In the port of Quanzhou in the Southern Song Dynasty, Said ibn Adil, the son of an Arab maritime merchant, married into the Li family of a Quanzhou maritime merchant family due to family changes. He keenly discovered that the balanced rudder that Song Ship was proud of had fatal lag when avoiding pirates at high speed. With his profound knowledge of Arabic trigonometry, he was determined to improve it. Starting from the shipbuilding workshop of his father-in-law Li Yan, Said, under the witness of his "nerdy" assistant Su Zizhan and the city's shipping department official Chen Jiulang, used sand table deductions and used trigonometric functions to deconstruct the mysteries of water flow and rudder angle, and finally created the "universal balanced rudder". When the ferocious "Black Tide" pirates attacked again, the new-rudder ship showed amazing maneuverability, not only protecting the caravan, but also becoming a weapon for tracking pirates. With the support of Zhao Yunming, the city's shipping secretary, Said united various maritime merchants to establish a "Navigation Safety Alliance" to share routes, star maps and anti-theft techniques. Integrate the compass essence of "Mengxi Bi Tan" with Arabic astrology to construct a "star navigation matrix". This is a navigation revolution driven by mathematics. With wisdom and responsibility, a son-in-law protects the lifeline of trade in the turbulent South China Sea and writes his own star rudder legend.
