Drawing 1
The bridgedeck was constructed to carry the twisting loads generated by the angular-displacement of the catamaran hulls working in a seaway, and consequently minimise torsion stresses on the hulls. This torsionally-stiff bridgedeck was constructed according to drawing below. During 5 years sailing this catamaran, it never displayed noticeable angular deflection of the hulls. Lifting up the bow of one hull caused the other hull to lift producing not more than 50 mm difference in vertical displace of the two bows. So I concluded the bridgedeck construction fulfilled this design objective.
I would like to know what aspect of this structure is responsible for this torsional stiffness. When I designed this structure I guessed the four 1500 mm square tubes with their ends clamped between the four 2250 mm square tubes, would produce the required torsional stiffness. Recent calculations showed that torsional stiffness of these 1500 mm tubes to low to be produce the bridgedeck stiffness. Maybe the tubes angled across the corners of the structure, produce this stiffness ?
I would appreciate comments on this design.
Drawing 1
Drawing 2
Photo 1 - Launching WRC5600 Jan 1995.