Question 33 ONC06 - Master LT 100 GRT

The Correct Answer is B **Explanation for Option B (67.5°):** Option B (67.5°) is correct because it aligns with the specifications set forth in the International Regulations for Preventing Collisions at Sea (COLREGs), Rule 21(d), which defines the arc of visibility for the stern light. * A stern light is defined as a white light positioned near the stern showing an unbroken light over an arc of the horizon of **135 degrees** and so fixed as to show the light **67.5 degrees** from right aft on each side of the vessel. * Therefore, the light shows from dead astern to 67.5 degrees on each side of the stern. (67.5° + 67.5° = 135° total arc). **Explanation for Incorrect Options:** **A) 22.5°:** This angle is incorrect. 22.5° represents the amount that the sidelights (red and green) extend *aft* of the beam (90°), making their total arc 112.5° (90° + 22.5°). This is unrelated to the stern light's arc of visibility. **C) 112.5°:** This angle is incorrect. 112.5° represents the total arc of visibility for a sidelight (showing from dead ahead to 112.5° on its respective side), not the angle of the stern light on one side of the stern. **D) 135.0°:** This angle is incorrect. 135.0° represents the **total** arc of visibility for the stern light (from port aft to starboard aft). The question specifically asks for the angle "on **each side** of the stern," which is half of the total arc (135° / 2 = 67.5°).