In which situation would risk of collision definitely exist?

• A. A vessel is on your starboard quarter, range decreasing, bearing is constant
• B. A vessel is on your port bow, moving away
• C. A vessel in your stern with increasing range
• D. A vessel crossing from ahead at increasing range

Answer: (A)

The situation that creates a definite risk of collision is when another vessel is on a fixed relative bearing and the distance between you is closing. If the other vessel remains at the same bearing in your sight while its range is decreasing, you and that vessel are on converging paths—the time to the closest point of approach is near or before you cross, so a collision could occur unless one of you changes course or speed.

In the described scenario, a vessel is on your starboard quarter with the range decreasing while the bearing stays constant. That fixed bearing means your tracks are heading toward a point where you would intersect unless action is taken, so the risk is definite.

The other options depict relative motion where the distance is not closing (or is increasing), or where the vessel is not coming toward you, so they do not indicate an imminent collision risk.