magillamelb said..
Is there a specific grade of Polystyrene used in the manufacture of SUP boards?

Should be H grade which is 25-30kg ish I think.

But depends upon what the outer layer is, PVC (divinycell) foam sandwich over the styro is way stronger so you can use lighter styro. May need denser styro if just glassing over and using a layer of bamboo / pine etc.

I'd go with option number 1, but only 5mm PVC foam in standing area, and 3mm everywhere else, is plenty.
Also carbon under the foam is not needed, just do 2oz glass between styro and the PVC in the standing area, nothing but resin under the rest, and your carbon on the outside only.
Presuming a very well sanded and faired blank, ie: no little foam voids, for maximum adhesion.


That would be same as a windsurf board designed for hard n fast over chop and limited jumping, so I reckon it will be plenty enough if board is under 9ft ish.

Caveat - I've never built a SUP. :)

I think the standard construction I detailed would be OK. Just a stringer would become necessary due to the length - 3mm d'cell with about 100gsm unidirectional carbon on each side, bonded down the middle of the stryo.

Gonna be expensive there is $600 ish materials in it

i would suggest the lightest, SL grade EPS
I think the stringers would be overkill , even though it will help overall board stiffness lots , you can easily buy carbon Double Bias 150 gsm 45/45 fibres which will add longitudinal stiffness and good skin strength

25 kg / m3 is what is used for surfing SUPs. But it will be heavy for high volume boards like a 16'.

Gong for instance has a 12'6" in 26 kg/m3 with a simple glassing, it weights 14kg (first models were even heavier than 17kg...)
Similar shape in 16 kg/m3 with a PVC sandwich deck + carbon layer to get strength in the skin weights 11kg

(See details at http://gongsupshop.com/epages/box1707.sf/fr_FR/?ObjectPath=/Shops/box1707/Products/GON4SUPSHERPABR gongsupshop.com/epages/box1707.sf/fr_FR/?ObjectPath=/Shops/box1707/Products/GON4SUPRAGEBR126 )

You may want to consider mixing densities, and use carbon for the string, as a full wood stringer can be heavy.

^^^ why anyone would use a wood stringer in such a large board is beyond belief anywyay.
Like I said, 3mm divinycell with thin uni carbon each side is farken stiff and half the weight of wood.