What must vessels do in restricted visibility?

In restricted visibility, vessels must be prepared to take action if there is a risk of collision. This is crucial because, in conditions where visibility is limited due to fog, rain, or other obstructions, it becomes challenging to detect other vessels, navigational aids, and obstructions. The International Regulations for Preventing Collisions at Sea (COLREGs) emphasize the need for vigilance and readiness to maneuver in such situations to ensure safety and prevent accidents.

Being prepared means actively listening to radar and ensuring lookout protocols are followed, as well as being ready to take avoidance measures if necessary. This might involve altering speed, changing course, or sounding alarms to alert nearby vessels.

The other options do not align with maritime safety protocols during restricted visibility. Maintaining a high speed is risky as it reduces the ability to react promptly to unforeseen obstacles or other vessels. Turning off navigation lights compromises visibility to others and can lead to serious accidents. The notion of reducing visibility does not make sense in navigation, as the goal is to maximize safety by adhering to regulations designed for such conditions.