What action should a vessel take when it sees another vessel showing a red light over white light?

When a vessel observes another vessel displaying a red light over a white light, it indicates that the other vessel is a sailing vessel that is under sail and has lost the use of its engine. According to the International Regulations for Preventing Collisions at Sea (COLREGs), the vessel showing this light configuration is classified as a sailing vessel that is constrained by its sailing mode.

In this scenario, the appropriate action is to give way to the sailboat. This is in accordance with the navigation rules that prioritize safe passage and collision avoidance. By giving way, the other vessel is provided with the right of way, allowing it to navigate without danger of collision. It's crucial for vessels to observe these light signals carefully to understand the maneuvering capabilities of other vessels on the water.

Maintaining course, sounding a warning signal, or accelerating to pass quickly would not align with the rules governing right-of-way for sailing vessels and could potentially lead to dangerous situations, such as collisions. Thus, giving way is the correct and prudent action in this situation.