Lofting from full size templates

Discussion in 'Boat Design' started by sharknet, Dec 19, 2013.

  1. sharknet
    Joined: Dec 2013
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    Location: Auckland New Zealand

    sharknet Junior Member

    Frames drawn to inside of stringers. That is the stringers screw/glue to the frames, planking (Ply) sits on top of these.

    So I will have to add about 1 1/2 inches to the frame sizes to get to the inside of the planking if I go strip.

    Same construction as the photo I posted above, if you can see in there.

    Edit: Just checked the plans again. Details call for 2 x 1/4" skins bottom, 2 x 3/8 skins transom, aft topsides 3/8 and bow flare 2x 3/16 double diagonal.

    We build 'em light here in NZ!
     
    Last edited: Dec 21, 2013
  2. SukiSolo
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    SukiSolo Senior Member

    Personally I would add that 38mm (1 1/2) to the frames, then trace the outsides onto a large flat surface (floor, wall?). Turn the frame around C/L and retrace to check symmetry. If you pop masking tape on the edges of the frames, glue won't stick when building or it at least gives you a half decent barrier so you can get the thing off. Useful inside the stringer area too at preventing any sticking points. Thin polythene sheet stapled to frames if it is going to get really messy ;).

    Nice little runabout, looks like she would be quite lively with that 15 hp. Good job on her, not the easiest with that low hull flare. You can probably understand why I laminated the stringers! If you start to 'fight' with any curvature I reckon on not stressing the frames/jig/mould and it is more accurate to laminate thinner strips. Had too many problems on one build (using designers plans) so take the longer but more accurate method now. If you get any 'sag' or to much spring planing the angles, it would be better to add extra frames or half frames in tricky areas.

    Just for fun I know of at least one pro builder who 'forgot' to check if the drawings were to inside or outside of skin.....

    What timber were you thinking of for strip planking/double diagonal? Maybe a ply with diagonal (or double diag) core?
     
  3. sharknet
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    sharknet Junior Member

    Thinking either cedar, (not too common here) or a local cypress. Both lighter than ply, and in the case of the cypress, cheaper too.

    Back to the dinghy, the stringers are 7/8 square, chines 7/8 x1 1/2, laminated to give the spray rails. (Broke two of them, finally steamed them)
     
  4. PAR
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    PAR Yacht Designer/Builder

    It doesn't sound like you have a complete set of plans or are attempting to convert them to a different building method. If attempting a conversion or trying to "wing it" with scantlings, you might find some difficulties. If the hull is hard chine and developed for sheet goods (plywood), then strip plank is possible, but this isn't the best employment of the technique. What design is it?
     
  5. FAST FRED
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    FAST FRED Senior Member

    To my mind the best use for full sized templates is IF the bulkheads are on stations and will be kept as part of the build.
     
  6. sharknet
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    sharknet Junior Member

    I do have the full set of plans, and plenty of Pelin hulls have been built either double diagonal timber, strip or plywood.

    Scantlings are given for either plywood or solid timber. (same either way)

    Strip planking is mentioned, as is foam core, but no dimensions given. (This hull was designed in the 70's, so strip/foam core-epoxy was reasonably new here then)

    Photos attached show a Pelin 8m planing hull stripped in 40 x 20mm kahikatea (NZ native white pine) sheathed with 8oz cloth inside and out.

    I'm just looking into it, I like the clean interior of strip planking, and as this would be on a trailer, the weight needs to be kept down. Marine ply is not exactly light...
    [​IMG]
     
  7. LCrosby
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    LCrosby Junior Member

    Built a 30' Cutter about 10 years ago.
    Stations came laser cut in 3/4 ply. Huge stack.
    After laying the keel, stem, deadwood and floor timbers we bolted up
    these laser cut stations. Framed and planked around them, then pulled
    them out before laying the deck.
    It was pretty efficient, no time lost lofting.
    Heavy Mothers though!
     
  8. tugboat

    tugboat Previous Member

    to the OP. I haven't read all the posts so- it possible this was already mentioned, if so- pls disregard...
    some great reference material for what you propose is T. MacNaughton's "rules for Sheathed strip construction"
    and Selway-fishers book "strip plank construction" altho, sounds like you already might have that one as he does suggest increasing your stations. this is to allow support for the long strips you will be using.
    however there is controversy surrounding his take on flat surfaces and the specific shapes that can be created in strip plank- his methods are outdated now. to me(just my opinion) using cold molding to go over an already composite structure seems redundant to me.
    I have done the frames for three boats using full size patterns. never had any issues all frames within tolerance...

    may I ask who they are from and what design?

    your idea of lofting and "gridding" the frames sound like a lot if work...I had to laugh at that - since I had the same exact idea for a design I own. I decided it just wasn't worth the extra effort. but- you will need extra stations-how you will get this- is a bit of a problem. you might be able to use the body plan and draw them in then loft them out. Not sure...either way its a lot of work.

    I understand you need about 18 inch spacing to be proper. although I question this a bit as I think 24 inch would be suitable but what do I know...
    In my experience- the dimensional stability of paper is really pretty negligible as long as you keep them dry. or in a place where they are not subject to humidity. even then - as long they are dry- the difference is quite small almost negligible in the problem with paper.
    if you own a cad program such as Rhino you might be able to reproduce it then get all your info from that.

    I wish you the best and hope your dream becomes reality!!

    good luck on it.
     

  9. sharknet
    Joined: Dec 2013
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    sharknet Junior Member

    Thanks for that.

    The design is a Frank Pelin Mascot, light (semi) displacement cruiser.

    I still need a lot of work to do regarding the planking method, I may just go ply after all, but I would like to have a go lofting.

    I agree about the cold molding over strip (Gougeon?) given the strength increases gained by sheathing in glass and epoxy, why add yet another layer?

    The hull built above was stripped on standard frame spacing, 3'. But 20mm kaihikatea is pretty stiff.

    Having all the frames lofted on the plans really does make it easier.
    They are even nested like a proper body plan, so just adding the waterlines and fairing the profile should get me most of the way there.

    Anyhow...

    The workshop floor is clear, so I have to do something, either that or fritter all my time away.
     
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