Waves and water are really hard to do in watercolours as you mostly have to leave the whites in the right places to get the effect that you want. I then saw a tutorial on youtube where they use an opaque watercolour called gouache to add in the critical whites which could not be left during the course of the painting. I thought that was quite interesting. I did not have gouache, but I tried using white acrylic, which is opaque anyway and gave this ambitious watercolour breaking wave tutorial a shot!