Extreme Lightweight Aluminum Construction

Discussion in 'Boat Design' started by TealTiger, Aug 27, 2014.

  1. TealTiger
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    TealTiger Junior Member

    Can anybody tell me a bit more about Extreme Lightweight Aluminum Construction? It's mentioned and illustrated in Boat Strength (ch17 Aluminum and Steel Alternate Construction Methods - Lightweight Aluminum Scantlings). The author says it's associated with Derecktor Shipyards. Is it their proprietary/protected method? Could any NA design using it? Would an NA have to have a lot of experience with the method to design well with it? Would the labour have to be highly skilled and or familiar to build well with it? I understand it's not common, and assume it's because of labour costs. I'd also appreciate any other thoughts on the subject. Thank you.
     
  2. TANSL
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    TANSL Senior Member

    I do not know this constructive method and therefore can not comment. What I can say is that the constructive method generally has little effect on the lightship weight. To reduce the weight of the hull is best to do a good Scantling by any of the direct calculation methods offered by the strength of materials. This method, which I call "Work well", can be used by any naval architect without asking anyone's permission. And I will add something else: any naval architect is obliged to use it.
    Could you, please, give more details of the method by which you mean ?. Thank you
     
  3. TealTiger
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    TealTiger Junior Member

    I appreciate your input TANSL; thank you.
    The only relevant accompanying text says:
    "Extreme lightweight construction system pioneered by Derecktor Shipyards.
    Closely spaced ring frames and longitudinals allow very thin plate.
    Numerous carefully engineered lightening holes further reduce weight.
    This construction gives hulls weights comparable to high-tech composite materials."
     

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  4. TANSL
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    TANSL Senior Member

    Would need to perform some calculations to check the advantages of the structure shown in the photo.
    At the moment I can point several ideas:
    - All Classification Societies give formulas to calculate the thickness of the plates, which depend, among other things, the separation of the reinforcements. But also give another formula that indicates the thickness shall not be less than a certain value, whatever the separation of reinforcements. So there comes a time that the thickness can not be decreased although much increase the number of reinforcements.
    - Increase the number of reinforcements greatly increases labor.
    - The lightening you see in the picture are too big. It is possible (my opinion) that the frames and floor plates are very weak and only the large number of these elements (frames) could compensate weakness due to lightening.
    In summary, I believe that this structure may be as light as any other well calculated. We would have to do some calculations. In any case I think that any naval architect can use that idea, if believed advantageous.
     
  5. PAR
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    PAR Yacht Designer/Builder

    This isn't anything new, just clever engineering, which is why it's included in Geer's book. You can take this approach with just about every hull material choice and framed building method. I'm sure Derecktor will consider this a proprietary process and limit access to details, but it's really just engineering 101.

    Simply put, ". . . Closely spaced ring frames and longitudinals allow very thin plate.
    Numerous carefully engineered lightening holes further reduce weight . . .", is a blatantly obvious thing to anyone with an engineering background, with the opposite of course being, widely spaced framing and a heavier planking schedule . . .
     
  6. TealTiger
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    TealTiger Junior Member

    I appreciate your input TANSL; thanks.
     
  7. TealTiger
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    TealTiger Junior Member

    I appreciate your input PAR; thanks.
     
  8. TealTiger
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    TealTiger Junior Member

    Does anyone know of NA's, yards, or boats that go to these extents?
     
  9. TANSL
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    TANSL Senior Member

    Everything good is copied. If anything is not very often seen may be because it is too expensive or because it is not as good as thought.
    I do not know the exact reason but after many years calculating structures, I have rarely seen this type of structure. Perhaps it is only acceptable for a very specific type of boat.
    Not sure to replace plate thickness for reinforcements gets a lighter structure. What is certain is that the structure will need much more labor and produce many more welding deformation.
    You also need to think if the shipyard has the tools necessary to attach and weld such structure.
     
  10. TealTiger
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    TealTiger Junior Member

    Those sound like good points TANSL; thanks.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Oh dear, not this old chestnut again :(

    As PAR and TANSL have noted it is simple panel aspect ratio. Make the panel size smaller ( Length x span) the plate thickness may be reduced, as per Class rules.

    BUT...what is never noted is the INCREASE in in internal frame weight. Since to reduce the panel size means the number of stiffeners and often frames increase, which..yup...adds weight.

    I've done the rounds of this increase/decrease frames/stiffeners since the late 80s, there is no panacea. Most sadly look at the thinner hull plate size...wow, we've saved weight...er nope. Once you do the sums, the difference is negligible. In some cases it adds more weight because the frames have minimum values as well as the stiffeners, for class compliance.

    Then there is the significant heat input, as more frames/stiffeners means more welding....and coupled to that, because the plate and often web thickness has been reduced, the welder is blowing too much heat into thin gauge alloy and the boat distorts and buckles and looks a mess. A classic hungry horse effect.

    Words like "Extreme light weight..." is just sales & marketing BS to catch the less informed into thinking there is something new...and hey, the squeaky wheel gets the oil. QED!
     
  12. PAR
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    PAR Yacht Designer/Builder

    Not to mention John, the labor assembling the structure with it's the additional frame and longitudinal counts. Maybe a process better suited in countries where welders are making $9 a day.
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    Exactly...and then there is the increase in gas bottles used, filler wire, grinding discs etc etc. and the electricity usage in the yard blah blah blah...

    Robbing Peter to pay Paul, doesn't work!...no such thing as a free lunch!
     
  14. PAR
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    PAR Yacht Designer/Builder

    Yes, it does, you can rob whomever and send it to me in an envelop anytime you like :)
     

  15. rxcomposite
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    rxcomposite Senior Member

    Make that two. I am changing my name to Paul.:D
     
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