The routes of Zheng He’s seven voyages to the West. [Photo/sina.com]

“It took Zheng about one and a half years for a round-trip, almost the same as the switching time among different monsoons,” Dong said. 

According to Dong, Zheng’s sixth voyage, which started in Taicang, Jiangsu province in March 1421, may have taken advantage of the northeast monsoon and realized a wind speed of five meters per second. 

Moreover, Dong believes that waves and current power also contributed to that sixth voyage. 

“Zheng’s sixth trip set off in spring. It was a time when the Yangtze River’s diluted water was moving southeast and the surface current along the Jiangsu waterfronts was turning from north to east, hence making it easy for Zheng’s fleet to sail from north to south,” Dong explained. 

Though winning a warm response from academic circles, Dong regards his devotion as “a sense of mission”. 

“When I was teaching marine science in the US, the textbooks didn’t include any information about Zheng’s seven voyages. That drove me to write a book describing Zheng’s brave and historic stories in detail,” the professor said.