Roll of a Ship in Astern Seas—Response to GM Fluctuations

An effect of astern seas on a ship is to produce fluctuations in the metacentric height (GM) of the ship. GM fluctuations are shown to produce an effect analogous to a reduction in the roll damping. Roll damping reductions are predicted for two extreme types of random GM fluctuations: wide-band and narrow-band random processes. Numerical simulations of the roll motion of a ship with realistic random GM fluctuations are used to compare with the predictions of damping reduction. Good agreement is found. Implications of a reduced roll damping are discussed.