The board shape is inspired by Kalama’s Barracuda and KT's Dragonfly.
Dimensions:
240 cm x 50 cm x 16 cm, 115 liters, 5.8 kg without pad
Construction materials:
- Foil tracks: LIO-TEC US FOIL Box 42 cm
- Track box: Airex 80 kg/m3
- EPS: Insulation EPS 15 kg/m3
- Sandwich Standing Area: Glass fiber 80 g/m2 and Airex C70.75 2 mm
- Carbon biaxial 45°, 220 g/m2, Carbon unidirectional 125 g/m2
1. Construction of the shape in CAD
In the free version of Fusion 360 (Autodesk) I constructed the board shape to be able to print the templates on paper.
2. Building the EPS blank
Since I couldn't find a large piece of EPS at an affordable price, I bought 6 x 10 cm thick EPS blocks for facade insulation at the hardware store. I sanded the surfaces as smooth as possible with 320 grit sandpaper. Then I glued them. First front sides with 3M 77 spray adhesive and then alternating the blocks to a blank with the dimensions of 250 x 50 x 20 cm. I chose the spray glue so I would be able to cut the glue joints with the hot wire and to add as little weight as possible.
3. Cutting the foam core
For the board shape, I had the templates plotted on paper. This was kindly done free of charge by a local architectural firm. I glued the plotted outlines of the top and bottom to painter's board with a spray adhesive and cut them into the individual pieces with scissors. For additional cuts two layers of painter's tape work as well, if you keep moving the wire constantly. I did all the cuts with the hot wire cutter from Proxxon and was able to get very accurate and clean cuts. I attached the templates to both sides of the EPS pieces with pins and kept all the negative cutouts to make it easier to continue working. In a first step I shaped only the top side.
4. Preparing the blank for the stringers
To connect the track box to the deck I decided to use 4 longitudinal stringers. In hindsight, horizontal stringers would have been easier. However, the cutting depth of my hot wire cutter was too small to get that far into the blank. It was only after the first cuts that I had the idea to extend the hot wire cutter with fondue forks. Which worked great. For the cuts, I again used cardboard templates. To get the hot wire through the blank, I heated a laboratory injection rod and melted vertical holes in the blank with a wooden gauge, after which I could pull the wire through directly with the injection rod.
5. Construction of the stringers and inserts
I cut the stringers from an airex block with the hot wire cutter. However, the process was very time consuming because the Proxxon hot wire cutter was a bit too weak. For the Leash- and Vent plug I also cut an insert out of airex. Last came the track box and the reinforcement for nose and tail. For the installation of the plugs, I cut out a recess in the EPS blank with a router and glued the airex and the plugs in place with an epoxy-micro balloon mix. The plugs themselves I filled with EPS scraps to prevent resin from getting in. Into the EPS I pressed two small magnetic beads to make them easier to find after lamination.
6. Installation of stringers and airex sandwich for standing area
I also glued the stringers in place with a mixture of epoxy and micro balloons. To get a smooth surface, and to better distribute the force of the stringers on the deck, I milled out the stringers and some of the surrounding EPS. I then filled these indentations with airex C70.75 and glued it in place. On top of this came Carbon biax 220 g/m2, Glass fiber 80 g/m2 and airex C70.75 2mm. I pressed the whole thing with screw clamps. Before I had sealed the EPS with colored epoxy resin and micro balloons with a squeegee.
7. Preparing the foil tracks
To attach the foil to the board I decided to use the longest available foil tracks I could get. The 42 cm long tracks from Indiana Foil. However, I did not want to laboriously grind them down along with the carbon after installation. Therefore, I milled them down flat on the top with a gauge made of wood and a router. This way I only had to cut the two slots out of the tracks after the final lamination and the carbon has the largest possible contact area to the tracks. I filled the tracks with EPS scraps and taped them down to make sure no resin gets into the tracks.
