What is the appropriate action if a vessel is showing no light in fog?

When a vessel is showing no lights in fog, the appropriate action is to slow down and proceed with caution. This response aligns with safe navigation practices under reduced visibility conditions. In fog, the potential for collisions increases significantly due to the limited ability to see other vessels and obstacles. Slowing down allows for greater reaction time to any unexpected situations or encounters with other vessels.

Additionally, proceeding with caution involves maintaining a proper lookout and being prepared to take evasive action if necessary. It ensures that the operator can respond to any signals or sounds from nearby vessels that might indicate their presence, as sound signals are more prominent than visual signals in fog.

Other options, like continuing on the same course or changing course immediately without caution, can lead to dangerous situations, especially since the other vessel's maneuvers or presence cannot be accurately assessed in fog. Anchoring is also not advisable as it may create hazards for other vessels navigating the same waters, and understanding your surroundings is critical when visibility is limited.