Scantling advice needed from a MA/NA/Designer

Discussion in 'Boat Design' started by longfellow, May 2, 2009.

  1. longfellow
    Joined: Apr 2009
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    Location: upstate NY

    longfellow Junior Member

    I have just finished lofting an E.Schock V-bottom daysailer (18' x 6') and have a question on planking. The plans call for EITHER 3/8" plywood or 3/4" solid longitudinal planks, carvell-style. My frames are two feet apart and this seems too large with planks and no intermediate frames or battens at the seams. Do you suppose that the designer expects the builder to know this and add the apprpriate reinforcement or is it truly ok to have such a span between frames? Gerr's book unfortunately isn't structured in a way to give me the answer, as those of you who have the text already know. I have found other plans of sawn framed V-bottom hulls with 2' spacing and some have intermediate frames bent in between (Atkins' Economy Jane), some have battens (Chapelle Sharpies) and some allow this span with nothing and are identically framed and planked (Benford 16' Conch). If I add in battens, do I need to beef up the molded dimension of the frames (currently about 2 3/4 inch) because of the material taken away by the inletting? I can also steam in intermediates but have no clue as to X-sect area or spacing. Chapelle actually mentions edge joining the planks with long dowels. He was awesome. No way I'm doing that with 3/4 inch planks. Thanks Much. Ed
     
  2. Gilbert
    Joined: Aug 2004
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    Location: Cathlamet, WA

    Gilbert Senior Member

    Your hunch is correct. For the carvel planking you should have a frame spacing of about a foot. All you need to do is lift frames in between the 2 foot spaces from your lofting.
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Yes, that sounds about right without running figures. With the 3/4" lumber planking, you can use widely spaced frames. With 3/8" plywood on the those frames she'd be weaker but more dynamically stable. If anything I'd prefer to see thicker plywood, say 5/8" or at least 1/2" on those frames, with that spacing. Conversely you could use 3/8" plywood planking but decrease frame spacing by 50% (12" centers).

    With planking and frame dimensions like this, you have a fairly well burdened 16' boat. The loads will be moderate and so you don't need intermediates or battens.

    This is a heavily planked, loosely framed boat. What you're use to is a thinly planked boat with much closer frame spacing. Both ways work, though the closer frame spacing, with thin planks technique usually produces a lighter boat. A typical lightly planked boat would have something like 1/4" topsides, 3/8" bottom planks over 3/4" square frames on 7" to 8" centers. You're just moving the bulk from the planking to the frames or vise a versa.
     
  4. longfellow
    Joined: Apr 2009
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    Location: upstate NY

    longfellow Junior Member

    Thank you gentlemen.
    Yes PAR this is not a familiar sight for me, to have thick (for a 16 footer) planking and wide frames to compensate. Gerr's book barely covers boats this small so his scantling curves are tough to use and not as reliable when you're barely on the curve, so I do appreciate the advice. One follow up if you don't mind. I know that plywood would be your choice if I told you that the boat may live on a cradle at the yacht club, rather than in the water. This is a disappointing possibility (that I don't get a slip in the year that the boat is completed and must dry sail it). Since I'd prefer to plank it with solid wood, should I use battens anyway to help keep her dry in scenario? If so I am pretty set in finding their size and method of fitting. Ed
     

  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Battens can be used, but they tend to limit the shapes you can work with. On a carvel hull you have to "back out" the planks to get them to lie down nice, without forcing edge set into them or making the fasteners cup the planks to the frames. With battens you have a flat landing along the plank edges for the batten to land flush on. I suppose with some careful measuring, you could still back out the middle of the planks, but it seems like a bother. This is why batten seams were used on powerboats predominately and on shapes that looked much like the developed forms of plywood hulls. They actually weren't developed shapes, but they look like it to some.

    You could do a tight seam plank job (no caulk, just very well fitted planks) or double plank her, which would take to dry sailing better. Double planking does quite well with dry sailing, carvel not so much. You could also strip plank, which will preserve the hull shapes without compromise and it takes to dry sailing well too.

    Of course these level of scantling changes will require some assessment and calculation, to bring them up to similar strength requirements of the original structure.
     
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