Question 19 ONC05 - Master or Mate of LT 200 GRT

The Correct Answer is A. A) **Why option A ("A vessel is on your starboard quarter, range decreasing, bearing is constant.") is correct:** The fundamental rule for determining collision risk (under both International—COLREGs Rule 7(a)(i)—and Inland rules) is the detection of **Constant Bearing, Decreasing Range (CBDR)**. When a vessel's bearing remains constant while the distance (range) to that vessel is decreasing, it indicates that the two vessels are on a collision course. While a vessel "on your quarter" usually suggests it is an overtaking vessel (which has the responsibility to keep clear), the existence of CBDR, regardless of position, means the risk of collision *definitely exists*. B) **Why option B is incorrect:** A constant bearing with **increasing range** means the distance between the vessels is growing, and they are moving away from each other. Therefore, no risk of collision exists. C) **Why option C is incorrect:** Although the range is decreasing, the **bearing is changing rapidly**. A rapidly changing bearing usually indicates that the vessels are passing clear of one another, even if they are currently quite close (e.g., they are on parallel or diverging courses). Since the bearing is not constant, the condition for definite risk of collision (CBDR) is not met. D) **Why option D is incorrect:** The range is **increasing**, meaning the vessels are moving apart. Furthermore, the bearing is changing, indicating they are not on a collision course. Therefore, no risk of collision exists.