Anyone who has ever gone swimming in heavy surf will tell you that if a wave is about to crash over you, the best thing to do is dive down, under the wave. why does this keep you from being swept up in the wave, like being in a washing machine?

It is true that when a wave is about to crash over you, you should dive down under the wave.  This is because the waves’ direction is also going down, and by following the flow of the waves, you will be safe.  Crashing with the waves lead to opposite force, which makes you to be swept away and cause drowning.