: So, how does this sound. 3mm ply, 2oz glass on the inside (applied
: pre-assembly per your technique) 4oz tightweave outside, further 2oz layer
: on bottom of hull. Stripped deck, 4oz tightweave top and bottom, bottom
: supported by foam/graphite ribs and stringers. Extra reinforcement around
: cockpit, aft-deck for re-entry.

I'd just buy 2 ounce cloth and put on two layers. Why? Cheaper, maybe with an additional discount due to the length, ability to use scraps pieced together, thinner weave to kill with fill coats of resin. can go to 3 or 4 layers for ding resistance where needed, less feathering at joints and overlaps, less sanding, faster wetout, smaller batches of resin to mix, applying on a bias gives good fit, and putting next layer at an angle to that bias gives good strength (Orient bottom layer 20-30 degrees right of keel and 2nd layer 20-30 degrees left of keel, for example)

: I'll experiment with some panels and my vacuum setup - if I can see a
: significant difference in weight between them (equal rigidity and fail
: strength) then I'll do it - otherwise I won't bother.

while your'e at it, use a scrap of your leftover 6 ounce cloth and compare it to 3 layers of 2 ounce cloth.

By the way, the reference to food packaging was meant to be a hint that you can draw a vacuum and seal the thing, like vacumm packed food. If the seal is good you don't need to keep the vacuum pump running. You may not get as much vacuum (is that a concept or what?) as with a constantly running vacuum pump, but you should get enough to draw the glass tight to the wood. With a good vacuum pump you might get a vacuum of 14 psi, but even with a vacuum of only 1 psi (well within the range of a home vacuum cleaner or shapvac) that is the same as 144 pounds per square foot of pressure -- or twice the pressure you would get from a sack of sand set on top. And sandbags are pretty good weights! Draw down the pressure and when the bag is sealed it stays under the crush of the atmosphere.

PGJ