The Song Chinese were world leaders in shipbuilding. Watertight bulkheads improved buoyancy and protected cargo. Stern-mounted or stern-post rudders (see right) improved steering. Sounding lines were used to determine depth. Some ships were powered by both oars and sails and large enough to hold several hundred men.
Also important to oceangoing travel was the perfection of the compass. The way a magnetic needle would point north-south had been known for some time, but in Song times the needle was reduced in size and attached to a fixed stem (rather than floating in water). In some cases it was put in a small protective case with a glass top, making it suitable for sea travel. The first reports of a compass used in this way date to 1119.
More about Shipbuilding during the Song Dynasty
• Ancient Ships from the Song Dynasty A Youtube video of the reconstructed Song dynasty ship now on display in the Quanzhou Bay Exhibtion Hall of Ancient Ships at the Kaiyuan Temple, Quanzhou.