longitudinals

Discussion in 'Metal Boat Building' started by alanrockwood, Jun 1, 2011.

  1. alanrockwood
    Joined: Jun 2009
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    Location: USA

    alanrockwood Senior Member

    I have a question about longitudinal frame members.

    Generally speaking, are they pieces cut to a curved shape to fit the hull, or are they straight pieces of sheet metal or plate that are bent to shape. If the latter, then how hard is it to bend the pieces? It would seem that bending them in the "wrong" direction (the direction measured in inches, not the directions measured in fractions of an inch or in feet) might be too hard.
     
  2. Wynand N
    Joined: Oct 2004
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    Wynand N Retired Steelboatbuilder

    The longitudinal get fitted in full length sizes. It actually bends very easily around the frames to the shape of the hull.
    Never cut longs to curve - just push them against the hull if it is away from the plating, sometimes in extreme cases it is necessary to use some for of help such as a hydraulic jack.
    Check out my webpage at the link below and you can see how it is done.
     
  3. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You can bend them with a bending machine. The curve doesn't need to be perfect because the metal is fairly flexible.
     
  4. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Firstly a frame is a transverse structural member,. If the member is longitudinal, and not just a ‘stiffener’ is it is primary structure, then it is a girder, not a frame.

    In the old days when we used to draw a lines plan, we used wooden splines and weights. The weight would hold the spline and the spline would be slowly coerced around to a smooth curve. It produces a fair curve.

    If the hull in question is long, the girder/longitudinal structural member, as noted above, can take the very same natural curve. The amount of “bending” required can appear to be a lot, but on a long length is minor. But if the hull is short in length, you’ll experience difficulties, especially if the member is very stiff in relation to its length. In this instance, best get a cut part, shaped to suit.
     
  5. welder/fitter
    Joined: Jun 2008
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    welder/fitter Senior Member

    I usually find a few saddles & wedges work best. You can align the stringer on it's reference marks & adjust it's stance with an extra wedge, if necessary. tack your saddles one side only, just enough to hold the tension. For really tough ones, a hand-pumped hydraulic ram in a wider saddle works well.
     

  6. welder/fitter
    Joined: Jun 2008
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    Location: Vancouver

    welder/fitter Senior Member

    Here's a basic drawing of a saddle & how the saddle works:
     

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