board build question

16 kg/m3 works well, strength wise.
Its the lightest available for me (NZ)
A squared blank for a 70 lit board weighs 1010gr.
Would be nice to get rid of some of that dead weight.
I hear 11kg is available in Aus.

Ok lightest it is! Was worried about fatigue as all my boards seem to go soft in front of back footstrap. Am going to router/inlay divinacell around straps and mast foot, am going to be bagging the laminate and was going to use double bias you guys know what weight and how many layers for deck and bottom was thinking 2 x 1 and patched accordingly. Thanks!

Flatwater, slalom style for moreton bay. Am going to pre shape using aku shaper.

If you use decent PVC (not divinicell) you'll get much better results. Seems to me that modern PVCs are so much stronger, you can get away with less outer laminate.
Herex H100 5mm hull with Airex R63.80 3mm deck is a good combo but fairly expensive.Have made some using H80 density 5mm hull and its good also.
Lately I'm using Corecell 5mm hull and 3mm deck and use R63.80 3mm just on the nose and tail where its better flexibility is easier to work with. I use it for 300mm on the nose and tail. This set up is less expensive.
Under the hull PVC I use 1 full 4oz glass layer ( I reckon its just a blotter for the resin)
Glue mix down the centre and outer edges on the PVC.
A Tee stringer down the centre from tail to 1400 mm.
Stringer is 100mm wide 200gr carbon pushed into a 40mm deep slot made with a short jig saw blade.
Tee stringer holds the rocker line while you build and they never get negative rocker between the straps.
Throw that lot on the rocker table and vac it for 18 hrs at 40 deg and max 0.3 bar vac. (you don't lose the rocker with lowish pressure)
Shape it.
Under the deck PVC, 150x200mm patches 200gr cf under front feet
Tee stringers here also if you're jumping, 200mm long.No foot dents with these.
160mm wide 200gr cf patch across the board at the back foot straps.
60mm wide strip of 450gr cf uni down the middle of the board to 1700mm.
270x110 wide fin box cap 200gr cf.
Glue mix down the middle on the PVC and along the rails.
I use a PVC block 40mm thick,310 long x 65 wide for the mast.Fitted in the poly blank with 2 x 4oz glass laterals and same weight longitudinals under the pvc block.
Route the mast track in after the PVC is bonded on and just glue the track in before laminating the deck.
For slalom boards, 1 layer of 200gr carbon for the outer layer, hull and deck.
I'd use 125gr if I could get it.
Jump boards I use 1 x 6 oz glass/ 1 x 72gr kevlar/ 1 x 4 oz glass. Strong and cheap.
This build set up works great, no dents,no negative rocker and haven't had any de-lam troubles. Weights come out same as Carbon Arts.
Wish I could get that 13kg poly mentioned, that would get rid of 200 gr.
Weight is in the resin content.
Use a poly lined table (I use an old core door for my table) lay your fabric on the table, pour the resin on and squeegy it using a steel squeegy (gets more resin out)
Roll it onto a cardboard poster tube to transfer it to the job. Most of the resin stays on the table and the tube rather than making your board heavy.
To bond the PVC onto the blank I use 48mm PVC tape and wrap the PVC on with this, then throw it on the vac table using a 3mm packer (to match the overlap) between the table and the board. I do the whole board in tape and the packer is taped on also.
The PVC tape shrinks and pulls the PVC on nicely.
All done with max 0.3 bar and the rockerline comes out accurate.
Long winded reply,but it's a big job and good on you for giving it a go.
Feels great sailing your own stuff.

Te Hau thanks for the info. Great starting point for my first foray into a sail board build! I will keep posting my work as it progresses cause youre right, theres no other ride like riding something you crafted! Now I gotta save for the carbon!

Pretty simple. I have black Polythene sheet hanging over the rocker table with an oil column heater (you ever hear of those in Aus?) in the resulting tent. Works great and gets plenty hot. I use the thermostat to control temp.

how much , my daughter lives there could be worth a trip, imagine what my garage would look like with something like that

Just did a quick ring around and can get a 2500mmx1200mmx600mm at 14kg/m3 for $150. Company said it becomes difficult to get the foam any lighter and still have an acceptable consistancy, beads expand too much it seems. I have the 17kg/m3 at work and its pretty tough, not like chilly bin foam!!!!

I knew a guy in Taranaki who was making his own boards with XPS.
He laminated straight onto it with no PVC. Certainly would be cheaper but not sure about the strength. I built my first one this way.Ended up being a test piece and went in the bin.
I was told by board builders that de-lam is common with XPS although I can't see why that should be.
You've got me thinking about it again. Much cheaper for experimentals. You could use thin low density PVC on the hull if strength was a problem.A stringer would help also.
I may do a little speedy with it and see how it works.

That's a fantastic price you can get about 10 boards out of that block. I must be paying a lot for them to cut it to an individual blank size.