Surf-Riding and Broaching

Surf-riding is the condition in which a ship in a following sea is captured by a wave and accelerated to the wave celerity instead of passing through the wave system. Broaching is the loss of directional control that can follow, in which the ship yaws violently across the sea despite full opposite rudder and heels sharply under the centrifugal and hydrodynamic loads of the uncontrolled turn.

The hazard is greatest for fast, fine-form ships in stern-quartering seas where the wave celerity is close to the ship speed, which puts small fast vessels, fishing vessels and naval craft at more risk than slow full-form merchant hulls. Rudder authority falls as the ship is carried on the wave face, so the failure is one of control rather than of static stability, which is why the criteria treat it separately from the other modes.

The full article will cover the surf-riding threshold and its dependence on the Froude number, the Level 1 and Level 2 vulnerability criteria of the Second Generation Intact Stability Criteria, the nonlinear dynamics behind the capture condition, the ship types and loading conditions exposed, and the speed and heading policy a master uses to stay clear of the regime.