Just wanted to say thanks to everyone for all the great info posted here and beyond. I gleaned enough to tackle my first attempt at a large cruising twin tip. I'm a beginner, kiting in junk Colorado mountain wind, but totally stoked- Check out what I came up with and provide any feedback/suggestions for improvement. I'm thinking about a foam-core thruster next round.
150cm x 45cm, maybe 3mm rocker, no concave, straight rails, slightly tapered tips, 10cm heelside fins. Straps and pads scavenged from an old windsurf board, materials $60 plus 20 hours labor. Hand Layup: 2 coats US Composites 635 Epoxy Graphics: plain bond computer-printed double-thumbed gonzo fist (Freak Power in '08!) 1coat Epoxy 3/8" Baltic Birch Core 3 oz. glass 3 coats epoxy w/ blue pgment
Ride report: I've been out on this board three times now. First of all it hasn't snapped in half under my 185 lbs. It gets me going way easier than my 138cm production board and allows my beginner ass to stay upwind better and in junkier wind. It seems to handle chop fine, but it's 1-2 lbs heavier than the production board, so it takes a little more to get it around. I'm pretty jazzed that it's possible to save $700, build something yourself, then go out and ride it without catastrophic results!
Use 2 pieces of AC or baltic birch, epoxy them together with 5 oz of epoxy and a little glass, add concave + rocker you wont be able to break the board. fargo the epoxy for finish, use poly, You'll add at least 12oz of wt with a epoxy finish.
Another ride report: Just got back from a week in South Padre. We has a lot of 12-15mph winds. The Gonzo board worked and didn't break. But it was too slow, too heavy, and too inefficient. I had four 2" fins on it and I think that was too much for light winds?? The board went, but I felt like it was dragging too much. Also, the transition in the rail from straight to a rounded corner pearled quite a bit and constantly splashed water in my face. And turning the thing is like maneuvering a salt barge due to too much mass.
Next attempt: 1/4" ply, 1/4"ply reinforcement under center, smooth parabolic rails, two coats epoxy, 6 oz. glass on bottom, shorter, still wide, smaller ply fins. Anybody have any more input?
Skimp on the epoxy/glass 8oz of epoxy adds 1/2 lb. For sealing and finish. quick dry poly is faster and just as durable as epoxy at a quarter of the wt, 7 coats can be done in less than 2 days and poly can be colored.