Weight of welds on aluminium

Discussion in 'Boat Design' started by Satan, Apr 19, 2017.

  1. Satan
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    Satan Designer

    Hi Guys , what about the weight of welds for a 8.8 meters aluminium center console using MIG ?How can it be estimate ? The aluminium is 5083 . I think about 3% but the shipyard estimated 30% but it upsets all my weight estimation and hydrostatic.
     
  2. TANSL
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    TANSL Senior Member

    Working with steel hulls I have always used a fictitious density of 8.00 kg / dm3, instead of 7.85 kg / dm3, to take into account the weight of the weldings. I think that percentage or maybe a little more, which as I say is backed by many years of practice, may also be valid for aluminum: 3%
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Satan, the 30% sounds hellishly expensive for welding wire !
     
  4. Satan
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    Satan Designer

    I hope that was misunderstanding....thank you so much for your precious support and clarification.
     
  5. daiquiri
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    daiquiri Engineering and Design

    30% is not possible, 3% is very reasonable.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    usually between 1-3% a good average is 2%
     
  7. Barry
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    Barry Senior Member

    Aluminum 1/8 3.2 mm fillet = 0.092 lb/ft 0.03 kg/m

    Aluminum 3/16 4.8 mm fillet = 0.026 lb/ft 0.04 kg/m

    Aluminum 1/4 6.4 mm fillet = 0.05 lb/ft 0.07 kg/m

    Aluminum 3/8 9.5 mm fillet = 0.06 lb/ft 0.09 kg/m

    Aluminum butt weld 13 mm plate 60 degree single V = 0.3 lb/ft 0.43kg/m

    Aluminum butt weld 18 mm plate 60 degree single V = 0.4 lb/ft 0.66kg/m

    Aluminum butt weld 25 mm plate 60 degree single V = 0.82 LB/FT 1.2kg/m

    Aluminum butt weld 38 mm plate 60 degree single V 1.7 lb/ft 2.6 kg/m

    Aluminum butt weld 50 mm plate 60 degre single V 2.8 lb/ft 4.2 kg/m

    Attached is a table captured from the internet with weight of aluminum weld per meter. As it appears that you are doing your own design, you will know how many meters of weld that you will have.

    If you paint the boat, I would expect that the paint will weigh more than the weld material.
     
  8. JSL
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    JSL Senior Member

    I usually allow 7% for 3 items
    1.weld,
    2.over-rolling of plate(not common but does happen) &
    3.misc. small clips and trip brackets.
     
  9. Barry
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    Barry Senior Member

    So a 12,000 pound 36 foot boat would have 840 pounds of aluminum wire??

    The last 36 foot we built, I purchased 48 pounds of a wire that from a manufacturer that we did not normally use and still had some rolls left over.
    Hull 1/4 inch, side and deck 3/16, roof and support 1/8inch, planing hull, sedan

    This is .4% of total weight.

    Do you perhaps mean that this is the amount that you allow for waste??
     
  10. JSL
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    JSL Senior Member

    No
    see my edited info.
    as to waste (crops), that's another matter altogether.
     
    Last edited: Apr 19, 2017
  11. Satan
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    Satan Designer

    An Out of argument question what do you think about the thickness of 5 mm for the bottom and 3-5 mm for deck ? It is accordant with ISO 12215-5 calculations but several boat use 6 mm for bottom it is due distortion of plates ?I would lighten the structure . The keelsons spacing is less then 350 mm and longitudinal deck stiffeners is 325 mm
     
  12. TANSL
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    TANSL Senior Member

    It depends on several things, as you know, and above all on the dimensions of the bottom panels (spacing between longitudinal and between transverse reinforcements) but I dare to assure that 6 mm are not needed, unless there is, for example, a problem of longitudinal strengh. Could we have a drawing of the structure, to give a more reasoned opinion?
    I recently made a study for a boat of 13 m in length, in aluminum, 36 knots. The bottom panels, in the central zone, were 250x650 and 4.85 mm thick. In the bow of 250x650x5,5 mm.
    If you do not want to make your project known and it seems appropriate, you can send me information by email. I will be happy to give you my opinion on your structure.
     
  13. TANSL
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    TANSL Senior Member

    Although I have invented most of the data and, therefore, my results are not reliable (see attached file), it seems clear that the scantlings of your boat are very oversized.
     

    Attached Files:

  14. Barry
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    Barry Senior Member

    If your loaded boat will weigh in the neighborhood of 2500 kg, the difference between using 5mm or 6mm might be around 100 kg. This is not a lot of difference that you will see any negligible difference in fuel. The 6mm will allow less distortion when welding. Sure you can use 5mm, and with a proper welding sequence you can get it quite fair. On the other hand, you can avoid some of the distortion issues by going to 6mm,

    3mm for the deck would be at the lower limit for a deck. Certainly, it is thick enough but you might have some flex between the supports. 4mm would be better.
     

  15. Barry
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    Barry Senior Member

    Re stringers or stiffeners.
    Without seeing the aft profile to see how the designer was going to deal with installing the deck, and I am assuming you are referring to the floor of the center console boat, I would not use the small scantlings in your specifications

    You have a 20 degree deadrise so you will probably be wanting to have a relatively flat floor. So the depth from the floor/deck will increase from the chine to the keel.

    Instead, (as was our procedure) we would form angle stringers in our hulls that might vary from 6 inches (150mm) in vertical depth from the keel moving out, getting down to 2 inches at the chine. The top flange of the angle would be installed level with all the others and the flange would provide a flat mounting surface to install the flat floor/deck.

    Yes these stringers will weigh more than the small stiffeners that you have listed BUT it is important to remember that somehow you will want to increase the vertical height by some method to get a flat floor/deck and it will have two real parameters.
    1) it will weight something and probably more than the weight of a taller stringer
    2) it will require a fastening method to attach your aluminum floor to the upright section
    3) if it is not aluminum, the raising material will not provide the same strength as a larger section modulus, longer legged angle

    Ie if you just run a series of 50 mm flats or 50x40 angle, you have to add something to raise the floor and make it flat.

    If you are really fussy, and you must be if you want to know how much the weight of
     
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