ABSTRACT: There have been several instances of ships being badly damaged due to heavy rolling motion in
sea state, which clearly shows the need for a method to estimate the potential danger in order to support the work
of the ships’ officers. In the paper a simplified but robust method is shown for the on-board calculation, based on
the comparison of the ships natural rolling period and the period of wave encounter to prepare a polar diagram
for synchronous and parametric resonance and other wave effects from basic data of the ship and the sea state,
even by manual calculation. It is also possible to include the potential danger of high wave group encounter or
Surf-riding and broaching respectively.A computer programARROW–Avoidance of Roll Resonance andWave
impact was developed to display the potential dangerous conditions of rolling resonances or other high wave
impacts on ships due to specific wave encounter situations. The tool allows for quick variation of the relevant
parameters and was implemented as a module into a ship weather routing program.