Question 33 ONC02 - Second Mate/Third Mate Unlimited Tonnage

The Correct Answer is B **Explanation of B (67.5°):** The regulations governing navigation lights are defined in the International Regulations for Preventing Collisions at Sea (COLREGs), which are adopted internationally and mirrored by national/inland rules (like the U.S. Inland Rules). Rule 21 defines the characteristics of lights. The definition of the **Sternlight** states that it must be a white light placed as nearly as practicable at 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 dead astern on each side of the vessel. Therefore, the light must show 67.5 degrees to port and 67.5 degrees to starboard, totaling 135 degrees. **Explanation of Incorrect Options:** * **A) 22.5°:** This arc is half of the required arc for the sidelights (which cover 112.5°). This is the angle used to define where the sidelights stop showing and where the masthead light or sternlight must take over (i.e., forward of the beam to 22.5° abaft the beam). It is not the required arc for the sternlight on one side. * **C) 112.5°:** This is the specified arc of visibility for the **sidelights** (a combination of the green light on the starboard side and the red light on the port side), which show from dead ahead to 22.5 degrees abaft the beam. This arc is incorrect for the sternlight. * **D) 135.0°:** This is the **total arc** of visibility for the sternlight (67.5° + 67.5°). The question asks for the degrees *on each side* of the stern, making 135.0° the total, not the angle per side.