What must every vessel maintain to avoid collisions?

Maintaining a safe speed appropriate to the circumstances is essential for every vessel to avoid collisions. This regulation emphasizes the importance of adaptability, as it allows vessels to consider various factors such as visibility, traffic density, weather conditions, and the vessel's own maneuverability. A safe speed ensures that there is adequate time to react to unforeseen situations and obstacles, thereby minimizing the risk of collisions.

In the context of maritime navigation, safe speed is not a fixed speed but rather a dynamic concept that varies with environmental conditions and the vessel's operational context. By understanding and applying this principle, vessels can make informed decisions that promote safety on the water.

The other options, while seemingly relevant, do not adequately address the need for situational awareness and responsiveness that a safe speed entails. A minimum speed does not account for circumstances that might require slowing down, and a constant speed fails to consider the changing conditions that could pose dangers. Additionally, relying on speeds determined by external authorities may not provide the flexibility needed for safe navigation in all situations.