Wow! this sponson thread really took off! In search of the perfect tubbie...
Anyway, since all the aftermarket sponsons are designed NOT TO FIT the FX-1, you are kinda forced to make your own. The FX I originally bought to hack up and use for plugs came with Blowsion Tubbies (originally for the Superjet). They were screwed on and adhered with brown construction adhesive.....they almost fit. There were some generous gaps that could have been sealed up better to look OK but....no. That's why I decided to make my own.
DIY-My approach was to make easy patterns using painters tape, all the while thinking about layering the 1/4"-3/4" foam on top as to get the overall rounded shape uniform. (it takes a few layers (and patterns) to get things where you want them. Then sanding the high spots to meet up with the layer outline below to create the flow. No added filler, just foam), and to be able to repeat the same exact shape on the other side (mirrored). The "copied" foam layers help keep the shape repeatable on both sides, as long as you glue them in the same position, on each side. Kinda like "paint by number". Then using 36-40 grit paper on a sanding block things come to shape quick. Just work on both sides at the same time to keep them the same. After they are shaped where you want them, use some fine conformable E-glass like 4-6-8oz Harness Satin or modified twill weave. That will be easier to drape and deal with than standard weave glass or chopped mat (EEEK!). Polyester is quicker to work with than epoxy, choose your poison... That's the basics, and a way to ditch the Barney purple.
Some additional Notes:
This kinda project isn't for everyone...
5oz. Divinycell foam, sands really easy
Use a heat gun to pre-shape the foam layers to match the side contour (less clamping needed)
Use ultra-lite easy sanding body filler as foam "glue"
The finer the E-glass, the less air bubbles in corners and edges...and stress
Your ski will be WAY different now, but look really cool
