If you want to draw rough seas then I don’t recommend solely using Pastel Pencils, the reason being that often light will need to be put back on top of the darker colours. However if you combine Pastel Pencils with Polychromos Pastel Sticks then it’s possible.
The Polychromos Sticks have a stronger pigment which does go on top of the Pastel Pencil. To help illustrate this technique, we have included a video uploaded in 2011 of a Speed Painting I did of rough seas. It’s a good example of combining mediums, I even use Soft Pastels too. The Pastel Pencils give you a very good base to work with and then the Polychromos and Soft Pastel and are the icing on the cake.