Aluminum crossbeam selection

[M. Ronn]

I am considering connecting 2 Hobie 16 ,or Prindle 16 cats. (9' beam) to make the completed cat. 32'+ long and 18' wide. Any designers, etc., with assistance in choice of the new 18' aluminum cross-beams? The original (Prindle) aluminum cross-beams are identical to the mast. Its too expensive to buy even used mast to complete---I do however have access to 4 1/2" round aluminum pipe/tubing, that is .083 (14ga.?) wall thickness. How can I determine the quality of aluminum pipe to be of sufficient strength, for this application? Any help is appreciated--Thanks!