Question 33 ONC03 - Master LT 500-1600 GRT

The Correct Answer is B. ### **Explanation for Option B (67.5°):** Option B (67.5°) is correct because it aligns precisely with the legal definitions for the required arc of visibility for a stern light under both the International Regulations for Preventing Collisions at Sea (COLREGs) and Inland Rules. A stern light must display an unbroken white light over an arc of the horizon of **135 degrees** (or 12 points of the compass) and must be fixed to show this light from dead astern to **67.5 degrees** (or 6 points) on each side of the stern of the vessel. ($67.5^\circ$ (Port side) + $67.5^\circ$ (Starboard side) = $135^\circ$ total arc, centered on dead astern.) *** ### **Explanation of Incorrect Options:** * **A) 22.5°:** This is incorrect. $22.5^\circ$ represents the visibility arc for only **one point** of the compass. This value is used in defining the transition boundaries between the required arcs of the sidelights (forward of $22.5^\circ$ abaft the beam) but is far too narrow for the stern light. * **C) 112.5°:** This is incorrect. $112.5^\circ$ is the required arc of visibility for a **sidelight** (red or green) which shows from dead ahead to $112.5^\circ$ abaft the beam. This defines the forward-facing arc, not the stern-facing arc. * **D) 135.0°:** This is incorrect. $135.0^\circ$ is the **total arc of visibility** for the stern light (from port $67.5^\circ$ to starboard $67.5^\circ$). The question specifically asks for the angle "on **each side** of the stern," which is half of the total arc.