8. Installing the track box and milling out the negative of the foil tracks
On the bottom side I milled the cutout for the track box into the EPS and the stringers. The negative shape of the foil tracks I milled only after a last check of the position. For this I used the cutter from Indian to achieve the best possible contact surface between track box and foil tracks. I glued the track box and the tracks together with epoxy resin. I degreased the foil tracks with isopropyl alcohol.
9. Installing the nose and tail reinforcements
Before the final shaping, I glued on the airex reinforcements for nose and tail with epoxy resin and micro balloons after cutting out the corresponding EPS parts with the hot wire cutter.
10. Final cuts with the hot wire cutter and final shaping
The last thing I did was cut all the diagonal cuts out of the EPS with the hot wire cutter and the cartoon templates. The surfaces were almost perfect. Still, I put the finishing touches on the entire blank and the edges with a 320-grit sandpaper. I rounded all edges in the front third the others I kept as sharp as possible while still being able to bend the carbon fibers over it.
11. Top lamination
Before lamination, I used wrapping paper to mold the templates for the laminate on the board. Then I sealed the top of the blank with colored epoxy resin and micro balloons and let it cure slightly. During this time, I transferred the templates to the carbon, taped it down and cut out the pieces. I impregnated all the cutouts with epoxy resin between two PP-foils on the bottom. I transferred all the cutouts to the blank with a PP wrapped cardboard tube. First came the reinforcement for the main stance area and the plugs, both biax. Then a layer of UD and then over the whole surface and rails again biax. After that, a tear-off cloth, fleece and then everything in the vacuum bag for 24h. I made the bag more elastic with water and smoothed it by hand with special attention to the edges.
12. Bottom lamination
Then came the same game for the bottom. After removing the tear-off cloth, I had to sand the edges only minimally at the corners and fill the unevenness with microballoons. Then I made templates from wrapping paper, sealed the underside of the blank and laminated it after partial curing. On the track box I put a reinforcement of biax, then a strip of DU and then again, a layer of biax over the complete underside and overlapping over the rails to the top. Then back into the vacuum bag, smoothing it out and hoping it all works out.
Fortunately, everything went great, and the lamination was almost perfect. Only on the top overlap did I have to smooth the edges slightly.
13. Filler coat
To get a smooth surface I applied a filler coat with microballoons and white paint with a squeegee. After curing, I sanded it smooth with 320-grit sandpaper. After that came a second filler coat and sanding again. After that I used a drill and a cutter knife to cut the track and the plugs free. Finding them was easy and precise with the magnets. All went very well but I used up several blades. Last I drilled through the vent plug into the EPS core. To save time, I mixed the filler coat with a fast-curing epoxy. Between the coats I rubbed the board with isopropyl alcohol.
14. Hot coat
I added transparent blue and metallic turquoise pigments to the hot coat. First came the top side again and then the bottom side. To have more time und to let the epoxy flatten itself out more evenly I used a slow curing epoxy. I cut off the masked transitions after a short curing time while the resin was still soft, to get clean edges. The most difficult thing was to get the pigments in the same shade on the top and bottom with the same thickness of the resin.
15. Polishing and attaching the pad
For the smoothest surface possible, I wet sanded the hot coat down to a 1000grit sandpaper and polished it with polishing paste and a polishing cloth. Last I rubbed everything again with isopropyl alcohol and put the pre-cut EVA pad on.
16. Testing and conclusion
After 5 days of final curing, I could finally venture into the UV sunlight with the board. The first tests I did with the Paddle and starting from the dock. Which went surprisingly well. Next came light wind winging. The board glides incredibly fast through the water and the release to the foil is super smooth. In the next few months, I will focus on flat water Paddle Ups when the lakes are not frozen and prepare for potential lake downwinders next year.
I am super happy with this build and already thinking of other shapes to try.
In terms of construction, next time I will use a more fluid resin for lamination and glue in all the inserts with a foaming resin. Also, I think I can reduce the size of the inserts. Overall, I think it should be possible to get below 5 kg.
