While waiting for my plans, I continued my FEM of a "tube" trimaran.
Here are a few result plots for a rig tension load case. Nothing unexpected for now, just plain obvious results. I think FEM will be more usefull when I have real hulls modeled with cutouts and folding struts. First plot shows cross-beams vertical bending moments and second plot shows vonmises stresses in the hull skin (small animation) . For this exercice, everything has the same thickness.