In the age of sail, generations of Hainan fishermen ventured deep into the South China Sea with nothing more than a boat, a compass and a Geng Lu Bu -- a traditional route book recording bearings, distances and destinations.What enabled them to travel so far into the deep blue? The answers lie in family memories, centuries-old navigation records and ancient shipwrecks resting 1,500 meters below the surface.A Miao Xiaojuan Studio FilmA Xinhua News Agency Production