  The kinematic properties of unsteady highly non-linear 3D wave groups have
been investigated using a numerical wave tank. Although carrier wave speeds
based on zero-crossing analysis remain within +-7% of linear theory
predictions, crests and troughs locally undertake a systematic cyclical leaning
from forward to backward as the crests/troughs transition through their maximum
amplitude. Consequently, both crests and troughs slow down by approximately 15%
of the linear velocity, in sharp contrast to the predictions of finite
amplitude Stokes steady wavetrain theory. Velocity profiles under the crest
maximum have been investigated and surface values in excess of 1.8 times the
equivalent Stokes velocity can be observed. Equipartitioning between
depth-integrated kinetic and potential energy holds globally on the scale of
the wave group. However, equipartitioning does not occur at crests and troughs
(even for low amplitude Stokes waves), where the local ratio of potential to
total energy varies systemically as a function of wave steepness about a mean
value of 0.67.
