The email made my day. Someone taking their first art class in part because they are inspired by my paintings. He was struggling with how to create thin lines. He wondered if I used a pallet knife or super thin brush. I responded to his email and decided to share this tip as a blog post as well.
The close up shows the moored ropes.
The tip is to paint the rope, then go back over the area with darker paint, thereby leaving only the thin line you desire.