Broach (nautical)

A wind gust can heel (lean) a sailing vessel, lifting its rudder out of the water.

Both power and sailing vessels can broach when wave action reduces the effectiveness of the rudder.

This risk occurs when traveling in the same general direction as the waves are moving.

[2] Any vessel that is traveling in the same direction and close to the same speed as large waves (relative to the vessel) risks losing directional control when the stern is lifted in the water by an overtaking wave.

Naval architects have only recently started to produce workable mathematical models of broaching: the complexity is due to the non-linear nature of the phenomenon.