Man, I’d grab a heavy‑weight sketchbook, not a napkin, and just let the pencil do the work. Start with a loose, shaky line for the horizon, then layer in those heavy, jagged strokes that mimic the cresting waves. Use a softer lead for the darker parts, maybe even a charcoal stick for a bit of depth. Don’t worry about clean edges – a few smudges and eraser marks can give the waves a restless feel. And if you want that stormy vibe, throw in some quick, cross‑hatch lines to suggest wind and spray. Finish with a touch of a brown pencil for the muddy sea floor. Keep your hand loose, let the paper soak up the motion, and you’ll have the tide’s rhythm on paper in no time.