UNFOLD acceptable errors

[iosif gross]

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

[Maarten]

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 🙂

[iosif gross]

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

[Maarten]

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..

[iosif gross]

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

[iosif gross]

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

[iosif gross]

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

[Icare]

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)

[iosif gross]

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

[Author]

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