White-capping or top-breaking is steepness-induced wave-breaking, which occurs in deeper water when the wave height becomes too large compared to the wavelength.
The occurrence of white capping depends on:
- the strength of the wind,
- the fetch (the distance over which the wind blows over the water surface),
- the duration of the wind field.
The white caps (also called 'white horses') are irregularly distributed over the water surface. They typically occur at wind speeds of 5 Bf or more (5 Bf ~ 8-11 m/s).