Frame notches for longitudinals

Discussion in 'Metal Boat Building' started by Love2boat, Jul 23, 2012.

  1. Love2boat
    Joined: Dec 2011
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    Love2boat Junior Member

    Hello,

    I'm planning to CNC cut my frames and my longitudinals are spec'd at 1/4" x 1 1/2. How large of a notch would you suggest I have cut? I'm just wondering how much "wiggle room" is normal/needed. Also, I've seen some examples where they put a half circle at the end (photo attached).. how common is this?

    Thanks,
    rja
     

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  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    You're going to have to define "wiggle room" as you understand it. You'll have to note the length of boat and the frame spacing as well as the scantlings of each, for anyone to provide a sensible answer.

    Yes a half circle above the top is common. It is to reduce the stress concentration, see here typ. example:

    FB cutout.jpg
     
  3. Love2boat
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    Love2boat Junior Member

    Thanks for the quick response! The boat length is 49', frame spacing is 3 1/2' and frames are spec'd at 5/16" x 5".

    Ah, makes sense. I've only seen it done in a few photos. I was thinking that it might reduce weldable area significantly but I guess not.

    -rja
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    You still haven't defined what you mean by wiggle room..
     
  5. Love2boat
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    Love2boat Junior Member

    A reasonable amount of space to slide the long into position w/o binding, yet close enough to be easy to weld.

    -rja
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    1mm should suffice
     

  7. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I normally work with shipyards that are not able to achieve tolerances as small as those required in your design. So I've always used solutions such as those in Fig. They are fully accepted by the Societies of ClasicaciĆ³n, may be somewhat more expensive, but allow the workshop to work with much more comfort which, ultimately, reduces costs.
    As for the "Wingle room", I would recommend 2 mm.
    This is my normal practice, that does not mean it's the only good or possible. Always work having in mind the media, material and human, which are in the shop that will do the work.
     

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