What is the primary concern of Rule 19?

The primary concern of Rule 19 is indeed the conduct of vessels in restricted visibility. This rule specifically addresses the precautions that mariners must take when they are navigating in conditions where visibility is limited due to factors such as fog, rain, or other obstructions. In such situations, the risk of collision increases significantly, making it crucial for vessels to follow prescribed guidelines to ensure safety.

Rule 19 outlines various actions and responsibilities for vessels, emphasizing the importance of reducing speed, using appropriate sound signal devices, and maintaining a proper lookout. These measures are intended to help vessels navigate safely and avoid potential collisions, reinforcing the core principles of the COLREGs regarding the safe conduct of vessels in challenging conditions.

The other options, while touching on important navigational rules, do not directly relate to the specific focus of Rule 19. Understanding the implications of restricted visibility is vital for all mariners to promote safe navigation and prevent accidents at sea.