This work presents an efficient numerical and modular approach to assessing viscous roll damping coefficients from free decay tests. In order to reduce the time consumed during analysis, numerical pre-processing of the data without visual inspection is suggested. The method involves breaking down multiple decay motions recorded in a single time series, numerically determining the beginning and the end of valid decay motion, eliminating the outlying data from the experimental analysis and obtaining the linear and non-linear roll damping coefficients. None of the pre-processing steps depend on each other and they can be used separately in a modular structure. The process is exemplified using decay test samples of a fishing vessel. To use these analysis results in numerical simulations that extend beyond identical conditions with the experiments, a 3D surface approach is examined. The surface also reveals the effect of speed on the coefficients obtained from the sample set.