Our Sailbird has aluminum tube crossbeams (akas), with hinges in between the vaka and the amas, which allow the amas to fold up over the main hull for trailering. They appear to be made out of 2.50″ SCH10 aluminum, which is pretty darn thin (2.875″ OD X 0.120″ WALL X 2.635″ ID). I’m assuming they are made out of T6061T6 alloy, but I’ve not been able to locate the tubes in that alloy, only in T6063T6, which has half the strength of the 6061. And since mine are all ovaled where the hinges slide into the tubes, I don’t want anything weaker.
I actually made up a swage die to resize the ends, and have some 6061 sleeves I can epoxy over the resized ends, but I just didn’t feel totally right about that cure. Especially since I know myself, and if the crimping worked, I’d likely not remove the amas from the main hull. Since I have work to do on the main hull, that would be bad.
So… I bought a 20′ piece of 2.5″ SCH40 T6061T6. I’ll have to ream out the ends to get the hinges in, but they will be much stronger than the original crossbeams. And with the additional thickness, I’m comfortable riveting hardware on if need be. The weight penalty is about 8 pounds… hefty, but liveable. I may still use the aluminum sleeves to reinforce the outer sections of the crosstubes… who knows!