How accurate does Seakeeper predict motions of catamarans?
Seakeeper uses strip theory to predict the coupled vertical plane motions of heave and pitch. The added mass, added inertia and damping terms are calculated from the 2D sectional added mass and damping which are computed using Lewis conformal mapping methods. The way you model a catamaran in Seakeeper is by modelling one demihull on the centreline, like a monohull. Dr Patrick Couser, Naval architect and Seakeeper senior software developer, has found in his model testing studies that you can get reasonable approximations to the heave and pitch motions of catamarans with symmetrical demihulls by simply modelling one demihull and assuming that there is no interaction between the hulls. In practice there is some interaction between the hulls but if you try to model this numerically in a 2D sense, the interactions are greatly overestimated and the results less accurate than if you modelled just one hull. Once the Fn starts to increase (around Fn=0.5 for a catamaran with a spacing/length rat
