Note from Shorty - This test was done in relation to discussion in the group about ultra light PD hull construction with various materials.
Picture to the right -- Puncture test setup.
The square of 3/8 ply is only to hold up the scales for the pic to be taken.
The gray patch on the 1/8 ply test piece is a 1/16" layer of epoxy
Here's the setup: a test piece of 1/8" ply (door skin) is clamped to the edge of a table,
then an awl placed on it, then a bathroom scale
placed on the awl, then weight applied to the scale until the awl
punches through the plywood. The pounds of pressure being applied a
the time of punch-through is noted.
I did this two times each with a piece of 1/4" corrugated cardboard,
a 1/8" piece of door skin plywood, a piece of door skin with 1/16"
layer of epoxy coating on it, and a piece of 1/4" inch B-C exterior
plywood.
So 1/8" ply is 4.7 times as puncture resistant as corrugated
cardboard but an epoxy coat increases puncture resistance to 8 times
that of cardboard. However, 1/4" ply is 14.7 times as puncture
resistant as cardboard.
Update
Final Puncture Test From left to right: 2 x 1/8", 1/8" with cloth coat, cardboard with cloth coat
Curiosity led me to try a puncture test on a section of 1/8" doorskin
that was coated on one side with Titebond II-soaked cloth. And as a
reference I tested a Titebond II-soaked cloth coated section of
cardboard. Also since I've seen it proposed to laminate 2 sheets of
1/8" to achieve the strength of 1/4" ply, I tried a section of that.
Here's a photo of the 3 types of material. The cloth is 50% combed
cotton/50% polyester, 200 thread count weave. I applied it by the
procedure detailed in Jason Nabors' post 7314, except no water was
added to the glue. I let the Titebond II dry for 3 days.
The glue-soaked cloth does increase the durability of material as it
did with the cardboard and with the 1/8" doorskin. Laminating 2 1/8"
sections of doorskin failed to achieve the strength of factory
produced 1/4" plywood.
As a side note, the cloth easily peeled away from the cardboard
because a thin outer layer of the cardboard easily goes with it. The
cloth on the doorskin, however, was tightly bonded and I couldn't
peel it away by hand strength. The combination of 1/8" plywood and a
cloth coat, plus some additional strength from paint, is something I
would consider for hull material.
Final Puncture Test From left to right: 2 x 1/8", 1/8" with cloth coat, cardboard with cloth coat