Broaching-to

Broaching-to is a sudden, uncontrollable loss of heading in following or stern-quartering seas, in which the ship yaws toward beam-on despite full opposite rudder and can heel heavily or capsize. It occurs when wave celerity approaches ship speed (high surf-riding Froude number, Fn near 0.3 and above), the vessel becomes captured on a wave front (surf-riding), and the rudder loses effectiveness as the stern is lifted. The IMO Second Generation Intact Stability Criteria treat surf-riding and broaching as a dedicated failure mode with level-1 and level-2 vulnerability checks. Fine-sterned, fast ships in steep following seas of length near ship length are most exposed.