季風是影響古代航海活動的重要因素，以往因欠缺洋面風場資料，一些鄭和 航海問題未能獲得合理說明。由於近年QuikSCAT提供的衛星微波觀測海面風場 和Google Earth的普及，提供了先進技術與研究方法。本文參照《前聞記》的航 海曰程、《鄭和航海圖》的航線圖、《順風相送》及《星槎勝覽》的文字敘述等， 據此得以解答下列三個問題。問題與簡答分別為（1)從亞齊開洋為何要「時月 早北邊過洋」？因為11月中旬孟加拉灣季風尚未吹到亞齊，船隊必須開拔到北 邊的翠蘭山渡洋。（2)抵達錫蘭海岸時為何「若船身高有鶯歌嘴」？由於時月早 季風偏北，船隻可能航抵錫蘭東北岸的鶯歌嘴。(3)從古里往忽魯謨斯為何要「沿 山使，用壬亥四十五更取丁得把昔」？由於在逆風情況下，船隻沿岸北駛四十五 更，從丁得把昔開洋較安全。總而言之，第一、二項問題乃是船隊因應孟加拉灣 季風變化的航行經驗，第三項問題則是冬季逆風狀況下，船隊沿著印度東岸北行 550公里至丁得把昔才離岸駛向沙姑馬山，以縮短洋面海程及增大側風角，如此 航行較安全。此外，鄭和船隊全程最大的航速，為沙姑馬山返航至古里這一段， 每曰平均為253公里。

Monsoon significantly affected navigation in ancient times. Some sailing records of Zheng He's expedition could not be properly analyzed due to insufficient oceanic wind data. However, sailing records can now be analyzed using QuikSCAT ocean surface wind, observed by satellite-based microwave sensors, and Google Earth mapping. This study analyzes the travel itinerary in Qian Wen Ji, and other related records such as Zheng He Navigation Charts, Sh-un Feng Xiang Song and Xing Cha Sheng Lan, to answer the following three questions about Zheng He's expedition:
(1) The ships set sail at Great Nicobar instead of Aceh when crossing Bay of Benga; because the northeast monsoon had not yet extended to Aceh in mid November. (2) The ships arrived at Trincomalee, even though their intended destination was Beruwala; because they sailed off at Great Nicobar with a higher-latitude northeast monsoon, and consequently arrived at a northern port. (3) The ships were advised to sail near the shoreline to Tondavali before launching offshore to Qalhat; because they were sailing against the wind. For safety, they had to sail 550 km northward to Tondavali, to reduce the open-sea distance and to catch the side-wind for better sailing. Tondavali was an important landmark in Zheng He's expedition, but its name is now forgotten. The best sailing speed of the journey was calculated as 253 km per day from Qalhat to Calicut.