Aluminum vs Carbon/Nomex!?

Discussion in 'Metal Boat Building' started by TealTiger, Aug 31, 2014.

  1. TealTiger
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    TealTiger Junior Member

    Could a 'cost no object' aluminum or hybrid cat come close to being as light (within 20%) as 'a cost no object' Gunboat (www.gunboat.com) of similar durability!?

    I'd have doubted it, but the author of Boat Strength (Mr. Dave Gerr), Aluminum and Steel Alternate Construction Methods - Lightweight Aluminum Scantlings (ch17). 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."

    Derecktor says: "The method...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. Adding "...it is a labor-intensive (costly)...(but) the hull structure represents only 10 to 20% of the final cost of the vessel."

    Again, could a 'cost no object' aluminum or hybrid cat come close to being as light (within 20%) as 'a cost no object' Gunboat (www.gunboat.com) of the similar durability!?

    If so, this method and/or something else?

    Thank you.
     

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    Last edited: Aug 31, 2014
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Without knowing the SOR, it is a meaningless question. Every boat is designed differently for its own unique SOR. In other words a compromise that is made for one is most likely not applicable for another, as design is a series of compromises. Thus you're comparing apples with oranges.
     
  3. upchurchmr
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    upchurchmr Senior Member

    In the Aerospace business graphite has significant benefits.
    However, in comparing the wings on two recent fighter aircraft, a unitized composite wing weighed 15% less than an equivalent 100% Aluminum wing.

    That is a real comparison of "cost is no object" design. Except of course the composite wing costs about 5x the composite wing.

    You would have to do the study with very good quality engineers, lots of testing, and a requirement for the same life span to get a real answer.

    Cubic bucks is what it takes and one engineering mistake or construction mistake will throw the whole comparison in the trash.

    My example is exactly apples to apples. But it was not a boat. So you really still did not get an answer.
     
  4. rxcomposite
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    rxcomposite Senior Member

    Whether it is a boat or an airplane, the engineering principle is the same. The method of construction is the same for single skin method to satisfy load, strength, deflection, requirements. It is a close frame and longitudinal spacing and deep webs to support a thin skin.

    You cannot use the same technique with single skin FRP as it is too "flexible". Increasing the depth of the supporting frame to increase stiffness will only add weight and reduce usable internal volume.

    Advanced Composites uses cored carbon composite skin which increases stiffness reducing the need for the support structure to prep up the surface skin.

    Attached images of aluminum Incat wavepiercer which the brochure says borrowed heavily from aerospace technology. Same way the RANS RV all aluminum aircraft is built. RANS is only a kit built experimental aircraft but the construction technique is the same. No advanced "aerospace technology".
     

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  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Teal tiger needs to specify what kind of boat he wants to apply lightweight construction methods too, otherwise it is a "lightweight" discussion.
     
  6. upchurchmr
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    upchurchmr Senior Member

    You certainly are correct, the Rans and the Wavepiercer have no advanced "aerospace technology".
    This is about 1940's level technology.

    You certainly can use the same technique for single skin fiberglass, you just might need even more substructure. There you go making a generalization based on the wrong assumptions. Who ever said you would want deeper substructure?

    Glass is inherently less stiff so it is not going to work as well as aluminum for weight.

    Why did you jump off into a completely different kind of construction - core stiffened composites? That has nothing to do with a grid stiffened shell construction.

    I might as well have started talking about SOF kayaks.
     
  7. rxcomposite
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    rxcomposite Senior Member

    1. You did.

    2. I said that.
     
  8. TealTiger
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    TealTiger Junior Member

    I appreciate your input Ad Hoc.
    I figured some might not know of Gunboat, hence the link.
    Thanks.
     
  9. TealTiger
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    TealTiger Junior Member

    I really appreciate your input upchurchmr.
    That’s interesting and somewhat surprising to me. It tends to corroborate Mr. Gerr, and Derecktor.
    Thank you.
     
  10. upchurchmr
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    upchurchmr Senior Member

    1. No I didn't, more substructure means closer spacing on the substructure. Both wings were 4% thick - not possible to have deeper substructure.

    2. No you didn't. You said you could not use the same technique on FRP.
    Completely wrong since the example I gave for composite was FRP, and the technique of "more" substructure works with either glass or carbon fiber.

    In fact the example I quoted was the result of not choosing a graphite/ core sandwich. One of the reasons was that the internal volume was reduced. Wings are full of fuel and the loss of fuel caused a loss of range.

    Never mind. I'm tired of trying to point out where simplistic statements mislead people. :D:D

     
  11. rxcomposite
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    rxcomposite Senior Member

    Oh I see upchurmer. Were you talking to me or you were just swiping at my post? Did you not notice the number on the post feedback to see who said things first?

    Oh I see. you wanted the glory instead of me explaning to Teal, my appreciation of the thread. Me posting more would not help any because you cannot restrain yourself at swiping at my post by saying "There you go making a generalization based on the wrong assumptions...............core stiffened composites? That has nothing to do with a grid stiffened shell construction."
     
  12. upchurchmr
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    upchurchmr Senior Member

    Glory. I have never seen any here.

    I don't like you misleading and overstating.

    I don't think I said anything about your appreciation of the thread. This is a typical misleading statement.
     
  13. rxcomposite
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    rxcomposite Senior Member

    Keep on dragging your net. Maybe somebody else will bite.
     
  14. PAR
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    PAR Yacht Designer/Builder

    Notice a theme with the blue/green Tiger posts folks, in spite of extensive previous exploration?
     

  15. yofish

    yofish Previous Member

    Am I missing something here? What's everyone so touchy about?

    What does this mean: "Notice a theme with the blue/green Tiger posts folks, in spite of extensive previous exploration?"

    After tomorrow, I'll be back in two weeks after a nice refreshing moose hunt with no teevee or computer and only a satphone for communication. I look forward to how this odd thread turns out; the cognoscenti chess game.
     
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