Extreme Lightweight Aluminum Construction

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

  1. TealTiger
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    TealTiger Junior Member

    FWIW, Derecktor says:
    "The method of aluminum construction to which you refer has been used successfully in a number of ocean racing mono-hulls, specifically Boomerang, the 12-meter Stars & Stripes and others.
    It provides a strong, fair and lightweight structure. ...However, it is a labor-intensive process and is therefore costly. ...(but) the hull structure represents only 10 to 20% of the final cost of the vessel."
     
  2. Ad Hoc
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    Ad Hoc Naval Architect


    This too is nothing new, we have built several vessels this way since the mid 90s. I even used 3M double sided tape on large fairings/bulwarks.

    The main issue to overcome is the simple one...Fire. The resistance to fire tends to make this method of construction limited in its application, and/or the mitigating procedure renders any gain null and void.
     
  3. BMcF
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    BMcF Senior Member

    But no duct tape? :p
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    Couldn't easily get LR approval for duct tape in those days :(
     
  5. TealTiger
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    TealTiger Junior Member

    Derecktor has also said:
    ""extreme lightweight construction" can mean many things, each with its own level of complexity and expense."

    I imagine a continuum with Strongall® (http://www.meta-chantier-naval.fr/web/notre-histoire/histoire-du-strongall/) at the strong end, conventional in the middle, and Derecktor's at the light end.

    Does anyone know of any lightweight methods more extreme, or outside of this continuum?

    Thank you.
     
    Last edited: Aug 31, 2014
  6. TANSL
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    TANSL Senior Member

    I truly believe that talking about "extreme lightweight construction" is misleading advertising. All structural designer must calculate the minimum weight structure for each of the ships designed . For that there is no constructive method to ensure a minimum weight but calculation procedures, some more sophisticated than others, that bring the designer to project the structure of minimum weight.
    I have not done any calculations but I doubt that the structure of Derecktor is the one with minimum possible weight. And, of course, is much more expensive than other structures. Therefore, according to my views, without knowing other reason, I see no reason to use a much more expensive structure than any other, which has been calculated correctly.
     
  7. TealTiger
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    TealTiger Junior Member

    I appreciate your input TANS;
    But I didn’t ask what makes financial sense. Before Gunboat, I doubted anyone would’ve said a 60’ cat in all carbon/Nomex honeycomb was reasonable/sensible. Today they’re backlogged.
    But I’m curious: You say, "I doubt that the structure of Derecktor is the one with minimum possible weight"
    Do you or anyone else know what other aluminum or hybrid method might possibly be lighter?
    Thank you.
     
    Last edited: Aug 31, 2014
  8. Ad Hoc
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    Ad Hoc Naval Architect

    T.T

    You're starting to mix up sales BS and hard engineering facts. In doing so you'll elicit replies that answer to both, but only 1 is sound the other is highly subjective and most likely emotive too.

    I assume from your Q you have never designed the structure of a boat before? Since as previously noted, it is simply the panel aspect ratio...the span x stiffener spacing with an applied load. It is that simple.

    How you arrange the structure is another matter. However, there is a load and then you have the response. The response is dictated by the load and more importantly, how the load is absorbed into the hull. That's the structural arrangement which has "load paths" to absorb the applied load into the hull effectively.

    There really is no magic to it at all, it is very simple construction and structural engineering.

    But to get an "edge", sales/marketing depts will hype up their company using highly subjective words and phrases which are totally meaningless to NAs in order to sound knowledgeable or important or as if the holy grail has been found. Only those who have designed and calculated such structures or have an understanding of the principals behind such calculations to design a structure that satisfies the applied load with a given response can really see through the smoke and mirrors put up by such sales/marketing BS.

    After which it is your prerogative whether you wish to continue believing the hype or the objective engineering facts as laid in front of you...only you can then decide which.
     
  9. TealTiger
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    TealTiger Junior Member

    I appreciate your input Ad Hoc; thanks.
     
  10. TANSL
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    TANSL Senior Member

    I advise you to re-read, in detail, some, all, the answers we've been here.
    In summary:
    - Constructive method does not produce by itself the structure of minimum weight.
    - GRP, carbon, aram ide, etc. can in some cases produce a lighter structure than aluminum. You should realize what ship you're talking about.
    - Probably, although I can not guarantee that even in aluminum can get a lighter structure. I would make a bet on this. There may be reasons unexplained until now, that make the structure Derecktor is the most desirable (no minimum weight)
    - Reread post # 38
     
  11. upchurchmr
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    upchurchmr Senior Member

    Teal,

    The difference between marketing and engineering is real as discussed above.

    The fastest way to get lighter weight for any construction is to reduce the "margin" or calculated excess strength.

    This will cut into the structures safety in extreme conditions, but will not show up until the boat doesn't come back (or is severely damaged).

    This is extremely difficult to recognize when someone has done this.
     
  12. SamSam
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    SamSam Senior Member

    I guess longevity has little to do with a boat of this type. With all that intricate thinned structure and thin skin with hundreds of catch pockets I imagine corrosion would quickly destroy it.

    [​IMG]
     
  13. TANSL
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    TANSL Senior Member

    In plate theory are used formulas like the one in attached drawing, which are valid only when the deflection in the center of the plate is less than 0.5 times the thickness of the plate.
    According to this formula, the worst case occurs when a / b = 2, for equal values ​​of "q" (load on the plate) and "t" (plate thicknes).
    Given this, it seems that the structure we are discussing, which seems to have a / b = 2, will not result in thicknesses / weights minimum.
     

    Attached Files:

  14. TealTiger
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    TealTiger Junior Member

    I appreciate your input upchurchmr; thanks.
     

  15. TealTiger
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    TealTiger Junior Member

    I appreciate your inpyr SamSam; thanks.
     
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