In which situation would risk of collision definitely exist?

In which situation would risk of collision definitely exist?

• A. Vessel on port bow with range increasing
• B. Vessel on starboard quarter, range decreasing, bearing constant
• C. Vessel ahead with bearing changing
• D. Vessel astern with range decreasing

Answer: (B)

Definite risk of collision occurs when the bearing to the other vessel stays fixed while the distance between you decreases. That combination—unchanging bearing and shrinking range—means you and the other vessel are on a collision course if you both keep current speed and direction. In this scenario, the other vessel is on your starboard quarter with range decreasing and bearing constant. That exact pattern shows you are closing on a line of approach and would reach the same point if no action is taken. Hence, collision risk is definite. The other cases don’t show that same definite pattern: range increasing means the vessels are moving apart; bearing changing indicates the situation is not a fixed collision line (more of a crossing situation); and a vessel astern with decreasing range could be closing, but without a constant bearing you can’t say collision risk is definite.

Definite risk of collision occurs when the bearing to the other vessel stays fixed while the distance between you decreases. That combination—unchanging bearing and shrinking range—means you and the other vessel are on a collision course if you both keep current speed and direction.

In this scenario, the other vessel is on your starboard quarter with range decreasing and bearing constant. That exact pattern shows you are closing on a line of approach and would reach the same point if no action is taken. Hence, collision risk is definite.

The other cases don’t show that same definite pattern: range increasing means the vessels are moving apart; bearing changing indicates the situation is not a fixed collision line (more of a crossing situation); and a vessel astern with decreasing range could be closing, but without a constant bearing you can’t say collision risk is definite.