What is the primary responsibility of a vessel navigating in restricted visibility according to the Rules?

The primary responsibility of a vessel navigating in restricted visibility is to keep a lookout for other vessels. This duty is crucial for ensuring safety when visibility is compromised due to factors such as fog, rain, or darkness. In such conditions, the ability to visually detect other vessels is significantly reduced, making the lookout more essential than ever. A vigilant lookout can help prevent collisions by alerting the vessel to the presence of other vessels or obstacles in the water, thereby allowing the crew to take appropriate action to avoid dangerous situations.

While maintaining a safe speed and adhering to navigational rules are important, the fundamental action that directly contributes to avoiding collisions in low visibility situations is having a proper lookout. The other options don’t prioritize the immediate and active vigilance required when navigating in such conditions. For instance, maintaining high speed could increase risk, turning on all navigation lights is necessary but does not substitute for the need for lookout, and simply following a course determined by current might not account for the presence of other vessels.