The 13 - sided mainframes were 49 ft ( 15 m ) apart .
The 13 - sided mainframes were made up of diamond - shaped trusses connected by 13 main and 12 secondary longitudinal girders and a trapezoidal keel .
The 13 - sided mainframes were 49 ft ( 15 m ) apart , and were made up of diamond - shaped trusses connected by 13 main and 12 secondary longitudinal girders and a trapezoidal keel .