Aluminum 4 OD X .125 WALL (3.750 ID) 6061-T6

a good deal thicker than stock tubes, which i measured at just under .08 wall.

I couldn't find confirmation of what grade Nacra uses, but considering the marine application, (corrosive resistance essential) and the fact that the integral kedar rail is welded in (machinability/weldability essential), i have a hard time believing they use a 7XXX series alloy which is stronger than my grade. -Most likely they used a 6-series T6 like i am. of course 6061 is the stronger end of the 6-series spectrum.

-I would've liked to go a couple hundredths thicker but it was .125 or .250, no in between. .25 would have been just stupid.

I did do my deflection rate calcs on the beams and i believe it looks ok. That being said, as a matter of principle, i will not be having 2 guys on the wire, ever, and this whole thing is designed as a singlehander, meaning just my 200 lbs to contend with.