  We calculate the rate of ocean waves energy dissipation due to whitecapping
by numerical simulation of deterministic phase resolving model for dynamics of
ocean surface. Two independent numerical experiments are performed. First, we
solve the $3D$ Hamiltonian equation that includes three- and four-wave
interactions. This model is valid for moderate values of surface steepness
only, $\mu < 0.09$. Then we solve the exact Euler equation for non-stationary
potential flow of an ideal fluid with a free surface in $2D$ geometry. We use
the conformal mapping of domain filled with fluid onto the lower half-plane.
This model is applicable for arbitrary high levels of steepness. The results of
both experiments are close. The whitecapping is the threshold process that
takes place if the average steepness $\mu > \mu_{cr} \simeq 0.055$. The rate of
energy dissipation grows dramatically with increasing of steepness. Comparison
of our results with dissipation functions used in the operational models of
wave forecasting shows that these models overestimate the rate of wave
dissipation by order of magnitude for typical values of steepness.
