Erez,

I would not use the 3mm ply as we have built F16 hulls from the Blade drawings & the folded up curve of the hulls turned out a little different than the frame drawings that were supplied. The 3mm did not stress the glass layers on the keel line enough to fold the hull into the desired shape. Stick with 4mm.

One other point - we used Gaboon 3 & 4mm grade marine ply & the quality was a little suspect. During the construction period, we encountered many problems with bits of core missing & the ply failed when stressing ( like Rolfe mentioned).

Ironically the ply came from Israel.??!!
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Regards