Question 19 ONC02 - Second Mate/Third Mate Unlimited Tonnage

The Correct Answer is A. A risk of collision is deemed to exist if the Compass Bearing of an approaching vessel does not appreciably change (Rule 7(d)(i) of the COLREGS). This is the key principle of the **Constant Bearing, Decreasing Range (CBDR)** situation. **Option A Explanation:** "A vessel is on your starboard quarter, range decreasing, bearing is constant." Although the quarter is traditionally considered a less dangerous aspect than ahead, the crucial combination here is **decreasing range** and **constant bearing**. According to Rule 7(d)(i), if the bearing remains constant and the vessels are approaching (range decreasing), a risk of collision definitely exists, regardless of the relative position (bow, beam, or quarter). --- **Why the other options are incorrect:** * **Option B is incorrect:** "A vessel is 22 degrees abaft your port beam, range increasing, bearing is constant." While the bearing is constant, the **range is increasing**. If the range is increasing, the vessels are moving away from each other, and no risk of collision exists. * **Option C is incorrect:** "A vessel is broad on your starboard beam, range decreasing, bearing changing rapidly to the right." The **bearing is changing rapidly**. A changing bearing (especially a rapid change) indicates that the other vessel is passing safely clear, thus eliminating the risk of collision, even if the range is still decreasing (which might happen briefly as they cross ahead or astern). * **Option D is incorrect:** "A vessel is 22 degrees on your port bow, range increasing, bearing changing slightly to the right." Both the **range is increasing** and the **bearing is changing**. Both factors indicate that the other vessel is moving clear, and therefore, no risk of collision exists.