Pixelating the waves was quite a challenge, and took me some time to get a clue of how it could be done.

I watched several television programs, such as Coast, Deadliest Catch, and Blue PlanetBlue Planet, besides referencing images to find out how a wave looks.

Initially I drew the top of the waves with small strokes, which are pointing towards the end of the wave where the wave falls apart.

I wasn't satisfied with the result, so I took another approach. This time I drew a sort of craquelure - which many old paintings have - on top of the wave and added a dithered transition from dark to light gray and vice versa.

I also noticed that the transition towards the falling apart of the wave was too obvious, too hard, so I reduced the contrast.
Along with this adjustment, I added more contrast underneath the wave, so the contrast between the white water drops increases.

In this case, I didn't focus on every water drop/pixel separately, but concentrated on the overall look.