據統計，大多數海上事故都是人為疏忽造成的，這是研發自主船(autonomous ship)的主因之一。自主船舶應具備自主航行系統(autonomous navigation system)，引導船舶安全抵達目的地，避碰就是其基本功能之一。大多數避碰策略是基於圓形船舶領域來決定避碰路徑。此策略所決定的避碰路徑，使讓路船能安全避碰，但卻明顯偏離其原來航路，也就是說它保證安全但航行效率不高。本文則改用橢圓形船舶領域來決策避碰路徑，並期望它既安全又高效。由於船舶外型瘦長，顯然橢圓船舶領域會比圓形船舶領域更合理。為了驗證此說法，本文設計並模擬測試多自主船避碰情境：四艘自主船具有相同的自主航行系統，它們僅能以操舵方式航行至各自終點。在模擬測試中，四艘自主船中任兩艘之間的最近距離至少有本船/目標船長度的七倍，此距離發生在迎艏正遇的兩船。很顯然，避碰過程中的這等距離是相當安全。此外，基於橢圓形船舶領域所決定的避碰路徑偏離原航路幅度比基於圓形船舶領域所決定的路徑小。這些測試結果說明橢圓形船舶領域能使避碰策略既安全又有效率。

According to statistics, most marine accidents are caused by human negligence. It is one of the main reasons for developing autonomous ships. Autonomous ships should have an autonomous navigation system to guide the ship safely arriving at the destination, and collision avoidance is one of its basic functions. Most strategies of avoiding collision is decided based on a circle ship domain. By such strategies, a new path is decided that keeps the give-way ship safely avoid collision but will much deviate from its original route, i.e. inefficient navigation strategy. This paper uses the ellipse ship domain to decide a path for collision avoidance and expect it both safe and efficient. Ellipse ship domain is more reasonable than a circle ship domain because ship bodies are long and thin. In order to verify the statement, a navigation scenario of multiple autonomous ships is designed and tested by simulation: four ships have same autonomous navigation system and they navigate towards their own destinations only by steering. During the simulation test, the closest distance between any two of the four autonomous ships is around seven times of the own/target ship length, which happened when the two ships were going head-on. Along the procedure of collision avoidance, such distance between two ships is apparently safe. Furthermore, when based on ellipse ship domain, the decided path for avoiding collision deviates less to the original route than it based on a circle ship domain. The test results show that the ellipse ship domain makes the strategy of collision avoidance both safe and efficient.