Whipping

Transient hull-girder vibration triggered by an impulsive load such as a bow slam or a green-water deck impact. The two-node vertical mode is excited and decays over several oscillations as structural damping absorbs the energy. Whipping superimposes on the wave-induced bending moment and can briefly drive total hull stress above the still-water-plus-wave envelope, making it a fatigue-relevant phenomenon for large bulk carriers and container ships. ISSC Committee II.2 reports characterise whipping; modern hull stress monitoring systems (IACS UR S11A) issue slam alarms triggered partly by detected whipping signatures.