I recently did whale project where I relied totally on corona renderer for foam shader. (believe me no other renderer were that good as corona)
To create foam shader, I created corona material, with diffuse amount 0.0 and reflection and refraction amount set to 1.0 with 1.33 IOR.
Turn on absorption and volume scattering, set volume scattering to whitish color and absorption color to greyish. and set absorption amount as per need.
I hope this will work for you.