This article: The most important nautical innovation of the Song period seems to have been the introduction of the magnetic mariner's compass, which permitted accurate navigation on the open sea regardless of the weather. The magnetized compass needle – known in Chinese as the "south-pointing needle" – was first described by Shen Kuo in his 1088 Dream Pool Essays and first mentioned in active use by sailors in Zhu Yu's 1119 Pingzhou Table Talks. There were other considerable advancements in hydraulic engineering and nautical technology during the Song dynasty. The 10th-century invention of the pound lock for canal systems allowed different water levels to be raised and lowered for separated segments of a canal, which significantly aided the safety of canal traffic and allowed for larger barges. There was the Song-era innovation of watertight bulkhead compartments that allowed damage to hulls without sinking the ships. If ships were damaged, the Chinese of the 11th century employed drydocks to repair them while suspended out of the water. The Song used crossbeams to brace the ribs of ships in order to strengthen them in a skeletal-like structure. Stern-mounted rudders had been mounted on Chinese ships since the 1st century, as evidenced with a preserved Han tomb model of a ship. In the Song period, the Chinese devised a way to mechanically raise and lower rudders in order for ships to travel in a wider range of water depths. The Song arranged the protruding teeth of anchors in a circular pattern instead of in one direction. David Graff and Robin Higham state that this arrangement "[made] them more reliable" for anchoring ships. contains an answer for the question: Who wrote about the first use of the magnetized compass needle?, what is it ?
Zhu Yu