When are vessels considered to be in "restricted visibility"?

Answer: B — When they cannot see each other by eye

Vessels are considered to be in "restricted visibility" when they cannot see each other by eye. This terminology applies to conditions where visibility is significantly reduced due to factors like fog, heavy rain, or darkness. Under these circumstances, the ability of vessels to detect one another using visual means is impaired, which increases the risk of collisions, necessitating specific navigational procedures outlined in the COLREGs. When vessels operate under restricted visibility, they must follow particular rules, such as navigating at a safe speed, using sound signal equipment, and being extra cautious. These measures help ensure safety when the visual identification of other vessels is compromised, reinforcing the importance of situational awareness and proper communications in these challenging conditions.