Which factor indicates a definite risk of collision?

Which factor indicates a definite risk of collision?

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

Answer: (D)

The essential signal of a definite collision risk is a constant bearing with decreasing range to another vessel. When the bearing from you to the other vessel stays the same while the distance between you shortens, you are on a collision course if you maintain your current speed and course. In this scenario, the other vessel is on your starboard quarter and the range to it is decreasing while the bearing remains constant, which means you and that vessel are on a fixed line of sight that is closing in. That combination is the clear CBDR pattern indicating an imminent risk if no action is taken. The other options do not show this same CBDR signature: either the range is increasing (moving apart), the bearing is changing (not a fixed line of sight), or the vessel is ahead rather than to the side (not the same CBDR cue). So this option best signals a definite risk of collision.

The essential signal of a definite collision risk is a constant bearing with decreasing range to another vessel. When the bearing from you to the other vessel stays the same while the distance between you shortens, you are on a collision course if you maintain your current speed and course. In this scenario, the other vessel is on your starboard quarter and the range to it is decreasing while the bearing remains constant, which means you and that vessel are on a fixed line of sight that is closing in. That combination is the clear CBDR pattern indicating an imminent risk if no action is taken. The other options do not show this same CBDR signature: either the range is increasing (moving apart), the bearing is changing (not a fixed line of sight), or the vessel is ahead rather than to the side (not the same CBDR cue). So this option best signals a definite risk of collision.