The windy season is just starting up in Sydney and after much longer than expected I finally finished my next board (bought the foil this time).
115cm x 43cm
50mm rocker (basically bugger all because with such a short board there is no point trying to recover a nose dive, just have to avoid them)
50mm XPS foam core
1 x 460gm double biases glass top and bottom
1 x 300gm basalt biaxial top and bottom
2 x 4mm marine ply stringers running the full length of the board and 2 x 40mm sub strings
2x 12 inch Chinook mast tracks for mounting the foil
Top coat of white flowcoat
Board weight with grip deck 3.3kg. this is a massive 1.5 kg lighter than last effort!! 6.5kg with foil.
Here's some construction shots:
I made a foam cutter and used a power supply salvaged from an old PC. 15-20W was the power through the Nichrome wire. Made for a very easy job of it but a bit rougher than hoped. On the bow for the wire cutter I used a bed spring to keep tension. However it wasn't strong enough and allowed the wire to gain and loose tension which translated to uneven cutting action. Next time I'll use twisted wire or string to avoid the stretching.
The two 4mm stringers I used on both sides of the foam block as guides to the wire cutting. The tail is 50mm thick and the nose about 20mm thick so 30mm rocker without trying. Then I cut the core into 3 and used polyurethane glue to bend the core and glue the stringers in place. This added about another 20mm rocker. Just wanted enough rocker to push through chop when the board is on the water. I'm not so worried about relying on the rocker for recovering from a touch down as I mostly manage to avoid touching down these days. Also, with a really short board I think it would take a load of rocker to be of any use for this so I decided to keep the rocker limited and make the build easier.
I used 2 straight edges and hot wire cutter to shave the rails way down
Mast tracks were a very tight fit which was perfect. Eventually qcell'd everything and on the back of the mast tracks I put tasmanian oak wood blocks to connect it through to the top layers of laminate.
I had to do the top laminate and lower laminate seperately and wrapped the rails. The double biased wrapped around better than I thought but not as good a twill. Something that worked well when I was putting under the vacuum was to stop just as the bag started to suck down and pull the bag around the edges, making big pleats on the opposite side of the board to the laminate. This consolidated the rails and deck with limited amount of sanding needed afterwards.
Another lesson learned was to buy good vacuum bag material. This was nylon vac bag material which I sealed with blu-tac (like you use for hanging posters) as it was much cheaper than tacky tape. I bought a knock off version of blu-tac from the Reject Shop and $4 for enough to seal the whole bag. I made the bag about 20cm longer than needed. This meant that after the vacuuming, rather than throw the bag away I just sliced off the blu-tac( or tacky tape) and there was enough bag left to be able to use it again. I managed to use bag 4 times ( the last time to press the deck grip down) and it never sprung a leak plus the seal was great. Even my dodgy old vac set up would hold about 24 inHg for 30mins before the pump kicked in. Saved so much waste and frustration trying to find pin holes.
After doing the laminating I did a bit of sanding but not too much. The nose of the deck only had 1 layer of 450gm double bias as I only partly covered the board in the basalt (bottom 2/3) so I didn't want to break through. There were a couple of major divits that filled in with qcell and then a light sand over. To cover over the remaining sins I did a top coat of flowcoat.
I'd never worked with flowcoat before so googled around on it. Flowcoat is polyester gelcoat with wax in styrene in it to create a airtight cover over the gelcoat so it will cure completely (otherwise it stay tacky). Big lesson learned. Old catalyst does not work. I later found out 6 months is about as long as you can trust it and its good to keep in in the fridge as its very temperature sensitive. I had catalyst that was about 1 1/2 years old and it did not kick. So 20 hours later the flowcoat was a liquid as when I put it on. So i had to wipe it off, acetone wipe down, 200 grit sanding. Then I invested $2.99 in new catalyst and redid it. Flowcoat went off in about 10 mins. I put a super thick coat on and its self leveling properties cover over all manner of problems with the surface finish and it ended up looking pretty good.
The reason I was okay with using flowcoat is that with the stringers and basalt there will be zero flex in the board so there won't be an issue of the different stiffnessess of polyester and epoxy causing it to shear off. I read around a lot on whether the polyester resin will stick to the epoxy and there were some very credible sites where they had done a very good job of creating and testing flowcoat on epoxy and found the bond strength as good as polyester on polyester and no delamination after some cycling of it. I've also used Bondo ( car body filler which is just polyester resin with chopped glass fibres ) on previous foil wing as filler directly on the epoxy and after a year of use no separation so I'm quietly confident it will be okay.
Tomorrows forcast looking good so hoping to test it out along with the aliexpress foil ( they had sold out by the time I order so I ended up getting one with some decoration that ummmmmmmm will have to go).