In which situation does a risk of collision exist?

Answer: A — vessel is on your starboard quarter, range decreasing, bearing is constant

A risk of collision exists when the relative positions of vessels indicate that they may come into close proximity to one another. In the case where a vessel is on your starboard quarter, the range is decreasing, and the bearing is constant, this indicates that the other vessel is not only getting closer but also maintaining its angle relative to your own vessel. A constant bearing with a decreasing range implies that the two vessels are heading towards an intersection point or a potential encounter, increasing the likelihood of a collision if no action is taken. This situation is critical because it highlights an impending risk where both vessels may not be able to avoid each other if appropriate maneuvers are not executed in time, making it essential for the navigating vessel to take measures to avert a collision. Recognizing such situations is vital in maritime navigation, ensuring safety at sea. The other situations either depict a safe distance or movement that does not pose a collision risk.