Sea foam is one of the most difficult subjects for an artist to paint. More challenging still is painting sea foam from nature rather than from a photograph. To paint water and sea foam effectively requires painting with a feeling for the fluidity of the water itself. Your painting style should reflect this, whether using oils or watercolors. A painting of sea foam should not be a laborious task for an artist as it should be painted with a flowing style.
Make a very basic sketch of the sea foam. Capturing the movement of water with a pencil is more difficult than with a brush. The sketch should be an outline of the foam, which will be helpful for you when you start your painting.
Build up the painting from the bottom up. Capture the color of the sea before painting the foam and the tips of any waves. You will need to observe very carefully the different shades of the sea. It should look alive rather than being a blob of color here and there.
Paint the foam using brisk brush strokes. Each brush stroke should also be one continuous sweep of your brush. Breakers will normally be more intricate to paint than one continuous wave. Breakers are free flowing, and by concentrating on the darker area of the sea, the waves will then gradually be revealed. Painting the base of a wave will be the easiest part to paint.
Add other areas outside of the sea foam to your painting. This can be nearly as important as the main subject itself. The sea foam can look even more dramatic and sparkling against a clear, blue sky, for instance.
Study old paintings of seascapes, particularly in museums and art galleries. Seeing a painting close up in oils will allow you to see the individual brush strokes made by the artist.
When painting from nature pick a calm day to paint. Rapid changes in the seascape can be disconcerting for all but the most experienced painter. Keep your main focus on the sea when painting. A beach may be full of people enjoying themselves, which would also be an interesting subject to paint, but this exercise is on painting sea foam.