In order to determine the viscous damping due to the bilge keels, the results of numerous tests performed for the past 25+ years from Maritime Research Institute Netherlands (MARIN) have been used to provide a formula relating the variance of the roll velocity, the bilge keel dimensions, the main particulars of the vessel and the loading conditions to the amount of additional damping.

The formula to determine the additional linearized viscous roll damping based on the Root Mean Square of the roll velocity is given by: