First of all, here is one link about wing construction for the Moth sailboat. They are using aluminium tubing and building carbon fiber sleeves and connections. It might be the easiest way to build one if you do not have access to a metal workshop

http://www.moth.asn.au/download/building_moth_hardware.pdf

There are some problems bending aluminium tube or pipe 90 degree. It can be done but it requires a special tooling and be certain to check with the metal shop that they have actually done that because aluminium tubing will crack if you are trying to bend it at 90 degrees. Even with the proper machine, you will limited with the bend radius because the 6061-T6 aluminium is already heat treated

As far as the brace is concern, I would go with a bigger diameter tubing instead of a brace. If you still think that the brace is required, use a smaller diameter pipe insteat of a plate, it is going to be almost as efficient and much safer. BTW the brace should be located on the bend closest to the catamaran, the other one near the seat is pretty much useless.

Don't forget that aluminium looses almost 40% of it's strength after welding so if you decide to go with a welded construction, you should put the brace to help with the strength of the welds or go with a bigger diameter tubing.

One last option is to use aluminium pipe elbows instead of 90 degrees bend and have the wings welded.

Unless you buld it with the Moth procedure, the wings are almost certain to be heavier than stock wings

As far as size of the tubing, If you want to trapeze out of your wing, you will need to have at least a 2" outside diamter for comfort. Anything above 3" of outside diameter is going to be too heavy. You can build using two diameter of tubing, one for the longitudinal tubes, one for the crossbar.

Charles Leblanc