Frame spacing

Discussion in 'Boat Design' started by learningtheway, Jun 27, 2011.

  1. learningtheway
    Joined: Jun 2011
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    learningtheway Junior Member

    I wanted to know is there some type of way you can calculate the strength of the boat with various frame spacing?

    I want to try to design a small 13-15 foot rowboat(possibly put a motor on the back) and picked up a few books on naval architecture, as well as been trolling these forums, but i cant seem to find anything on how many frames to put or how far to space them, how much stronger it would be if i put an extra frame or two...

    any help on this topic would be great, thanks
     
  2. messabout
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    messabout Senior Member

    For the small boat you are contemplating, the appropriate spacing of frames depends on several variables. Skin thickness, skin material, geometric shape of the sections of the boat, presence or absence of fore deck, aft deck, side decking, method of joining at the chines and sheer or other intersections between separate parts. Many boats have no frames at all. other small boats may have dozens of them.

    Frames have several functions. They hold the shape of the sections, they may help support some of the longitudinals such a keelson, they also provide a stopping place for decks or other top cover, they help resist the twist of a boat with too thin a skin, and more.

    Tell us more about the boat that you have in mind and you can get more specific information.
     
  3. learningtheway
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    learningtheway Junior Member

    Hmm well I guess the boat I had in mind would be wooden made of plywood and I have some oak wood already so use that for the frames, what other information do you need? 14' ? Just a fishing boat deep v bottom with a regular bow (not John boat style) I want it to have bench type seats goin from side to side fit 4 people....

    Thanks for the quick response again not sure what info u need but let me know what else I can let u kno about to assist with this frame spacing situation
     
  4. gonzo
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    gonzo Senior Member

    What books did you pick up? Frame dimensions and spacing is on of the basics of any design book.
     
  5. BATAAN
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    BATAAN Senior Member

    Build an Atkin design.
     
  6. viking north
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    viking north VINLAND

    Check out just about any the stitch and glue system. Most don't require any frames. Sam Devlin Designs being but one that pops into my head--or with one of the designers on the forum--PAR--TAD--I believe they both have plans for such or can direct you to a forum member that does---Geo.
     
  7. lewisboats
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    lewisboats Obsessed Member

    What is the beam? How deep is the deadrise, How deep is the hull? How much HP? What method of construction? How much flare? Any decking? What kind of athwartship furniture (full box seats or just planks on stringers/cleats)? A sketch or picture of what you have in mind would be nice.

    What kind of Oak is it?
     
  8. learningtheway
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    learningtheway Junior Member

    The beam I wanted to be 5'9", maybe around 15 degree deadrise, HP doesnt really matter 10 i guess not trying to go fast, seating would be planks no decking

    pretty sure its red oak that i have here ill work on a picture today...

    If you can use those things to tell me the spacing could you show me how you did it also, maybe a formula or something


    I have principles of naval architecture, basic naval architecture and how to design a boat
    i havent gotten through all of them yet but as i was reading how to design a boat it said to divide the frames equally along the Lwl but that didnt satisfy me, Im thinking there has to be some type of formula or something out there...

    I dont want to take someone elses design I want to learn to design it myself

    Thanks
    LTW
     
  9. learningtheway
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    learningtheway Junior Member

    maybe about 27"-30" deep hull
     
  10. Squidly-Diddly
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    Squidly-Diddly Senior Member

    good luck trying to actually calculate the added/decreased

    strengths of different amounts of framing in a hull, as far as simple hard numbers on how much more/less a hull will flex as framing is adjusted.

    The frames will work with the hull shape and its own strength, and then there are often tensions from bent wood, and wood being wood the way it is fastened and plywooded together will make a big difference, and you have wood grain, etc.

    I'd guess even the best CAD programs really struggle with all metal designs when you start adding riveted or bolted members, clearance and flex.


    But as others have stated there are lots of tried and true "rules of thumb", and I think it is OK (and easy) to reenforce wooden frames later after the boat is built.
     
  11. learningtheway
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    learningtheway Junior Member

  12. viking north
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    viking north VINLAND

    Don't use red oak for marine applications--especially if it is subject to wet/dry cycles. It will go to powder faster than you can sneeze. White oak an entirelly different story---Geo.
     
  13. learningtheway
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    learningtheway Junior Member

    Oh wow thanks alot! Saved me alot of time and money
     
  14. PAR
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    PAR Yacht Designer/Builder

    Do yourself a really big favor LTW and buy a set of plans. The boat you're looking to build, is about as common as freckles on a redhead and most are quite inexpensive. I say this based on the very limited knowledge, of the various engineering disciplines you seem to suffer from. This isn't intended as an insult, but purely an observation based on your questions. You could spend a few years learning how to design, which typically requires higher education courses or you can spend $50 to $100 bucks on a solid set of plans, where the engineering is already done and she'll float with the decks facing up come launching day.
    [​IMG]
    This is the Console Skiff from Glen-L and at the larger end of your scale (15' 9"), there are hundreds of others in this size range, from very plain to quite fancy.
     

  15. Willallison
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    Willallison Senior Member

    Dave Gerr's Elements of Boat Strength is just about as simple a method for calculating the required scantlings as you will come across. It will allow you establish a reasonable set of scantlings... what it won't do is allow you to design a boat without at least some fundamental knowledge on the subject.
    I would re-iterate PAR's suggestion - go buy a set of good plans.
    If you're still hell bent on doing some design work, then do a lot of reading and see if you can figure out the engineering and reasoning behind the design that you've just bought....
     
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