What navigational rule requires all vessels to keep a proper lookout?

The Rule of Responsibility is essential in boating safety, as it emphasizes that all vessels must keep a proper lookout at all times. This rule mandates that operators monitor both their surroundings and the behavior of other vessels to prevent potential collisions and ensure safe navigation. Maintaining a proper lookout involves vigilance, which includes using all available means, such as eyesight and hearing, to be aware of nearby boats, obstacles, weather changes, and other hazards. This heightened level of awareness is crucial in busy waterways where various boats may be operating under different conditions.

By adhering to this rule, boat operators can make informed decisions and take timely actions to avoid accidents, thereby enhancing safety for everyone on the water. The other possible rules, while related to safe navigation practices, do not specifically focus on the necessity of maintaining a proper lookout in the same way.