OSV Framing Conventions

Discussion in 'Boat Design' started by bateaudemoi, Jan 14, 2021.

  1. bateaudemoi
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    bateaudemoi Junior Member

    Hello all,

    Very general question I guess, but I'm wondering if supply vessels, say 80-90m would usually be transversely framed. If so, what could a typical tranverse frame spacing be? And then with that, what could a typical longitudinal stiffener spacing be?
    I get that there are rules to follow and that the spacing is optimized by meeting minimum MOI, etc., but I'm just wondering if someone really familiar could throw out some numbers. I would really appreciate it.

    Cheers
     
  2. TANSL
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    TANSL Senior Member

    Classification Societies usually have formulas to define the most advisable frame spacing. To start calculating, a relation stiffener span/spacing of value 2 may be correct. But the designer is the only one who can set these dimensions in a way that will lead him to achieve the optimal structure for his boat. And the word "optimal" for each designer or for each boat can mean different things.
     
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  3. bateaudemoi
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    bateaudemoi Junior Member

    Thank you,
    I really appreciate you sharing that ratio that may be correct. Exactly the type of knowledge I was hoping a senior member to drop. Would you say it is true that OSVs around 80-90m are primarily transversely framed?
     
  4. TANSL
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    TANSL Senior Member

    The supply vessels that I have known all had a transverse structure but their length was around 40-50 m. In a 90 m boat you should check if there may be any longitudinal strength problem (large hatches, very heavy loads on deck, L/B or L/D ratios very far from normal in these boats ...) that advises placing the structure longitudinal.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    Yes.
    What is the purpsoe of the question..are you a student?

    As with most things, it depends.
    It is a trade off between the amount of welding one wishes to do, and the change in weight it may or may not bring....
    Factored into this is the available bulb bar (or tee) stiffeners the shipyard are able to purchase, this also influences the stiffener spacing.
     
  6. bateaudemoi
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    bateaudemoi Junior Member

    I am indeed a Nav Arch student. I appreciate your answer. Indeed, the availability of types of stiffeners would affect section moduli and hence spacing.

    I'm starting more of an open-ended design and have since begun with ABS rules for steel vessels. Because of the nature of the project, I am free to choose the cross-section of my stiffeners, although I will be trying to reduce weight.

    Thanks for the response
     
  7. TANSL
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    TANSL Senior Member

  8. Ad Hoc
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    Ad Hoc Naval Architect

    Exactly.
    Then the frames, well, the spans play a big part...in that are the spans full span or half span....ie from turn of bilge to turn of bilge, or turn of bilge to CL....for example.
    Are there means/ways to create a natural "structural" support in the spans to reduce the span and hence reduce the modulus required?
    Thus, there are many factors that can ultimately dictate the frame spacing...

    I would suggest searching for vessel of similar size and see what/why they have selected the spacing they have... it may provide some further insights. Since no 2 boats are the same.
    And suggesting a frame spacing of say 1.0m or 2.0m, for example, may be misleading to you..as the "bigger picture" (the comprehension) will be lost ...
     
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  9. bateaudemoi
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    bateaudemoi Junior Member

    Thanks (again) for the great responses Ad Hoc and TANSL. Just for the sake of this thread, I've attached what I found in ABS.

    Cheers
     

    Attached Files:

  10. Ad Hoc
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    Ad Hoc Naval Architect

    The excerpt, is just a "suggestion" as a starting point. It is not a fixed rule per se.
     

  11. bateaudemoi
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    bateaudemoi Junior Member

    Ad Hoc, this is exactly what I was asking for. Not saying this is the only way to go.
     
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