Plus the glue and the edges.  And we have not got any properties yet.  But worth a look..

With the thickness we are talking, cheap 1/2" foam gives a 1" core, Which has to have hella shear, no?

Depends on the foam properties, not the thickness..  Although 1" core will be a lot stiffer.

I meant, a core of bidirectional trapezoidal  400gsm fiberglass tubes must have very high shear?

I would guess way higher than any foam?

 If the corrugations are stiff enough not to need faces, they will be lighter and cheaper, albeit ugly (not a problem for hidden bulkheads and things like floors where either one side or neither side is visible), harder to build and challenging to fillet and tab.  

If you can source a vacable cheap foam (even EPS), and do a square corrugated, that you can infuse, you could have a whole system.

https://www.thermalps.com.au/imagesDB/wysiwyg/TDS_Expanded_Polystyrene.pdf

I think H or VH would work.

assuming VH you add ~0.35 KG/m^2

These guys, and many others in Aus, blow the polystyrene.  Assuming VH is the same from all suppliers, it squashes under vacuum.  

Not that big a deal for the foam, but the cloth wrinkles.  The only foam to use is the extruded polystyrene. I will look into this, but from memory, Foamular Aus do not stock the higher densities.

BAH! I assumed VH with it's 165kpa could hold 100kpa vac ok. I thought it might be perfect as it still might warp to a gentle hull curve under vac. If cheap enough vs XPS, hit it with a thin coat of resin/sealer?

Maybe.  I suspect it would crack under vacuum as the core compressed.     Another problem with blown polystyrene is that it soaks up water.  Not a problem if it is treated right.

Infused it should be water tight, but more resin weight and cost.

but XPS is probably resin uptake then EPS, minimal skin resin absorbed by XPS, and thus less net cost and weight I guess.

 

Foamular Aus has under concrete slab foam, so they must have something thats 170+KPA

Could be, but last time I asked, they didn't, but could get it if I ordered a truck load.

https://www.foamular.com.au/images/Tech_Sheets/761644850-Foamular-Metric-Insulation-Physical-Properties-fm300.april2016.pdf

Was that for the FM650, or also the FM250?

You vacced the cheap XPS. Did it move enough to fold/kink the carbon?

If you are getting glass from china, perhaps, if XPS works, get that too?

The glued together 400 gsm corro sheets are quite stiff.  The 200 gsm not so much.  Both are in the sun for a post cure, I will pronbably break them tomorrow.  The sanding and spot gluing was a pain.  Next test is one sheet of 12mm semicircular corrugated with a flat each side, all co-cured,  400 gsm double bias for the corro, 400 biax for the faces.

Pic before and after breaking would be cool.

Calculating square corrugations.

I guessed a flat and a slat ratio of one to one. so, ( \_ ). This is, of course configurable.

But the slant portion of the square corrugated would be the hypotenuse of a square, which is sqrt(2) = ~1.4, which is also how long it is vs mold length. so just slants, and only glue at just points ( \/\/ ), would be 40% longer. any flats would make it proportionally less.

Got to have the flats, and the slant angle has to be slightly rounded.  How much of each needs testing, but probably not much, if it is reliable.

To be clear this is what I mean.

Do these corners need rounded? I guess one could drag a sanding block over too sharp corners.

This might be obvious, but, these trapezoid short parts are the same width as the foam height. The slants are 45s. The base is 3x the height.

Could you guess if you think this is a good ratio? Or is a smaller flat better?

I am not sure. Part of me thinks this "looks good", but another thought is any flat length longer than needed to load to the skin is waste. So just enough flat to glue/infuse/load to the skin and more 'slant' is adding the most stiffness/shear.

So a Shorter flat (5 or 10mm?) and lighter glass (200gsm) might be lighter and have enough shear?

And, it seems, if this core is good, you might not need two layers?

You could lay up hot wired trapezoids (yellow), (bevel cut the edges, beveled on an angle along curves?) replacing the 'II' core, and lay up a core glass corrugation over them. place the top trapezoids. And continue as usual.

With skins, complete the glass trapezoids should be very stiff in both directions. But, if there is a doubt, you could cross lay up a stack down the middle of them for stringers. Again, the foam don't matter to the core properties. Its just a cheap/light way to make corrugated glass.

Perhaps at this point it would be neat to take it to a composite engineer and see what shapes would give optimal outcomes? Could someone on boatdesign help?

Maybe.  The deal i have with the prototype cargo proa includes access to some of the best engineers and testing equipment in the country.  More on this in the next week or so, but sailing by Xmas is back on the agenda.

WAHOO!