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The motion analysis of a vessel is performed by means of 3D or 2D (striptheory) potential methods, aimed at the calculation of motion transfer functions.These transfer functions (RAOs) are subsequently used to determine the vesselmotion under the excitation from the environment in analyses aimed at definingthe vessel operability and the safety of offshore operations. While thesemethods are generally accurate including the dominating potential contribution,for the roll degree of freedom it’s important to include other phenomena (eddy-making,viscous effects, presence of bilge keels) especially for ship-shaped vessels. Anumber of tools have been developed to be used in engineering phase, mainlyempirical or semi-analytical, while common system identification techniques canemployed in basin tests. The use of RDM is proposed to obtain roll dampingidentification in full scale, from response measurement only, for eachexperienced environmental condition. As such, it does not need specificallydesigned campaigns and can be performed during operation, and it is desirablefor tuning and verification of values assessed during engineering phase.