This painting is all about getting the dark value in the sky and the white plumes of the surf stated from the start of the painting, the rocks need to be painted with angular brush marks and dark value with the highlights scraped with bold large lights.
Paint a wash of cobalt blue and ultramarine blue with a 1.5 inch flat brush painted with angular downward brush marks, leaving lights at the horizon.
Brush over top of the blue wash a burnt sienna and ultramarine blue gray to tone down the original blue. Grade the sky from dark to light right to left, again leaving light at the horizon. Lift out patterns of surf with a damp paper towel.
detail of the lift for the surf, you need to make the lift while the original wash is still wet and the paper towel is damp.
Still using the 1.5 inch flat brush paint in the rocks with a dark mixture of burnt sienna, ultramarine blue, alizirin crimson. Work on making all of the rocks different sizes and shapes with texture on the bottom of the rocks.
Scrape the rocks while they are still damp, with a light cool grey and a small round paint the shadow patterns in the surf, and then splatter titanium white above the surf for a spray.
detail of the surf
Great demos of how to paint surf and rocks. Thank you for sharing