Complex bends in aluminium

Discussion in 'Boat Design' started by Storm_Eagle, Aug 19, 2020.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    That's not correct stormy, a great many boats designed with the "hard" chine, are free of compound curvature. But you can be pretty certain that if there is no chine, it is compound curved, somewhere along the length of it.
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  2. KeithO
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    KeithO Senior Member

    It seems to depend on how much the customer is paying. Expensive vessels dont seem to be bound by any restrictions on hull shape regardless of the technology needed for forming the plates. But certainly cheaper hulls dispense with compound curvature as a mater of economy. The plates are laser or water jet cut and then fitted without the need for fancy processing. Even the radius bilge plating can give people fits to install, I have seen a couple building a steel boat who received pre-made plates for the radius build and they didnt fit the first time, nor did they fit the second time after nearly 6 months of delays in waiting to get replacements... It ultimately took Bruce Roberts 3 attempts at the radius plates to get them right....

  3. aktxyz123
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    aktxyz123 Junior Member

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  4. Ilan Voyager
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    Ilan Voyager Senior Member

    Some remarks.
    The canoes are made with an alu alloy series 6, heat treated. The plates used for a canoe are generally a 6061 state T1-T2 max T3 ie very ductile and as rigid as too cooked lasagnes with a thickness largely under 3 mm. You can form it with the hands. The rigidity of the final canoes comes from the shape. These canoes are riveted and weldings are kept to a minimum as the the HAZ will cook the 6061 to state T0, as rigid as a freshly chewed chewing gum.
    The alu alloys employed in marine are in the series 5, which are strain hardened often state T110. Very different mechanically from the series 6. Great advantage these alloys are perfectly weldable and are not too much affected by the HAZ. But in the other side if you strain them too much while forming they can become brittle or very sensitive to fatigue and corrosion.
    So often the forming is kept to the bare minimum. When you look at the big ferry catamarans and trimarans you see immediately that the curves are extremely simple, and most parts of the ships are flat.
    On alu monohulls, shipyards can form a lot but with more tender alloys, a lot of structure is needed under. A lot of alu yachts are hard chine with a minimal forming so a "harder" alloy can be used, with far less structure and thicker plates thus less weldings to do. Besides the plates are stronger and less prone to deformations while welding.
    Aluminium and small multihulls are practically incompatible, so alu has been abandoned since more than 30 years. I won't detail here the reasons.
    All that work need a lot of tooling and very well trained people. It's a job with a pretty steep learning curve over a few years. We are very far from the DIY boat.
    As said supra if you want very complex curves you go to composites, GRP, or other fibers mainly sandwiches of glass, foam and resin. Another alternative is wood strip plank a bit tedious but perfect for the DIY.
    If you look well at the pic of the catamaran of the first post only the bottoms are complex curves, the topsides are rather simple with no compound or very little. That is perfectly feasible in mix of strip plank (foam or wood) for the bottom and rather flat topsides whatever in composite foam sandwich or wood strips and plywood.
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  5. Storm_Eagle
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    Storm_Eagle Junior Member

    Can it be a soft heat treat for forming, and then heat treated to be harder after the forming?
  6. Barry
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    Barry Senior Member

    Certainly, if you find a place that could do the following, practical, not really

    ( grabbed from the internet, not my wording as the paragraph wording seems to focus on "hardness" after the first process while really the alloy has increased hardness but also changes in max tensile strength, ductility and a host of other characteristics)

    A few of the other characteristics that will change during the process
    Pulled from the net as well, and there will be others
    Proof Stress 0.20% (MPa) Tensile Strength (MPa) Shear Strength (MPa) Elongation A5 (%) Elongation A50 (%) Hardness Brinell HB Hardness Vickers HV Fatigue Endur. Limit (MPa


    The process of taking a 6061 aluminum part in O condition to a stronger, more durable condition begins by heat treating the parts at 985 degrees Fahrenheit for an hour in a drop bottom furnace. At that point, the basket containing the parts is dropped into a quench tank. The quench liquid circulates to cool the parts rapidly. The key to this process is speed and even cooling; the parts are quenched within six seconds of the drop bottom furnace door opening.

    With that process done, the quenched aluminum part is now in W condition. In this condition the material can be formed or straightened. Because time and room-temperature air can also have a hardening effect, setting these newly treated parts in the open on the workroom floor for 96 hours will bring the parts to T4 hardness. 6061-T4 aluminum is part way to the hardest that this aluminum alloy can be. The hardening process can be stopped by placing aluminum parts in a freezer until they’re ready to be hit on the press again.

    After this secondary pressing, the parts go through an aging heat treatment process. Aging aluminum 6061 is done between 350 to 500 degrees Fahrenheit, and—depending on thickness and other factors—the parts stay in the oven for 12-24 hours.

    Following this aging, the parts are now at a T6 condition. In general, T6 is the most common temper for aluminum, and because 6061 aluminum is often used in heavy-duty structures, the strength and limited formability of metal at that temper is important.


    In general, T6 is the most common temper for aluminum, maybe for 6061 series, for all aluminum, mmm??
    Last edited: Aug 24, 2020

  7. wet feet
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    wet feet Senior Member

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