1. The problem statement, all variables and given/known data There is a catamaran, with design forces F0, F3 and F31. Design a simple model which is useable to determine forces which can be used to scantle cross beams and the hull. Scantling joints of hull and crossbeams and hull and masts is not an objective. 2. Relevant equations 3. The attempt at a solution The masts and crossbeams are considered to be beams, the hull is replaced with a pipe. The model is drawn with yellow. I have added some forces to keep the system in place (F4-F7). Added three moments to represent torsion in port hull (M1-M3). Now the scantling of cross beams can be calculated by M1, F4, F31 (fore), and M3, F5, F3. The hull scantling can be done by M1, M2, M3. rv is choosen to be half of the beam at crossbeams. Questions: - Does the replacement of hull with a pipe which have much less diameter than the hull makes sense? - Any other error or oversight?