Question 19 GLI05 - Master or Mate of LT 200 GRT

The Correct Answer is A. A risk of collision is deemed to exist if the bearing of an approaching vessel does not appreciably change (Rule 7(a)(i) of the COLREGs). A **constant bearing, decreasing range (CBDR)** is the primary and definitive indicator that two vessels are on a collision course. **Explanation for Option A (Correct):** Option A describes a vessel that is "on your starboard quarter" (approaching from behind/astern), the "range decreasing," and the "bearing is constant." The constant bearing combined with decreasing range immediately meets the criteria for CBDR, confirming that the vessels are converging directly towards the same point simultaneously, meaning a risk of collision **definitely exists**. (Note: While Rule 13 (Overtaking) applies here, stating the vessel being overtaken must maintain course and speed, the risk of collision, by definition, still exists until action is taken or the situation is resolved.) **Explanation of Incorrect Options:** **B) 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, meaning there is no risk of collision. **C) A vessel is broad on your starboard beam, range decreasing, bearing changing rapidly to the right.** The **bearing is changing rapidly**. A rapid change in bearing, even with decreasing range, indicates that the vessel is crossing ahead or astern and will likely pass clear. The necessary condition for a definite risk (constant bearing) is not met. **D) A vessel is 22 degrees on your port bow, range increasing, bearing changing slightly to the right.** Both the **range is increasing** (vessels moving apart) and the **bearing is changing** (not on a collision course). No risk of collision exists.