In due course towing tanks were built in many di¤erent countries. These were often …tted with wave makers which allowed the behavior of model ships in waves to be studied at leisure and provided, for the …rst time, a technique for re…ning a full-scale design to ensure adequate performance in rough weather. These model experiments were usually con…ned to tests in regular head or following waves with occasional tests at zero speed in beam waves. Tests at other headings or in more realistic irregular waves were impossible because