Under what condition does Rule 19a apply?

Rule 19a of the COLREGs comes into play specifically when navigating in or near areas of restricted visibility. In such situations, the regulations are designed to ensure that vessels maintain safety and take appropriate actions to avoid collisions, as visibility limitations can hinder a vessel's ability to detect other vessels and potential hazards.

This rule emphasizes the importance of exercising caution during conditions such as fog, heavy rain, or any other environmental factors that significantly reduce visibility. It requires vessels to take extra measures to ensure safe navigation, including sounding fog signals and maintaining a safe speed.

Navigating in restricted visibility is particularly critical because the risks of collision increase significantly when visual cues are diminished. Hence, the applicability of Rule 19a under these specific conditions underscores the necessity for heightened awareness and adherence to the regulations to prevent accidents in such challenging environments.