Estimation of ship roll damping—A comparison of the decay and the harmonic excited roll motion technique for a post panamax container ship

• Pros and cons of established roll damping estimation techniques in calm water.
• Detailed evaluation of decay and Harmonic Excited Roll Motion analysis methods.
• Comparison of decay and HERM measurement results including uncertainty analysis.
• Development of a method to determine restoring moments based on the HERM technique.
• Investigations and results for benchmarking container ship Duisburg Test Case (DTC).

The decay motion as well as the harmonic excited roll motion are established techniques to estimate roll damping for ships. This paper compares the advantages and disadvantages of both techniques and focuses on their applicability. Different analysis methods for both techniques to determine the nonlinear roll damping moment are investigated with the aim of developing an accurate estimation approach without additional filtering, curve fitting and offset manipulation of the recorded time series. Damping coefficients of both techniques are compared for available experiments of the benchmarking post panamax container ship model Duisburg Test Case (DTC). Reasons for deviations are investigated, and the importance of an accurate estimation of the current nonlinear hydrostatic roll moment will be shown. A method for the determination of the nonlinear hydrostatic moment during a harmonic excited roll motion test is introduced. Different approximations of roll damping based on series expansion are investigated. Limitations of the widely used linear-quadratic and linear-cubic function approaches are discussed based on the results.