4 mm as shell plating for aluminum catamaran

Discussion in 'Metal Boat Building' started by LePrince, Oct 20, 2022.

  1. LePrince
    Joined: Apr 2011
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    LePrince Junior Member

    Dear all
    I am working on design of 26 aluminum catamaran, after using DNV rules, the shell plating thickness was 4 mm

    my question is how feasible is using 4 mm as shell plating, I mean from a welding point of view? will it as any problems when applying butt and fillet welds ?

    or should i go for 5 mm ?

    Thanks alot
  2. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    What do you mean with "26 aluminium catamaran", is it 26 feet or 26 meters or ??

    Then to the welding; there is nothing special with 4 mm alu, as long as you apply the normal procedures for aluminium welding. It's all a question of knowing the how's and what's; including welder skill.
    bajansailor likes this.
  3. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    I presume that this cat is 26 metres long?

    If the DNV rules say that you can use 4 mm plate then that is fine. It is possible to weld 4 mm plate fairly easily.
    I presume though that your frame and stringer spacing is less than if you used 5 mm thick plate?

    Is this just a design exercise, or is there a good chance of it being built?
    Can you supply some more details about the cat please, such as a General Arrangement drawing?
    You could even let this thread develop into a design and build Blog for your cat.
  4. LePrince
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    LePrince Junior Member

    Sorry, it is 26 meters and thanks for your answer
  5. LePrince
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    LePrince Junior Member

    Thanks alot

    it is a design exercise but i wanted to know how close can i go to the reality
  6. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    There is more to it that just that.
    Welding is just one variable as the designer you need to take into account.

    The objective of "design" is to design a structure that is fit-for-purpose.
    So, just simply running the numbers, as you have done, does not necessarily mean it is good or bad.
    You have rightly questioned, is 4mm acceptable. But that depends upon the intended purpose of the vessel, as well as how you have arranged the frames and stringers.

    If the vessel is a workboat, then no, 4mm is too thin...why?..because it is a workboat which will get bashed hit bumped into a myriad of items on a daily basis, not to mention coming along side for berthing in heavy weather.

    Whereas, if the vessel is for a low wash light weight catamaran running on the river...then yes, 4mm can be "acceptable" - with given caveats for suitable frame and stringer spacing, general daily usage of berthing debris in the water and of course production etc etc.

    As with everything in design..it depends!
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  7. TANSL
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    TANSL Senior Member

    4 mm may be sufficient although, as has already been said, it depends on the type of ship and its working conditions. If you do not see yourself capable of welding 4 mm well and you decide to increase the thickness, try to at least take advantage of this circumstance by increasing the separation between reinforcements to save weight and labor.
    bajansailor likes this.

  8. comfisherman
    Joined: Apr 2009
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    comfisherman Senior Member

    4mm is a tad over 1/8th. Definitely weldable especially considering the prevalence of pulse mig. 26 m you gonna get good at cutting seams on that a good pulse mig and a push pull gun would seem a necessity.

    All that said, I've known a few guys use .157 for superstructure on a couple boats. All who've used it wish they had gone thicker. Between the need for corrugation or lots of stringers print through was unacceptable even for a commercial boat. My last boat had 3/16 superstructure and I was happy with it.
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