Question 33 MODU01 - Offshore Installation Manager

The Correct Answer is B **Explanation for Option B (67.5°):** Option B (67.5°) is correct because it aligns with the rules regarding the positioning and arc of visibility for the stern light, as defined in both the International Regulations for Preventing Collisions at Sea (COLREGs) (Rule 21(c)) and the Inland Rules. * A stern light is required to show an unbroken light over an arc of the horizon of **135 degrees** (Rule 21(c)). * This arc must be fixed to show $67.5$ degrees from right dead astern on one side to $67.5$ degrees from right dead astern on the other side ($67.5^{\circ} + 67.5^{\circ} = 135^{\circ}$). * Therefore, the stern light must show $67.5^{\circ}$ on each side of the stern of the vessel. **Why the other options are incorrect:** * **A) 22.5°:** This angle is half the arc of visibility for the masthead light (which covers $225^{\circ}$) relative to the vessel's bow ($112.5^{\circ}$ on each side), but it is not the arc required for the stern light on one side. * **C) 112.5°:** This is the arc of visibility required for the sidelights (green and red) on each side of the vessel, extending from dead ahead to $112.5^{\circ}$ aft on that side. It is not the arc required for the stern light. * **D) 135.0°:** This value represents the **total** arc of visibility required for the stern light ($67.5^{\circ} + 67.5^{\circ}$). The question asks how many degrees the light shows "on each side of the stern," which is half of the total arc.