Let’s start from the fundamentals. A twintip kiteboard is essentially a fibreglass tea tray. Sure, you can add all sorts of contours or fancy grooves. You can finely tune the flex characteristics to give just the right amount of “pop”. You can even run computational simulations to calculate the optimised layup, orientation, and thickness of fibres. Or not.
Instead let’s strip back the complexity and acknowledge that it’s just a fucking tea tray.
Problem is, it’s a bendy tea tray. We’re going to need to implement some sort of curved table as a mould, for what is then a relatively straightforward GRP Panel.
Barebones, this rocker table is a simple construction. A thin sheet of plywood bent over some MDF stringers. The stringers have two options, lateral or longitudinal. Now longitudinal would be nice. Very nice. You get complete control over the rate of curve of the table, and you can contour by keeping some curves flatter than others. Sounds great, but there’s a risk: I’m marking out and cutting these cats by hand, and I don’t trust myself to keep the accuracy.
I’ll stick with the lateral option. This is done pretty simply, with easy to measure rectangles. Resin wash and polish the mould surface. Screw and glue some pine battens for overall stiffness. And SHAZAM, rocker table ready to use.
Now we have a mould, we can push forward with the board itself. Sticking roughly to convention, these tend to go together with five main ingredients. Fibreglass for the top and bottom, a core in the middle for stiffness, fastening inserts, rails, and resin to stick it all together. To figure out the best way to do each component, we need to consider what it’s likely to go through.
The fibreglass is going to take load in a few ways, but the overriding factor is going to be torsion. So we’ll use a couple of layers of nice heavy biaxial glass to account for this. But it also is going to have to laminate well, so I’ll sandwich that with some 6oz plain weave.
For the resin we have two options. Polyester or Epoxy. Polyester isn’t as strong, Epoxy isn’t as cheap. Epoxy smells like cat piss, Polyester smells worse. Seeing as I have tubs of both and therefore don’t have to buy any, we’ll stick with Epoxy as it’s just better. It sucks with UV damage, but a coat of paint can help with that.
The core is the next thing. Around half an inch thick is about normal so I’ll just copy the experts. I have some extruded polystyrene sheet left from insulating the floor of the van, it’s compatible with epoxy, so I might as well see if it works!
The Industry standard for fastening down the pads, straps, handles, and fins is with M6 thread. I’ll use 316 Stainless steel as it’s going in the sea. For now I’ll just use normal nuts, and I’ll 3D print some recessed blocks to hold them in place.
The rails are a tricky one. They have to define the outline of the board, be tough enough to take knocks and be compatible with my choice of resin. Luckily, I have a 3D printer which will give better dimensional control than anything I can cut by hand, and I can use ABS filament to work with the Epoxy, so that’s what I’ll do. To join the rail segments, they can be friction welded with a Dremel. This way, no extra chemicals are thrown into the mix.
To get a decent, strong lamination, we only need a fairly simple wet layup, followed by vacuum bagging for consolidation. Currently, I don’t have a vacuum pump so a henry hoover will have to do. The hose is a bit big, so a pasta pot made a good enough chamber to step down the diameter to go into the vacuum bag.
After the lamination is done, the outline of the board can be trimmed to the rails. The trimming is easy, start with a rough cut using a jigsaw, and finish with a surform. Also, don’t breath the dust. Really, really, please. do. not. breath. the. dust.
Most of the way there now, it just needs a can of spray paint, and all the peripherals to be screwed in place.
Callum McCullough 