of the bow however rarely exits from the water on such ships. Vibration from whipping may also increase the extreme loading of ships potentially resulting in vessels breaking in two in severe storms. In the extreme cases springing may cause severe fatigue cracking of critical structural details, especially in moderate to rough head seas with low peak periods. Vibration is normally more easily excited by waves in ballast condition than in cargo condition. The converse may also be true since some ships experience more head wind and waves in ballast conditions, while other ships may experience more head wind and waves in cargo condition, thereby vibrating less overall. Ocean-going ships have not had this problem until recently, when high tensile strength steel was introduced as a common material in the whole ship to reduce initial costs. This makes the ships less stiff and the nominal stress level higher. Today's ship specifications do not account for springing which may be the dominant fatigue factor for some vessels. References Naval architecture