If you are drawing or painting waves, the sea-foam can help you show the planes of the surfaces of the waves or it can flatten your drawing. A few observations about foreshortening foam make a huge difference. Once you learn the tricks of how to draw sea-foam, your waves will begin to roll.
The diagram above holds the key to understanding how sea-foam foreshortens. In the rectangle on the left, note that the holes in the foam can form any shape from oblong to round. This is completely random and a function of how the surface tension of the bubbles binds them together. In the middle drawing, I have foreshortened the same image. Notice how the holes now tend to form horizontal ellipses. Even if the hole is round when seen from above, it becomes a flattened oval when observed from a low angle. 
What does this mean for a crashing wave? Study the third image above. The water at the base of the wave will be flat and the foam holes upon it will form horizontal ellipses. As the surface of the water is tilted up by the oncoming wave, your perspective becomes perpendicular to the surface and you can see the more open or rounded shapes of some of the foam holes. By drawing foam holes open on the wave face, and elliptical at the base you suggest the curvature of the wave itself!
There is one other phenomenon that you should be aware of as you start drawing waves. Imagine a set of vertical lines on the face of a wave. If you were to look into the face of an oncoming wave, the line that is straight in front of you would be vertical. However, as you look up and down the beach, you would see these vertical lines curving along the face of the wave. And so it is with sea-foam. As you look up the beach, you will see sea-foam following the curved contour of the wave. This curl helps put roundness into your wave surface. If you incorporate these details into your drawings, your waves will begin to flow. Surf’s up. Let’s go draw!
