: Four mm ply and 4 oz. glass would produce a light boat
Chris,
Sample--Thick-----Glass------#'s to---Panel
#---------ness-----Schedule----Failure--Weight--Deflection
OKOUME MAHOGANY PLYWOOD
1F-----5/32"-----1 Layer 4oz.----211-------8.5----1.47
2F-----7/32"-----1 Layer 4oz.----325------10.9----1.01
3F-----1/4"------1 Layer 4oz.----429------12.8-----.79

1E-----5/32"-----NO GLASS---------45-------6.9----1.60
2E-----7/32"-----NO GLASS--------149-------9.1----1.20
3E-----1/4"------NO GLASS--------225------10.7-----.63

BIRCH 5 PLY
4E-----1/4"------NO GLASS--------400------14.4-----.73

These are some test results I posted last week. The test panels were sheathed on both sides. You can see as your breaking strength goes up so does you weight and resistence to flexing. If your building under 12' 4mm should be fine. You should sheath the bottom with 6oz. glass for abrasion resistance. If you're going over 12' you may want to consider 4 or 6oz. glass on the interior of your 4mm or step up to 5mm. Just try to keep it on top of the car, it won't bounce well at 60mph.