UNFOLD acceptable errors

DELFTship forum General Questions UNFOLD acceptable errors

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    • #39024
      iosif gross
      Participant

      Hi

      I would like to ask a question regarding acceptable unfold errors.
      On my new simple V shape 3 meter motor boat I am getting the bellow results for unfold:
      Max. edge stress -0.796 %
      MAX. face stress 0.659 %
      Area difference 0.00010 (m2)
      What is acceptable stress/difference?

      Best wishes
      Iosif

    • #39027
      Maarten
      Keymaster

      Hi Iosif,

      What is acceptable depends on the material you want to use- how much can it deform without breaking / tearing? Ideally you’d want stress to be 0%, but that would be very optimistic 🙂

    • #39028
      iosif gross
      Participant

      Thanks for the answer Maarten 🙂

      I am using 6 mm plywood for a 3 meter by 1.3 meter V shape boat, will use stitch & glue Technic
      Will try to reduce the stress as much as I can
      What you think, a stress of less than 1% on the plywood is acceptable?

      Best wishes
      Iosif

    • #39029
      Maarten
      Keymaster

      Hi Iosif,

      I trust you’ll understand that I can’t speak for material properties… My recommendation would be to check with the supplier, and / or do some rigorous testing yourself..

    • #39032
      iosif gross
      Participant

      Thanks again Maarten

      I will build the boat within 2 months and I will report the results.
      In the mean time, will try to reduce the stress to minimum.
      I am reading the documentation to see if I can see the stress % change while moving the points
      If can’t, will do it manually using a table I prepared

      Best wishes
      Iosif

    • #39040
      iosif gross
      Participant

      Hi

      After the corrections I made, I got worst case of:
      Max. edge stress -0.345 %
      MAX. face stress 0.149 %
      Area difference 0.00017 (m2)
      It altered the boat forward section, it have a more aggressive shape now, but above the water line 👿
      I will report back how was the construction, hopefully within two or three months

      Best wishes
      Iosif

    • #39062
      iosif gross
      Participant

      In the mean time loaded the .fbm of the trimaran two AMA I built already.
      The AMA have a V shape and have a transom to connect it to the VAKA by the bamboo AKA
      On L/B/H of 3200/300/364 mm I got:
      Max. edge stress -1.029 %
      MAX. face stress 0.666 %
      Area difference 0.00048 (m2)
      I built it from 6 mm plywood with the stitch & glue method.
      The build was not difficult, but I got the last 500 mm back to the transom a shape that I had to stabilize with a temporary external string for the sheer to stay in the correct place.
      So maybe in the size I mention those irregularity are acceptable

      Best wishes
      Iosif

    • #39063
      Icare
      Participant

      Hi Iosif!

      Do you know that plywood can be bent using steam. This leaves the plywood with all its solidity.
      (https://www.wikihow.com/Bend-Wood)

    • #39067
      iosif gross
      Participant

      Hi Icare
      Thank you for the link. Very helpful.
      I know it can be done, never tried before.
      I am wandering how it can be done on big peaces of plywood.

      Best wishes
      Iosif

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